diff --git a/docs/chat-session-lifetime.md b/docs/chat-session-lifetime.md
index 9b14eed7..577d4501 100644
--- a/docs/chat-session-lifetime.md
+++ b/docs/chat-session-lifetime.md
@@ -20,9 +20,9 @@ until morning. Officer would have killed it about an hour after the browser sock
 - `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
+- 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`."*
+  `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.
@@ -38,7 +38,7 @@ There is also `stallTimer` for a turn that claims to be generating but has emitt
 - 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.
+  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.
@@ -49,7 +49,7 @@ There is also `stallTimer` for a turn that claims to be generating but has emitt
 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
+   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
@@ -59,7 +59,7 @@ agent keeps generating and keeps committing to `chat_session_events`. Only offic
 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
+## 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
@@ -71,10 +71,15 @@ the sidecar's heartbeat in a second place, which is how these two drifted apart
 **The blocker.** `src/servers/channels/send-claude-code.ts:65-69` welds them together:
 
 ```ts
-return { kill: () => { sidecar.killClaude(params.sessionKey); unsub(); } }
+return {
+  kill: () => {
+    sidecar.killClaude(params.sessionKey);
+    unsub();
+  },
+};
 ```
 
-`unsub` is a closure reachable only *through* `kill`, so officer cannot let go without killing.
+`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.
@@ -96,9 +101,19 @@ 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
+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
@@ -108,7 +123,7 @@ officer can answer "what is running right now" and surface it.
 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
+**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
diff --git a/src/servers/api/chat/session-manager.ts b/src/servers/api/chat/session-manager.ts
index 27552dec..af4d4531 100644
--- a/src/servers/api/chat/session-manager.ts
+++ b/src/servers/api/chat/session-manager.ts
@@ -1,5 +1,5 @@
-import type { UserSession } from "./types";
-import { logger } from "./logger";
+import type { UserSession } from './types';
+import { logger } from './logger';
 
 class SessionManager {
   private sessions = new Map<string, UserSession>();
@@ -26,13 +26,13 @@ class SessionManager {
         ws: null,
         lastActivity: Date.now(),
         idleTimer: null,
-        streamBuffer: "",
+        streamBuffer: '',
         isGenerating: false,
         systemContextSent: false,
         messages: [],
         meta: {
           id: sessionId,
-          title: "",
+          title: '',
           model,
           cwd,
           groupSlug: groupSlug || null,
@@ -66,19 +66,36 @@ class SessionManager {
 
   getUserSessions(email: string): UserSession[] {
     const sessionIds = this.userSessions.get(email) || [];
-    return sessionIds
-      .map((id) => this.sessions.get(id))
-      .filter((s): s is UserSession => s !== undefined);
+    return sessionIds.map((id) => this.sessions.get(id)).filter((s): s is UserSession => s !== undefined);
   }
 
-  deleteSession(sessionId: string): void {
-    const session = this.sessions.get(sessionId);
-    if (!session) return;
-
+  /** Drop this process's record of a session. Shared by `deleteSession` and `releaseSession`. */
+  private forget(session: UserSession): void {
     if (session.idleTimer) {
       clearTimeout(session.idleTimer);
     }
 
+    this.sessions.delete(session.sessionId);
+
+    const userSessionIds = this.userSessions.get(session.email);
+    if (userSessionIds) {
+      const filtered = userSessionIds.filter((id) => id !== session.sessionId);
+      if (filtered.length > 0) {
+        this.userSessions.set(session.email, filtered);
+      } else {
+        this.userSessions.delete(session.email);
+      }
+    }
+  }
+
+  /**
+   * End the session for good: kill the agent upstream, drop the subscription, forget the record. This is
+   * what an explicit "disconnect" means — the user said stop.
+   */
+  deleteSession(sessionId: string): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+
     // Clean up sidecar subscriptions
     if (session._sidecarUnsub) {
       session._sidecarUnsub();
@@ -87,19 +104,35 @@ class SessionManager {
       session._claudeKill();
     }
 
