stack/agents/dewey/work/chat-02/BRIEF.md

# CHAT-02 brief: read-only histories and Age (#1507, row 5)

Author: Dewey, 2026-09-26. R4. Filbert approved R3 (`3b81a3f2…`). R4
applies his two non-blocking nits: F17 and §1.1 item 1. His review, with the
R2 verdict and the R3 approval, is
`agents/filbert/work/chat-02-brief-r2-review-2026-09-26.md`. Earlier revisions
are frozen as `BRIEF-r1-314da8b0.md`, `BRIEF-r2-ed177bf6.md` and
`BRIEF-r3-3b81a3f2.md`. §6 maps his R2 findings to their changes. No source
edits.

Plan row: `docs/plans/2026-09-13_webui-session-chat.md` line 214. Depends on
CHAT-01 (`28d4e98a`) and uses the CHAT-01C companion (`b023841c`).

## 1. Is there a second defect in the return path?

Short answer: no second return-path defect has shown up for repository Pi
seats. Two legs are shown directly: answers reach the transcript, and the
board serves them. The Console leg is shown only by replaying the 09-13
code (item 4), until Jason answers the §1.4 question about today's send.

The best explanation for what Jason hit on 09-13 is the product gap. The
board collapses the last answer to 240 characters
(`packages/control-board/src/scan.mjs`, `TEXT_LIMIT`, line 23 at ea00ec66
and line 25 at HEAD). The Console showed that one clipped field in an
inspector, with no conversation view and no pending signal. 42c08d52 fixed
the pending display. CHAT-02 covers the clip and the missing view, which means
the new history routes must not go through the board's summary text.

I found one real defect on the send side (§1.3). While reviewing the new
routes, I found a missing Host check on the board (§1.5).

### 1.1 Evidence so far

1. **Transcripts.** `evidence/sends.mjs` walks every `.pi/state/*/sessions`
   file. That is five seat directories: darkwing, dewey, filbert, researcher
   and sage, and sage has no board sends. For each board send, the script
   records the *first* later assistant entry with `stopReason: stop`. The
   output is `evidence/board-sends-repo-pi.jsonl`.
   - Of 30 sends, 29 are followed by a stop answer in the same file.
   - Latency is 1.5 s minimum, 14.6 s median and 1019 s maximum.
   - 16 of the 29 answers exceed 240 characters, so the board clipped them.
   - The attribution is by file order only. In 7 of the 29, another
     user-role entry lands between the send and the answer, so the answer may
     also cover that later input. Filbert rechecked: all 7 are peer
     agent-sends (dewey to darkwing three times, rocko to darkwing, darkwing
     to dewey twice, filbert to dewey). Jason's 09-13 question (item 3) is not
     one of the 7.
   - Filbert confirmed that none of the nine files involved branches, so file
     order equals branch order.
2. **The unanswered send.** Filbert, 2026-09-12T16:33:17Z. The seat started
   working on it and read files until 16:35:44Z. The last entry is an
   `aborted` assistant turn, and a new filbert session began at 16:36:26Z.
   The seat was relaunched mid-turn, so the answer was lost in the seat, not
   in the return path. §2.3 point 5 turns this into a test.
3. **Jason's report window.** At 2026-09-13T00:49:59Z he asked dewey "What
   are the Gate E criteria?". The answer landed at 00:50:07Z: 365 characters,
   which the board clipped to 240. He wrote the report at 00:56:51Z. It says
   the sessions "are all cards within the project dashboard and not available
   as independent chat interfaces". That describes the missing view, not a
   missing answer.
4. **The 09-13 Console, replayed.** The pinned files are in
   `evidence/replay-0913/`: the test, the diff against 42c08d52, the TAP
   output and a README.
   - The scratch extract of `ea00ec66` is byte-identical to that commit (45
     files checked).
   - The test is the 42c08d52 return-flow test with the Age, pending and
     clear-once assertions removed, since ea00ec66 has none of those.
   - It passed (1/1, 20.7 s): the new answer arrived through the 10 s poll,
     once, in the open inspector.
   - The replay's answer is short, so it does not exercise the clip.
5. **Jason's live send today.** Researcher, user entry at
   2026-09-26T20:10:57.429Z, answer "pong" at 20:11:06.173Z (8.7 s).
   - At 20:15:18Z, `/api/board` showed the row `idle`, with
     `lastAssistantText: "pong"`, the same `sessionFile` and a live
     registration (`evidence/board-researcher-*.json`).
   - The live WebUI (pid 1266267, port 7330) serves `app.js` byte-identical
     to HEAD (`d1a51646…`). Its server code has not changed since that
     process started on 09-13 at 16:19 CDT.
   - The board (pid 3977979, port 7331) started today at 15:03 CDT.

