fix(sessions): leave a pending idle alert to the user through a keep-alive turn

Only a human spends an idle alert, but the keep-alive turn resolved an unseen one three ways: its working transition, its stop hook, and its own idle prompt replacing the item with a pre-acknowledged one. While the turn runs, a pending idle item is now left exactly as found, the page's stop handler returns on the keep-alive reason before clearing hooks or raising Response Complete, and session:working/session:idle carry keepAlive so the stuck-detection timer neither restarts nor re-arms.

The window that marks the turn closes on its own idle prompt or any other submit instead of a fixed three minutes, which a slow turn's idle prompt (sent a minute after the turn ends) could outlast. The service keeps the default and cap in memory, read through a strict reader so a mid-write read is retried rather than kept, and the cap is clamped before the strict settings save.

docs/api-reference.md

@@ -1160,7 +1160,7 @@ Claude Code reports the main conversation's prompt-cache state on its statusline
 | ------ | ---------------------------------- | ------------------------------------ | ----- |
 | `POST` | `/api/v1/sessions/:id/keep-warm`   | `{ "enabled": true \| false \| null }` | Sets the session's choice; `null` clears it so the app-wide default applies. `200` with `{ keepWarm: { enabled, status } }`. `400 INVALID_INPUT` for a CLI that reports no cache telemetry on its statusline (anything but Claude today). |
 
-`status` is `{ enabled, idleCompactionOff, state, nextCheckAt?, reason?, nudges, lastNudgeAt?, budgetEndsAt? }` (`idleCompactionOff`: whether the session's current launch carries that opt-out) with `state` one of `off`, `armed` (waiting for the due time), `waiting` (due, deferred by a guard named in `reason`), `nudged` (sent, waiting for the next cache report) or `stopped` (`reason` says why). Two SSE events carry changes: `session:promptCache` (`{ sessionId, ...promptCache }`) and `session:keepWarm` (`{ sessionId, ...status }`), both change-only. The keep-alive turn's `hook:stop` and `hook:idle_prompt` broadcasts carry `acknowledgedReason: "cache keep-alive"`, and no push is sent for them.
+`status` is `{ enabled, idleCompactionOff, state, nextCheckAt?, reason?, nudges, lastNudgeAt?, budgetEndsAt? }` (`idleCompactionOff`: whether the session's current launch carries that opt-out) with `state` one of `off`, `armed` (waiting for the due time), `waiting` (due, deferred by a guard named in `reason`), `nudged` (sent, waiting for the next cache report) or `stopped` (`reason` says why). Two SSE events carry changes: `session:promptCache` (`{ sessionId, ...promptCache }`) and `session:keepWarm` (`{ sessionId, ...status }`), both change-only. The keep-alive turn's `hook:stop` and `hook:idle_prompt` broadcasts carry `acknowledgedReason: "cache keep-alive"`, and no push is sent for them; an idle approval already pending stays as it was (only a person spends its alert). Its `session:working` and `session:idle` broadcasts carry `keepAlive: true`.
 
 ## Webhook notifications
 

docs/architecture-invariants.md

@@ -161,7 +161,7 @@ Further detail: the handheld OFF default comes from the mobile block in `getDefa
 
