row 264a (#1769 , T1 item 7): bus schema 3j to 3k, sessions below a thread

sessions and session_defaults are new and append-only. thread_claims, message_threads and thread_opens are rebuilt in place with a session column, and thread_claims gains a generation counted from claim rows. Each existing thread gets a default session with the thread's id; new threads get a random one. Holder, per-run, release and delivery triggers key on the session, and two id triggers keep session and thread ids apart (Duckworth checks 1-7, duckworth-0106). The broker binds a thread run to a session (the default when the record names none), and thread.open, thread.send and thread.messages take an optional session. New verbs session.list and session.create (idempotent on op). Tests: sessions.test.mjs for T1 bus half, T2 and T7 with a pinned 3j fixture; count, version and verb pins; hand-made test threads write the legacy default session. Not run yet: every run waits for Sage's CLEAR.
gizmoduck: row 264a bus design in the build notes: sessions and session_defaults, thread_claims, message_threads and thread_opens rebuilt with a session (legacy default id = thread id), generation, broker lookups by session, verbs, tests and pinned lists
2026-10-21 18:58:05 -05:00 · 2026-10-21 18:40:02 -05:00 · 2026-10-21 18:35:04 -05:00 · 2026-10-21 18:32:08 -05:00
25 changed files with 1545 additions and 140 deletions
@@ -0,0 +1,190 @@
+# Row 264 build notes (Gizmoduck)
+
+T1 item 7: independent sessions, compaction counts and clear context. Gitea #1769, Vikunja 463
+(design) and 466 (Claude compaction format, T3's dependency, linked and not built here). Brief:
+docs/plans/2026-10-21_t1-sessions.md, "T1 item 7: independent sessions, compaction counts and clear
+context" (blob ff0be0c79). Reviewer Duckworth, gate owner Sage. Branch gizmoduck/row264 from refactor
+da9555ca2. MVP due 10-27.
+
+The brief pins its code citations at cca206cdc. `git diff --stat cca206cdc da9555ca2` over every cited
+source file is empty, so F1-F11 still hold line for line. Only docs/prd/mosaic-stack.md moved.
+
+## Phase A: what the code has today
+
+- Bus. `threads` binds one `instance` per thread (schema.sql:240-250). `thread_claims` keys on
+  `thread` alone (:251-261), and `message_threads` maps a message to a thread (:262-265). Schema is
+  3j (store.mjs:17). The thread tables first appear in migrations/3d-3e.sql.
+- Launcher. `check()` refuses a second run for the same instance and thread
+  (launcher.mjs:233-240, `registry.running(b.id, instance, thread)`).
+- Seat. `threadStore()` makes one `session/` and one `claude-projects/` per thread
+  (session.mjs:51-74). The registry's running key is business, instance and thread (:215-218).
+- Runner. `stop()` sends TERM to the child group, then KILL after 5 s (runner.mjs:402-414). It has
+  no drain, no idle acknowledgement and no dequeue fence. D7 step 2 needs all three.
+
+## Consumer audit (D9), first pass
+
+`git grep -F` over packages/*/src/* and adapters/* at da9555ca2:
+
+| Name | Files and hits |
+| --- | --- |
+| `thread_claims` | broker.mjs 12, store.mjs 1 |
+| `message_threads` | broker.mjs 9 |
+| `thread_opens` | broker.mjs 4, store.mjs 1 |
+| `threadStore` | launcher.mjs 4, sandbox.mjs 7, session.mjs 3 |
+| `running(` | launcher.mjs 5, session.mjs 1 |
+
+Still to read: the broker holder, agents, end, usage, reply correlation and pending-approval paths
+named in D9, the two adapters (F5), both harness plugins, the conversation reader (F8) and the
+Console. Each gets a file:line row here before the first code commit.
+
+## Proposed slices
+
+One seat can't build D1-D9 in six days and keep every slice reviewable. I propose five candidates
+under row 264, each with its own manifest and Duckworth round:
+
+1. 264a bus. Session tables, claim key `(organization, thread, instance, session)` with a
+   generation, the D3 default session, the D9 bus mapping, `session.list` and `session.create`, and an
+   optional session selector on the thread verbs. Tests: T1 bus half, T2 claims, T7 legacy clients and
+   the rollback refusal.
+2. 264b seat and launcher. Per-session native store and workspace, the single-writer fence, the
+   registry key with session, sandbox mounts of the selected store only, and pinned native ids in both
+   adapters. Tests: T1 run half, T2 workspace and path mutants.
+3. 264c compaction count. Host collector, exact for Pi. Claude shows `unknown` with the 466 reason
+   until that format is pinned. Tests: T3 Pi half.
+4. 264d clear. The D7 journal, the runner drain fence and idle acknowledgement, stop proof, then
+   retirement and successor in one transaction. Tests: T4, T6.
+5. 264e surface. `mosaic session` CLI and the Console chooser, count and clear confirmation. Tests:
+   T5 for the legacy single human, T7 Console half.
+
+## Phase A rulings (sage-2235)
+
+Q1-Q7 went to Sage in gizmoduck-0154. Sage's answers are in agents/sage/work/queue-264/RULINGS.md at
+5f5b51dd6. In short:
+
+- Q1. Five candidates in the order a, b, c, d, e, each with its own manifest, Duckworth round and
+  landing. Row 264 carries 264a. Sage adds rows for 264b-264e. All five are MVP.
+- Q2. 264a builds as 3j-3k.sql. If 236 or 206 lands first, I rebase onto a new branch name, take the
+  next label, and rerun the whole bus suite, the schema.test.mjs counts and the T46 lists.
+- Q3. PRD 1.13 has landed, and REQ-ROLE-2 (mosaic-stack.md:323-329) already carries the session
+  text. Build to it.
+- Q4. Row 194's lifecycle path owns the stop. honker/row194-b5 dfabbbe8a is read-only reference.
+  264d rebases onto 194's landing. The runner's dequeue fence and idle acknowledgement are new code
+  and a named review item. No 194 code gets copied.
+- Q5. One shared admission hook for every session start, using today's limits and revocation. Of
+  191 and 264b, whichever lands second wires 191's checks in. No setting turns it off, and a check
+  that's configured but unavailable fails closed.
+- Q6. 264c lands with Pi exact and Claude `unknown` with the 466 reason. The Claude half of T3 stays
+  open on row 264 and Vikunja 466.
+- Q7. Legacy single human only. Collaborator and share paths refuse. A4 and the full matrix go to
+  whichever of 264 and 193 lands second.
+
+## 264a design: the bus
+
+Line numbers are at da9555ca2 unless they say otherwise.
+
+### Schema 3j-3k
+
+- `sessions`, new and immutable: `id`, `at`, `business`, `thread`, `instance`, `owner`, `name`, `op`
+  (the creation operation key) and `predecessor` (null until 264d's clear). UNIQUE `(thread, name)`
+  and `(thread, op)`, so a repeated create with the same key finds the first row. Guard triggers
+  check that the business, instance and owner match the thread's, and that a predecessor sits in
+  the same thread.
+- `session_defaults`, new and append-only: `thread`, `session`, `at`, `by`. The latest row per
+  thread is that thread's default (D3). A trigger checks that the session is in the thread.
+- `thread_claims`, `message_threads` and `thread_opens` are rebuilt, each with a `session` column,
+  and `thread_claims` also gets `generation`. Rows are copied with their seq values and every old
+  column as it was, and the sequence carries over, as 3h-3i.sql did for `usage_records`. That is a
+  named review item: the copy adds two derived columns and changes nothing else.
+- Each existing thread gets one legacy default session with **id equal to the thread id**, the
+  name `default`, op `legacy-3k`, and the thread's own `at` and owner. Every copied row names that
+  session. This is D9's immutable mapping. 264b binds it to the existing native store at
+  `threads/<business>/<thread>/session/`. A new thread's default session gets a random id.
+- `generation` is the claim's number within its session, counting from 1. A release or revoke
+  carries its claim's number. On copy, it's the count of claim rows in the thread up to that row.
+- Triggers keyed on the thread now key on the session: one holder, release only while held, only the
+  holder releases, and a generation check. These two keep their thread meaning: one held session per
+  run per business, and the business check. New checks: the claim's, message's and open's session
+  is in the named thread. `delivery_same_thread` becomes `delivery_same_session`, which sends a
+  threaded message only to its own session's holder.
+- A 3j binary refuses a 3k store with `schema-mismatch` (store.mjs:181-186), which covers D9's
+  rollback refusal. T7 tests it.
+
+### Broker
+
+- Run binding. `bindLaunch` takes an optional `session`. When it's missing, the run gets the
+  thread's default session, which is the D3 path for today's launcher. The binding refuses a
+  session that isn't in its thread. The run's `s.session` then drives `role.claim`, `#own`,
+  `message.receive` and the reply routing.
+- Lookups. `#threadHolder(thread)` becomes `#sessionHolder(session)`, which `#recipient`,
+  `#routeThread`, `#threadHolders`, `#claimEnd`, `threadIdle` and run end all use.
+  `#threadFor` returns a thread and its session: a thread run's own, or the session of the nearest
+  threaded message up the reply chain. `#specThread` uses the opened thread's default session.
+- Launcher view. `threadsState` and `threadIdle` keep their row shape, one row per thread computed
+  on its default session. Until 264b, the launcher starts only default sessions. Messages to another
+  session wait, and nothing reaches the default session's run.
+- Verbs:
+  - The thread verbs take an optional `session`, and leaving it out uses the default (D3).
+    `thread.create` also makes the default session. `thread.messages` without a session reads the
+    default session.
+  - `session.list {thread}` and `session.create {thread, name, op}` (D8: metadata only). The build
+    dropped `session.get`, `session.open` and `session.send`. `thread.open`, `thread.send` and
+    `thread.messages` take an optional `session`, which does the same job with one owner check and
+    one code path.
+  - All of them are human or tester only, through `#human`/`#thread`, the same owner check as the
+    thread verbs (Q7: single human, no shares). They go into `TESTER_VERBS`.
+- Other readers. `#grantNotice`, `#raisedThread` and the decision-close path (:736, :1500, :2941)
+  read the holder run's claim row. The rebuilt `thread_claims` keeps that query working, and the
+  session comes along from the same row.
+
+### Tests and lists
+
+- New file `packages/bus/tests/sessions.test.mjs`:
+  - T1 bus half: two sessions in one thread, distinct histories, receive and reply isolation, and a
+    non-thread role refused.
+  - T2: one holder per session, generation fencing, sibling delivery refused by the trigger.
+  - T7: legacy clients, the 3j-3k migration from a fixture (default session id = thread id, rows
+    copied with seq), and the rollback refusal.
+- A new `fixtures/schema-3j.sql`.
+- Update the schema.test.mjs pins (:519-525), the `'3j'` version pins in the migration tests,
+  `COUNTED` in scripts/stack-release.sh:404, and the T46 lists in
+  packages/cli/tests/stack-release.test.mjs:860-934. Also `timedTables` (store.mjs:65-79) and the
+  broker clock-seed list (:325-336).
+
+### Duckworth's design checks (duckworth-0106)
+
+Duckworth had no objection to the in-place rebuild and asked for seven checks. Where each one is:
+
+1. The cross-table trigger. 3j-3k.sql drops `delivery_same_thread` before any rename and creates
+   `delivery_same_session` after the new tables.
+2. Index names. The step drops `thread_claims_thread` and `message_threads_thread` before the
+   renames, so the new tables can reuse the names.
+3. Per-table triggers. The step drops each guard and append-only trigger and creates it again with
+   text that matches schema.sql. The digest check at store.mjs:231 enforces that, and the T7
+   `sqlite_master` comparison shows it.
+4. Generation counts claim rows only. T7's fixture is Duckworth's: claim, release, claim, revoke,
+   giving 1, 1, 2, 2, with t2's claim between them.
+5. Sequences. Rows keep their seq values, `sqlite_sequence` carries over, and T7 checks that the
+   next insert is 41 after 40.
+6. Id collisions. A legacy session id is its thread's id. `sessions_id_not_thread` refuses a session
+   id that names another thread, and `threads_id_not_session` refuses a thread id that names a
+   session. New ids come from randomUUID.
+7. `thread_one_per_run`. The inner `max(seq)` is per session.
+
+### Dry run
+
+Before writing any node test, I ran 3j-3k.sql in an in-memory Python sqlite3 on a 3j fixture
+(gizmo-264-out/dry-3k.py, no repo code). The claims were kept with generations 1, 1, 1, 2, 2 in seq
+order for the mixed t1/t2 fixture. Seq 40 carried over and the next insert was 41. The migrated
+`sqlite_master` matched a fresh schema.sql, 119 rows each. Every guard refused its bad write.
+
+### Hand-made threads in tests
+
+A thread that a test writes by hand has no default session, because only `thread.create` and the
+migration write one. The broker refuses such a thread with `session-not-found`, and the launcher view
+leaves it out. So every test that inserts a `threads` row now also writes the legacy-shape default
+session (`DEFAULT_SESSION` in threads, end-launch, thread-cli, thread-launch and chat tests). That
+mirrors the migration's rows rather than inventing a third shape.
+
+## Runs
+
+None yet. Every run waits for Sage's CLEAR.
@@ -236,9 +236,11 @@ a receipt with empty `changes`. A refusal is `action.refused` with its code alon
 | `project.list` | No args; human sessions only. The business's projects, oldest first. |
 | `thread.create` | `{project,name}`; human sessions only. The thread belongs to the caller and to the business's one thread instance (Projects and threads, below). Returns `{id,instance}`. Refuses `project-not-found`, `thread-exists`, `thread-instance-missing` or `thread-instance-ambiguous`. |
 | `thread.list` | `{project?}`; human sessions only. The caller's own threads, oldest first. |
-| `thread.open` | `{thread}`; human sessions only. Records a `thread_opens` row, which asks the launcher to start the thread's session. Returns `{opened}`. |
-| `thread.send` | `{thread,body,class?}`; human sessions only. A message to the thread's instance, in that thread, with its `human.input` event as `request`. Returns `{id,request}`. |
-| `thread.messages` | `{thread,after?,limit?}`; human sessions only. The thread's messages oldest first, after the message `after` names (`message-not-found` when it isn't in the thread), at most `limit` (default 50, 1 to 200). Writes nothing. |
+| `thread.open` | `{thread,session?}`; human sessions only. Records a `thread_opens` row, which asks the launcher to start the thread's session. Returns `{opened}`. |
+| `thread.send` | `{thread,session?,body,class?}`; human sessions only. A message to the thread's instance, in that thread, with its `human.input` event as `request`. Returns `{id,request}`. |
+| `thread.messages` | `{thread,session?,after?,limit?}`; human sessions only. The session's messages oldest first, after the message `after` names (`message-not-found` when it isn't in the session), at most `limit` (default 50, 1 to 200). Writes nothing. |
+| `session.list` | `{thread}`; human and tester sessions (row 264a, #1769). The thread's sessions oldest first, `[{id,at,name,predecessor,default}]`. Writes nothing. |
+| `session.create` | `{thread,name,op}`; human and tester sessions. A new session of the thread, metadata only. A retry with the same `op` and name returns the first row; another name under that `op` refuses `session-op-conflict`, and a taken name `session-exists`. Returns `{id,thread,name}`. |

 ### Projects and threads (row 121, #1615)

@@ -306,6 +308,33 @@ the threads they made. A revoked run can't claim its thread again (`run-revoked`
 thread run can still be stopped another way: the launcher stops it once the thread is idle, the
 human stops it with `mosaic stop <run>`, and the run's end releases its claim. `thread_revoke_needs_decision` guards the table against a direct write.

+### Sessions (row 264a, #1769)
+
+Schema `3k` puts sessions below a thread. `sessions` and `session_defaults` are new and
+append-only. `thread_claims`, `message_threads` and `thread_opens` each gain a `session`
+column, and `thread_claims` gains `generation`, the claim's number in its session counting
+from 1. A release or revoke carries its claim's number.
+
+Every thread has a default session, the latest `session_defaults` row (D3). `thread.create`
+writes one with a random id. The 3j→3k step gives each existing thread a default session whose
+id is the thread's own, named `default` with op `legacy-3k`, and files every old claim, message
+and open under it. A thread verb, or a `bindLaunch` record, that names no `session` works the
+default, so a client from before 3k keeps working. A `session` from another thread refuses
+`session-not-found`, and a non-thread role that names one refuses `thread-not-allowed`.
+
+The thread rules above hold per session. One run holds a session at a time, and a run holds at
+most one session in its business, while sibling sessions of a thread may each have a holder.
+A thread run receives and replies in its own session, and the chief of staff's reply returns
+to the session that sent the work. `threadsState` and `threadIdle` keep one row per thread,
+computed on its default session; 264b's launcher starts the others.
+
+The triggers check that a session has its thread's business, instance and owner, that its
+predecessor and any default, claim, message or open name a session of the same thread, and that
+a claim's generation is the one its session expects. `delivery_same_session` replaces
+`delivery_same_thread`. `sessions_id_not_thread` and `threads_id_not_session` keep a session id
+from naming another thread and a thread id from naming a session. A 3j engine refuses a 3k
+store with `schema-mismatch`.
+
 ### Agent state (row 59, #1548)

 For a human or reader session, `agents` derives each held role's state from
@@ -711,10 +740,10 @@ scope probes and rotation/expiry notifications; S2 never probes real services.

