diff --git a/agents/gizmoduck/work/queue-264/BUILD.md b/agents/gizmoduck/work/queue-264/BUILD.md
index bb968704b..3dfba9c9b 100644
--- a/agents/gizmoduck/work/queue-264/BUILD.md
+++ b/agents/gizmoduck/work/queue-264/BUILD.md
@@ -170,6 +170,36 @@ Duckworth had no objection to the in-place rebuild and asked for seven checks. W
    session. New ids come from randomUUID.
 7. `thread_one_per_run`. The inner `max(seq)` is per session.
 
+### Duckworth's early look (duckworth-0107) and Sage's ruling (sage-2257)
+
+Duckworth read 312cf33a1 with git only and found nothing blocking. Round 2 (gizmoduck/row264-r2,
+rebased on dcd8d4dda with no shared paths) answers his notes:
+
+1. Retired-generation replay. Sage ruled it into 264a (sage-2257). `#agent` now fences a thread run
+   by generation: the session's latest claim must have the generation of the run's own latest
+   claim (`#runGeneration`). A new sessions.test case has a released run and a revoked run each try
+   `decision.withdraw`, `message.receive` and `message.read` after another run claims the next
+   generation. All refuse `not-holder` and every table's row count stays the same. The workspace
+   and path halves of T2 stay in 264b.
+2. `assistant.stop` keeps returning `{thread, run}`. Adding `session` would change the pins in
+   tester-threads.test and threads.test for a field no caller reads yet. The Console stop in 264e
+   is the first reader, so the field goes there.
+3. `#route` refuses an unknown session with `session-not-found` instead of a TypeError.
+4. The README's session section says the `default` retry answers on new threads only, because a
+   migrated default has op `legacy-3k`.
+5. The Row 155 comment at the role.revoke end now says "held thread session".
+
+### Mutants
+
+Each runs on a copy of the candidate tree with one edit, and the named test must fail.
+
+- M1 (sage-2257). In `#agent`, replace `h.generation !== this.#runGeneration(s)` with `false`.
+  Killed by sessions.test "a released or revoked run's retired generation".
+- M2. In `message.receive`, drop the `mt.session=?` filter (the session clause and its argument).
+  Killed by sessions.test T1, where a1 would take the second session's message.
+- M3. In 3j-3k.sql, count every claim row for `generation` instead of `op='claim'` rows only.
+  Killed by sessions.test T7, generations 1, 1, 1, 2, 2.
+
 ### Dry run
 
 Before writing any node test, I ran 3j-3k.sql in an in-memory Python sqlite3 on a 3j fixture
diff --git a/packages/bus/README.md b/packages/bus/README.md
index 411eccb11..5f1d2b246 100644
--- a/packages/bus/README.md
+++ b/packages/bus/README.md
@@ -333,6 +333,15 @@ A thread run receives and replies in its own session, and the chief of staff's r
 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.
 