### 1.2 What is still unverified

- **What Jason's screen showed.** I have the transcript and the board JSON
  for today's send, but not the Console DOM. The Console leg for a live send
  is unproven until Jason answers §1.4.
- **The 09-13 processes.** The board keeps no reply receipts, and the 09-13
  processes are gone. Item 4 shows that the same code works. It cannot show
  what those processes served.
- **Fleet seats.** I did not scan `~/.mosaic` transcripts. They are out of
  scope for CHAT-02.
- **The clip in a live send.** "pong" is 4 characters, so today's send
  doesn't exercise the clip.

### 1.3 Send-side defect found in passing

Today's user entry starts with `/`:

    /[dragon-lin:control-board -> dragon-lin:researcher] ping

`agent-send.sh` adds the header, so the `/` was already in the Pi composer
when the paste arrived. `send-message.sh` pastes onto whatever the composer
holds, then presses Enter. Here Pi treated the result as plain text. If the
composer had held a real command prefix, a board reply could have become a
Pi slash command.

Sage confirmed this as a safety gap under CHAT-03I/B3 and recorded it in
DEFERRED.md. It is on #1507 (comment 26538). There is no `tools/tmux` change
now.

### 1.4 Evidence that settles it

Sage is putting one question to Jason: **after today's ping, did "pong"
appear in the Console inspector without pressing Refresh?**

- **Yes:** there is no second defect, and CHAT-02 proceeds as a
  product-gap fix.
- **No:** `/api/board` had the answer, so the defect is in the Console or the
  WebUI proxy. Capture the Console DOM and the `/api/board` network log during
  one send.
- **Missing from `/api/board`:** that would point at the scanner. **Missing
  from the transcript:** that would point at transport or the seat. Neither
  happened today.

One more live send, asking for an answer over 240 characters, would show
the clip ending in "…".

### 1.5 Board Host check (found while reviewing D3)

The Console server checks `Host` and `Origin`
(`packages/webui/src/serve.mjs` lines 54–59). The board server does not. It
checks only the bind address.

A DNS-rebinding page that reaches port 7331 could:

- read `/api/board`: 240 characters per row, plus task and cwd;
- `POST /api/reply` with `application/json`. The board requires that content
  type but not a same-origin `Host`, so the text would be pasted into a live
  seat pane.

Modern browsers restrict some local-network requests, but I have not tested
any browser against this. That makes it a finding, not a demonstrated
exploit.

The new D3 routes must carry the guard (§2.1). Whether the same guard should
be applied to the existing board routes in that `serve.mjs` change is Sage's
decision. I recommend doing it.

## 2. Scope

CHAT-02 per the plan, narrowed by D2:

- a Pi catalogue;
- safe, full branch history, with pagination and cursors;
- separate timestamps;
- relative Age from last activity;
- no writes to logs.

It is read-only. Opening a conversation never resumes, forks, launches or
controls anything.

### 2.1 Backend: `packages/conversation/**` (Dewey, D4)

**Catalogue sources.** Only approved source roots count: the board's
repository specs (`<repo>/.pi/state/<seat>/sessions`). There is no global
scan, and no path comes from the browser. A seat registration is
seat-written, so it is a hint, not authority (CHAT-01 line 62). Its
`sessionFile` is accepted only when the file is under an approved root for
the same project. Each conversation gets an opaque ID, which the server maps
to a file. Catalogue creation time, engine launch time and last activity are
separate nullable fields.

**Opening a file safely.**
- Check every path component with `lstat`: no symlinks, and it stays inside
  the root.
- Open with `O_RDONLY | O_NOFOLLOW`, then `fstat` the descriptor. The
  descriptor's (dev, ino) must match the checked path.
- Read only from that descriptor.
- Never use `SessionManager.open`, which can migrate files (CHAT-00 line 67).

**Parser.**
- Build the `id`/`parentId` tree and select a leaf explicitly. The default is
  the last appended entry, which the implementer confirms against the pinned
  Pi session docs. Other leaves are read-only branches.
- Compaction entries render as markers.
- Pi `get_entries` order is not a branch transcript (CHAT-00 line 66), so it
  is not used.
- The parser never follows `parentSession`. The conversation still renders,
  with a "forked from an earlier session" marker, and the parent file is never
  opened.
- If the Pi header's `cwd` names another project, the conversation is refused.
- A malformed line becomes an unavailable part at its position, and reading
  continues. A truncated trailing line is incomplete, not an error.

**Pages.**
- CHAT-01 limits: at most 100 parts, at most 8 MiB of serialized UTF-8 bytes
  (enforced on bytes, not characters), 64 blocks per part, and 262144
  characters per string.
- Oversize content splits into continuation parts and is never clipped.