 ## Schema and verification

-`schema.sql` is v3j, SHA-256
-`0a7b633ce7eec9d0bb37c3255f4244d97bd0c8eac38db91a11b4ef6cc982ec8c`.
-It has 18 tables, 72 triggers and five views. Source digest and a trusted full
-sqlite_master digest are checked at open, alongside schema version `3j`, WAL,
+`schema.sql` is v3k, SHA-256
+`860374bde3f063ecfd72618913e05924587b7c39b87b763eee4c6aeb59922f46`.
+It has 20 tables, 87 triggers and five views. Source digest and a trusted full
+sqlite_master digest are checked at open, alongside schema version `3k`, WAL,
 quick_check and foreign-key integrity. Missing metadata refuses; it never
 reinitializes an existing file. Full synchronous WAL transactions either commit
 or roll back. SQL UPDATE, DELETE and INSERT OR REPLACE refuse on evidence tables.
@@ -248,11 +248,34 @@ CREATE TABLE threads (
  name TEXT NOT NULL,
  UNIQUE (project, name)
 ) STRICT;
+CREATE TABLE sessions (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  instance TEXT NOT NULL,
+  owner TEXT NOT NULL,
+  name TEXT NOT NULL,
+  op TEXT NOT NULL,
+  predecessor TEXT REFERENCES sessions(id),
+  UNIQUE (thread, name),
+  UNIQUE (thread, op)
+) STRICT;
+CREATE TABLE session_defaults (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
+  by TEXT NOT NULL
+) STRICT;
 CREATE TABLE thread_claims (
  seq INTEGER PRIMARY KEY AUTOINCREMENT,
  at TEXT NOT NULL,
  business TEXT NOT NULL,
  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
+  generation INTEGER NOT NULL CHECK (generation >= 1),
  op TEXT NOT NULL CHECK (op IN ('claim','release','revoke')),
  holder_run TEXT NOT NULL,
  harness TEXT NOT NULL, address TEXT,
@@ -261,55 +284,95 @@ CREATE TABLE thread_claims (
 ) STRICT;
 CREATE TABLE message_threads (
  message TEXT PRIMARY KEY REFERENCES messages(id),
-  thread TEXT NOT NULL REFERENCES threads(id)
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id)
 ) STRICT;
 CREATE TABLE thread_opens (
  seq INTEGER PRIMARY KEY AUTOINCREMENT,
  at TEXT NOT NULL,
  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
  by TEXT NOT NULL
 ) STRICT;
 CREATE INDEX thread_claims_thread ON thread_claims (thread, seq);
+CREATE INDEX thread_claims_session ON thread_claims (session, seq);
 CREATE INDEX message_threads_thread ON message_threads (thread);
+CREATE INDEX message_threads_session ON message_threads (session);
+CREATE INDEX session_defaults_thread ON session_defaults (thread, seq);
 CREATE TRIGGER threads_project_business BEFORE INSERT ON threads
  WHEN (SELECT business FROM projects WHERE id = NEW.project) IS NOT NEW.business
  BEGIN SELECT RAISE(ABORT, 'a thread belongs to its project''s business'); END;
+CREATE TRIGGER sessions_thread_match BEFORE INSERT ON sessions
+  WHEN NOT EXISTS (SELECT 1 FROM threads t WHERE t.id = NEW.thread AND t.business = NEW.business AND t.instance = NEW.instance AND t.owner = NEW.owner)
+  BEGIN SELECT RAISE(ABORT, 'a session has its thread''s business, instance and owner'); END;
+CREATE TRIGGER sessions_predecessor BEFORE INSERT ON sessions
+  WHEN NEW.predecessor IS NOT NULL AND (SELECT thread FROM sessions WHERE id = NEW.predecessor) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a session''s predecessor is in its thread'); END;
+CREATE TRIGGER sessions_id_not_thread BEFORE INSERT ON sessions
+  WHEN NEW.id IS NOT NEW.thread AND EXISTS (SELECT 1 FROM threads WHERE id = NEW.id)
+  BEGIN SELECT RAISE(ABORT, 'a session id names another thread'); END;
+CREATE TRIGGER threads_id_not_session BEFORE INSERT ON threads
+  WHEN EXISTS (SELECT 1 FROM sessions WHERE id = NEW.id)
+  BEGIN SELECT RAISE(ABORT, 'a thread id names a session'); END;
+CREATE TRIGGER session_defaults_match BEFORE INSERT ON session_defaults
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a default session is in its thread'); END;
 CREATE TRIGGER thread_one_holder BEFORE INSERT ON thread_claims
-  WHEN NEW.op = 'claim' AND (SELECT op FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1) = 'claim'
-  BEGIN SELECT RAISE(ABORT, 'thread already held'); END;
+  WHEN NEW.op = 'claim' AND (SELECT op FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) = 'claim'
+  BEGIN SELECT RAISE(ABORT, 'session already held'); END;
 CREATE TRIGGER thread_one_per_run BEFORE INSERT ON thread_claims
  WHEN NEW.op = 'claim' AND EXISTS (SELECT 1 FROM thread_claims c WHERE c.holder_run = NEW.holder_run AND c.business = NEW.business
-    AND c.seq = (SELECT max(seq) FROM thread_claims WHERE thread = c.thread) AND c.op = 'claim')
-  BEGIN SELECT RAISE(ABORT, 'run already holds a thread'); END;
+    AND c.seq = (SELECT max(seq) FROM thread_claims WHERE session = c.session) AND c.op = 'claim')
+  BEGIN SELECT RAISE(ABORT, 'run already holds a session'); END;
 CREATE TRIGGER thread_release_by_holder BEFORE INSERT ON thread_claims
-  WHEN NEW.op IN ('release','revoke') AND COALESCE((SELECT op FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1),'') <> 'claim'
-  BEGIN SELECT RAISE(ABORT, 'thread is not held'); END;
+  WHEN NEW.op IN ('release','revoke') AND COALESCE((SELECT op FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1),'') <> 'claim'
+  BEGIN SELECT RAISE(ABORT, 'session is not held'); END;
 CREATE TRIGGER thread_release_same_run BEFORE INSERT ON thread_claims
-  WHEN NEW.op = 'release' AND (SELECT holder_run FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1) <> NEW.holder_run
+  WHEN NEW.op = 'release' AND (SELECT holder_run FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) <> NEW.holder_run
  BEGIN SELECT RAISE(ABORT, 'only the holder releases; others revoke'); END;
+CREATE TRIGGER thread_claim_generation BEFORE INSERT ON thread_claims
+  WHEN NEW.generation IS NOT (CASE WHEN NEW.op = 'claim'
+    THEN 1 + (SELECT count(*) FROM thread_claims WHERE session = NEW.session AND op = 'claim')
+    ELSE (SELECT generation FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) END)
+  BEGIN SELECT RAISE(ABORT, 'a claim row names its session''s generation'); END;
 CREATE TRIGGER thread_revoke_needs_decision BEFORE INSERT ON thread_claims
  WHEN NEW.op = 'revoke' AND NEW.decision IS NULL AND NEW.reason IS NULL
  BEGIN SELECT RAISE(ABORT, 'revoke needs a resolved decision or a reason'); END;
 CREATE TRIGGER thread_claims_business BEFORE INSERT ON thread_claims
  WHEN (SELECT business FROM threads WHERE id = NEW.thread) IS NOT NEW.business
  BEGIN SELECT RAISE(ABORT, 'a thread claim names the thread''s business'); END;
+CREATE TRIGGER thread_claims_session BEFORE INSERT ON thread_claims
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a claim''s session is in its thread'); END;
 CREATE TRIGGER message_threads_match BEFORE INSERT ON message_threads
  WHEN NOT EXISTS (SELECT 1 FROM messages m JOIN threads t ON t.id = NEW.thread
    WHERE m.id = NEW.message AND m.business = t.business AND t.instance IN (m.to_role, m.from_role))
  BEGIN SELECT RAISE(ABORT, 'a threaded message is to or from the thread''s instance'); END;
-CREATE TRIGGER delivery_same_thread BEFORE INSERT ON deliveries
+CREATE TRIGGER message_threads_session BEFORE INSERT ON message_threads
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a threaded message''s session is in its thread'); END;
+CREATE TRIGGER thread_opens_session BEFORE INSERT ON thread_opens
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'an open''s session is in its thread'); END;
+CREATE TRIGGER delivery_same_session BEFORE INSERT ON deliveries
  WHEN NEW.op IN ('routed','delivered') AND (NEW.op = 'delivered' OR NEW.holder_run IS NOT NULL)
    AND EXISTS (SELECT 1 FROM message_threads mt JOIN messages m ON m.id = mt.message JOIN threads t ON t.id = mt.thread
      WHERE mt.message = NEW.message AND m.to_role = t.instance
-        AND NOT EXISTS (SELECT 1 FROM thread_claims c WHERE c.seq = (SELECT max(seq) FROM thread_claims WHERE thread = t.id)
+        AND NOT EXISTS (SELECT 1 FROM thread_claims c WHERE c.seq = (SELECT max(seq) FROM thread_claims WHERE session = mt.session)
          AND c.op = 'claim' AND c.holder_run IS NEW.holder_run))
-  BEGIN SELECT RAISE(ABORT, 'a threaded message goes only to its thread''s holder'); END;
+  BEGIN SELECT RAISE(ABORT, 'a threaded message goes only to its session''s holder'); END;
 CREATE TRIGGER projects_no_update BEFORE UPDATE ON projects BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
 CREATE TRIGGER projects_no_delete BEFORE DELETE ON projects BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
 CREATE TRIGGER projects_no_replace BEFORE INSERT ON projects WHEN EXISTS (SELECT 1 FROM projects WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
 CREATE TRIGGER threads_no_update BEFORE UPDATE ON threads BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
 CREATE TRIGGER threads_no_delete BEFORE DELETE ON threads BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
 CREATE TRIGGER threads_no_replace BEFORE INSERT ON threads WHEN EXISTS (SELECT 1 FROM threads WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
+CREATE TRIGGER sessions_no_update BEFORE UPDATE ON sessions BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER sessions_no_delete BEFORE DELETE ON sessions BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER sessions_no_replace BEFORE INSERT ON sessions WHEN EXISTS (SELECT 1 FROM sessions WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER session_defaults_no_update BEFORE UPDATE ON session_defaults BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
+CREATE TRIGGER session_defaults_no_delete BEFORE DELETE ON session_defaults BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
+CREATE TRIGGER session_defaults_no_replace BEFORE INSERT ON session_defaults WHEN EXISTS (SELECT 1 FROM session_defaults WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
 CREATE TRIGGER thread_claims_no_update BEFORE UPDATE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
 CREATE TRIGGER thread_claims_no_delete BEFORE DELETE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
 CREATE TRIGGER thread_claims_no_replace BEFORE INSERT ON thread_claims WHEN EXISTS (SELECT 1 FROM thread_claims WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
@@ -116,7 +116,9 @@ export const TASK_VERBS = Object.freeze(ACTIONS.filter((a) => a.startsWith('task
 // Row 177 (#1675, Q173): the tester's own threads, owner `tester`, and a stop of their runs.
 export const TESTER_VERBS = Object.freeze(['message.send', 'message.receive', 'message.read', 'inbox', 'agents', 'tasks', 'trail', 'decisions', 'messages', 'replies',
  'usage', 'names', 'limits', 'plugins', 'instances', 'project.list', 'thread.list', 'name.set', 'project.create', 'credentials',
-  'thread.create', 'thread.open', 'thread.send', 'thread.messages', 'assistant.stop']);
+  'thread.create', 'thread.open', 'thread.send', 'thread.messages', 'assistant.stop',
+  // Row 264a (#1769): the sessions of the tester's own threads.
+  'session.list', 'session.create']);
 // Row 175: the organization verbs a tester may call. Its writes run every check the human's do
 // and log actor `tester`; row 176 adds routes reads; limits.set, organization.set and organization.revision refuse it.
 export const TESTER_ORGANIZATION_VERBS = Object.freeze(['limits', 'plugins', 'instances', 'plugins.set', 'instances.set', 'routes.set', 'routes']);
@@ -329,6 +331,8 @@ export class Broker {
      'task_snapshots',
      'projects',
      'threads',
+      'sessions',
+      'session_defaults',
      'thread_claims',
      'thread_opens',
    ]) {
@@ -389,37 +393,49 @@ export class Broker {
  #threaded(business, role) {
    return this.#business(business).roles[role]?.definition === THREAD_DEFINITION;
  }
-  #threadHolder(thread) {
-    return this.#store.get('SELECT * FROM thread_claims WHERE thread=? ORDER BY seq DESC LIMIT 1', thread);
+  // Row 264a (#1769): a claim holds one session of a thread, and each session has its own holder.
+  #sessionHolder(session) {
+    return this.#store.get('SELECT * FROM thread_claims WHERE session=? ORDER BY seq DESC LIMIT 1', session);
  }
-  // Row 155 (#1649): the held claims of every thread of a thread instance, oldest thread first, or
+  // D3: the thread's default session, the latest session_defaults row. thread.create and the 3j-3k
+  // migration write one for every thread.
+  #defaultSession(thread) {
+    return this.#store.get('SELECT session FROM session_defaults WHERE thread=? ORDER BY seq DESC LIMIT 1', thread)?.session ?? fail('session-not-found');
+  }
+  // The session a thread verb names, or the thread's default when it names none.
+  #threadSession(t, session) {
+    if (session === undefined) return this.#defaultSession(t.id);
+    if (!this.#store.get('SELECT 1 FROM sessions WHERE id=? AND thread=?', identifier(session), t.id)) fail('session-not-found');
+    return session;
+  }
+  // Row 155 (#1649): the held claims of every session of a thread instance, oldest thread first, or
  // only the threads `owner` made. An end of the instance ends each of them.
  #threadHolders(business, instance, owner = null) {
    return this.#store.all(
-      "SELECT c.* FROM threads t JOIN thread_claims c ON c.seq=(SELECT max(seq) FROM thread_claims WHERE thread=t.id) WHERE t.business=? AND t.instance=? AND (? IS NULL OR t.owner=?) AND c.op='claim' ORDER BY t.seq",
+      "SELECT c.* FROM threads t JOIN sessions se ON se.thread=t.id JOIN thread_claims c ON c.seq=(SELECT max(seq) FROM thread_claims WHERE session=se.id) WHERE t.business=? AND t.instance=? AND (? IS NULL OR t.owner=?) AND c.op='claim' ORDER BY t.seq, se.seq",
      business,
      instance,
      owner,
      owner,
    );
  }
-  // The claim a run acts under: its thread's for a thread run, its role's otherwise.
+  // The claim a run acts under: its session's for a thread run, its role's otherwise.
  #own(s) {
-    return s.thread ? this.#threadHolder(s.thread) : this.#holder(s.business, s.role);
+    return s.thread ? this.#sessionHolder(s.session) : this.#holder(s.business, s.role);
  }
-  // Who a message to `to` goes to now: the thread's holder when the message is in a thread of
-  // `to`, the role's otherwise. Null while nobody holds it, and the message waits.
-  #recipient(business, to, thread) {
-    const h = thread && this.#threaded(business, to) ? this.#threadHolder(thread) : this.#holder(business, to);
+  // Who a message to `to` goes to now: the session's holder when the message is in a session of a
+  // thread of `to`, the role's otherwise. Null while nobody holds it, and the message waits.
+  #recipient(business, to, session) {
+    const h = session && this.#threaded(business, to) ? this.#sessionHolder(session) : this.#holder(business, to);
    return h?.op === 'claim' ? h : null;
  }
-  // The thread a new message belongs to (REQ-MSG-1). A thread run's message is in its thread.
-  // A message to a thread instance from anyone else is in the thread of the nearest message up
-  // its in_reply_to chain that has one, so the chief of staff's reply returns to the thread
+  // The session a new message belongs to (REQ-MSG-1). A thread run's message is in its session.
+  // A message to a thread instance from anyone else is in the session of the nearest message up
+  // its in_reply_to chain that has one, so the chief of staff's reply returns to the session
  // that sent the work. Messages are append-only and in_reply_to names an earlier message, so
  // the chain has an end; `seen` stops the walk there and needs no depth constant.
-  #threadFor(s, to, inReplyTo) {
-    if (s.thread) return s.thread;
+  #sessionFor(s, to, inReplyTo) {
+    if (s.thread) return s.session;
    if (!this.#threaded(s.business, to)) return null;
    // The user names the thread with thread.send, which checks the owner (REQ-USER-2).
    if (s.human) fail('thread-required-use-thread-send');
@@ -427,18 +443,20 @@ export class Broker {
    for (let at = inReplyTo ?? null; at !== null && !seen.has(at); ) {
      seen.add(at);
      const m = this.#store.get(
-        'SELECT m.in_reply_to, m.from_role, m.body, t.thread FROM messages m LEFT JOIN message_threads t ON t.message=m.id WHERE m.id=? AND m.business=?',
+        'SELECT m.in_reply_to, m.from_role, m.body, t.thread, t.session FROM messages m LEFT JOIN message_threads t ON t.message=m.id WHERE m.id=? AND m.business=?',
        at,
        s.business,
      );
      if (m?.thread) {
        if (this.#store.get('SELECT instance FROM threads WHERE id=?', m.thread).instance !== to) fail('thread-instance-mismatch');
-        return this.#testerOwns(s, m.thread);
+        this.#testerOwns(s, m.thread);
+        return m.session;
      }
-      // Row 143: a chain that reaches a spec notice belongs to the user's thread in that notice's project.
+      // Row 143: a chain that reaches a spec notice belongs to the user's thread in that notice's
+      // project, in its default session.
      if (m?.from_role === NOTICE_ROLE && m.body.startsWith(SPEC_NOTICE)) {
        const spec = this.#specThread(s, to, m.body);
-        if (spec) return this.#testerOwns(s, spec);
+        if (spec) return this.#defaultSession(this.#testerOwns(s, spec));
      }
      at = m?.in_reply_to ?? null;
    }
@@ -500,26 +518,30 @@ export class Broker {
    const key = record.business + ':' + identifier(record.run);
    const session = this.#runs.get(key) ?? fail('unknown-run');
    if (this.#ended.has(key)) fail('run-ended');
-    // A run holds at most one thread, so this also refuses another thread and a non-thread run.
+    // A run holds at most one session, so this also refuses another thread and a non-thread run.
+    // Row 264a: the row is the thread's default session's, so a run of another session is refused too.
    const [t] = this.#threadRows('t.business=? AND t.id=?', record.business, identifier(record.thread));
    if (t?.holder !== record.run) fail('not-holder');
    if (t.pending || t.unread) return { released: false, pending: t.pending, unread: t.unread };
-    this.#store.transaction(() => this.#claimEnd(session, this.#threadHolder(t.thread), 'release', null));
+    this.#store.transaction(() => this.#claimEnd(session, this.#own(session), 'release', null));
    return { released: true };
  }
+  // Row 264a (#1769): each row is the thread's default session's. Until 264b the launcher starts
+  // default sessions only, so another session's messages wait.
  #threadRows(where, ...params) {
    return this.#store
      .all(
        `SELECT t.id, t.instance,
-          (SELECT count(*) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.thread=t.id AND m.to_role=t.instance
+          (SELECT count(*) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.session=ds.session AND m.to_role=t.instance
            AND NOT EXISTS(SELECT 1 FROM deliveries d WHERE d.message=m.id AND d.op IN ('delivered','read'))) AS pending,
-          (SELECT count(*) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.thread=t.id AND m.to_role=t.instance
+          (SELECT count(*) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.session=ds.session AND m.to_role=t.instance
            AND c.op='claim' AND EXISTS(SELECT 1 FROM deliveries d WHERE d.message=m.id AND d.op='delivered' AND d.holder_run=c.holder_run)
            AND NOT EXISTS(SELECT 1 FROM deliveries d WHERE d.message=m.id AND d.op='read')) AS unread,
-          (SELECT max(m.at) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.thread=t.id) AS last_message,
-          (SELECT max(at) FROM thread_opens WHERE thread=t.id) AS last_open,
+          (SELECT max(m.at) FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.session=ds.session) AS last_message,
+          (SELECT max(at) FROM thread_opens WHERE session=ds.session) AS last_open,
          c.at AS claim_at, c.op AS claim_op, c.holder_run AS holder_run
-        FROM threads t LEFT JOIN thread_claims c ON c.seq=(SELECT max(seq) FROM thread_claims WHERE thread=t.id)
+        FROM threads t JOIN session_defaults ds ON ds.seq=(SELECT max(seq) FROM session_defaults WHERE thread=t.id)
+          LEFT JOIN thread_claims c ON c.seq=(SELECT max(seq) FROM thread_claims WHERE session=ds.session)
        WHERE ${where} ORDER BY t.seq`,
        ...params,
      )
@@ -538,7 +560,7 @@ export class Broker {
  bindLaunch(record) {
    keys(
      record,
-      ['business', 'role', 'run', 'harness', 'address', 'pid', 'startTime', 'thread', 'provider', 'model', 'account', 'transcript'],
+      ['business', 'role', 'run', 'harness', 'address', 'pid', 'startTime', 'thread', 'session', 'provider', 'model', 'account', 'transcript'],
      ['business', 'role', 'run', 'harness'],
    );
    const b = this.#business(identifier(record.business));
@@ -561,10 +583,13 @@ export class Broker {
      if (record.thread === undefined) fail('thread-required');
      if (!this.#store.get('SELECT 1 FROM threads WHERE id=? AND business=? AND instance=?', identifier(record.thread), record.business, record.role))
        fail('thread-not-found');
-    } else if (record.thread !== undefined) fail('thread-not-allowed');
+    } else if (record.thread !== undefined || record.session !== undefined) fail('thread-not-allowed');
+    // Row 264a (#1769): a thread run works one session of its thread, the thread's default when the
+    // record names none (D3).
+    const bound = record.thread === undefined ? null : this.#threadSession({ id: record.thread }, record.session);
    const key = record.business + ':' + record.run;
    if (this.#runs.has(key)) fail('duplicate-run');
-    const session = { ...record, address: record.address ?? null, thread: record.thread ?? null, human: false };
+    const session = { ...record, address: record.address ?? null, thread: record.thread ?? null, session: bound, human: false };
    this.#secretCheck(record);
    const old = this.#store.get(
      "SELECT actor_role,body FROM events WHERE business=? AND kind='session.launched' AND subject=? ORDER BY seq LIMIT 1",
@@ -578,6 +603,8 @@ export class Broker {
      pid: record.pid ?? null,
      startTime: record.startTime ?? null,
      ...(record.thread === undefined ? {} : { thread: record.thread }),
+      // A record without a session keeps the body it had before row 264a.
+      ...(record.session === undefined ? {} : { session: record.session }),
    };
    // A run an earlier broker bound is bound again unchanged (the host's recover()), even after its
    // harness was switched off, so it can be ended.
@@ -733,14 +760,14 @@ export class Broker {
  // close is.
  #grantNotice(business, decision, body) {
    const d = this.#store.get('SELECT raised_by_role,raised_by_run FROM decisions WHERE id=?', decision);
-    const thread = this.#threaded(business, d.raised_by_role)
+    const session = this.#threaded(business, d.raised_by_role)
      ? (this.#store.get(
-          "SELECT thread FROM thread_claims WHERE business=? AND holder_run=? AND op='claim' ORDER BY seq DESC LIMIT 1",
+          "SELECT session FROM thread_claims WHERE business=? AND holder_run=? AND op='claim' ORDER BY seq DESC LIMIT 1",
          business,
          d.raised_by_run,
-        )?.thread ?? null)
+        )?.session ?? null)
      : null;
-    for (const [to, t] of [['human', null], [d.raised_by_role, thread]]) {
+    for (const [to, t] of [['human', null], [d.raised_by_role, session]]) {
      const mid = randomUUID();
      this.#store.run(
        'INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,in_reply_to,decision,corrects,body) VALUES(?,?,?,?,?,?,?,?,?,?,?)',
@@ -1958,7 +1985,7 @@ export class Broker {
      null,
      body,
    );
-    this.#route(s.business, mid, s.role, s.thread);
+    this.#route(s.business, mid, s.role, s.session);
  }
  // Trusted launcher API: whether the role, in the thread (null for a role run), holds a merge
  // decision a landing could use: cross-role, raised there with a task ref as its target, resolved
@@ -2647,22 +2674,25 @@ export class Broker {
        keys(a, []);
        if (s.human) fail('agent-required');
        // Row 121: a thread run claims its thread, so idle threads hold nothing (REQ-THREAD-2).
+        // Row 264a (#1769): the claim is the run's session's, with the session's next generation.
        if (s.thread) {
-          if (this.#store.get("SELECT 1 FROM thread_claims WHERE thread=? AND holder_run=? AND op='revoke' LIMIT 1", s.thread, s.run))
+          if (this.#store.get("SELECT 1 FROM thread_claims WHERE session=? AND holder_run=? AND op='revoke' LIMIT 1", s.session, s.run))
            fail('run-revoked');
-          if (this.#threadHolder(s.thread)?.op === 'claim') fail('thread-already-held');
+          if (this.#sessionHolder(s.session)?.op === 'claim') fail('thread-already-held');
          this.#store.run(
-            'INSERT INTO thread_claims(at,business,thread,op,holder_run,harness,address,by) VALUES(?,?,?,?,?,?,?,?)',