+A thread run's claim fences by generation (T2). A run acts only while its session's latest claim
+row has the generation of the run's own latest claim. After a release or revoke, once another run
+claims the session, the old run's `decision.withdraw`, `message.receive` and `message.read`
+refuse `not-holder` and write nothing.
+
+`thread.create` writes the default session with op `default`, so a `session.create` retry naming
+`default` with op `default` answers with it. A migrated thread's default has op `legacy-3k`, and
+the same retry there refuses `session-exists`.
+
 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
diff --git a/packages/bus/src/broker.mjs b/packages/bus/src/broker.mjs
index ae3301b86..b90c33d07 100644
--- a/packages/bus/src/broker.mjs
+++ b/packages/bus/src/broker.mjs
@@ -812,9 +812,15 @@ export class Broker {
     if (s.reader) fail('read-only');
     if (s.human) fail('agent-required');
     const h = this.#own(s);
-    if (h?.op !== 'claim' || h.holder_run !== s.run) fail('not-holder');
+    if (h?.op !== 'claim' || (s.thread ? h.generation !== this.#runGeneration(s) : h.holder_run !== s.run)) fail('not-holder');
     return h;
   }
+  // Row 264a (#1769, T2): the generation a thread run holds, its latest claim's in its session, or
+  // null if it never claimed. Once another run claims the session, the run's own generation is
+  // retired, and #agent refuses its approvals, deliveries and reads.
+  #runGeneration(s) {
+    return this.#store.get("SELECT max(generation) AS g FROM thread_claims WHERE session=? AND holder_run=? AND op='claim'", s.session, s.run).g;
+  }
   #human(s) {
     if (s.reader) fail('read-only');
     if (!s.human || s.via !== 'cli' || s.outsideAgent !== true) fail('human-required');
@@ -4872,7 +4878,8 @@ 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 session, so the end revokes each one.
+        // Row 155 (#1649): a thread instance holds a claim per held thread session (264a), 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');
@@ -5973,7 +5980,7 @@ export class Broker {
   // 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);
+      const { thread } = this.#store.get('SELECT thread FROM sessions WHERE id=?', session) ?? fail('session-not-found');
       this.#store.run('INSERT INTO message_threads(message,thread,session) VALUES(?,?,?)', mid, thread, session);
     }
     this.#delivery(mid, 'routed', this.#recipient(business, to, session));
diff --git a/packages/bus/tests/sessions.test.mjs b/packages/bus/tests/sessions.test.mjs
index fd0b73655..6614c94e9 100644
--- a/packages/bus/tests/sessions.test.mjs
+++ b/packages/bus/tests/sessions.test.mjs
@@ -172,6 +172,55 @@ test('T2 REQ-ROLE-2: one holder per session, generations count its claims, and a
   store.run("INSERT INTO deliveries(message,at,op,holder_run) VALUES(?,?,'delivered',?)", m.id, now(), 'x-run');
 });
 
+test('T2 sage-2257: a released or revoked run\'s retired generation refuses its approval, delivery and read, and writes nothing', (t) => {
+  const { call, launch, claim, claims, store, A, D } = setup(t);
+  const tables = store.all("SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'").map((r) => r.name);
+  const counts = () => Object.fromEntries(tables.map((n) => [n, store.get(`SELECT count(*) AS n FROM "${n}"`).n]));
+  // The run raises a decision, takes one message and leaves a second waiting.
+  const prepare = (name) => {
+    launch(name, 'assistant', { thread: A });
+    claim(name);
+    const d = call(name, 'decision.raise', {
+      action: 'spend',
+      target: 'demo',
+      question: 'spend?',
+      options: [
+        { key: 'yes', text: 'Yes' },
+        { key: 'no', text: 'No' },
+      ],
+      recommendation: 'no',
+      blocking: false,
+    });
+    call('human', 'thread.send', { thread: A, body: `for ${name}` });
+    const [taken] = call(name, 'message.receive');
+    call('human', 'thread.send', { thread: A, body: `waiting after ${name}` });
+    return { d, taken };
+  };
+  const refused = (name, { d, taken }) => {
+    const before = counts();
+    assert.throws(() => call(name, 'decision.withdraw', { id: d.id }), { code: 'not-holder' }, 'approval');
+    assert.throws(() => call(name, 'message.receive'), { code: 'not-holder' }, 'delivery');
+    assert.throws(() => call(name, 'message.read', { id: taken.id }), { code: 'not-holder' }, 'read');
+    assert.deepEqual(counts(), before);
+  };
+  // Released: generation 1 is retired once a2 claims generation 2.
+  const one = prepare('a1');
+  call('a1', 'role.release');
+  const two = prepare('a2');
+  refused('a1', one);
+  // Revoked by the human's stop: generation 2 is retired once a3 claims generation 3.
+  call('human', 'assistant.stop', { instance: 'assistant' });
+  prepare('a3');
+  refused('a2', two);
+  assert.deepEqual(claims(D).map((r) => [r.op, r.holder_run, r.generation]), [
+    ['claim', 'a1-run', 1],
+    ['release', 'a1-run', 1],
+    ['claim', 'a2-run', 2],
+    ['revoke', 'a2-run', 2],
+    ['claim', 'a3-run', 3],
+  ]);
+});
+
 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' });