platform/docs/chat-session-lifetime.md

Chat session lifetime — findings and plan

Written 2026-08-09, before implementation. The investigation is done; the code is not.

The trigger. A laptop ran out of battery overnight while an agent on the home lab was running a 15-minute background loop (review new commits, restart the server). The session should have survived until morning. Officer would have killed it about an hour after the browser socket dropped.

What is actually there — verified, not remembered

Two independent idle policies exist, in two processes, answering different questions.

The sidecar's — the real one

src/servers/sidecar/claude/claude-manager.ts

• IDLE_TIMEOUT_MS = 30 * 60 * 1000 (:39) — thirty minutes with no new turn.
• armIdle (:284-295) is a heartbeat, not a one-shot: on expiry it re-checks and re-arms if isGenerating || pendingTasks.size > 0, so it can never collect a session that is still working.
• pendingTasks: Set<string> (:174) holds background tasks started but not yet notified. task:started adds the id and clears the idle timer outright (:406-411); task:notification removes it and re-arms only if nothing else is outstanding (:413-414).
• Its own comment states the intent: "never GC a session that's mid-turn or still has background tasks running — a long silent run_in_background job would otherwise be killed along with its pending task_notification."

So the sidecar already detects long-running background work with no declaration from the user. The "mark a session permanent" feature is not needed for this case.

There is also stallTimer for a turn that claims to be generating but has emitted nothing, and SEND_TIMEOUT_MS = 30 * 60 * 1000 (:10).

Officer's — the blunt one

src/servers/api/chat/websocket.ts, src/servers/api/chat/session-manager.ts

• IDLE_TIMEOUT_MS = 60 * 60 * 1000 (websocket.ts:48).
• Armed by the socket closing, not by it being unresponsive: close(ws) → detachWs + setIdleTimeout (websocket.ts:151-163). Unresponsiveness matters only upstream — Bun closes a WS idle for 60s and there is a per-connection heartbeat, so a dead laptop loses the socket about a minute in, and that starts the hour.
• Expiry runs deleteSession (session-manager.ts:74-102), which calls _sidecarUnsub() then _claudeKill() → sidecar.killClaude(sessionId).
• attachWs clears the timer (session-manager.ts:104-116), so reconnecting cancels it cleanly.

Three defects follow:

1. It kills sessions the sidecar has deliberately protected. Officer has no view of pendingTasks.
2. It does not survive pm2 restart officer — a setTimeout on an in-memory record, in the process designed to bounce. If the browser never returns, nothing re-arms it.
3. On a flat battery the sidecar's 30 minutes normally fires first anyway, so officer's hour is mostly redundant except in the one case where it does damage — a session with background work, which the sidecar keeps and officer kills.

What is already fine

pm2 restart officer does not kill running sessions. Sidecars are PM2 peers, not children; the agent keeps generating and keeps committing to chat_session_events. Only officer's in-memory binding dies, and adoptOrphanedSession (websocket.ts:559) rebuilds it — including the session-scoped subscription, without which a reconnected client replays and then goes silent for the rest of the turn.

Step 1 — officer's timer releases instead of kills — DONE

Officer's idle timer is doing two unrelated jobs: garbage-collecting its own binding (its business) and terminating the agent (the sidecar's). Split them and leave the agent's lifetime to the process that already reasons about it correctly.

Rejected alternative: teaching officer about pendingTasks over the protocol. That re-implements the sidecar's heartbeat in a second place, which is how these two drifted apart to begin with.

The blocker. src/servers/channels/send-claude-code.ts:65-69 welds them together:

return {
  kill: () => {
    sidecar.killClaude(params.sessionKey);
    unsub();
  },
};

unsub is a closure reachable only through kill, so officer cannot let go without killing.

The seam already exists. _sidecarUnsub is declared (types.ts:310) and called separately in deleteSession (session-manager.ts:83-84) — and nothing ever assigns it. Populating it is the fix.

Work:

1. send-claude-code.ts — return { kill, detach }; kill stays as-is, detach is unsub alone.
2. Same for the OpenCode path (websocket.ts:452 assigns handle.kill there too).
3. websocket.ts:361 / :452 — also assign session._sidecarUnsub = handle.detach.
4. session-manager.ts — add releaseSession(sessionId): clear the idle timer, call _sidecarUnsub, drop from sessions/userSessions. Do not call _claudeKill.
5. setIdleTimeout's callback → releaseSession, not deleteSession.
6. Leave deleteSession alone — explicit disconnect (handleDisconnect) must still kill.

Check while doing it: adoptOrphanedSession notes that handleChat treats an absent _claudeKill as "first turn of this session" and would open a second subscription, delivering every message twice. Make sure a released-then-readopted session cannot land in that state.

Consequence to accept: after an hour a returning browser goes through the adopt path rather than finding a live record. That path already runs on every officer restart.

As built. detach added beside kill on both streaming handles; _sidecarUnsub populated at all three sites (Claude first turn, OpenCode, and adoptOrphanedSession — that last one was not in the original list and would have leaked a listener per adopt-then-idle); forget factored out of deleteSession; releaseSession added; the idle timer points at it. deleteSession still kills, so an explicit disconnect is unchanged.

The double-subscription trap does not arise: releaseSession unsubscribes and drops the record, so a returning browser either adopts (fresh single subscription) or starts a first turn with no stale listener behind it. unsub is a Set.delete, so deleteSession calling it twice is harmless.

Step 2 — enumerate live sessions

After an officer restart a live session is invisible until a browser reconnects to it by id; adoption is on-demand only. There is no list verb in the sidecar protocol (checked).

Add claude:list returning each live sessionKey with isGenerating and pendingTasks.size, so officer can answer "what is running right now" and surface it.

Do not try to persist a running session. A live session is a running query() with an open stream; it cannot be serialised. The durable part — the output — is already in chat_session_events, which is what makes replay work.

Hard limit: if the agent sidecar restarts, a mid-turn is lost regardless. Officer restarts are survivable; officer-agent restarts are not.

Deliberately not decided

Keeping an idle session alive — nothing generating, no background work — is a separate decision and the only part that would need the user to mark anything. Steps 1 and 2 cover sessions with work in flight, which is the case that actually bit. A 15-minute loop re-arms the sidecar's 30-minute timer on every turn, so it never idles out on its own.