+            "INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,address,by) VALUES(?,?,?,?,1+(SELECT count(*) FROM thread_claims WHERE session=? AND op='claim'),?,?,?,?,?)",
            this.#now(),
            s.business,
            s.thread,
+            s.session,
+            s.session,
            'claim',
            s.run,
            s.harness,
            s.address,
            by,
          );
-          this.#routeThread(s.thread);
+          this.#routeSession(s.session);
          return { role: s.role, run: s.run, thread: s.thread };
        }
        if (
@@ -2711,7 +2741,7 @@ export class Broker {
          identifier(a.decision);
          this.#consumeAuthority(s, 'role.revoke', { decision: a.decision, target: a.role });
        }
-        // Row 155 (#1649): a thread instance holds a claim per thread, so the end revokes each one.
+        // Row 155 (#1649): a thread instance holds a claim per session, so the end revokes each one.
        if (this.#threaded(s.business, a.role)) {
          const held = this.#threadHolders(s.business, a.role);
          if (held.length === 0) fail('not-held');
@@ -2934,14 +2964,14 @@ export class Broker {
            op === 'resolved'
              ? `resolved by ${by}: ${a.choice} (${JSON.parse(d.options).find((o) => o.key === a.choice).text})`
              : `withdrawn by ${by}`;
-          // A close to a thread instance goes to the thread the raising run held. A decision
+          // A close to a thread instance goes to the session the raising run held. A decision
          // raised before row 121 has no thread claim and stays unthreaded.
-          const thread = this.#threaded(s.business, d.raised_by_role)
+          const session = this.#threaded(s.business, d.raised_by_role)
            ? (this.#store.get(
-                "SELECT thread FROM thread_claims WHERE business=? AND holder_run=? AND op='claim' ORDER BY seq DESC LIMIT 1",
+                "SELECT session FROM thread_claims WHERE business=? AND holder_run=? AND op='claim' ORDER BY seq DESC LIMIT 1",
                s.business,
                d.raised_by_run,
-              )?.thread ?? null)
+              )?.session ?? null)
            : null;
          const mid = randomUUID();
          this.#store.run(
@@ -2958,7 +2988,7 @@ export class Broker {
            null,
            `Decision ${d.id} on ${d.action} was ${outcome}.${a.note === undefined ? '' : `\nNote: ${a.note}`}`,
          );
-          this.#route(s.business, mid, d.raised_by_role, thread);
+          this.#route(s.business, mid, d.raised_by_role, session);
        }
        return grant ? { id: d.id, op, grant: 'started' } : { id: d.id, op };
      }
@@ -3025,7 +3055,7 @@ export class Broker {
        }
        if (a.class === 'BLOCK') this.#checkBlock(s, to, a.in_reply_to);
        if (a.decision) this.#decision(s, a.decision);
-        const thread = this.#threadFor(s, to, a.in_reply_to);
+        const thread = this.#sessionFor(s, to, a.in_reply_to);
        // Row 170 (#1667): a tester's message to a role nobody holds is refused before it is
        // stored, so a PM test never waits for the role's next run. A run launched but not yet
        // claimed counts as no holder, as in #waiting. No lock: a holder that releases once the
@@ -3062,14 +3092,14 @@ export class Broker {
          this.#received.add(s.business + ':' + s.run);
        }
        const role = s.human ? 'human' : s.role;
-        // A thread run receives its own thread's messages only (REQ-THREAD-1).
+        // A thread run receives its own session's messages only (REQ-THREAD-1, row 264a).
        const rows = this.#store.all(
          "SELECT * FROM messages m WHERE business=? AND to_role=? AND NOT EXISTS(SELECT 1 FROM deliveries d WHERE d.message=m.id AND d.op IN ('delivered','read'))" +
-            (s.thread ? ' AND EXISTS(SELECT 1 FROM message_threads mt WHERE mt.message=m.id AND mt.thread=?)' : '') +
+            (s.thread ? ' AND EXISTS(SELECT 1 FROM message_threads mt WHERE mt.message=m.id AND mt.session=?)' : '') +
            ' ORDER BY seq LIMIT 100',
          s.business,
          role,
-          ...(s.thread ? [s.thread] : []),
+          ...(s.thread ? [s.session] : []),
        );
        for (const m of rows)
          this.#delivery(
@@ -3481,6 +3511,8 @@ export class Broker {
          this.#owner(s),
          a.name,
        );
+        // Row 264a (#1769, D3): every thread has a default session from the start.
+        this.#newSession(s, { id: tid, business: s.business, instance: instances[0], owner: this.#owner(s) }, 'default', 'default', true);
        return { id: tid, instance: instances[0] };
      }
      // Row 177 (#1675): each lists its own threads. The human's list leaves out the tester's,
@@ -3498,20 +3530,23 @@ export class Broker {
          ...(a.project === undefined ? [] : [a.project]),
        );
      }
-      // Opening a thread asks the launcher to start its session (REQ-LAUNCH-1).
+      // Opening a thread asks the launcher to start its session (REQ-LAUNCH-1). Row 264a: a thread
+      // verb names one session of the thread, or works on its default (D3).
      case 'thread.open': {
        if (!s.tester) this.#human(s);
-        keys(a, ['thread'], ['thread']);
+        keys(a, ['thread', 'session'], ['thread']);
        const t = this.#thread(s, a.thread);
-        this.#store.run('INSERT INTO thread_opens(at,thread,by) VALUES(?,?,?)', this.#now(), t.id, this.#owner(s));
+        const session = this.#threadSession(t, a.session);
+        this.#store.run('INSERT INTO thread_opens(at,thread,session,by) VALUES(?,?,?,?)', this.#now(), t.id, session, this.#owner(s));
        return { opened: t.id };
      }
      // Row 177 (#1675): a tester's message is the tester's, from tester-cli, and writes no
      // human.input, as on message.send. In its own thread the lists read it as the human.
      case 'thread.send': {
        if (!s.tester) this.#human(s);
-        keys(a, ['thread', 'body', 'class'], ['thread', 'body']);
+        keys(a, ['thread', 'session', 'body', 'class'], ['thread', 'body']);
        const t = this.#thread(s, a.thread);
+        const session = this.#threadSession(t, a.session);
        // Row 120's lists hold here as on message.send: the instance must hear from the human.
        this.#checkMessaging(s.business, 'human', t.instance);
        string(a.body, 32768);
@@ -3531,31 +3566,60 @@ export class Broker {
          null,
          a.body,
        );
-        this.#route(s.business, mid, t.instance, t.id);
+        this.#route(s.business, mid, t.instance, session);
        return { id: mid, request: s.tester ? null : this.#event(s, 'human.input', { kind: 'instruction', message: mid }, mid) };
      }
      // The thread's history, oldest first. Reading writes nothing.
      case 'thread.messages': {
        if (!s.tester) this.#human(s);
-        keys(a, ['thread', 'after', 'limit'], ['thread']);
+        keys(a, ['thread', 'session', 'after', 'limit'], ['thread']);
        const t = this.#thread(s, a.thread);
+        const session = this.#threadSession(t, a.session);
        const limit = a.limit ?? THREAD_PAGE;
        if (!Number.isInteger(limit) || limit < 1 || limit > THREAD_PAGE_MAX) fail('invalid-request');
        let after = 0;
        if (a.after !== undefined) {
          after = this.#store.get(
-            'SELECT m.seq FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE m.id=? AND mt.thread=?',
+            'SELECT m.seq FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE m.id=? AND mt.session=?',
            identifier(a.after),
-            t.id,
+            session,
          )?.seq;
          if (after === undefined) fail('message-not-found');
        }
        return this.#store.all(
-          `SELECT m.* FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.thread=? AND m.seq>? ORDER BY m.seq LIMIT ${limit}`,
-          t.id,
+          `SELECT m.* FROM messages m JOIN message_threads mt ON mt.message=m.id WHERE mt.session=? AND m.seq>? ORDER BY m.seq LIMIT ${limit}`,
+          session,
          after,
        );
      }
+      // Row 264a (#1769, T1 item 7): a thread's sessions, oldest first, and which one is the default.
+      // Each user reaches only their own threads' sessions (REQ-USER-2); there are no shares (Q7).
+      case 'session.list': {
+        if (!s.tester) this.#human(s);
+        keys(a, ['thread'], ['thread']);
+        const t = this.#thread(s, a.thread);
+        const fallback = this.#defaultSession(t.id);
+        return this.#store
+          .all('SELECT id,at,name,predecessor FROM sessions WHERE thread=? ORDER BY seq', t.id)
+          .map((r) => ({ ...r, default: r.id === fallback }));
+      }
+      // D8: a new session is metadata only. Its run starts when the launcher starts it (264b).
+      // The op key makes a retry find the first row: the same op and name answer it, another name
+      // under the same op refuses.
+      case 'session.create': {
+        if (!s.tester) this.#human(s);
+        keys(a, ['thread', 'name', 'op'], ['thread', 'name', 'op']);
+        if (!name(a.name)) fail('invalid-request');
+        identifier(a.op);
+        const t = this.#thread(s, a.thread);
+        const old = this.#store.get('SELECT id,name FROM sessions WHERE thread=? AND op=?', t.id, a.op);
+        if (old) {
+          if (old.name !== a.name) fail('session-op-conflict');
+          return { id: old.id, thread: t.id, name: old.name };
+        }
+        if (this.#store.get('SELECT 1 FROM sessions WHERE thread=? AND name=?', t.id, a.name)) fail('session-exists');
+        return { id: this.#newSession(s, t, a.name, a.op, false), thread: t.id, name: a.name };
+      }
      case 'replies': {
        if (!s.human && !s.reader) fail('human-required');
        keys(a, ['id'], ['id']);
@@ -3611,10 +3675,12 @@ export class Broker {
  #claimEnd(s, h, op, decision, reason = null, by = s.run ?? s.human) {
    if (h.thread)
      return this.#store.run(
-        'INSERT INTO thread_claims(at,business,thread,op,holder_run,harness,address,by,decision,reason) VALUES(?,?,?,?,?,?,?,?,?,?)',
+        'INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,address,by,decision,reason) VALUES(?,?,?,?,?,?,?,?,?,?,?,?)',
        this.#now(),
        s.business,
        h.thread,
+        h.session,
+        h.generation,
        op,
        h.holder_run,
        h.harness,
@@ -3657,7 +3723,7 @@ export class Broker {
  }
  // The message a review verb sends, routed like message.send's.
  #reviewMessage(s, mid, { to, cls, in_reply_to = null, decision = null, body }) {
-    const thread = this.#threadFor(s, to, in_reply_to);
+    const thread = this.#sessionFor(s, to, in_reply_to);
    this.#store.run(
      'INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,in_reply_to,decision,corrects,body) VALUES(?,?,?,?,?,?,?,?,?,?,?)',
      mid,
@@ -3675,9 +3741,35 @@ export class Broker {
    this.#route(s.business, mid, to, thread);
  }
  // Row 121: a message names its thread (REQ-MSG-1) and goes to the holder that may have it.
-  #route(business, mid, to, thread) {
-    if (thread) this.#store.run('INSERT INTO message_threads(message,thread) VALUES(?,?)', mid, thread);
-    this.#delivery(mid, 'routed', this.#recipient(business, to, thread));
+  // Row 264a (#1769): it names one session of the thread, and the session's holder may have it.
+  #route(business, mid, to, session) {
+    if (session) {
+      const { thread } = this.#store.get('SELECT thread FROM sessions WHERE id=?', session);
+      this.#store.run('INSERT INTO message_threads(message,thread,session) VALUES(?,?,?)', mid, thread, session);
+    }
+    this.#delivery(mid, 'routed', this.#recipient(business, to, session));
+  }
+  // Row 264a (#1769): a session row and, for a new thread, its default. The 3j-3k migration made the
+  // legacy defaults, whose id is the thread id; a new session's id is random, and a trigger refuses
+  // one that names another thread.
+  #newSession(s, t, sessionName, op, makeDefault) {
+    const sid = randomUUID();
+    const at = this.#now();
+    this.#store.run(
+      'INSERT INTO sessions(id,at,business,thread,instance,owner,name,op,predecessor) VALUES(?,?,?,?,?,?,?,?,?)',
+      sid,
+      at,
+      t.business,
+      t.id,
+      t.instance,
+      t.owner,
+      sessionName,
+      op,
+      null,
+    );
+    if (makeDefault)
+      this.#store.run('INSERT INTO session_defaults(at,thread,session,by) VALUES(?,?,?,?)', at, t.id, sid, this.#owner(s));
+    return sid;
  }
  // Row 146 (#1640): a message.send that nobody holds the target for waits for a claim. Null when
  // the message was routed to a holder, or is the human's, a tester's, or in a thread to a thread
@@ -3804,12 +3896,12 @@ export class Broker {
    );
    for (const m of rows) this.#delivery(m.id, 'routed', h);
  }
-  // A new thread holder gets the thread's waiting messages to the instance.
-  #routeThread(thread) {
-    const h = this.#threadHolder(thread);
+  // A new session holder gets the session's waiting messages to the instance.
+  #routeSession(session) {
+    const h = this.#sessionHolder(session);
    const rows = this.#store.all(
-      "SELECT m.id FROM messages m JOIN message_threads mt ON mt.message=m.id JOIN threads t ON t.id=mt.thread WHERE mt.thread=? AND m.to_role=t.instance AND NOT EXISTS(SELECT 1 FROM deliveries WHERE message=m.id AND op IN ('delivered','read'))",
-      thread,
+      "SELECT m.id FROM messages m JOIN message_threads mt ON mt.message=m.id JOIN threads t ON t.id=mt.thread WHERE mt.session=? AND m.to_role=t.instance AND NOT EXISTS(SELECT 1 FROM deliveries WHERE message=m.id AND op IN ('delivered','read'))",
+      session,
    );
    for (const m of rows) this.#delivery(m.id, 'routed', h);
  }
@@ -0,0 +1,168 @@
+-- Row 264a (#1769, T1 item 7): sessions below a thread. Each existing thread gets one legacy default
+-- session whose id is the thread id, and its claims, messages and opens name that session (D9's
+-- mapping). thread_claims, message_threads and thread_opens are rebuilt with a session column, and
+-- thread_claims gains generation, the claim's number in its session. Rows are copied with their seq
+-- values and old columns as they were, and the sequences carry over, as 3h-3i did. The guards and the
+-- delivery trigger that read the old tables are dropped first, so the renames rewrite nothing.
+DROP TRIGGER thread_one_holder;
+DROP TRIGGER thread_one_per_run;
+DROP TRIGGER thread_release_by_holder;
+DROP TRIGGER thread_release_same_run;
+DROP TRIGGER thread_revoke_needs_decision;
+DROP TRIGGER thread_claims_business;
+DROP TRIGGER message_threads_match;
+DROP TRIGGER delivery_same_thread;
+DROP TRIGGER thread_claims_no_update;
+DROP TRIGGER thread_claims_no_delete;
+DROP TRIGGER thread_claims_no_replace;
+DROP TRIGGER message_threads_no_update;
+DROP TRIGGER message_threads_no_delete;
+DROP TRIGGER message_threads_no_replace;
+DROP TRIGGER thread_opens_no_update;
+DROP TRIGGER thread_opens_no_delete;
+DROP TRIGGER thread_opens_no_replace;
+DROP INDEX thread_claims_thread;
+DROP INDEX message_threads_thread;
+ALTER TABLE thread_claims RENAME TO thread_claims_3j;
+ALTER TABLE message_threads RENAME TO message_threads_3j;
+ALTER TABLE thread_opens RENAME TO thread_opens_3j;
+CREATE TABLE sessions (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  instance TEXT NOT NULL,
+  owner TEXT NOT NULL,
+  name TEXT NOT NULL,
+  op TEXT NOT NULL,
+  predecessor TEXT REFERENCES sessions(id),
+  UNIQUE (thread, name),
+  UNIQUE (thread, op)
+) STRICT;
+CREATE TABLE session_defaults (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
+  by TEXT NOT NULL
+) STRICT;
+INSERT INTO sessions(at,business,thread,id,instance,owner,name,op,predecessor)
+  SELECT at,business,id,id,instance,owner,'default','legacy-3k',NULL FROM threads ORDER BY seq;
+INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads ORDER BY seq;
+CREATE TABLE thread_claims (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
+  generation INTEGER NOT NULL CHECK (generation >= 1),
+  op TEXT NOT NULL CHECK (op IN ('claim','release','revoke')),
+  holder_run TEXT NOT NULL,
+  harness TEXT NOT NULL, address TEXT,
+  by TEXT NOT NULL, reason TEXT,
+  decision TEXT
+) STRICT;
+CREATE TABLE message_threads (
+  message TEXT PRIMARY KEY REFERENCES messages(id),
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id)
+) STRICT;
+CREATE TABLE thread_opens (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  session TEXT NOT NULL REFERENCES sessions(id),
+  by TEXT NOT NULL
+) STRICT;
+INSERT INTO thread_claims(seq,at,business,thread,session,generation,op,holder_run,harness,address,by,reason,decision)
+  SELECT c.seq,c.at,c.business,c.thread,c.thread,
+    (SELECT count(*) FROM thread_claims_3j p WHERE p.thread = c.thread AND p.op = 'claim' AND p.seq <= c.seq),
+    c.op,c.holder_run,c.harness,c.address,c.by,c.reason,c.decision FROM thread_claims_3j c ORDER BY c.seq;
+INSERT INTO message_threads(message,thread,session) SELECT message,thread,thread FROM message_threads_3j ORDER BY rowid;
+INSERT INTO thread_opens(seq,at,thread,session,by) SELECT seq,at,thread,thread,by FROM thread_opens_3j ORDER BY seq;
+DELETE FROM sqlite_sequence WHERE name IN ('thread_claims','thread_opens');
+INSERT INTO sqlite_sequence(name,seq) SELECT 'thread_claims', seq FROM sqlite_sequence WHERE name='thread_claims_3j';
+INSERT INTO sqlite_sequence(name,seq) SELECT 'thread_opens', seq FROM sqlite_sequence WHERE name='thread_opens_3j';
+DROP TABLE thread_claims_3j;
+DROP TABLE message_threads_3j;
+DROP TABLE thread_opens_3j;
+CREATE INDEX thread_claims_thread ON thread_claims (thread, seq);
+CREATE INDEX thread_claims_session ON thread_claims (session, seq);
+CREATE INDEX message_threads_thread ON message_threads (thread);
+CREATE INDEX message_threads_session ON message_threads (session);
+CREATE INDEX session_defaults_thread ON session_defaults (thread, seq);
+CREATE TRIGGER sessions_thread_match BEFORE INSERT ON sessions
+  WHEN NOT EXISTS (SELECT 1 FROM threads t WHERE t.id = NEW.thread AND t.business = NEW.business AND t.instance = NEW.instance AND t.owner = NEW.owner)
+  BEGIN SELECT RAISE(ABORT, 'a session has its thread''s business, instance and owner'); END;
+CREATE TRIGGER sessions_predecessor BEFORE INSERT ON sessions
+  WHEN NEW.predecessor IS NOT NULL AND (SELECT thread FROM sessions WHERE id = NEW.predecessor) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a session''s predecessor is in its thread'); END;
+CREATE TRIGGER sessions_id_not_thread BEFORE INSERT ON sessions
+  WHEN NEW.id IS NOT NEW.thread AND EXISTS (SELECT 1 FROM threads WHERE id = NEW.id)
+  BEGIN SELECT RAISE(ABORT, 'a session id names another thread'); END;
+CREATE TRIGGER threads_id_not_session BEFORE INSERT ON threads
+  WHEN EXISTS (SELECT 1 FROM sessions WHERE id = NEW.id)
+  BEGIN SELECT RAISE(ABORT, 'a thread id names a session'); END;
+CREATE TRIGGER session_defaults_match BEFORE INSERT ON session_defaults
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a default session is in its thread'); END;
+CREATE TRIGGER thread_one_holder BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'claim' AND (SELECT op FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) = 'claim'
+  BEGIN SELECT RAISE(ABORT, 'session already held'); END;
+CREATE TRIGGER thread_one_per_run BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'claim' AND EXISTS (SELECT 1 FROM thread_claims c WHERE c.holder_run = NEW.holder_run AND c.business = NEW.business
+    AND c.seq = (SELECT max(seq) FROM thread_claims WHERE session = c.session) AND c.op = 'claim')
+  BEGIN SELECT RAISE(ABORT, 'run already holds a session'); END;
+CREATE TRIGGER thread_release_by_holder BEFORE INSERT ON thread_claims
+  WHEN NEW.op IN ('release','revoke') AND COALESCE((SELECT op FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1),'') <> 'claim'
+  BEGIN SELECT RAISE(ABORT, 'session is not held'); END;
+CREATE TRIGGER thread_release_same_run BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'release' AND (SELECT holder_run FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) <> NEW.holder_run
+  BEGIN SELECT RAISE(ABORT, 'only the holder releases; others revoke'); END;
+CREATE TRIGGER thread_claim_generation BEFORE INSERT ON thread_claims
+  WHEN NEW.generation IS NOT (CASE WHEN NEW.op = 'claim'
+    THEN 1 + (SELECT count(*) FROM thread_claims WHERE session = NEW.session AND op = 'claim')
+    ELSE (SELECT generation FROM thread_claims WHERE session = NEW.session ORDER BY seq DESC LIMIT 1) END)
+  BEGIN SELECT RAISE(ABORT, 'a claim row names its session''s generation'); END;
+CREATE TRIGGER thread_revoke_needs_decision BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'revoke' AND NEW.decision IS NULL AND NEW.reason IS NULL
+  BEGIN SELECT RAISE(ABORT, 'revoke needs a resolved decision or a reason'); END;
+CREATE TRIGGER thread_claims_business BEFORE INSERT ON thread_claims
+  WHEN (SELECT business FROM threads WHERE id = NEW.thread) IS NOT NEW.business
+  BEGIN SELECT RAISE(ABORT, 'a thread claim names the thread''s business'); END;
+CREATE TRIGGER thread_claims_session BEFORE INSERT ON thread_claims
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a claim''s session is in its thread'); END;
+CREATE TRIGGER message_threads_match BEFORE INSERT ON message_threads
+  WHEN NOT EXISTS (SELECT 1 FROM messages m JOIN threads t ON t.id = NEW.thread
+    WHERE m.id = NEW.message AND m.business = t.business AND t.instance IN (m.to_role, m.from_role))
+  BEGIN SELECT RAISE(ABORT, 'a threaded message is to or from the thread''s instance'); END;
+CREATE TRIGGER message_threads_session BEFORE INSERT ON message_threads
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'a threaded message''s session is in its thread'); END;
+CREATE TRIGGER thread_opens_session BEFORE INSERT ON thread_opens
+  WHEN (SELECT thread FROM sessions WHERE id = NEW.session) IS NOT NEW.thread
+  BEGIN SELECT RAISE(ABORT, 'an open''s session is in its thread'); END;
+CREATE TRIGGER delivery_same_session BEFORE INSERT ON deliveries
+  WHEN NEW.op IN ('routed','delivered') AND (NEW.op = 'delivered' OR NEW.holder_run IS NOT NULL)
+    AND EXISTS (SELECT 1 FROM message_threads mt JOIN messages m ON m.id = mt.message JOIN threads t ON t.id = mt.thread
+      WHERE mt.message = NEW.message AND m.to_role = t.instance
+        AND NOT EXISTS (SELECT 1 FROM thread_claims c WHERE c.seq = (SELECT max(seq) FROM thread_claims WHERE session = mt.session)
+          AND c.op = 'claim' AND c.holder_run IS NEW.holder_run))
+  BEGIN SELECT RAISE(ABORT, 'a threaded message goes only to its session''s holder'); END;
+CREATE TRIGGER sessions_no_update BEFORE UPDATE ON sessions BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER sessions_no_delete BEFORE DELETE ON sessions BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER sessions_no_replace BEFORE INSERT ON sessions WHEN EXISTS (SELECT 1 FROM sessions WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'sessions is append-only'); END;
+CREATE TRIGGER session_defaults_no_update BEFORE UPDATE ON session_defaults BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
+CREATE TRIGGER session_defaults_no_delete BEFORE DELETE ON session_defaults BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
+CREATE TRIGGER session_defaults_no_replace BEFORE INSERT ON session_defaults WHEN EXISTS (SELECT 1 FROM session_defaults WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'session_defaults is append-only'); END;
+CREATE TRIGGER thread_claims_no_update BEFORE UPDATE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER thread_claims_no_delete BEFORE DELETE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER thread_claims_no_replace BEFORE INSERT ON thread_claims WHEN EXISTS (SELECT 1 FROM thread_claims WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER message_threads_no_update BEFORE UPDATE ON message_threads BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER message_threads_no_delete BEFORE DELETE ON message_threads BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER message_threads_no_replace BEFORE INSERT ON message_threads WHEN EXISTS (SELECT 1 FROM message_threads WHERE message = NEW.message) BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER thread_opens_no_update BEFORE UPDATE ON thread_opens BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
+CREATE TRIGGER thread_opens_no_delete BEFORE DELETE ON thread_opens BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
+CREATE TRIGGER thread_opens_no_replace BEFORE INSERT ON thread_opens WHEN EXISTS (SELECT 1 FROM thread_opens WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
@@ -13,8 +13,8 @@ import { join, isAbsolute } from 'node:path';
 import { createHash } from 'node:crypto';