**Snapshots and epochs.**
- The page reads up to the snapshot length that its cursor pins, so growth
  during a read is cut there.
- A source epoch is (dev, ino) plus a SHA-256 of the prefix the snapshot
  covers. Growth past that prefix is the same epoch.
- A different inode, a shorter file, or a changed prefix digest (an in-place
  rewrite with the same inode) is a new epoch.

**Cursors.**
- A cursor binds actor, purpose, conversation, branch, snapshot, source epoch
  and expiry.
- These all refuse, keep the old view and show a reconcile marker: an
  unknown, foreign, expired or source-replaced cursor.
- Nothing ever switches files silently.
- On this unauthenticated loopback route there is one actor,
  `local-operator`, and cursors bind to it. That is not multi-actor safety.
  Authenticated actors come with CHAT-04R and must not be claimed here.

**Board routes (D3).** Two read-only `GET` routes, catalogue and page.
- `Host` must be the loopback name and the board's own port.
- A cross-origin `Origin` is refused.
- No CORS headers are sent.
- Responses are `application/json` with `nosniff` and `no-store`.

**Fixtures.** Each one names its expected refusal or result.

| # | Fixture | Expected |
|---|---|---|
| F1 | Malformed line | Unavailable part at its position, reading continues |
| F2 | Truncated trailing line | Incomplete marker |
| F3 | Replaced file (new inode) | Old cursors refuse, reconcile |
| F4 | Same-inode prefix rewrite | Old cursors refuse, reconcile |
| F5 | Touched: growth between two pages and during one read | Same epoch, page cut at the pinned length |
| F6 | Unknown, foreign (actor, purpose, conversation or branch) and expired cursor | Each refuses and keeps the old view |
| F7 | Symlink at the file and at a directory component | Refused, never opened |
| F8 | File swapped for a symlink between catalogue and read | Refused (O_NOFOLLOW or a dev/ino mismatch) |
| F9 | Registration naming a file outside the roots, a symlink, or another project's file | Refused, never opened |
| F10 | Pi header `cwd` naming another project | Refused |
| F11 | `parentSession` pointing outside the root | Renders with a marker, and the parent is never opened |
| F12 | Branched file with two leaves | Default leaf shown, other branch readable, no merge |
| F13 | Compaction | Marker, then retained content |
| F14 | A string over 262144 characters, and a multibyte page reaching 8 MiB before 100 parts | Continuation parts, reassembled exactly, byte cap enforced |
| F15 | Claude harness | `unsupported-harness` refusal (D2) |
| F16 | Foreign `Host` and a cross-origin `Origin` on both routes | 403, no CORS headers |
| F17 | No writes | Before and after every reader operation (catalogue, open, page), in every fixture, including the ones that mutate files on purpose between reads (F3, F4, F5, §2.3 point 6): size, SHA-256, mtime, (dev, ino), and the session directory listing (no new files) are unchanged. Atime is excluded because relatime can update it on read. |

### 2.2 Console: `packages/webui/**` (Dewey)

This is the smallest thing that answers the 09-13 complaint: a read-only
conversation view per session, opened from the card, the table or the
inspector.
- It renders the selected branch in full, with nothing clipped: user text,
  assistant text, and tool calls and results collapsed.
- Thinking is hidden by default.
- Markdown is untrusted, so it has no active HTML, no unsafe URLs and no
  terminal escapes.
- Age stays as 42c08d52 shipped it.
- Reply keeps the existing board path. The view gets new answers through
  polling. Streaming belongs to CHAT-03.

The full chat UI (sidebar, composer, queue, approvals and uploads) stays in
CHAT-05.

**Hostile-render fixture (R1).** Assistant text and tool output contain:
- HTML, including `<script>` and `<img onerror>`;
- a `javascript:` link;
- ANSI and OSC terminal escapes.

All of it renders as inert text. The test asserts that no element, handler or
navigation was created.

### 2.3 Return-flow regression (required by the plan)

The regression runs on the real board, the real D3 routes and the real
WebUI, the way the existing test does. Nothing is injected into the WebUI.
1. **Path.** Send from the conversation view. The seat then appends a user
   entry, a toolCall, a toolResult and a final answer.
2. **Exactness.** The answer has a sentinel after character 240 and another
   at the very end. The view shows the exact text, with no "…", once.
3. **Continuation.** A second answer is long enough to split into
   continuation parts. The test checks that it reassembles exactly and in
   order.
4. **Thread order.** In the view, the sent message comes first, then the
   collapsed tool call and result, then the answer.
5. **Interleaving.** A peer agent-send lands before the final answer, as in
   §1.1 item 1. Both entries show, in file order.
6. **Relaunch mid-turn,** modelled on the 09-12 filbert case. A new session
   file appears. The open view keeps its file, shows the reconcile marker and
   never switches silently.
7. **Timing.** A delayed-result variant has the toolResult land after a poll.
   The draft and caret survive, and no manual refresh is used.