 ### Prompt-cache keep-warm
 
-**Prompt-cache keep-warm** (`src/prompt-cache-keepwarm.ts`; per-session opt-in `keepWarmEnabled` on the Respawn tab, app-wide default `promptCacheKeepWarm` and cap `promptCacheKeepWarmMaxHours` under App Settings → System → Automation, both SYNCED, default OFF and 2 h; step 2 of Discussion #554): shortly before an idle claude session's prompt cache would expire, Codeman sends ONE keep-alive turn (`KEEP_WARM_NUDGE`, under 100 characters so Claude Code never reads the burst as a paste) so the next real prompt still reads the conversation from cache. Measured on two sessions of ~110k tokens: the nudge read 109,831 tokens from cache and wrote 70, replied `ok` in three seconds with no tool use, and a real turn seven minutes past the original expiry stayed a hit while the un-nudged control re-wrote 89,882 tokens with `last_miss_cause: ttl_expired_1h`; the payoff on real usage is concentrated in gaps of one to four hours, which is why there is a cap after the last real prompt rather than an indefinite loop (2 h by default: the maintainer's simulation over 30 days of gaps came out slightly cheaper than 3 h). ⚠️ **Codeman owns the idle policy for a keep-warm session.** Claude Code 2.1.289+ can compact an idle 1h-cache session by itself at 90% of the TTL (a server-flagged experiment, `fireAtFraction` tunable down to 0.5), which on the default timing always lands a minute before the nudge and leaves only a summary to keep warm. So a launch with keep-warm on carries `"idleCompaction": false`, folded LAST into the ONE `--settings` JSON with ultracode, the advisor and the statusLine exporter (`buildSpawnCommandFromRegistry`; never a second `--settings` flag, Claude Code takes one), so a keep-warm-off launch is byte-identical to one from before keep-warm (`test/cli-registry-spawn-golden.test.ts`). The `--settings` flag outranks user, project and local settings, which is why the key is conditional: everywhere else it would take Claude Code's own behaviour away with no way back. `decideIdleCompactionOptOut()` (tmux-manager.ts, pure) decides it once per create and respawn: keep-warm on (`keepWarmOn()`: the session's choice, else the app default, read fresh by `readKeepWarmSettings()`), the exporter `injected` (without `prompt_cache` reports keep-warm cannot run, and the opt-out alone would only cost the user the idle compaction), and claude's `idleCompactionSetting` gate (`capabilities.gates`, 2.1.290, the first release whose settings schema has the key; 2.1.289 already idle-compacts with no opt-out), fail-closed through `launchGatePasses()` exactly like `--name`: an unknown version means no key, and a log line says so. The result is recorded on the mux record (`MuxSession.idleCompactionOff`, like `statusLine`, persisted in mux-sessions.json) and published in the keep-warm status as `idleCompactionOff`; a session switched on after launch is kept warm best-effort (a relaunch to install the opt-out would cost exactly the re-write being avoided) and its readout says Claude Code's idle compaction may still run until its next launch, which any relaunch (dead-pane recovery, a custom-model `restartCli()`) fixes for free since every relaunch re-decides. ⚠️ The deadline is the statusline's `prompt_cache.expires_at` (`Session.promptCache`), never idle detection or the plan tier, and a `5m` lifetime is a hard stop (a nudge every four minutes costs more than the miss it prevents; API-key users get the hour from `CLAUDE_CODE_PROMPT_CACHE_TTL=1h` in `envOverrides`). ⚠️ `decideKeepWarm()` is the ONE rulebook and every guard lives in it, tested as a table: the effective opt-in (`keepWarmOn()`; a session an agent spawned, `parentSessionId`, does not inherit the app default, since an idle worker that reported done looks exactly like one that will be prompted again and most never are; its own switch still works), the launch's `statusLineExporter` is `injected` (which also stops every CLI without cache telemetry; the toggle line says why in the readout's own `PROMPT_CACHE_NOT_COLLECTED` words), a warm cache with an expiry, no `compactedAt` this gap (a compaction already replaced the context, and the stamp is dropped at the next request, which re-opens the next gap), not a `5m` lifetime, at least `KEEP_WARM_MIN_TOKENS` at stake, a live pane (a pid AND no recorded `paneExit`: an agent that exited in a `remain-on-exit` pane keeps its pid), no usage-limit pause (auto-resume's, or, read off the same pane capture as the composer, a usage-limit message whose reset is still ahead, since auto-resume tracks pauses only while it is on), no automation (respawn running, a Ralph loop active, a task assigned, or an agent long-polling `wait`), inside the cap measured from `lastRealPromptAt` (else `createdAt`), due at `expires_at` minus `KEEP_WARM_LEAD_MS` but not within `KEEP_WARM_LAST_CHANCE_MS`, idle, no open permission or question dialog, an EMPTY composer (`composerIsEmpty()` in session-submit-verifier.ts reads the last glyph line AND its Line truncated