 const ddl = readFileSync(new URL('../schema.sql', import.meta.url), 'utf8');
-export const SCHEMA_SHA256 = '0a7b633ce7eec9d0bb37c3255f4244d97bd0c8eac38db91a11b4ef6cc982ec8c';
-export const SCHEMA_VERSION = '3j';
+export const SCHEMA_SHA256 = '860374bde3f063ecfd72618913e05924587b7c39b87b763eee4c6aeb59922f46';
+export const SCHEMA_VERSION = '3k';
 // Ordered, named offline steps. New schema changes append a step and keep prior DDL pinned.
 const legacyDDL = readFileSync(new URL('./migrations/3b.sql', import.meta.url), 'utf8');
 const LEGACY_SHA256 = '179ffe356d4ff19a49b5ebad39b6c6bfd7771deb8e1b7c55b5e746f039d69e65';
@@ -61,6 +61,12 @@ const migrations = [{
  from: '3i',
  to: '3j',
  sql: readFileSync(new URL('./migrations/3i-3j.sql', import.meta.url), 'utf8'),
+}, {
+  // Row 264a (#1769): sessions below a thread. Each thread gets a default session whose id is the
+  // thread id, and thread_claims, message_threads and thread_opens are rebuilt to name it.
+  from: '3j',
+  to: '3k',
+  sql: readFileSync(new URL('./migrations/3j-3k.sql', import.meta.url), 'utf8'),
 }];
 const timedTables = [
  'events',
@@ -72,6 +78,8 @@ const timedTables = [
  'task_snapshots',
  'projects',
  'threads',
+  'sessions',
+  'session_defaults',
  'thread_claims',
  'thread_opens',
  'instance_names',
@@ -15,6 +15,9 @@ const AT = '2026-10-18T00:00:00.000Z';
 const SEQUENCE = 50;
 const ddl3h = readFileSync(new URL('./fixtures/schema-3h.sql', import.meta.url), 'utf8');
 const here = (p) => new URL(p, import.meta.url);
+// Row 264a (#1769): what the 3j→3k step rebuilds or adds. sessions.test.mjs tests those objects.
+const SESSIONS_3K = ['sessions', 'session_defaults', 'thread_claims', 'message_threads', 'thread_opens'];
+const later3k = (r) => SESSIONS_3K.includes(r.tbl_name) || ['delivery_same_thread', 'delivery_same_session'].includes(r.name);
 function source3h(t) {
  const root = mkdtempSync(join(tmpdir(), 'account-migrate-'));
  t.after(() => rmSync(root, { recursive: true, force: true }));
@@ -70,6 +73,7 @@ async function engine(root, name, { store, schema, step = (s) => s }) {
    copyFileSync(here('../src/migrations/' + file), join(moduleRoot, 'src/migrations', file));
  writeFileSync(join(moduleRoot, 'src/migrations/3h-3i.sql'), step(readFileSync(here('../src/migrations/3h-3i.sql'), 'utf8')));
  copyFileSync(here('../src/migrations/3i-3j.sql'), join(moduleRoot, 'src/migrations/3i-3j.sql'));
+  copyFileSync(here('../src/migrations/3j-3k.sql'), join(moduleRoot, 'src/migrations/3j-3k.sql'));
  return (await import(pathToFileURL(join(moduleRoot, 'src/store.mjs')))).Store;
 }

@@ -77,7 +81,7 @@ test('REQ-LIMIT-4 3h copy migrates to 3i: every row keeps its seq, the sequence
  const { root, path } = source3h(t), before = snapshot(path), was = master(path);
  assert.throws(() => new Store(root), /schema-mismatch/);
  new Store(root, { migrateSchema: true }).close();
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
  // Every table's rows as they were, usage_records with its seq values and sqlite_sequence with 50.
  assert.deepEqual(snapshot(path, before.columns).rows, before.rows);
  assert.deepEqual(before.rows.usage_records.map(r => r.seq), [1, 2, 3]);
@@ -87,7 +91,7 @@ test('REQ-LIMIT-4 3h copy migrates to 3i: every row keeps its seq, the sequence
  assert.equal(was.filter(r => r.sql?.includes(old)).map(r => r.name).join(), 'usage_records');
  // Row 234 (#1740) adds 3i→3j's own objects after this step. Its test is grant-migration.test.mjs.
  const later = ['hosts', 'host_grants', 'events_grant_actor', 'sqlite_autoindex_hosts_1', 'sqlite_autoindex_host_grants_1'];
-  assert.deepEqual(master(path).filter(r => !later.includes(r.name)), was.map(r => r.name === 'usage_records' ? { ...r, sql: r.sql.replace(old, '  account TEXT,\n') } : r));
+  assert.deepEqual(master(path).filter(r => !later.includes(r.name) && !later3k(r)), was.filter(r => !later3k(r)).map(r => r.name === 'usage_records' ? { ...r, sql: r.sql.replace(old, '  account TEXT,\n') } : r));
  assert.equal(was.filter(r => r.type === 'trigger' && r.tbl_name === 'usage_records').length, 3);
  const store = new Store(root);
  try {
@@ -125,7 +129,7 @@ test('REQ-LIMIT-4 a 3h→3i step that fails partway leaves the store at 3h with
  assert.deepEqual(snapshot(path, before.columns).rows, before.rows);
  // Still a whole 3h store: the real step migrates it.
  new Store(root, { migrateSchema: true }).close();
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
  assert.deepEqual(snapshot(path, before.columns).rows, before.rows);
 });

@@ -137,14 +141,14 @@ test('REQ-LIMIT-4 the 3h engine refuses a migrated store, migrating or not, and
    schema: ddl3h,
    store: (source) => source
      .replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${createHash('sha256').update(ddl3h).digest('hex')}';`)
-      .replace("export const SCHEMA_VERSION = '3j';", "export const SCHEMA_VERSION = '3h';")
+      .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3h';")
      .replace(/\}, \{\n {2}\/\/ Row 126 \(#1620\)[\s\S]*?\}\];\nconst timedTables/, '}];\nconst timedTables'),
  });
  const pinned = readFileSync(join(root, 'engine-3h/src/store.mjs'), 'utf8');
  assert.ok(pinned.includes("export const SCHEMA_VERSION = '3h';") && !pinned.includes('3h-3i'), 'the 3h engine has no 3h→3i step');
  assert.throws(() => new Store3h(root), /schema-mismatch/);
  assert.throws(() => new Store3h(root, { migrateSchema: true }), /schema-mismatch/);
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
  assert.deepEqual(master(path), was);
  assert.deepEqual(snapshot(path, after.columns).rows, after.rows);
 });
@@ -606,7 +606,7 @@ async function database3c(t) {
  let source = readFileSync(here('../src/store.mjs'), 'utf8');
  const pinned = source
    .replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${createHash('sha256').update(ddl3c).digest('hex')}';`)
-    .replace("export const SCHEMA_VERSION = '3j';", "export const SCHEMA_VERSION = '3c';")
+    .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3c';")
    .replace(/\}, \{\n {2}from: '3c',[\s\S]*?\}\];\nconst timedTables/, '}];\nconst timedTables');
  assert.notEqual(pinned, source);
  assert.ok(!pinned.includes('3c-3d'), 'the 3c engine has no 3c→3d step');
@@ -630,7 +630,7 @@ test('REQ-ROLE-2, REQ-COS-1: the 3c→3d migration lets the chief of staff end a
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
  t.after(() => store.close());
-  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
  assert.equal(store.get("SELECT body FROM events WHERE id='preserved'").body, '{"fixture":true}');
  assert.equal(store.get("SELECT holder_run FROM role_claims WHERE role='coder'").holder_run, 'coder-run');
  const b = new Broker({ store, businesses: demo(), organization: null });
@@ -33,7 +33,7 @@ test('explicit 3b copy migration preserves evidence and opens as 3g; normal star
  const original = readFileSync(source);
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
-  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
  assert.equal(store.get("SELECT body FROM events WHERE id='preserved'").body, '{"fixture":true}');
  assert.equal(store.get('SELECT count(*) n FROM task_comment_cursors').n, 0);
  const epoch = store.get("SELECT value FROM meta WHERE key='comment_cursor_epoch'").value;
@@ -75,15 +75,15 @@ test('named migration registry chains 3b through 3g to a fixture-only future ver
  const sha = createHash('sha256').update(futureDDL).digest('hex');
  let source = readFileSync(new URL('../src/store.mjs', import.meta.url), 'utf8');
  source = source.replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${sha}';`)
-    .replace("export const SCHEMA_VERSION = '3j';", "export const SCHEMA_VERSION = '3k';")
-    .replace('}];\nconst timedTables', `}, { from: '3j', to: '3k', sql: ${JSON.stringify(futureSQL)} }];\nconst timedTables`);
+    .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3l';")
+    .replace('}];\nconst timedTables', `}, { from: '3k', to: '3l', sql: ${JSON.stringify(futureSQL)} }];\nconst timedTables`);
  writeFileSync(join(moduleRoot, 'src/store.mjs'), source);
  writeFileSync(join(moduleRoot, 'schema.sql'), futureDDL);
-  for (const name of ['3b.sql', '3b-3c.sql', '3c-3d.sql', '3d-3e.sql', '3e-3f.sql', '3f-3g.sql', '3g-3h.sql', '3h-3i.sql', '3i-3j.sql'])
+  for (const name of ['3b.sql', '3b-3c.sql', '3c-3d.sql', '3d-3e.sql', '3e-3f.sql', '3f-3g.sql', '3g-3h.sql', '3h-3i.sql', '3i-3j.sql', '3j-3k.sql'])
    copyFileSync(new URL('../src/migrations/' + name, import.meta.url), join(moduleRoot, 'src/migrations', name));
  const { Store: FutureStore } = await import(pathToFileURL(join(moduleRoot, 'src/store.mjs')));
  const future = new FutureStore(root, { migrateSchema: true });
-  assert.equal(future.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
+  assert.equal(future.get("SELECT value FROM meta WHERE key='schema_version'").value, '3l');
  assert.equal(future.get("SELECT name FROM sqlite_master WHERE name='future_fixture'").name, 'future_fixture');
  assert.equal(future.get("SELECT count(*) n FROM task_comment_cursors").n, 0);
  assert.equal(future.get("SELECT id FROM events").id, 'preserved');
@@ -109,7 +109,7 @@ test('offline command migrates only the supplied fixture root and reports usage
  const command = new URL('../src/migrate-schema.mjs', import.meta.url).pathname;
  const migrated = spawnSync(process.execPath, [command, root], { encoding: 'utf8' });
  assert.equal(migrated.status, 0, migrated.stderr);
-  assert.match(migrated.stdout, /bus schema 3j ready/);
+  assert.match(migrated.stdout, /bus schema 3k ready/);
  new Store(root).close();
  const usage = spawnSync(process.execPath, [command], { encoding: 'utf8' });
  assert.equal(usage.status, 2);
@@ -8,6 +8,12 @@ import { join } from 'node:path';
 import { Store } from '../src/store.mjs';
 import { Broker } from '../src/broker.mjs';
 import { Client } from '../src/client.mjs';
+// Row 264a (#1769): a thread made by hand gets the default session the 3j-3k migration gives a
+// legacy thread, with the thread's id.
+const DEFAULT_SESSION = [
+  'INSERT INTO sessions(at,business,thread,id,instance,owner,name,op) SELECT at,business,id,id,instance,owner,'default','legacy-3k' FROM threads WHERE id=?',
+  'INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads WHERE id=?',
+];