This covers Pi only (D2).

## 3. Decisions (Sage, 2026-09-26)

- **D1: moved.**
  - `docs/plans/chat-01/README.md:342` defers "the actual execution/writer-claim
    record" to CHAT-02.
  - `docs/plans/chat-01c/README.md:217–218` puts R3-1 (reconciling dispatched
    but unconsumed input) in "CHAT-02 adapter evidence".
  - A read-only reader needs neither, so both move to CHAT-03, which owns
    binding and the single writer.
  - The published CHAT-01 and CHAT-01C text stays as it is. The move is
    recorded on #1507 (comment 26538) and in
    `docs/plans/2026-09-26_lead-decisions.md` item 8, so a reader of line
    342 can find it.
- **D2: accepted.**
  - Pi ships in CHAT-02. Claude's catalogue waits for B1, which is defined at
    `docs/plans/chat-00/README.md:193` and restated at
    `chat-01/README.md:382`. Line 66 of CHAT-00 is the capability row that
    shows the gap: Claude's persisted branch format and leaf selection.
  - `unsupported-harness` is a **new CHAT-02 reason value**, not an existing
    contract code. The CHAT-01 schema has only a nullable `unsupportedReason`
    field, and this value fills it.
  - This narrows the plan's "both harnesses". Sage records it in the lead
    decisions file.
  - Owner after B1 (proposed; Sage confirms): CHAT-03 supplies the Claude
    catalogue and history. It already owns Claude engine integration and is
    gated by B1. That gives CHAT-06's both-harness gate an owner.
- **D3: accepted.** `packages/conversation` is a library with no server. The
  board adds the two read-only routes, with the §2.1 guard, in
  `packages/control-board/src/serve.mjs` and `scan.mjs`. Darkwing reviews
  that change before it lands. The coordination note goes to him when the
  backend reaches review. §1.5 asks Sage whether the guard should also cover
  the existing routes.
- **D4: Dewey authors both.** Backend first, then the Console against its
  fixtures. Filbert reviews the brief now and the code after.
- **D5: stays with Jason.** Sage's live reply test passed on the transcript
  and board legs. The Console leg waits for Jason's §1.4 answer. Sage is
  asking him for the go on CHAT-02. No code goes under
  `packages/conversation` until Sage relays his answer.

## 4. Acceptance

- Every fixture in §2.1 (F1–F17) and the §2.2 hostile-render fixture is
  covered by a test, and those tests pass.
- The §2.3 regression passes on the served WebUI, through the real board
  routes.
- These still pass: `node docs/plans/chat-00/check.mjs`, `chat-01/check.mjs`,
  `chat-01c/check.mjs`, and the control-board, webui and seat suites.
- Browser evidence: the conversation view at 320 and 1440, in both themes,
  showing:
  - a long answer;
  - a tool call;
  - the hostile-content fixture rendered inert;
  - a malformed-line marker;
  - a reconcile marker.

  There is no horizontal overflow at 320.
- Filbert approves the exact candidate hashes, and Darkwing reviews the
  board routes.
- Live check: one board send with a long answer, shown in full in the view.

## 5. Not in scope

- live adapters, control, streaming, queues, uploads and approvals;
- fleet seats;
- Claude history until B1;
- changes to `tools/tmux/**`, `roles/**` or session logs;
- the `/` paste hazard (CHAT-03I);
- authenticated multi-actor cursors (CHAT-04R).

## 6. R2 findings and where R3 answers them

| Filbert R2 | R3 |
|---|---|
| §1 finding 1: Console leg overclaimed; D5 "passed" | §1 opening; §1.2; D5 |
| §1 finding 2: order-only attribution, 7 interleaved | §1.1 item 1; §2.3 point 5 |
| §1 finding 3: the clip is in the board | §1 opening; §2.3 point 2 |
| §1 finding 4: item 4 unpinned | `evidence/replay-0913/`; §1.1 item 4 |
| §1 finding 5: five directories scanned | §1.1 item 1 |
| §2 finding 1: cursor refusals | F6 |
| §2 finding 2: touched logs | F5 |
| §2 finding 3: same-inode rewrite | Epoch rule; F4 |
| §2 finding 4: registrations, cwd | Catalogue sources; F9; F10 |
| §2 finding 5: parentSession | Parser; F11 |
| §2 finding 6: symlink race | Opening a file safely; F8 |
| §2 finding 7: no-write check | F17 |
| §2 finding 8: Host check, actor | Board routes; Cursors; F16; §1.5 |
| §2 finding 9: byte cap, renderer | F14; §2.2 hostile-render fixture |
| §3 points 1–5 | §2.3 points 1–6 |
| §4: D1 line; D2 citations, reason value, owner | §3 D1, D2 |