+**Prompt-cache keep-warm** (`src/prompt-cache-keepwarm.ts`; per-session opt-in `keepWarmEnabled` on the Respawn tab, app-wide default `promptCacheKeepWarm` and cap `promptCacheKeepWarmMaxHours` under App Settings → System → Automation, both SYNCED, default OFF and 2 h; step 2 of Discussion #554): shortly before an idle claude session's prompt cache would expire, Codeman sends ONE keep-alive turn (`KEEP_WARM_NUDGE`, under 100 characters so Claude Code never reads the burst as a paste) so the next real prompt still reads the conversation from cache. Measured on two sessions of ~110k tokens: the nudge read 109,831 tokens from cache and wrote 70, replied `ok` in three seconds with no tool use, and a real turn seven minutes past the original expiry stayed a hit while the un-nudged control re-wrote 89,882 tokens with `last_miss_cause: ttl_expired_1h`; the payoff on real usage is concentrated in gaps of one to four hours, which is why there is a cap after the last real prompt rather than an indefinite loop (2 h by default: the maintainer's simulation over 30 days of gaps came out slightly cheaper than 3 h). ⚠️ **Codeman owns the idle policy for a keep-warm session.** Claude Code 2.1.289+ can compact an idle 1h-cache session by itself at 90% of the TTL (a server-flagged experiment, `fireAtFraction` tunable down to 0.5), which on the default timing always lands a minute before the nudge and leaves only a summary to keep warm. So a launch with keep-warm on carries `"idleCompaction": false`, folded LAST into the ONE `--settings` JSON with ultracode, the advisor and the statusLine exporter (`buildSpawnCommandFromRegistry`; never a second `--settings` flag, Claude Code takes one), so a keep-warm-off launch is byte-identical to one from before keep-warm (`test/cli-registry-spawn-golden.test.ts`). The `--settings` flag outranks user, project and local settings, which is why the key is conditional: everywhere else it would take Claude Code's own behaviour away with no way back. `decideIdleCompactionOptOut()` (tmux-manager.ts, pure) decides it once per create and respawn: keep-warm on (`keepWarmOn()`: the session's choice, else the app default, read fresh by `readKeepWarmSettings()`), the exporter `injected` (without `prompt_cache` reports keep-warm cannot run, and the opt-out alone would only cost the user the idle compaction), and claude's `idleCompactionSetting` gate (`capabilities.gates`, 2.1.290, the first release whose settings schema has the key; 2.1.289 already idle-compacts with no opt-out), fail-closed through `launchGatePasses()` exactly like `--name`: an unknown version means no key, and a log line says so. The result is recorded on the mux record (`MuxSession.idleCompactionOff`, like `statusLine`, persisted in mux-sessions.json) and published in the keep-warm status as `idleCompactionOff`; a session switched on after launch is kept warm best-effort (a relaunch to install the opt-out would cost exactly the re-write being avoided) and its readout says Claude Code's idle compaction may still run until its next launch, which any relaunch (dead-pane recovery, a custom-model `restartCli()`) fixes for free since every relaunch re-decides. ⚠️ The deadline is the statusline's `prompt_cache.expires_at` (`Session.promptCache`), never idle detection or the plan tier, and a `5m` lifetime is a hard stop (a nudge every four minutes costs more than the miss it prevents; API-key users get the hour from `CLAUDE_CODE_PROMPT_CACHE_TTL=1h` in `envOverrides`). ⚠️ `decideKeepWarm()` is the ONE rulebook and every guard lives in it, tested as a table: the effective opt-in (`keepWarmOn()`; a session an agent spawned, `parentSessionId`, does not inherit the app default, since an idle worker that reported done looks exactly like one that will be prompted again and most never are; its own switch still works), the launch's `statusLineExporter` is `injected` (which also stops every CLI without cache telemetry; the toggle line says why in the readout's own `PROMPT_CACHE_NOT_COLLECTED` words), a warm cache with an expiry, no `compactedAt` this gap (a compaction already replaced the context, and the stamp is dropped at the next request, which re-opens the next gap), not a `5m` lifetime, at least `KEEP_WARM_MIN_TOKENS` at stake, a live pane (a pid AND no recorded `paneExit`: an agent that exited in a `remain-on-exit` pane keeps its pid), no usage-limit pause (auto-resume's, or, read off the same pane capture as the composer, a usage-limit message whose reset is still ahead, since auto-resume tracks pauses only while it is on), no automation (respawn running, a Ralph loop active, a task assigned, or an agent long-polling `wait`), inside the cap measured from `lastRealPromptAt` (else `createdAt`), due at `expires_at` minus `KEEP_WARM_LEAD_MS` but not within `KEEP_WARM_LAST_CHANCE_MS`, idle, no open permission or question dialog, an EMPTY composer (`composerIsEmpty()` in session-submit-verifier.ts reads the last glyph line AND its Line truncated
 