 const businesses = {
  demo: {
@@ -149,7 +155,8 @@ test('broker process: launch ops authorize role.launch, record refusals and end
  const side = new Store(data);
  side.run('INSERT INTO projects(id,at,business,name,repo,created_by) VALUES(?,?,?,?,?,?)', 'p-1', '2026-10-15T00:00:00.000Z', 'demo', 'work', null, 'jason');
  side.run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)', 'th-1', '2026-10-15T00:00:00.000Z', 'demo', 'p-1', 'coder', 'jason', 'one');
-  side.run('INSERT INTO thread_opens(at,thread,by) VALUES(?,?,?)', '2026-10-15T00:00:01.000Z', 'th-1', 'jason');
+  for (const sql of DEFAULT_SESSION) side.run(sql, 'th-1');
+  side.run('INSERT INTO thread_opens(at,thread,session,by) VALUES(?,?,?,?)', '2026-10-15T00:00:01.000Z', 'th-1', 'th-1', 'jason');
  side.close();
  const ready = await ask(child, {
    op: 'boot',
@@ -0,0 +1,396 @@
+PRAGMA journal_mode = WAL;
+PRAGMA foreign_keys = ON;
+CREATE TABLE meta (key TEXT PRIMARY KEY, value TEXT NOT NULL) STRICT;
+CREATE TABLE events (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  kind TEXT NOT NULL CHECK (kind IN (
+    'session.launched',
+    'session.ended',
+    'action.allowed',
+    'action.refused',
+    'task.created',
+    'task.assigned',
+    'task.state',
+    'task.closed',
+    'task.changed.external',
+    'task.conflict',
+    'task.missing',
+    'review.requested',
+    'review.verdict',
+    'human.input',
+    'config.refused',
+    'credential.expiring',
+    'credential.expired',
+    'credential.changed',
+    'launch.revoked',
+    'launch.restored',
+    'digest.sent')),
+  actor_role TEXT, actor_run TEXT,
+  subject TEXT,
+  corrects TEXT REFERENCES events(id),
+  body TEXT NOT NULL CHECK (json_valid(body))
+) STRICT;
+CREATE TABLE role_claims (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL, role TEXT NOT NULL,
+  op TEXT NOT NULL CHECK (op IN ('claim','release','revoke')),
+  holder_run TEXT NOT NULL,
+  harness TEXT NOT NULL, address TEXT,
+  by TEXT NOT NULL, reason TEXT,
+  decision TEXT
+) STRICT;
+CREATE TABLE decisions (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL, project TEXT,
+  raised_by_role TEXT NOT NULL, raised_by_run TEXT NOT NULL,
+  class TEXT NOT NULL CHECK (class IN ('routine','within-role','cross-role','gated')),
+  action TEXT NOT NULL,
+  route_to TEXT NOT NULL,
+  question TEXT NOT NULL,
+  options TEXT NOT NULL CHECK (json_valid(options) AND json_array_length(options) BETWEEN 2 AND 9),
+  recommendation TEXT NOT NULL,
+  task_ref TEXT CHECK (task_ref IS NULL OR (task_ref GLOB 'vikunja:[1-9]*/[1-9]*' AND NOT substr(task_ref, 9) GLOB '*[^0-9/]*' AND NOT substr(task_ref, 9) GLOB '*/*/*')), requirement_ref TEXT,
+  blocking INTEGER NOT NULL CHECK (blocking IN (0,1)),
+  supersedes TEXT REFERENCES decisions(id)
+, spec_path TEXT, spec_commit TEXT) STRICT;
+CREATE TABLE decision_events (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  decision TEXT NOT NULL REFERENCES decisions(id),
+  at TEXT NOT NULL,
+  op TEXT NOT NULL CHECK (op IN ('seen','resolved','withdrawn','expired')),
+  by TEXT NOT NULL,
+  choice TEXT, note TEXT, via TEXT
+) STRICT;
+CREATE TABLE messages (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  from_role TEXT NOT NULL, from_run TEXT NOT NULL,
+  to_role TEXT NOT NULL,
+  class TEXT NOT NULL,
+  in_reply_to TEXT REFERENCES messages(id),
+  decision TEXT REFERENCES decisions(id),
+  corrects TEXT REFERENCES messages(id),
+  body TEXT NOT NULL
+, to_name TEXT) STRICT;
+CREATE TABLE deliveries (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  message TEXT NOT NULL REFERENCES messages(id),
+  at TEXT NOT NULL,
+  op TEXT NOT NULL CHECK (op IN ('routed','delivered','failed','read')),
+  holder_run TEXT, transport TEXT, address TEXT, detail TEXT
+) STRICT;
+CREATE TABLE task_snapshots (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  task_ref TEXT NOT NULL CHECK (task_ref GLOB 'vikunja:[1-9]*/[1-9]*' AND NOT substr(task_ref, 9) GLOB '*[^0-9/]*' AND NOT substr(task_ref, 9) GLOB '*/*/*'),
+  updated TEXT NOT NULL,
+  etag TEXT,
+  digest TEXT NOT NULL CHECK (length(digest) = 64 AND NOT digest GLOB '*[^0-9a-f]*'),
+  fields TEXT NOT NULL CHECK (json_valid(fields)),
+  source TEXT NOT NULL CHECK (source IN ('self','poll')),
+  via TEXT CHECK (via IN ('board','cursor','task','reconcile')),
+  read_at TEXT,
+  role TEXT, run TEXT,
+  CHECK ((source = 'self') = (role IS NOT NULL AND run IS NOT NULL)),
+  CHECK ((source = 'poll') = (via IS NOT NULL AND read_at IS NOT NULL)),
+  CHECK (json_type(fields, '$.bucket') IS 'integer'
+         OR (source IS 'poll' AND via IS 'task' AND json_type(fields, '$.gone') IS 'text'))
+) STRICT;
+CREATE INDEX task_snapshots_ref ON task_snapshots (business, task_ref, seq);
+CREATE TRIGGER decisions_resolve_once BEFORE INSERT ON decision_events
+  WHEN NEW.op IN ('resolved','withdrawn','expired') AND EXISTS (
+    SELECT 1 FROM decision_events WHERE decision = NEW.decision AND op IN ('resolved','withdrawn','expired'))
+  BEGIN SELECT RAISE(ABORT, 'decision already closed'); END;
+CREATE TRIGGER decisions_resolved_choice BEFORE INSERT ON decision_events
+  WHEN NEW.op = 'resolved' AND (NEW.choice IS NULL OR NOT EXISTS (
+    SELECT 1 FROM decisions d, json_each(d.options) o WHERE d.id = NEW.decision AND json_extract(o.value,'$.key') = NEW.choice))
+  BEGIN SELECT RAISE(ABORT, 'resolution must name one of the options'); END;
+CREATE TRIGGER role_one_holder BEFORE INSERT ON role_claims
+  WHEN NEW.op = 'claim' AND (SELECT op FROM role_claims WHERE business = NEW.business AND role = NEW.role ORDER BY seq DESC LIMIT 1) = 'claim'
+  BEGIN SELECT RAISE(ABORT, 'role already held'); END;
+CREATE TRIGGER role_release_by_holder BEFORE INSERT ON role_claims
+  WHEN NEW.op IN ('release','revoke') AND COALESCE((SELECT op FROM role_claims WHERE business = NEW.business AND role = NEW.role ORDER BY seq DESC LIMIT 1),'') <> 'claim'
+  BEGIN SELECT RAISE(ABORT, 'role is not held'); END;
+CREATE TRIGGER role_release_same_run BEFORE INSERT ON role_claims
+  WHEN NEW.op = 'release' AND (SELECT holder_run FROM role_claims WHERE business = NEW.business AND role = NEW.role ORDER BY seq DESC LIMIT 1) <> NEW.holder_run
+  BEGIN SELECT RAISE(ABORT, 'only the holder releases; others revoke'); END;
+CREATE TRIGGER role_revoke_needs_decision BEFORE INSERT ON role_claims
+  WHEN NEW.op = 'revoke' AND NEW.decision IS NULL AND NEW.reason IS NULL
+  BEGIN SELECT RAISE(ABORT, 'revoke needs a resolved decision or a reason'); END;
+CREATE TRIGGER meta_no_update BEFORE UPDATE ON meta BEGIN SELECT RAISE(ABORT, 'meta is append-only'); END;
+CREATE TRIGGER meta_no_delete BEFORE DELETE ON meta BEGIN SELECT RAISE(ABORT, 'meta is append-only'); END;
+CREATE TRIGGER events_no_update BEFORE UPDATE ON events BEGIN SELECT RAISE(ABORT, 'events is append-only'); END;
+CREATE TRIGGER events_no_delete BEFORE DELETE ON events BEGIN SELECT RAISE(ABORT, 'events is append-only'); END;
+CREATE TRIGGER role_claims_no_update BEFORE UPDATE ON role_claims BEGIN SELECT RAISE(ABORT, 'role_claims is append-only'); END;
+CREATE TRIGGER role_claims_no_delete BEFORE DELETE ON role_claims BEGIN SELECT RAISE(ABORT, 'role_claims is append-only'); END;
+CREATE TRIGGER decisions_no_update BEFORE UPDATE ON decisions BEGIN SELECT RAISE(ABORT, 'decisions is append-only'); END;
+CREATE TRIGGER decisions_no_delete BEFORE DELETE ON decisions BEGIN SELECT RAISE(ABORT, 'decisions is append-only'); END;
+CREATE TRIGGER decision_events_no_update BEFORE UPDATE ON decision_events BEGIN SELECT RAISE(ABORT, 'decision_events is append-only'); END;
+CREATE TRIGGER decision_events_no_delete BEFORE DELETE ON decision_events BEGIN SELECT RAISE(ABORT, 'decision_events is append-only'); END;
+CREATE TRIGGER messages_no_update BEFORE UPDATE ON messages BEGIN SELECT RAISE(ABORT, 'messages is append-only'); END;
+CREATE TRIGGER messages_no_delete BEFORE DELETE ON messages BEGIN SELECT RAISE(ABORT, 'messages is append-only'); END;
+CREATE TRIGGER deliveries_no_update BEFORE UPDATE ON deliveries BEGIN SELECT RAISE(ABORT, 'deliveries is append-only'); END;
+CREATE TRIGGER deliveries_no_delete BEFORE DELETE ON deliveries BEGIN SELECT RAISE(ABORT, 'deliveries is append-only'); END;
+CREATE TRIGGER meta_no_replace BEFORE INSERT ON meta WHEN EXISTS (SELECT 1 FROM meta WHERE key = NEW.key) BEGIN SELECT RAISE(ABORT, 'meta is append-only'); END;
+CREATE TRIGGER events_no_replace BEFORE INSERT ON events WHEN EXISTS (SELECT 1 FROM events WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'events is append-only'); END;
+CREATE TRIGGER role_claims_no_replace BEFORE INSERT ON role_claims WHEN EXISTS (SELECT 1 FROM role_claims WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'role_claims is append-only'); END;
+CREATE TRIGGER decisions_no_replace BEFORE INSERT ON decisions WHEN EXISTS (SELECT 1 FROM decisions WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'decisions is append-only'); END;
+CREATE TRIGGER decision_events_no_replace BEFORE INSERT ON decision_events WHEN EXISTS (SELECT 1 FROM decision_events WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'decision_events is append-only'); END;
+CREATE TRIGGER messages_no_replace BEFORE INSERT ON messages WHEN EXISTS (SELECT 1 FROM messages WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'messages is append-only'); END;
+CREATE TRIGGER deliveries_no_replace BEFORE INSERT ON deliveries WHEN EXISTS (SELECT 1 FROM deliveries WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'deliveries is append-only'); END;
+CREATE TRIGGER task_snapshots_no_update BEFORE UPDATE ON task_snapshots BEGIN SELECT RAISE(ABORT, 'task_snapshots is append-only'); END;
+CREATE TRIGGER task_snapshots_no_delete BEFORE DELETE ON task_snapshots BEGIN SELECT RAISE(ABORT, 'task_snapshots is append-only'); END;
+CREATE TRIGGER task_snapshots_no_replace BEFORE INSERT ON task_snapshots WHEN EXISTS (SELECT 1 FROM task_snapshots WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'task_snapshots is append-only'); END;
+CREATE TRIGGER decisions_blocking_needs_task BEFORE INSERT ON decisions
+  WHEN NEW.blocking = 1 AND NEW.task_ref IS NULL
+  BEGIN SELECT RAISE(ABORT, 'a blocking decision cites the task it blocks'); END;
+CREATE TRIGGER events_launch_by_human BEFORE INSERT ON events
+  WHEN NEW.kind IN ('launch.revoked','launch.restored') AND (NEW.actor_role IS NOT NULL OR NEW.actor_run IS NOT NULL)
+  BEGIN SELECT RAISE(ABORT, 'only the human revokes or restores launching'); END;
+CREATE TRIGGER events_credential_body BEFORE INSERT ON events
+  WHEN NEW.kind GLOB 'credential.*' AND (
+    json_extract(NEW.body, '$.service') IS NULL OR json_extract(NEW.body, '$.service') NOT IN ('gitea','vikunja')
+    OR json_extract(NEW.body, '$.instance') IS NULL)
+  BEGIN SELECT RAISE(ABORT, 'credential events name a service and a role instance'); END;
+CREATE TRIGGER events_task_missing_body BEFORE INSERT ON events
+  WHEN NEW.kind = 'task.missing' AND (
+    json_extract(NEW.body, '$.reason') IS NULL OR json_extract(NEW.body, '$.reason') NOT IN ('moved','not-found','no-access')
+    OR (json_extract(NEW.body, '$.reason') = 'moved' AND json_type(NEW.body, '$.project') IS NOT 'integer'))
+  BEGIN SELECT RAISE(ABORT, 'task.missing carries a reason, and the new project when moved'); END;
+CREATE TRIGGER events_task_subject BEFORE INSERT ON events
+  WHEN NEW.kind GLOB 'task.*' AND (NEW.subject IS NULL OR NOT (NEW.subject GLOB 'vikunja:[1-9]*/[1-9]*' AND NOT substr(NEW.subject, 9) GLOB '*[^0-9/]*' AND NOT substr(NEW.subject, 9) GLOB '*/*/*'))
+  BEGIN SELECT RAISE(ABORT, 'a task event names its task in subject'); END;
+CREATE TRIGGER events_task_created_body BEFORE INSERT ON events
+  WHEN NEW.kind = 'task.created' AND (
+    json_type(NEW.body, '$.request') IS NOT 'text'
+    OR NOT EXISTS (SELECT 1 FROM events WHERE id = json_extract(NEW.body, '$.request')
+                   AND kind = 'human.input' AND business = NEW.business)
+    OR json_type(NEW.body, '$.requirement') IS NOT 'text'
+    OR NOT json_extract(NEW.body, '$.requirement') GLOB 'REQ-[A-Z]*-[1-9]*'
+    OR json_extract(NEW.body, '$.requirement') GLOB 'REQ-*[^A-Z0-9-]*')
+  BEGIN SELECT RAISE(ABORT, 'task.created cites the human.input that asked for it and a requirement id'); END;
+CREATE VIEW launch_state AS
+  SELECT business, CASE kind WHEN 'launch.revoked' THEN 'revoked' ELSE 'allowed' END AS state, at
+  FROM events e WHERE kind IN ('launch.revoked','launch.restored')
+    AND seq = (SELECT max(seq) FROM events WHERE business = e.business AND kind IN ('launch.revoked','launch.restored'));
+CREATE VIEW task_external_changes AS
+  SELECT p.business, p.task_ref, p.seq, p.via, p.updated, p.digest, ls.digest AS self_digest
+  FROM task_snapshots p
+  LEFT JOIN task_snapshots ls ON ls.seq = (SELECT max(seq) FROM task_snapshots
+                                           WHERE business = p.business AND task_ref = p.task_ref AND source = 'self')
+  WHERE p.source = 'poll'
+    AND p.seq = (SELECT max(seq) FROM task_snapshots WHERE business = p.business AND task_ref = p.task_ref)
+    AND (ls.seq IS NULL OR (p.updated >= ls.updated AND p.read_at > ls.at AND p.digest <> ls.digest));
+CREATE VIEW task_current AS
+  SELECT s.seq, s.at, s.business, s.task_ref, s.updated, s.etag, s.digest, s.fields, s.source, s.via, s.read_at, s.role, s.run
+  FROM task_snapshots s
+  WHERE s.seq = (SELECT max(c.seq) FROM task_snapshots c
+                 WHERE c.business = s.business AND c.task_ref = s.task_ref
+                   AND (c.source = 'self'
+                        OR c.read_at > coalesce((SELECT ls.at FROM task_snapshots ls
+                                                 WHERE ls.business = c.business AND ls.task_ref = c.task_ref AND ls.source = 'self'
+                                                 ORDER BY ls.seq DESC LIMIT 1), '')));
+CREATE VIEW tasks_open AS
+  SELECT s.business, s.task_ref, json_extract(s.fields, '$.bucket') AS bucket, s.seq
+  FROM task_current s
+  WHERE json_type(s.fields, '$.gone') IS NULL
+    AND json_extract(s.fields, '$.done') = 0;
+CREATE VIEW urgent_inbox AS
+  SELECT d.id, d.business, d.task_ref, d.question, d.at
+  FROM decisions d
+  WHERE d.class = 'gated' AND d.blocking = 1
+    AND NOT EXISTS (SELECT 1 FROM decision_events x WHERE x.decision = d.id AND x.op IN ('resolved','withdrawn','expired'));
+CREATE TABLE task_comment_cursors (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  business TEXT NOT NULL,
+  task_id INTEGER NOT NULL CHECK (task_id > 0),
+  last_comment INTEGER NOT NULL CHECK (last_comment > 0)
+) STRICT;
+CREATE INDEX task_comment_cursors_latest ON task_comment_cursors (business, task_id, seq);
+CREATE TRIGGER task_comment_cursors_no_update BEFORE UPDATE ON task_comment_cursors
+  BEGIN SELECT RAISE(ABORT, 'task_comment_cursors is append-only'); END;
+CREATE TRIGGER task_comment_cursors_no_delete BEFORE DELETE ON task_comment_cursors
+  BEGIN SELECT RAISE(ABORT, 'task_comment_cursors is append-only'); END;
+CREATE TRIGGER task_comment_cursors_no_replace BEFORE INSERT ON task_comment_cursors
+  WHEN EXISTS (SELECT 1 FROM task_comment_cursors WHERE seq = NEW.seq)
+  BEGIN SELECT RAISE(ABORT, 'task_comment_cursors is append-only'); END;
+CREATE TRIGGER task_comment_cursors_forward BEFORE INSERT ON task_comment_cursors
+  WHEN NEW.last_comment <= COALESCE((SELECT last_comment FROM task_comment_cursors
+    WHERE business = NEW.business AND task_id = NEW.task_id ORDER BY seq DESC LIMIT 1), 0)
+  BEGIN SELECT RAISE(ABORT, 'comment cursor must advance'); END;
+CREATE TABLE projects (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  name TEXT NOT NULL,
+  repo TEXT,
+  created_by TEXT NOT NULL,
+  UNIQUE (business, name)
+) STRICT;
+CREATE TABLE threads (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  id TEXT NOT NULL UNIQUE,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  project TEXT NOT NULL REFERENCES projects(id),
+  instance TEXT NOT NULL,
+  owner TEXT NOT NULL,
+  name TEXT NOT NULL,
+  UNIQUE (project, name)
+) STRICT;
+CREATE TABLE thread_claims (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  op TEXT NOT NULL CHECK (op IN ('claim','release','revoke')),
+  holder_run TEXT NOT NULL,
+  harness TEXT NOT NULL, address TEXT,
+  by TEXT NOT NULL, reason TEXT,
+  decision TEXT
+) STRICT;
+CREATE TABLE message_threads (
+  message TEXT PRIMARY KEY REFERENCES messages(id),
+  thread TEXT NOT NULL REFERENCES threads(id)
+) STRICT;
+CREATE TABLE thread_opens (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  thread TEXT NOT NULL REFERENCES threads(id),
+  by TEXT NOT NULL
+) STRICT;
+CREATE INDEX thread_claims_thread ON thread_claims (thread, seq);
+CREATE INDEX message_threads_thread ON message_threads (thread);
+CREATE TRIGGER threads_project_business BEFORE INSERT ON threads
+  WHEN (SELECT business FROM projects WHERE id = NEW.project) IS NOT NEW.business
+  BEGIN SELECT RAISE(ABORT, 'a thread belongs to its project''s business'); END;
+CREATE TRIGGER thread_one_holder BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'claim' AND (SELECT op FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1) = 'claim'
+  BEGIN SELECT RAISE(ABORT, 'thread already held'); END;
+CREATE TRIGGER thread_one_per_run BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'claim' AND EXISTS (SELECT 1 FROM thread_claims c WHERE c.holder_run = NEW.holder_run AND c.business = NEW.business
+    AND c.seq = (SELECT max(seq) FROM thread_claims WHERE thread = c.thread) AND c.op = 'claim')
+  BEGIN SELECT RAISE(ABORT, 'run already holds a thread'); END;
+CREATE TRIGGER thread_release_by_holder BEFORE INSERT ON thread_claims
+  WHEN NEW.op IN ('release','revoke') AND COALESCE((SELECT op FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1),'') <> 'claim'
+  BEGIN SELECT RAISE(ABORT, 'thread is not held'); END;
+CREATE TRIGGER thread_release_same_run BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'release' AND (SELECT holder_run FROM thread_claims WHERE thread = NEW.thread ORDER BY seq DESC LIMIT 1) <> NEW.holder_run
+  BEGIN SELECT RAISE(ABORT, 'only the holder releases; others revoke'); END;
+CREATE TRIGGER thread_revoke_needs_decision BEFORE INSERT ON thread_claims
+  WHEN NEW.op = 'revoke' AND NEW.decision IS NULL AND NEW.reason IS NULL
+  BEGIN SELECT RAISE(ABORT, 'revoke needs a resolved decision or a reason'); END;
+CREATE TRIGGER thread_claims_business BEFORE INSERT ON thread_claims
+  WHEN (SELECT business FROM threads WHERE id = NEW.thread) IS NOT NEW.business
+  BEGIN SELECT RAISE(ABORT, 'a thread claim names the thread''s business'); END;
+CREATE TRIGGER message_threads_match BEFORE INSERT ON message_threads
+  WHEN NOT EXISTS (SELECT 1 FROM messages m JOIN threads t ON t.id = NEW.thread
+    WHERE m.id = NEW.message AND m.business = t.business AND t.instance IN (m.to_role, m.from_role))
+  BEGIN SELECT RAISE(ABORT, 'a threaded message is to or from the thread''s instance'); END;
+CREATE TRIGGER delivery_same_thread BEFORE INSERT ON deliveries
+  WHEN NEW.op IN ('routed','delivered') AND (NEW.op = 'delivered' OR NEW.holder_run IS NOT NULL)
+    AND EXISTS (SELECT 1 FROM message_threads mt JOIN messages m ON m.id = mt.message JOIN threads t ON t.id = mt.thread
+      WHERE mt.message = NEW.message AND m.to_role = t.instance
+        AND NOT EXISTS (SELECT 1 FROM thread_claims c WHERE c.seq = (SELECT max(seq) FROM thread_claims WHERE thread = t.id)
+          AND c.op = 'claim' AND c.holder_run IS NEW.holder_run))
+  BEGIN SELECT RAISE(ABORT, 'a threaded message goes only to its thread''s holder'); END;
+CREATE TRIGGER projects_no_update BEFORE UPDATE ON projects BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
+CREATE TRIGGER projects_no_delete BEFORE DELETE ON projects BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
+CREATE TRIGGER projects_no_replace BEFORE INSERT ON projects WHEN EXISTS (SELECT 1 FROM projects WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'projects is append-only'); END;
+CREATE TRIGGER threads_no_update BEFORE UPDATE ON threads BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
+CREATE TRIGGER threads_no_delete BEFORE DELETE ON threads BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
+CREATE TRIGGER threads_no_replace BEFORE INSERT ON threads WHEN EXISTS (SELECT 1 FROM threads WHERE seq = NEW.seq OR id = NEW.id) BEGIN SELECT RAISE(ABORT, 'threads is append-only'); END;
+CREATE TRIGGER thread_claims_no_update BEFORE UPDATE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER thread_claims_no_delete BEFORE DELETE ON thread_claims BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER thread_claims_no_replace BEFORE INSERT ON thread_claims WHEN EXISTS (SELECT 1 FROM thread_claims WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'thread_claims is append-only'); END;
+CREATE TRIGGER message_threads_no_update BEFORE UPDATE ON message_threads BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER message_threads_no_delete BEFORE DELETE ON message_threads BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER message_threads_no_replace BEFORE INSERT ON message_threads WHEN EXISTS (SELECT 1 FROM message_threads WHERE message = NEW.message) BEGIN SELECT RAISE(ABORT, 'message_threads is append-only'); END;
+CREATE TRIGGER thread_opens_no_update BEFORE UPDATE ON thread_opens BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
+CREATE TRIGGER thread_opens_no_delete BEFORE DELETE ON thread_opens BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
+CREATE TRIGGER thread_opens_no_replace BEFORE INSERT ON thread_opens WHEN EXISTS (SELECT 1 FROM thread_opens WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'thread_opens is append-only'); END;
+CREATE TABLE instance_names (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  instance TEXT NOT NULL,
+  name TEXT NOT NULL,
+  by TEXT NOT NULL
+) STRICT;
+CREATE TRIGGER instance_names_unique BEFORE INSERT ON instance_names
+  WHEN EXISTS (SELECT 1 FROM instance_names n WHERE n.business = NEW.business AND n.name = NEW.name
+    AND n.instance <> NEW.instance
+    AND n.seq = (SELECT max(seq) FROM instance_names WHERE business = n.business AND instance = n.instance))
+  BEGIN SELECT RAISE(ABORT, 'an instance name is unique in its business'); END;
+CREATE TRIGGER instance_names_no_update BEFORE UPDATE ON instance_names BEGIN SELECT RAISE(ABORT, 'instance_names is append-only'); END;
+CREATE TRIGGER instance_names_no_delete BEFORE DELETE ON instance_names BEGIN SELECT RAISE(ABORT, 'instance_names is append-only'); END;
+CREATE TRIGGER instance_names_no_replace BEFORE INSERT ON instance_names WHEN EXISTS (SELECT 1 FROM instance_names WHERE seq = NEW.seq) BEGIN SELECT RAISE(ABORT, 'instance_names is append-only'); END;
+-- Row 124 (#1618): immutable source snapshots and turn outcomes, never transcript text.
+CREATE TABLE usage_records (
+  seq INTEGER PRIMARY KEY AUTOINCREMENT,
+  at TEXT NOT NULL,
+  business TEXT NOT NULL,
+  run TEXT NOT NULL,
+  instance TEXT NOT NULL,
+  provider TEXT,
+  model TEXT,
+  account TEXT,
+  turn TEXT NOT NULL,
+  source TEXT NOT NULL,
+  phase TEXT NOT NULL CHECK (phase IN ('begin','end')),
+  status TEXT NOT NULL CHECK (status IN ('known','unknown')),
+  code TEXT,
+  cursor TEXT CHECK (cursor IS NULL OR json_valid(cursor)),
+  input INTEGER,
+  output INTEGER,
+  cache_write INTEGER,
+  cache_read INTEGER,
+  UNIQUE (business,run,turn,source,phase),
+  CHECK ((status='unknown' AND input IS NULL AND output IS NULL AND cache_write IS NULL AND cache_read IS NULL)
+    OR (status='known' AND input >= 0 AND output >= 0 AND cache_write >= 0 AND cache_read >= 0
+      AND input IS NOT NULL AND output IS NOT NULL AND cache_write IS NOT NULL AND cache_read IS NOT NULL))
+) STRICT;
+CREATE TRIGGER usage_records_no_update BEFORE UPDATE ON usage_records BEGIN SELECT RAISE(ABORT, 'usage_records is append-only'); END;
+CREATE TRIGGER usage_records_no_delete BEFORE DELETE ON usage_records BEGIN SELECT RAISE(ABORT, 'usage_records is append-only'); END;
+CREATE TRIGGER usage_records_no_replace BEFORE INSERT ON usage_records WHEN EXISTS (SELECT 1 FROM usage_records WHERE seq=NEW.seq OR (business=NEW.business AND run=NEW.run AND turn=NEW.turn AND source=NEW.source AND phase=NEW.phase)) BEGIN SELECT RAISE(ABORT, 'usage_records is append-only'); END;
+CREATE TABLE hosts (
+  business TEXT NOT NULL,
+  host TEXT NOT NULL,
+  address TEXT NOT NULL,
+  port INTEGER NOT NULL CHECK (port BETWEEN 1 AND 65535),
+  user TEXT NOT NULL,
+  sudo INTEGER NOT NULL CHECK (sudo IN (0,1)),
+  host_keys TEXT NOT NULL CHECK (json_valid(host_keys) AND json_type(host_keys) = 'array' AND json_array_length(host_keys) > 0),
+  installer_fingerprint TEXT,
+  state TEXT NOT NULL CHECK (state IN ('pending-install','ready')),
+  decision TEXT NOT NULL REFERENCES decisions(id),
+  checked_at TEXT,
+  PRIMARY KEY (business, host),
+  CHECK (state = 'pending-install' OR (installer_fingerprint IS NOT NULL AND checked_at IS NOT NULL))
+) STRICT;
+CREATE TABLE host_grants (
+  business TEXT NOT NULL,
+  agent TEXT NOT NULL,
+  host TEXT NOT NULL,
+  commands TEXT NOT NULL CHECK (json_valid(commands) AND json_type(commands) = 'array' AND json_array_length(commands) > 0),
+  rotate_by TEXT NOT NULL,
+  tag TEXT NOT NULL CHECK (length(tag) = 39 AND tag GLOB 'mosaic-*' AND NOT substr(tag, 8) GLOB '*[^0-9a-f]*'),
+  decision TEXT NOT NULL REFERENCES decisions(id),
+  PRIMARY KEY (business, agent, host),
+  FOREIGN KEY (business, host) REFERENCES hosts(business, host)
+) STRICT;
+CREATE TRIGGER events_grant_actor BEFORE INSERT ON events
+  WHEN NEW.kind = 'action.allowed'
+    AND (json_extract(NEW.body, '$.action') GLOB 'grant.*' OR json_extract(NEW.body, '$.operation') GLOB 'grant.*')
+    AND NOT (NEW.actor_role IS NULL AND NEW.actor_run IS 'grant')
+  BEGIN SELECT RAISE(ABORT, 'only the grant writer records grant events'); END;
@@ -16,6 +16,9 @@ const TAG = 'mosaic-' + 'a'.repeat(32);
 const ddl3i = readFileSync(new URL('./fixtures/schema-3i.sql', import.meta.url), 'utf8');
 const here = (p) => new URL(p, import.meta.url);
 const NEW = ['hosts', 'host_grants', 'events_grant_actor', 'sqlite_autoindex_hosts_1', 'sqlite_autoindex_host_grants_1'];
+// Row 264a (#1769): what the 3j→3k step rebuilds or adds. sessions.test.mjs tests those objects.
+const SESSIONS_3K = ['sessions', 'session_defaults', 'thread_claims', 'message_threads', 'thread_opens'];
+const later3k = (r) => SESSIONS_3K.includes(r.tbl_name) || ['delivery_same_thread', 'delivery_same_session'].includes(r.name);
 function source3i(t) {
  const root = mkdtempSync(join(tmpdir(), 'grant-migrate-'));
  t.after(() => rmSync(root, { recursive: true, force: true }));
@@ -35,7 +38,7 @@ function source3i(t) {
 function rows(path) {
  const db = new DatabaseSync(path, { readOnly: true });
  try {
-    return Object.fromEntries(db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name NOT IN ('hosts','host_grants')").all()
+    return Object.fromEntries(db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name NOT IN ('hosts','host_grants','sessions','session_defaults')").all()
      .map(({ name }) => [name, db.prepare(`SELECT * FROM ${name} ORDER BY rowid`).all()
        .filter(r => name !== 'meta' || !['schema_version', 'schema_digest'].includes(r.key)).map(r => ({ ...r }))]));
  } finally { db.close(); }
@@ -61,6 +64,7 @@ async function engine(root, name, { store, schema, step = (s) => s }) {
  for (const file of ['3b.sql', '3b-3c.sql', '3c-3d.sql', '3d-3e.sql', '3e-3f.sql', '3f-3g.sql', '3g-3h.sql', '3h-3i.sql'])
    copyFileSync(here('../src/migrations/' + file), join(moduleRoot, 'src/migrations', file));
  writeFileSync(join(moduleRoot, 'src/migrations/3i-3j.sql'), step(readFileSync(here('../src/migrations/3i-3j.sql'), 'utf8')));
+  copyFileSync(here('../src/migrations/3j-3k.sql'), join(moduleRoot, 'src/migrations/3j-3k.sql'));
  return (await import(pathToFileURL(join(moduleRoot, 'src/store.mjs')))).Store;
 }
 function fresh(t) {
@@ -84,10 +88,10 @@ test('3i copy migrates to 3j: every row kept, and sqlite_master gains only the t
  const { root, path } = source3i(t), before = rows(path), was = master(path);
  assert.throws(() => new Store(root), /schema-mismatch/);
  new Store(root, { migrateSchema: true }).close();
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
  assert.deepEqual(rows(path), before);
  const now = master(path);
-  assert.deepEqual(now.filter(r => !NEW.includes(r.name)), was);
+  assert.deepEqual(now.filter(r => !NEW.includes(r.name) && !later3k(r)), was.filter(r => !later3k(r)));
  assert.deepEqual(now.filter(r => NEW.includes(r.name)).map(r => r.name).sort(), [...NEW].sort());
  const store = new Store(root);
  try {
@@ -109,10 +113,10 @@ test('a 3i→3j step that fails partway leaves the store at 3i with every row an
  assert.deepEqual(master(path), was);
  assert.deepEqual(rows(path), before);
  new Store(root, { migrateSchema: true }).close();
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
 });