 ### Cron jobs
 

docs/wiki/Keeping-Agents-Running.md

@@ -113,9 +113,9 @@ Claude Code 2.1.251 and newer reports the cache state on the statusline after ev
 
 It only fires when there is nothing else going on: the session is idle with an empty prompt, no permission or question dialog is open, nobody has typed in the last few minutes, no respawn loop, Ralph loop or waiting agent is driving the session, and the session is not paused on a usage limit. If any of those hold it waits a minute and looks again, and gives up a minute before the expiry rather than race it. It also stops by itself a few hours after your last prompt (**Keep warm for at most**, under App Settings → System → Automation, default 2 hours), because the saving is concentrated in gaps of one to four hours and an overnight run of hourly keep-alives would cost more than the single cold turn in the morning. It stands down for the rest of a gap once the context has been compacted. The readout's Status line gains a `Keep-alive:` line that says what it is doing: the next keep-alive and when the window closes, waiting and why, sent at a time with a count, or stopped and why. A session started without the cache readout (Plan Usage off at launch, a workspace with its own statusLine, a remote or Docker session) cannot be kept warm: the switch is greyed out and cannot be switched on (one that is already on can still be switched off), and the Status line says why.
 
-Recent Claude Code builds can compact a large idle session on their own shortly before the cache expires, which would leave only a summary to keep warm. So a session **started** with keep-warm on also launches with Claude Code's idle compaction switched off (Claude Code 2.1.290 or newer); Codeman then owns the idle policy for it. A session you switch on after it started is still kept warm, but Claude Code may compact it first until its next launch, and the Status line says so. Sessions with keep-warm off launch exactly as before.
+Recent Claude Code builds can compact a large idle session on their own shortly before the cache expires, which would leave only a summary to keep warm. So a session **started** with keep-warm on also launches with Claude Code's idle compaction switched off (Claude Code 2.1.290 or newer); Codeman then owns the idle policy for it. A session you switch on after it started is still kept warm, but Claude Code may compact it first until its next launch, and the Status line says so; one you switch off keeps Claude Code's idle compaction off until its next launch, and the Status line says that too. Sessions with keep-warm off launch exactly as before.
 
-**Keep prompt caches warm** in the same Automation group is the default for sessions that have not chosen on their Respawn tab; the per-session switch always wins. A session another agent started (a worker) does not follow the default: most workers are never prompted again once they report done, so turn it on for one by hand if you will come back to it. The keep-alive turn is Codeman's, not yours: it does not restart the **Keep warm for at most** window, does not rename a tab, Read My Mind ignores it, and the response it ends with raises no alert, toast, push or webhook. It is refused on the five-minute cache lifetime, which is what an API key, a cloud provider or extra-usage credits get; a session on an API key can ask Claude Code for the hour with `CLAUDE_CODE_PROMPT_CACHE_TTL=1h` in its environment overrides.
+**Keep prompt caches warm** in the same Automation group is the default for sessions that have not chosen on their Respawn tab; the per-session switch always wins. A session another agent started (a worker) does not follow the default: most workers are never prompted again once they report done, so turn it on for one by hand if you will come back to it. The keep-alive turn is Codeman's, not yours: it does not restart the **Keep warm for at most** window, does not rename a tab, Read My Mind ignores it, and the response it ends with raises no alert, toast, push or webhook. It never clears an alert that was already waiting for you. It is refused on the five-minute cache lifetime, which is what an API key, a cloud provider or extra-usage credits get; a session on an API key can ask Claude Code for the hour with `CLAUDE_CODE_PROMPT_CACHE_TTL=1h` in its environment overrides.
 
 ## The plan usage chip