-test('the 3i engine refuses a 3j store, migrating or not, and leaves it at 3j', async t => {
+test('the 3i engine refuses a migrated store, migrating or not, and leaves it as it was', async t => {
  const { root, path } = source3i(t);
  new Store(root, { migrateSchema: true }).close();
  const after = rows(path), was = master(path);
@@ -120,14 +124,14 @@ test('the 3i engine refuses a 3j store, migrating or not, and leaves it at 3j',
    schema: ddl3i,
    store: (source) => source
      .replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${createHash('sha256').update(ddl3i).digest('hex')}';`)
-      .replace("export const SCHEMA_VERSION = '3j';", "export const SCHEMA_VERSION = '3i';")
+      .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3i';")
      .replace(/\}, \{\n {2}\/\/ Row 234 \(#1740\)[\s\S]*?\}\];\nconst timedTables/, '}];\nconst timedTables'),
  });
  const pinned = readFileSync(join(root, 'engine-3i/src/store.mjs'), 'utf8');
  assert.ok(pinned.includes("export const SCHEMA_VERSION = '3i';") && !pinned.includes('3i-3j'), 'the 3i engine has no 3i→3j step');
  assert.throws(() => new Store3i(root), /schema-mismatch/);
  assert.throws(() => new Store3i(root, { migrateSchema: true }), /schema-mismatch/);
-  assert.equal(version(path), '3j');
+  assert.equal(version(path), '3k');
  assert.deepEqual(master(path), was);
  assert.deepEqual(rows(path), after);
 });
@@ -55,7 +55,7 @@ test('3f copy migrates to 3g preserving every old column/row, with an empty inst
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
  try {
-    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
    assert.deepEqual({ ...store.get('SELECT to_name FROM messages') }, { to_name: null });
    assert.equal(store.get('SELECT count(*) AS n FROM instance_names').n, 0);
    assert.deepEqual({ ...store.get('SELECT spec_path,spec_commit FROM decisions') }, { spec_path: 'docs/spec.md', spec_commit: 'c'.repeat(40) });
@@ -520,7 +520,8 @@ test('v3b prototype refusals, views and append-only mutations', (t) => {
  // Row 141 (#1635) adds instance_names and its 4 triggers; names.test.mjs tests them.
  // Row 124 adds usage_records and its three append-only triggers.
  // Row 234 (#1740) adds hosts, host_grants and the events_grant_actor guard; grant-migration.test.mjs tests them.
-  assert.equal(count('table') - 1, 18);
-  assert.equal(count('trigger'), 71);
+  // Row 264a (#1769) adds sessions, session_defaults and 15 triggers; sessions.test.mjs tests them.
+  assert.equal(count('table') - 1, 20);
+  assert.equal(count('trigger'), 86);
  assert.equal(count('view'), 5);
 });
@@ -0,0 +1,392 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { DatabaseSync } from 'node:sqlite';
+import { chmodSync, copyFileSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { createHash } from 'node:crypto';
+import { fileURLToPath, pathToFileURL } from 'node:url';
+import { Store, schemaDigest } from '../src/store.mjs';
+import { Broker } from '../src/broker.mjs';
+
+// Row 264a (#1769, T1 item 7): sessions below a thread, in the bus. T1's bus half, T2 and T7 of
+// docs/plans/2026-10-21_t1-sessions.md. The launcher, seat and Console halves are 264b-264e's.
+const shipped = (name) =>
+  JSON.parse(readFileSync(fileURLToPath(new URL(`../../../roles/${name}.json`, import.meta.url)), 'utf8'));
+const roles = {
+  chief: { definition: 'chief-of-staff', authority: { withinRole: ['message.send'], crossRole: [] } },
+  assistant: { definition: 'assistant', authority: { withinRole: ['message.send'], crossRole: [] } },
+  pm: { definition: 'pm', authority: { withinRole: ['message.send'], crossRole: [] } },
+};
+const businesses = {
+  demo: {
+    id: 'demo',
+    human: 'jason',
+    arbiters: { technical: 'pm', delivery: 'chief' },
+    roles,
+    definitions: { 'chief-of-staff': {}, assistant: { messaging: shipped('assistant').messaging }, pm: {} },
+    projects: { stack: { root: '/nonexistent' } },
+  },
+};
+const AT = '2026-10-21T00:00:00.000Z';
+const now = () => new Date().toISOString();
+const here = (p) => new URL(p, import.meta.url);
+const ddl3j = readFileSync(here('./fixtures/schema-3j.sql'), 'utf8');
+
+function broker(t, store) {
+  const b = new Broker({ store, businesses });
+  const human = b.bindHuman({ business: 'demo', human: 'jason', via: 'cli', outsideAgent: true });
+  const caps = { human };
+  const call = (who, verb, args = {}) => b.request(caps[who], { verb, args });
+  const launch = (name, role, extra = {}) => {
+    caps[name] = b.bindLaunch({ business: 'demo', role, run: `${name}-run`, harness: 'pi', ...extra });
+    return caps[name];
+  };
+  const claim = (name) => call(name, 'role.claim');
+  const sessionOf = (message) => store.get('SELECT session FROM message_threads WHERE message=?', message)?.session ?? null;
+  const claims = (session) => store.all('SELECT op, holder_run, generation FROM thread_claims WHERE session=? ORDER BY seq', session).map((r) => ({ ...r }));
+  return { b, store, caps, call, launch, claim, sessionOf, claims };
+}
+
+function setup(t) {
+  const root = mkdtempSync(join(tmpdir(), 'bus-sessions-'));
+  const store = new Store(root);
+  t.after(() => {
+    store.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  const ctx = broker(t, store);
+  const project = ctx.call('human', 'project.create', { name: 'stack work', repo: 'stack' }).id;
+  const A = ctx.call('human', 'thread.create', { project, name: 'alpha' }).id;
+  for (const r of ['chief', 'pm']) {
+    ctx.launch(r, r);
+    ctx.claim(r);
+  }
+  const [first] = ctx.call('human', 'session.list', { thread: A });
+  return { ...ctx, root, project, A, D: first.id };
+}
+
+test('T1 REQ-ROLE-2: two sessions of one thread keep their own history, delivery and replies', (t) => {
+  const { call, launch, claim, sessionOf, store, project, A, D } = setup(t);
+  // thread.create made one default session, with a random id that isn't the thread's.
+  assert.deepEqual(call('human', 'session.list', { thread: A }).map((r) => [r.name, r.predecessor, r.default]), [['default', null, true]]);
+  assert.notEqual(D, A);
+  assert.match(D, /^[a-f0-9-]{36}$/);
+  const S = call('human', 'session.create', { thread: A, name: 'second', op: 'op-second' }).id;
+  assert.deepEqual(call('human', 'session.list', { thread: A }).map((r) => [r.id, r.name, r.default]), [
+    [D, 'default', true],
+    [S, 'second', false],
+  ]);
+  // A run with no session named works the default (D3). Each session has its own holder.
+  launch('a1', 'assistant', { thread: A });
+  launch('a2', 'assistant', { thread: A, session: S });
+  assert.deepEqual(claim('a1'), { role: 'assistant', run: 'a1-run', thread: A });
+  assert.deepEqual(claim('a2'), { role: 'assistant', run: 'a2-run', thread: A });
+  const toDefault = call('human', 'thread.send', { thread: A, body: 'to the default' });
+  const toSecond = call('human', 'thread.send', { thread: A, session: S, body: 'to the second' });
+  assert.equal(sessionOf(toDefault.id), D);
+  assert.equal(sessionOf(toSecond.id), S);
+  assert.deepEqual(call('a1', 'message.receive').map((m) => m.body), ['to the default']);
+  assert.deepEqual(call('a2', 'message.receive').map((m) => m.body), ['to the second']);
+  assert.deepEqual(call('a1', 'message.receive'), []);
+  // A reply stays in its run's session, and each history reads only its own.
+  const reply = call('a2', 'message.send', { to: 'human', body: 'second answers', in_reply_to: toSecond.id });
+  assert.equal(sessionOf(reply.id), S);
+  assert.deepEqual(call('human', 'thread.messages', { thread: A }).map((m) => m.body), ['to the default']);
+  assert.deepEqual(call('human', 'thread.messages', { thread: A, session: S }).map((m) => m.body), ['to the second', 'second answers']);
+  // The chief's reply to the second session's work comes back to that session.
+  const ask = call('a2', 'message.send', { to: 'chief', body: 'need help', class: 'REQUEST' });
+  const back = call('chief', 'message.send', { to: 'assistant', body: 'here', in_reply_to: ask.id });
+  assert.equal(sessionOf(back.id), S);
+  assert.deepEqual(call('a2', 'message.receive').map((m) => m.body), ['here']);
+  assert.deepEqual(call('a1', 'message.receive'), []);
+  // An open names its session too.
+  call('human', 'thread.open', { thread: A, session: S });
+  assert.equal(store.get('SELECT session FROM thread_opens ORDER BY seq DESC LIMIT 1').session, S);
+  // A non-thread role names no session, and a session of another thread is refused.
+  assert.throws(() => launch('p2', 'pm', { session: S }), { code: 'thread-not-allowed' });
+  const B = call('human', 'thread.create', { project, name: 'beta' }).id;
+  assert.throws(() => launch('a3', 'assistant', { thread: B, session: S }), { code: 'session-not-found' });
+  assert.throws(() => call('human', 'thread.send', { thread: B, session: S, body: 'x' }), { code: 'session-not-found' });
+  assert.throws(() => call('human', 'thread.messages', { thread: B, session: 'no-such-session' }), { code: 'session-not-found' });
+});
+
+test('T2 REQ-ROLE-2: one holder per session, generations count its claims, and a sibling session\'s message never reaches the other holder', (t) => {
+  const { b, call, launch, claim, claims, store, project, A, D } = setup(t);
+  const S = call('human', 'session.create', { thread: A, name: 'second', op: 'op-second' }).id;
+  launch('a1', 'assistant', { thread: A });
+  claim('a1');
+  launch('a1b', 'assistant', { thread: A });
+  assert.throws(() => claim('a1b'), { code: 'thread-already-held' });
+  // A sibling session is free to claim while the default is held.
+  launch('a2', 'assistant', { thread: A, session: S });
+  claim('a2');
+  // Release and claim again: the second claim is generation 2, and its release carries it.
+  call('a2', 'role.release');
+  launch('a3', 'assistant', { thread: A, session: S });
+  claim('a3');
+  b.endLaunch({ business: 'demo', run: 'a3-run', reason: 'idle' });
+  assert.deepEqual(claims(S), [
+    { op: 'claim', holder_run: 'a2-run', generation: 1 },
+    { op: 'release', holder_run: 'a2-run', generation: 1 },
+    { op: 'claim', holder_run: 'a3-run', generation: 2 },
+    { op: 'release', holder_run: 'a3-run', generation: 2 },
+  ]);
+  // The human's stop revokes each held session, with that claim's generation.
+  launch('a4', 'assistant', { thread: A, session: S });
+  claim('a4');
+  assert.deepEqual(call('human', 'assistant.stop', { instance: 'assistant' }), {
+    stopped: [
+      { thread: A, run: 'a1-run' },
+      { thread: A, run: 'a4-run' },
+    ],
+  });
+  assert.deepEqual(claims(D).at(-1), { op: 'revoke', holder_run: 'a1-run', generation: 1 });
+  assert.deepEqual(claims(S).at(-1), { op: 'revoke', holder_run: 'a4-run', generation: 3 });
+  // The triggers hold these for a write that skips the broker.
+  const raw = (thread, session, generation, run) =>
+    store.run(
+      "INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,by) VALUES(?,'demo',?,?,?,'claim',?,'pi',?)",
+      now(),
+      thread,
+      session,
+      generation,
+      run,
+      run,
+    );
+  assert.throws(() => raw(A, S, 5, 'x-run'), /a claim row names its session's generation/);
+  assert.throws(() => raw(A, S, 3, 'x-run'), /a claim row names its session's generation/);
+  const B = call('human', 'thread.create', { project, name: 'beta' }).id;
+  const [{ id: BD }] = call('human', 'session.list', { thread: B });
+  assert.throws(() => raw(A, BD, 1, 'x-run'), /a claim's session is in its thread/);
+  raw(A, S, 4, 'x-run');
+  assert.throws(() => raw(B, BD, 1, 'x-run'), /run already holds a session/);
+  // A threaded message goes only to its own session's holder.
+  launch('a5', 'assistant', { thread: A });
+  claim('a5');
+  const m = call('human', 'thread.send', { thread: A, session: S, body: 'for x' });
+  assert.throws(
+    () => store.run("INSERT INTO deliveries(message,at,op,holder_run) VALUES(?,?,'delivered',?)", m.id, now(), 'a5-run'),
+    /a threaded message goes only to its session's holder/,
+  );
+  store.run("INSERT INTO deliveries(message,at,op,holder_run) VALUES(?,?,'delivered',?)", m.id, now(), 'x-run');
+});
+
+test('session.create is idempotent on its op, refuses a reused op or a taken name, and reaches only the owner\'s threads', (t) => {
+  const { call, store, project, A, D } = setup(t);
+  const first = call('human', 'session.create', { thread: A, name: 'second', op: 'op-1' });
+  assert.deepEqual(call('human', 'session.create', { thread: A, name: 'second', op: 'op-1' }), first);
+  assert.throws(() => call('human', 'session.create', { thread: A, name: 'third', op: 'op-1' }), { code: 'session-op-conflict' });
+  assert.throws(() => call('human', 'session.create', { thread: A, name: 'second', op: 'op-2' }), { code: 'session-exists' });
+  assert.throws(() => call('human', 'session.create', { thread: A, name: 'default', op: 'op-3' }), { code: 'session-exists' });
+  // thread.create's op answers a retry that names the default.
+  assert.deepEqual(call('human', 'session.create', { thread: A, name: 'default', op: 'default' }), { id: D, thread: A, name: 'default' });
+  for (const args of [{ thread: A, name: 'x\ny', op: 'op-4' }, { thread: A, name: 'x' }, { thread: A, name: 'x', op: 'op-5', extra: 1 }])
+    assert.throws(() => call('human', 'session.create', args), { code: 'invalid-request' });
+  assert.equal(store.get('SELECT count(*) n FROM sessions WHERE thread=?', A).n, 2);
+  // Another owner's thread, made by hand with the session the broker would write.
+  const other = 'thread-of-someone-else';
+  store.run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)', other, now(), 'demo', project, 'assistant', 'someone-else', 'theirs');
+  store.run("INSERT INTO sessions(id,at,business,thread,instance,owner,name,op) VALUES('s-theirs',?,'demo',?,'assistant','someone-else','default','default')", now(), other);
+  store.run("INSERT INTO session_defaults(at,thread,session,by) VALUES(?,?,'s-theirs','someone-else')", now(), other);
+  for (const [verb, args] of [
+    ['session.list', { thread: other }],
+    ['session.create', { thread: other, name: 'mine', op: 'op-6' }],
+    ['thread.send', { thread: other, session: 's-theirs', body: 'hi' }],
+  ])
+    assert.throws(() => call('human', verb, args), { code: 'thread-not-owned' }, verb);
+  assert.throws(() => call('human', 'session.list', { thread: 'nope' }), { code: 'thread-not-found' });
+  // Agents don't call the session verbs.
+  assert.throws(() => call('pm', 'session.list', { thread: A }), { code: 'human-required' });
+});
+
+test('the 3k triggers keep sessions in their thread and session ids apart from thread ids', (t) => {
+  // A bare database from schema.sql, so only the triggers stand between a write and the tables.
+  const root = mkdtempSync(join(tmpdir(), 'bus-sessions-sql-'));
+  const db = new DatabaseSync(join(root, 'bus.sqlite'));
+  t.after(() => {
+    db.close();
+    rmSync(root, { recursive: true, force: true });
+  });
+  db.exec(readFileSync(here('../schema.sql'), 'utf8'));
+  const run = (sql, ...args) => db.prepare(sql).run(...args);
+  const session = (id, thread, extra = {}) =>
+    run(
+      'INSERT INTO sessions(id,at,business,thread,instance,owner,name,op,predecessor) VALUES(?,?,?,?,?,?,?,?,?)',
+      id,
+      now(),
+      extra.business ?? 'demo',
+      thread,
+      extra.instance ?? 'assistant',
+      extra.owner ?? 'jason',
+      extra.name ?? id,
+      extra.op ?? id,
+      extra.predecessor ?? null,
+    );
+  run("INSERT INTO projects(id,at,business,name,repo,created_by) VALUES('p-1',?,'demo','work',NULL,'jason')", now());
+  for (const id of ['th-1', 'th-2'])
+    run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,'demo','p-1','assistant','jason',?)", id, now(), id);
+  session('s-1', 'th-1');
+  // The legacy shape: a session whose id is its own thread's.
+  session('th-1', 'th-1', { name: 'default', op: 'legacy-3k' });
+  // A session id that names another thread, and a thread id that names a session, are refused.
+  assert.throws(() => session('th-2', 'th-1'), /a session id names another thread/);
+  assert.throws(
+    () => run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES('s-1',?,'demo','p-1','assistant','jason','x')", now()),
+    /a thread id names a session/,
+  );
+  // A session has its thread's business, instance and owner, and its predecessor is in its thread.
+  for (const extra of [{ business: 'other' }, { instance: 'pm' }, { owner: 'someone-else' }])
+    assert.throws(() => session('s-x', 'th-1', extra), /a session has its thread's business, instance and owner/, JSON.stringify(extra));
+  assert.throws(() => session('s-x', 'th-2', { predecessor: 's-1' }), /a session's predecessor is in its thread/);
+  session('s-2', 'th-1', { predecessor: 's-1' });
+  // The names and op keys are unique in a thread.
+  assert.throws(() => session('s-3', 'th-1', { name: 's-1' }), /UNIQUE/);
+  assert.throws(() => session('s-3', 'th-1', { op: 's-1' }), /UNIQUE/);
+  // A default is a session of its thread.
+  assert.throws(() => run("INSERT INTO session_defaults(at,thread,session,by) VALUES(?,'th-2','s-1','jason')", now()), /a default session is in its thread/);
+  run("INSERT INTO session_defaults(at,thread,session,by) VALUES(?,'th-1','s-1','jason')", now());
+  // A message's and an open's session is in their thread.
+  run("INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,body) VALUES('m-1',?,'demo','human','human-cli','assistant','INFO','hi')", now());
+  assert.throws(() => run("INSERT INTO message_threads(message,thread,session) VALUES('m-1','th-2','s-1')"), /a threaded message's session is in its thread/);
+  assert.throws(() => run("INSERT INTO thread_opens(at,thread,session,by) VALUES(?,'th-2','s-1','jason')", now()), /an open's session is in its thread/);
+});
+
+// T7: a 3j store from the pinned 3j schema (the parent of this change's schema.sql) and fixture
+// rows. No live store is read or copied.
+function source3j(t) {
+  const root = mkdtempSync(join(tmpdir(), 'sessions-migrate-'));
+  t.after(() => rmSync(root, { recursive: true, force: true }));
+  mkdirSync(join(root, 'bus'), { mode: 0o700 });
+  const path = join(root, 'bus/bus.sqlite'), db = new DatabaseSync(path);
+  assert.equal(createHash('sha256').update(ddl3j).digest('hex'), '0a7b633ce7eec9d0bb37c3255f4244d97bd0c8eac38db91a11b4ef6cc982ec8c');
+  db.exec(ddl3j);
+  const run = (sql, ...args) => db.prepare(sql).run(...args);
+  run('INSERT INTO meta VALUES (?,?)', 'schema_version', '3j');
+  run('INSERT INTO meta VALUES (?,?)', 'schema_digest', schemaDigest(db));
+  run('INSERT INTO meta VALUES (?,?)', 'comment_cursor_epoch', AT);
+  run('INSERT INTO projects(id,at,business,name,repo,created_by) VALUES(?,?,?,?,?,?)', 'p-1', AT, 'demo', 'stack work', 'stack', 'jason');
+  for (const id of ['t1', 't2'])
+    run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)', id, AT, 'demo', 'p-1', 'assistant', 'jason', id);
+  // Duckworth's fixture: claim, release, claim, revoke on t1, with t2's claim between, at seqs
+  // with gaps so a renumbered copy would show.
+  const claimRow = (seq, thread, op, holder, extra = {}) =>
+    run(
+      'INSERT INTO thread_claims(seq,at,business,thread,op,holder_run,harness,by,reason) VALUES(?,?,?,?,?,?,?,?,?)',
+      seq, AT, 'demo', thread, op, holder, 'pi', extra.by ?? holder, extra.reason ?? null,
+    );
+  claimRow(10, 't1', 'claim', 'a-run');
+  claimRow(11, 't2', 'claim', 'b-run');
+  claimRow(12, 't1', 'release', 'a-run');
+  claimRow(20, 't1', 'claim', 'c-run');
+  claimRow(40, 't1', 'revoke', 'c-run', { by: 'jason', reason: 'stuck' });
+  for (const [id, thread] of [['m-1', 't1'], ['m-2', 't2'], ['m-3', 't1']]) {
+    run('INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,body) VALUES(?,?,?,?,?,?,?,?)', id, AT, 'demo', 'human', 'human-cli', 'assistant', 'INFO', id);
+    run('INSERT INTO message_threads VALUES(?,?)', id, thread);
+  }
+  run('INSERT INTO thread_opens(seq,at,thread,by) VALUES(?,?,?,?)', 7, AT, 't1', 'jason');
+  db.close(); chmodSync(path, 0o600);
+  return { root, path };
+}
+const master = (path) => {
+  const db = new DatabaseSync(path, { readOnly: true });
+  try {
+    return db.prepare('SELECT type,name,tbl_name,sql FROM sqlite_master ORDER BY type,name').all().map((r) => ({ ...r }));
+  } finally { db.close(); }
+};
+const rows = (path) => {
+  const db = new DatabaseSync(path, { readOnly: true });
+  try {
+    return Object.fromEntries(['sessions', 'session_defaults', 'thread_claims', 'message_threads', 'thread_opens', 'meta']
+      .map((name) => [name, db.prepare(`SELECT * FROM ${name} ORDER BY rowid`).all().map((r) => ({ ...r }))]));
+  } finally { db.close(); }
+};
+const version = (path) => {
+  const db = new DatabaseSync(path, { readOnly: true });
+  try { return db.prepare("SELECT value FROM meta WHERE key='schema_version'").get().value; } finally { db.close(); }
+};
+
+test('T7: a 3j store migrates to 3k, each thread\'s default session has the thread\'s id, and old rows keep their seqs', (t) => {
+  const { root, path } = source3j(t);
+  assert.throws(() => new Store(root), /schema-mismatch/);
+  new Store(root, { migrateSchema: true }).close();
+  assert.equal(version(path), '3k');
+  // The migrated schema is the fresh one, object for object.
+  const freshRoot = mkdtempSync(join(tmpdir(), 'sessions-fresh-'));
+  t.after(() => rmSync(freshRoot, { recursive: true, force: true }));
+  new Store(freshRoot).close();
+  assert.deepEqual(master(path), master(join(freshRoot, 'bus/bus.sqlite')));
+  const store = new Store(root);
+  t.after(() => store.close());
+  assert.deepEqual(store.all('SELECT id,at,business,thread,instance,owner,name,op,predecessor FROM sessions ORDER BY seq').map((r) => ({ ...r })), ['t1', 't2'].map((id) => (
+    { id, at: AT, business: 'demo', thread: id, instance: 'assistant', owner: 'jason', name: 'default', op: 'legacy-3k', predecessor: null })));
+  assert.deepEqual(store.all('SELECT at,thread,session,by FROM session_defaults ORDER BY seq').map((r) => ({ ...r })), ['t1', 't2'].map((id) => (
+    { at: AT, thread: id, session: id, by: 'migration-3k' })));
+  // Generation counts claim rows only: claim, release, claim, revoke on t1 is 1, 1, 2, 2.
+  assert.deepEqual(store.all('SELECT seq,thread,session,op,generation FROM thread_claims ORDER BY seq').map((r) => ({ ...r })), [
+    { seq: 10, thread: 't1', session: 't1', op: 'claim', generation: 1 },
+    { seq: 11, thread: 't2', session: 't2', op: 'claim', generation: 1 },
+    { seq: 12, thread: 't1', session: 't1', op: 'release', generation: 1 },
+    { seq: 20, thread: 't1', session: 't1', op: 'claim', generation: 2 },
+    { seq: 40, thread: 't1', session: 't1', op: 'revoke', generation: 2 },
+  ]);
+  assert.deepEqual(store.all('SELECT message,thread,session FROM message_threads ORDER BY rowid').map((r) => ({ ...r })), [
+    { message: 'm-1', thread: 't1', session: 't1' },
+    { message: 'm-2', thread: 't2', session: 't2' },
+    { message: 'm-3', thread: 't1', session: 't1' },
+  ]);
+  assert.deepEqual({ ...store.get('SELECT seq,thread,session,by FROM thread_opens') }, { seq: 7, thread: 't1', session: 't1', by: 'jason' });
+  for (const [name, seq] of [['thread_claims', 40], ['thread_opens', 7]])
+    assert.equal(store.get('SELECT seq FROM sqlite_sequence WHERE name=?', name).seq, seq, name);
+  assert.equal(store.get('PRAGMA quick_check').quick_check, 'ok');
+  assert.deepEqual(store.all('PRAGMA foreign_key_check'), []);
+  // A legacy client names no session and gets the default: t2's holder releases at generation 1,
+  // and t1's next claim is its third.
+  const { call, launch, claim, claims, sessionOf } = broker(t, store);
+  for (const r of ['chief', 'pm']) {
+    launch(r, r);
+    claim(r);
+  }
+  assert.throws(() => call('human', 'session.create', { thread: 't1', name: 'default', op: 'op-new' }), { code: 'session-exists' });
+  store.run("INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,by) VALUES(?,'demo','t2','t2',1,'release','b-run','pi','b-run')", now());
+  assert.equal(store.get("SELECT seq FROM thread_claims WHERE thread='t2' ORDER BY seq DESC LIMIT 1").seq, 41);
+  launch('d', 'assistant', { thread: 't1' });
+  claim('d');
+  assert.deepEqual(claims('t1').at(-1), { op: 'claim', holder_run: 'd-run', generation: 3 });
+  const sent = call('human', 'thread.send', { thread: 't1', body: 'after the step' });
+  assert.equal(sessionOf(sent.id), 't1');
+  assert.deepEqual(call('d', 'message.receive').map((m) => m.body), ['m-1', 'm-3', 'after the step']);
+  assert.deepEqual(call('human', 'thread.messages', { thread: 't1' }).map((m) => m.body), ['m-1', 'm-3', 'after the step']);
+});
+
+// The 3j engine is store.mjs at this change with the 3j schema and version and no 3j→3k step.
+async function engine3j(root) {
+  const moduleRoot = join(root, 'engine-3j');
+  mkdirSync(join(moduleRoot, 'src/migrations'), { recursive: true });
+  const source = readFileSync(here('../src/store.mjs'), 'utf8');
+  const edited = source
+    .replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${createHash('sha256').update(ddl3j).digest('hex')}';`)
+    .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3j';")
+    .replace(/\}, \{\n {2}\/\/ Row 264a \(#1769\)[\s\S]*?\}\];\nconst timedTables/, '}];\nconst timedTables');
+  assert.ok(edited.includes("export const SCHEMA_VERSION = '3j';") && !edited.includes('3j-3k'), 'the 3j engine has no 3j→3k step');
+  writeFileSync(join(moduleRoot, 'src/store.mjs'), edited);
+  writeFileSync(join(moduleRoot, 'schema.sql'), ddl3j);
+  for (const file of ['3b.sql', '3b-3c.sql', '3c-3d.sql', '3d-3e.sql', '3e-3f.sql', '3f-3g.sql', '3g-3h.sql', '3h-3i.sql', '3i-3j.sql'])
+    copyFileSync(here('../src/migrations/' + file), join(moduleRoot, 'src/migrations', file));
+  return (await import(pathToFileURL(join(moduleRoot, 'src/store.mjs')))).Store;
+}
+
+test('T7 D9: the 3j engine refuses a 3k store, migrating or not, and leaves it as it was', async (t) => {
+  const { root, path } = source3j(t);
+  new Store(root, { migrateSchema: true }).close();
+  const was = master(path), before = rows(path);
+  const Store3j = await engine3j(root);
+  assert.throws(() => new Store3j(root), /schema-mismatch/);
+  assert.throws(() => new Store3j(root, { migrateSchema: true }), /schema-mismatch/);
+  assert.equal(version(path), '3k');
+  assert.deepEqual(master(path), was);
+  assert.deepEqual(rows(path), before);
+  // The same engine opens a fresh 3j store, so the refusal is the version's and not a broken copy.
+  const { root: old } = source3j(t);
+  new Store3j(old).close();
+});
@@ -53,7 +53,7 @@ test('3e copy migrates through 3f to 3g preserving every old column/row and addi
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
  try {
-    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
    assert.deepEqual({ ...store.get('SELECT spec_path,spec_commit FROM decisions') }, { spec_path: null, spec_commit: null });
    assert.equal(store.get('PRAGMA quick_check').quick_check, 'ok');
    assert.deepEqual(store.all('PRAGMA foreign_key_check'), []);
@@ -21,6 +21,8 @@ test('row 175: TESTER_VERBS and the organization branch tester set are pinned',
    'usage', 'names', 'limits', 'plugins', 'instances', 'project.list', 'thread.list', 'name.set', 'project.create', 'credentials',
    // Row 177 (#1675): the tester's own threads.
    'thread.create', 'thread.open', 'thread.send', 'thread.messages', 'assistant.stop',
+    // Row 264a (#1769): the sessions of the tester's own threads.
+    'session.list', 'session.create',
  ]);
  assert.deepEqual([...TESTER_ORGANIZATION_VERBS], ['limits', 'plugins', 'instances', 'plugins.set', 'instances.set', 'routes.set', 'routes']);
  assert.ok(Object.isFrozen(TESTER_VERBS) && Object.isFrozen(TESTER_ORGANIZATION_VERBS));
@@ -49,7 +49,7 @@ async function database3d(t) {
  const source = readFileSync(here('../src/store.mjs'), 'utf8');
  const pinned = source
    .replace(/export const SCHEMA_SHA256 = '[a-f0-9]+';/, `export const SCHEMA_SHA256 = '${createHash('sha256').update(ddl3d).digest('hex')}';`)
-    .replace("export const SCHEMA_VERSION = '3j';", "export const SCHEMA_VERSION = '3d';")
+    .replace("export const SCHEMA_VERSION = '3k';", "export const SCHEMA_VERSION = '3d';")
    .replace(/\}, \{\n {2}from: '3d',[\s\S]*?\}\];\nconst timedTables/, '}];\nconst timedTables');
  assert.ok(!pinned.includes('3d-3e'), 'the 3d engine has no 3d→3e step');
  writeFileSync(join(moduleRoot, 'src/store.mjs'), pinned);
@@ -101,7 +101,7 @@ test('REQ-THREAD-1 REQ-ORG-2: the 3d→3e migration adds the thread tables and l
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
  t.after(() => store.close());
-  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+  assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
  for (const table of ['projects', 'threads', 'thread_claims', 'message_threads', 'thread_opens'])
    assert.equal(store.get(`SELECT count(*) n FROM ${table}`).n, 0, table);
  // Parked: the undelivered ones are counted per business and role, and none is changed or given a thread.
@@ -161,5 +161,5 @@ test('REQ-THREAD-1: the offline command prints the kept-message counts before th
  const command = new URL('../src/migrate-schema.mjs', import.meta.url).pathname;
  const migrated = spawnSync(process.execPath, [command, root], { encoding: 'utf8' });
  assert.equal(migrated.status, 0, migrated.stderr);
-  assert.equal(migrated.stdout, [...REPORT, 'bus schema 3j ready', ''].join('\n'));
+  assert.equal(migrated.stdout, [...REPORT, 'bus schema 3k ready', ''].join('\n'));
 });
@@ -7,6 +7,12 @@ import { join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { Store } from '../src/store.mjs';
 import { Broker, THREAD_PAGE } from '../src/broker.mjs';
+// Row 264a (#1769): a thread made by hand gets the default session the 3j-3k migration gives a
+// legacy thread, with the thread's id.
+const DEFAULT_SESSION = [
+  'INSERT INTO sessions(at,business,thread,id,instance,owner,name,op) SELECT at,business,id,id,instance,owner,'default','legacy-3k' FROM threads WHERE id=?',
+  'INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads WHERE id=?',
+];

 // Row 121 (#1615): projects and threads in the bus. The assistant's messaging lists are the
 // shipped roles/assistant.json's, so the chain below runs under the lists the stack runs.
@@ -81,32 +87,36 @@ test('REQ-ROLE-2 REQ-THREAD-1: one holder per thread, through the broker and the
  const { b, store, call, launch, claim, A, B } = twoThreads(t);
  launch('a2', 'assistant', { thread: A });
  assert.throws(() => claim('a2'), { code: 'thread-already-held' });
-  // The trigger refuses a second claim that skips the broker.
+  // The trigger refuses a second claim that skips the broker. Row 264a: the claim is of the
+  // thread's default session, with the generation the trigger expects.
+  const sessionOf = (thread) => store.get('SELECT session FROM session_defaults WHERE thread=?', thread).session;
  const second = () =>
    store.run(
-      "INSERT INTO thread_claims(at,business,thread,op,holder_run,harness,by) VALUES(?,?,?,'claim',?,?,?)",
+      "INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,by) VALUES(?,?,?,?,2,'claim',?,?,?)",
      now(),
      'demo',
      A,
+      sessionOf(A),
      'a2-run',
      'pi',
      'a2-run',
    );
-  assert.throws(second, /thread already held/);
-  // Second case: one run holds one thread. a-run already holds A.
+  assert.throws(second, /session already held/);
+  // Second case: one run holds one session. a-run already holds A's.
  call('b', 'role.release');
  assert.throws(
    () =>
      store.run(
-        "INSERT INTO thread_claims(at,business,thread,op,holder_run,harness,by) VALUES(?,?,?,'claim',?,?,?)",
+        "INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,by) VALUES(?,?,?,?,2,'claim',?,?,?)",
        now(),
        'demo',
        B,
+        sessionOf(B),
        'a-run',
        'pi',
        'a-run',
      ),
-    /run already holds a thread/,
+    /run already holds a session/,
  );
  // A released thread can be claimed again by a new run; the claim is the thread's, not the role's.
  launch('b2', 'assistant', { thread: B });
@@ -128,12 +138,20 @@ test('REQ-ROLE-2 REQ-THREAD-1: the 3e triggers refuse writes that skip the broke
  });
  db.exec(readFileSync(new URL('../schema.sql', import.meta.url), 'utf8'));
  const run = (sql, ...args) => db.prepare(sql).run(...args);
+  // Row 264a (#1769): a claim row names its session and the generation thread_claim_generation
+  // expects, so each refusal below comes from the trigger it names.
+  const generation = (op) =>
+    op === 'claim'
+      ? 1 + db.prepare("SELECT count(*) n FROM thread_claims WHERE session='s-1' AND op='claim'").get().n
+      : (db.prepare("SELECT generation FROM thread_claims WHERE session='s-1' ORDER BY seq DESC LIMIT 1").get()?.generation ?? null);
  const claim = (op, run_, extra = {}) =>
    run(
-      'INSERT INTO thread_claims(at,business,thread,op,holder_run,harness,by,reason,decision) VALUES(?,?,?,?,?,?,?,?,?)',
+      'INSERT INTO thread_claims(at,business,thread,session,generation,op,holder_run,harness,by,reason,decision) VALUES(?,?,?,?,?,?,?,?,?,?,?)',
      now(),
      extra.business ?? 'demo',
      extra.thread ?? 'th-1',
+      's-1',
+      generation(op),
      op,
      run_,
      'pi',
@@ -143,9 +161,11 @@ test('REQ-ROLE-2 REQ-THREAD-1: the 3e triggers refuse writes that skip the broke
    );
  run("INSERT INTO projects(id,at,business,name,repo,created_by) VALUES('p-1',?,'demo','work',NULL,'jason')", now());
  run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES('th-1',?,'demo','p-1','assistant','jason','one')", now());
-  run("INSERT INTO thread_opens(at,thread,by) VALUES(?,'th-1','jason')", now());
+  run("INSERT INTO sessions(id,at,business,thread,instance,owner,name,op) VALUES('s-1',?,'demo','th-1','assistant','jason','default','default')", now());
+  run("INSERT INTO session_defaults(at,thread,session,by) VALUES(?,'th-1','s-1','jason')", now());
+  run("INSERT INTO thread_opens(at,thread,session,by) VALUES(?,'th-1','s-1','jason')", now());
  run("INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,body) VALUES('m-1',?,'demo','human','human-cli','assistant','INFO','hi')", now());
-  run("INSERT INTO message_threads(message,thread) VALUES('m-1','th-1')");
+  run("INSERT INTO message_threads(message,thread,session) VALUES('m-1','th-1','s-1')");
  // A thread is in its project's business.
  assert.throws(
    () => run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES('th-x',?,'other','p-1','assistant','jason','x')", now()),
@@ -154,20 +174,22 @@ test('REQ-ROLE-2 REQ-THREAD-1: the 3e triggers refuse writes that skip the broke
  // A claim names the thread's business.
  assert.throws(() => claim('claim', 'a-run', { business: 'other' }), /a thread claim names the thread's business/);
  // Nothing releases or revokes a thread nobody holds.
-  assert.throws(() => claim('release', 'a-run'), /thread is not held/);
-  assert.throws(() => claim('revoke', 'a-run', { reason: 'stuck' }), /thread is not held/);
+  assert.throws(() => claim('release', 'a-run'), /session is not held/);
+  assert.throws(() => claim('revoke', 'a-run', { reason: 'stuck' }), /session is not held/);
  claim('claim', 'a-run');
  // Only the holder releases; a revoke needs a decision or a reason.
  assert.throws(() => claim('release', 'b-run'), /only the holder releases; others revoke/);
  assert.throws(() => claim('revoke', 'a-run'), /revoke needs a resolved decision or a reason/);
  claim('revoke', 'a-run', { reason: 'stuck' });
-  // Every 3e table is append-only: no UPDATE, no DELETE, no INSERT OR REPLACE.
+  // Every 3e table, and row 264a's two, is append-only: no UPDATE, no DELETE, no INSERT OR REPLACE.
  const rows = {
    projects: ["id='p-1'", 'name', "INSERT OR REPLACE INTO projects(seq,id,at,business,name,created_by) SELECT seq,id,at,business,name,created_by FROM projects WHERE id='p-1'"],
    threads: ["id='th-1'", 'name', "INSERT OR REPLACE INTO threads(seq,id,at,business,project,instance,owner,name) SELECT seq,id,at,business,project,instance,owner,name FROM threads WHERE id='th-1'"],
-    thread_claims: ['seq=1', 'reason', 'INSERT OR REPLACE INTO thread_claims(seq,at,business,thread,op,holder_run,harness,by) SELECT seq,at,business,thread,op,holder_run,harness,by FROM thread_claims WHERE seq=1'],
-    message_threads: ["message='m-1'", 'thread', "INSERT OR REPLACE INTO message_threads(message,thread) VALUES('m-1','th-1')"],
-    thread_opens: ['seq=1', 'by', 'INSERT OR REPLACE INTO thread_opens(seq,at,thread,by) SELECT seq,at,thread,by FROM thread_opens WHERE seq=1'],
+    sessions: ["id='s-1'", 'name', "INSERT OR REPLACE INTO sessions(seq,id,at,business,thread,instance,owner,name,op) SELECT seq,id,at,business,thread,instance,owner,name,op FROM sessions WHERE id='s-1'"],
+    session_defaults: ['seq=1', 'by', 'INSERT OR REPLACE INTO session_defaults(seq,at,thread,session,by) SELECT seq,at,thread,session,by FROM session_defaults WHERE seq=1'],
+    thread_claims: ['seq=1', 'reason', 'INSERT OR REPLACE INTO thread_claims(seq,at,business,thread,session,generation,op,holder_run,harness,by) SELECT seq,at,business,thread,session,generation,op,holder_run,harness,by FROM thread_claims WHERE seq=1'],
+    message_threads: ["message='m-1'", 'thread', "INSERT OR REPLACE INTO message_threads(message,thread,session) VALUES('m-1','th-1','s-1')"],
+    thread_opens: ['seq=1', 'by', 'INSERT OR REPLACE INTO thread_opens(seq,at,thread,session,by) SELECT seq,at,thread,session,by FROM thread_opens WHERE seq=1'],
  };
  for (const [table, [where, col, replace]] of Object.entries(rows)) {
    const only = new RegExp(`${table} is append-only`);
@@ -225,7 +247,7 @@ test('REQ-MSG-1: a message to or from the assistant names its thread, or is refu
  // The store refuses a thread on a message the instance is not party to.
  const pmOnly = call('pm', 'message.send', { to: 'coder', body: 'unrelated' });
  assert.throws(
-    () => store.run('INSERT INTO message_threads(message,thread) VALUES(?,?)', pmOnly.id, A),
+    () => store.run('INSERT INTO message_threads(message,thread,session) VALUES(?,?,(SELECT session FROM session_defaults WHERE thread=?))', pmOnly.id, A, A),
    /to or from the thread's instance/,
  );
  void b;
@@ -277,8 +299,10 @@ test('REQ-MSG-1: a reply can\'t carry one thread instance\'s thread to another t
  const helper = { definition: 'assistant', authority: { withinRole: ['message.send'], crossRole: [] } };
  const { store, call, launch, claim, count } = setup(t, demo({ roles: { ...roles, helper } }));
  const project = call('human', 'project.create', { name: 'two instances' }).id;
-  for (const [id, instance] of [['th-a', 'assistant'], ['th-h', 'helper']])
+  for (const [id, instance] of [['th-a', 'assistant'], ['th-h', 'helper']]) {
    store.run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)', id, now(), 'demo', project, instance, 'jason', id);
+    for (const sql of DEFAULT_SESSION) store.run(sql, id);
+  }
  launch('chief', 'chief');
  claim('chief');
  launch('a', 'assistant', { thread: 'th-a' });
@@ -437,6 +461,7 @@ test('Q169 REQ-USER-2: assistant.stop ends the human\'s own assistant thread run
    'someone-else',
    'theirs',
  );
+  for (const sql of DEFAULT_SESSION) store.run(sql, other);
  launch('o', 'assistant', { thread: other });
  claim('o');
  const last = (thread) => ({
@@ -486,6 +511,7 @@ test('REQ-USER-2: the human verbs refuse another owner\'s thread', (t) => {
    'someone-else',
    'theirs',
  );
+  for (const sql of DEFAULT_SESSION) store.run(sql, other);
  for (const [verb, args] of [
    ['thread.open', { thread: other }],
    ['thread.send', { thread: other, body: 'hi' }],
@@ -51,12 +51,12 @@ function snapshot(path, columns) {
    return { columns, rows };
  } finally { db.close(); }
 }
-test('REQ-LIMIT-4 3g copy migrates through 3h and 3i to 3j preserving every old column, row and sequence; new usage table is empty', t => {
+test('REQ-LIMIT-4 3g copy migrates through 3h, 3i and 3j to 3k preserving every old column, row and sequence; new usage table is empty', t => {
  const { root, path, copy } = source3g(t), before = snapshot(path), untouched = readFileSync(copy);
  assert.throws(() => new Store(root), /schema-mismatch/);
  const store = new Store(root, { migrateSchema: true });
  try {
-    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3j');
+    assert.equal(store.get("SELECT value FROM meta WHERE key='schema_version'").value, '3k');
    assert.deepEqual({ ...store.get('SELECT to_name FROM messages') }, { to_name: null });
    assert.equal(store.get('SELECT count(*) AS n FROM usage_records').n, 0);
    assert.equal(store.get('SELECT name FROM instance_names').name, 'Builder');
@@ -858,7 +858,7 @@ const COUNTED=/^COUNTED="([^"]*)"$/m.exec(srText)[1].split(' ');
 const STORE_JS=/^STORE_JS='([\s\S]*?)'$/m.exec(srText)[1];
 // sage-1163's list 2, written out so that a table dropped from the script's COUNTED fails T45 as
 // well as T46.
-const LISTED=['role_claims','thread_claims','decision_events','messages','deliveries','task_snapshots','projects','threads','thread_opens','instance_names','usage_records'];
+const LISTED=['role_claims','thread_claims','decision_events','messages','deliveries','task_snapshots','projects','threads','sessions','session_defaults','thread_opens','instance_names','usage_records'];
 const LATE='2999-01-01T00:00:00.000Z';
 const addRow=(file,table,at=LATE)=>{const db=new DatabaseSync(file);db.exec(`CREATE TABLE IF NOT EXISTS ${table} (seq INTEGER PRIMARY KEY, at TEXT NOT NULL)`);db.prepare(`INSERT INTO ${table} (at) VALUES (?)`).run(at);db.close()};

@@ -17,6 +17,12 @@ import { run } from "../src/cli.mjs";
 import { CliError } from "../src/errors.mjs";
 import { busExit } from "../src/transport.mjs";
 import { humanEnv, io } from "./helpers.mjs";
+// Row 264a (#1769): a thread made by hand gets the default session the 3j-3k migration gives a
+// legacy thread, with the thread's id.
+const DEFAULT_SESSION = [
+  "INSERT INTO sessions(at,business,thread,id,instance,owner,name,op) SELECT at,business,id,id,instance,owner,'default','legacy-3k' FROM threads WHERE id=?",
+  "INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads WHERE id=?",
+];

 const shipped = (name) => JSON.parse(readFileSync(fileURLToPath(new URL(`../../../roles/${name}.json`, import.meta.url)), "utf8"));
 const roles = {
@@ -185,6 +191,7 @@ test("REQ-CLI-1 a thread is its id, an id prefix of 8 characters or more, or <pr
  const at = new Date().toISOString();
  for (const n of ["1", "2"]) {
    s.store.run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)", `abcdef01-0000-4000-8000-00000000000${n}`, at, "demo", s.project, "assistant", "jason", `twin${n}`);
+    for (const sql of DEFAULT_SESSION) s.store.run(sql, `abcdef01-0000-4000-8000-00000000000${n}`);
  }
  const resolve = async (ref) => (await s.cli(["thread", "open", ref]));
  const opened = (r) => r.out.trim();
@@ -322,6 +329,7 @@ test("REQ-USER-2 a thread of another user is refused for talk, open, read and fo
  const theirs = randomUUID();
  s.store.run("INSERT INTO projects(id,at,business,name,repo,created_by) VALUES(?,?,?,?,?,?)", "p-theirs", at, "demo", "theirs", "stack", "someone-else");
  s.store.run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)", theirs, at, "demo", "p-theirs", "assistant", "someone-else", "private");
+  for (const sql of DEFAULT_SESSION) s.store.run(sql, theirs);
  // A message waiting for the user: message.receive would write a delivery row for it.
  s.call("chief", "message.send", { to: "human", body: "waiting", class: "INFO" });
  const before = s.writes();
@@ -27,6 +27,12 @@ import { bootConfig, loadSystem } from "../src/config.mjs";
 import { startTimeOf } from "../src/host.mjs";
 import { createLauncher } from "../src/launcher.mjs";
 import { fakeHarnesses, fixture, tmp } from "./helpers.mjs";
+// Row 264a (#1769): a thread made by hand gets the default session the 3j-3k migration gives a
+// legacy thread, with the thread's id.
+const DEFAULT_SESSION = [
+  "INSERT INTO sessions(at,business,thread,id,instance,owner,name,op) SELECT at,business,id,id,instance,owner,'default','legacy-3k' FROM threads WHERE id=?",
+  "INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads WHERE id=?",
+];

 const ADAPTER = fileURLToPath(new URL("./fixtures/thread-adapter.mjs", import.meta.url));
 const skip = sandboxProblem() ?? false;
@@ -356,7 +362,8 @@ test("REQ-THREAD-2 REQ-LAUNCH-1 a thread id that isn't a safe segment, or a thre
  store.run("INSERT INTO projects(id,at,business,name,repo,created_by) VALUES(?,?,?,?,?,?)", "p-hand", at(), "acme", "hand made", "stack", "jason");
  for (const [id, instance] of [["../evil", "assistant"], ["coder-thread", "coder"]]) {
    store.run("INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)", id, at(), "acme", "p-hand", instance, "jason", id);
-    store.run("INSERT INTO thread_opens(at,thread,by) VALUES(?,?,?)", at(), id, "jason");
+    for (const sql of DEFAULT_SESSION) store.run(sql, id);
+    store.run("INSERT INTO thread_opens(at,thread,session,by) VALUES(?,?,?,?)", at(), id, id, "jason");
  }
  store.close();

@@ -5,6 +5,12 @@ import { createChat } from '../src/chat.mjs';
 import { startServer } from '../src/serve.mjs';
 import { BusReadError } from '../src/bus.mjs';
 import { close } from './fixture.mjs';
+// Row 264a (#1769): a thread made by hand gets the default session the 3j-3k migration gives a
+// legacy thread, with the thread's id.
+const DEFAULT_SESSION = [
+  'INSERT INTO sessions(at,business,thread,id,instance,owner,name,op) SELECT at,business,id,id,instance,owner,'default','legacy-3k' FROM threads WHERE id=?',
+  'INSERT INTO session_defaults(at,thread,session,by) SELECT at,id,id,'migration-3k' FROM threads WHERE id=?',
+];

 const P = '10000000-0000-4000-8000-000000000001';
 const T = '20000000-0000-4000-8000-000000000002';
@@ -220,15 +226,17 @@ test('REQ-USER-2 real broker: owned catalog, create/name/filter, isolated histor
  const other = '40000000-0000-4000-8000-000000000004';
  store.run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)',
    other, new Date().toISOString(), 'demo', project, 'assistant', 'someone-else', 'PRIVATE-NAME');
+  for (const sql of DEFAULT_SESSION) store.run(sql, other);
  store.run('INSERT INTO messages(id,at,business,from_role,from_run,to_role,class,body) VALUES(?,?,?,?,?,?,?,?)',
    M, new Date().toISOString(), 'demo', 'human', 'human-cli', 'assistant', 'INFO', 'PRIVATE-BODY');
-  store.run('INSERT INTO message_threads(message,thread) VALUES(?,?)', M, other);
+  store.run('INSERT INTO message_threads(message,thread,session) VALUES(?,?,?)', M, other, other);
  const foreignProject = '50000000-0000-4000-8000-000000000005';
  const foreignThread = '60000000-0000-4000-8000-000000000006';
  store.run('INSERT INTO projects(id,at,business,name,repo,created_by) VALUES(?,?,?,?,?,?)',
    foreignProject, new Date().toISOString(), 'foreign', 'FOREIGN-PROJECT', null, 'jason');
  store.run('INSERT INTO threads(id,at,business,project,instance,owner,name) VALUES(?,?,?,?,?,?,?)',
    foreignThread, new Date().toISOString(), 'foreign', foreignProject, 'assistant', 'jason', 'FOREIGN-THREAD');
+  for (const sql of DEFAULT_SESSION) store.run(sql, foreignThread);
  assert.equal((await get('/api/chat/threads')).data.rows.length, 2);
  const before = ['messages', 'thread_opens', "events WHERE kind='action.allowed'"].map(table => store.get(`SELECT count(*) n FROM ${table}`).n);
  for (const id of [other, T, foreignThread]) for (const suffix of ['messages', 'open']) {
@@ -401,7 +401,7 @@ plugin_checks() {
 # Row 181: the tables a bus writer fills without an event in the same transaction, in schema
 # order. A restore drops their rows after STAMP as it drops events, so the guard counts them too.
 # BUILD.md for row 181 names each writer; the T46 guard classifies every table in the schema.
-COUNTED="role_claims thread_claims decision_events messages deliveries task_snapshots projects threads thread_opens instance_names usage_records"
+COUNTED="role_claims thread_claims decision_events messages deliveries task_snapshots projects threads sessions session_defaults thread_opens instance_names usage_records"

 STORE_JS='
 const {DatabaseSync}=require("node:sqlite");const {pathToFileURL}=require("node:url");
Author	SHA1	Message	Date
jason.woltje	312cf33a11	row 264a (#1769 , T1 item 7): bus schema 3j to 3k, sessions below a thread sessions and session_defaults are new and append-only. thread_claims, message_threads and thread_opens are rebuilt in place with a session column, and thread_claims gains a generation counted from claim rows. Each existing thread gets a default session with the thread's id; new threads get a random one. Holder, per-run, release and delivery triggers key on the session, and two id triggers keep session and thread ids apart (Duckworth checks 1-7, duckworth-0106). The broker binds a thread run to a session (the default when the record names none), and thread.open, thread.send and thread.messages take an optional session. New verbs session.list and session.create (idempotent on op). Tests: sessions.test.mjs for T1 bus half, T2 and T7 with a pinned 3j fixture; count, version and verb pins; hand-made test threads write the legacy default session. Not run yet: every run waits for Sage's CLEAR.	2026-10-21 18:58:05 -05:00
jason.woltje	62253c288b	gizmoduck: row 264a bus design in the build notes: sessions and session_defaults, thread_claims, message_threads and thread_opens rebuilt with a session (legacy default id = thread id), generation, broker lookups by session, verbs, tests and pinned lists	2026-10-21 18:40:02 -05:00
jason.woltje	b851fd8c51	gizmoduck: row 264 build notes record Sage's Q1-Q7 rulings (sage-2235, `5f5b51dd6`)	2026-10-21 18:35:04 -05:00
jason.woltje	8652158d32	gizmoduck: row 264 phase A build notes, code at `da9555ca2`, consumer audit first pass, five proposed slices and Q1-Q7 to Sage (sage-2233, #1769 , Vikunja 463)	2026-10-21 18:32:08 -05:00