-    this.sessions.delete(sessionId);
+    this.forget(session);
+  }
 
-    const userSessionIds = this.userSessions.get(session.email);
-    if (userSessionIds) {
-      const filtered = userSessionIds.filter(
-        (id) => id !== sessionId
-      );
-      if (filtered.length > 0) {
-        this.userSessions.set(session.email, filtered);
-      } else {
-        this.userSessions.delete(session.email);
-      }
+  /**
+   * Let go WITHOUT killing: unsubscribe, forget the record, leave the agent running.
+   *
+   * This is what the idle GC should always have done. Officer's timer was doing two unrelated jobs —
+   * collecting its own in-memory binding, which is its business, and terminating the agent, which is the
+   * sidecar's. The sidecar already refuses to collect a session that is mid-turn or holding background
+   * tasks (`claude-manager.ts` → `pendingTasks`, and an `armIdle` that re-checks rather than firing
+   * once); officer knew none of that and killed anyway. A `run_in_background` job outliving the browser
+   * — a laptop that ran out of battery — died an hour later for no reason.
+   *
+   * Nothing is stranded by forgetting the record. The sidecar keeps committing to `chat_session_events`,
+   * and a returning browser goes through `adoptOrphanedSession`, which rebuilds the record and a fresh
+   * subscription. That is the same path every `pm2 restart officer` already takes.
+   */
+  releaseSession(sessionId: string): void {
+    const session = this.sessions.get(sessionId);
+    if (!session) return;
+
+    // Only the listener goes. `_claudeKill` is deliberately NOT called — and must not be left behind
+    // either: the record is being dropped, so the next turn starts from `adoptOrphanedSession`, which
+    // installs its own kill and subscription.
+    if (session._sidecarUnsub) {
+      session._sidecarUnsub();
     }
+
+    this.forget(session);
   }
 
   attachWs(sessionId: string, ws: any): void {
@@ -132,8 +165,11 @@ class SessionManager {
     }
 
     session.idleTimer = setTimeout(() => {
-      logger.info('Session idle timeout reached, cleaning up', { sessionId, timeoutMs });
-      this.deleteSession(sessionId);
+      logger.info('Session idle timeout reached, releasing binding (agent left running)', {
+        sessionId,
+        timeoutMs,
+      });
+      this.releaseSession(sessionId);
     }, timeoutMs);
   }
 
diff --git a/src/servers/api/chat/websocket.ts b/src/servers/api/chat/websocket.ts
index 583c30ed..4bdca57a 100644
--- a/src/servers/api/chat/websocket.ts
+++ b/src/servers/api/chat/websocket.ts
@@ -344,7 +344,9 @@ async function handleClaudeCodeChat(
   try {
     if (!session._claudeKill) {
       // First turn of this session: open the persistent session + a SESSION-scoped event subscription
-      // (survives turn-end so background task:notifications keep flowing). handle.kill tears both down.
+      // (survives turn-end so background task:notifications keep flowing). `kill` tears both down for an
+      // explicit disconnect; `detach` drops only the listener, which is what the idle GC uses so an
+      // absent browser stops taking a live agent with it.
       const handle = await sendClaudeCodeStreaming({
         userId,
         email,
@@ -359,6 +361,7 @@ async function handleClaudeCodeChat(
       });
       session.piProcess = sessionId as any;
       session._claudeKill = handle.kill;
+      session._sidecarUnsub = handle.detach;
     } else {
       // Session already live: push this turn onto the existing persistent session (no new subscription).
       await sidecar.spawnClaudeStreaming({
@@ -450,6 +453,7 @@ async function handleOpenCodeChat(
     // Store the abort handle so handleStop can end the turn (OpenCode is aborted via this handle).
     session.piProcess = sessionId as any;
     session._claudeKill = handle.kill;
+    session._sidecarUnsub = handle.detach;
   } catch (err) {
     logger.error('Failed to start OpenCode streaming', { sessionId, error: String(err) });
     sendToClient(ws, { type: 'error', message: 'Failed to start OpenCode' });
@@ -583,6 +587,10 @@ function adoptOrphanedSession(ws: ServerWebSocket<WSData>, sessionId: string, mo
     else sidecar.killOpenCode(sessionId);
     unsub();
   };
+  // An adopted session can idle out and be released like any other, and releasing detaches through this
+  // field alone. Leaving it unset would drop the record while the listener stayed subscribed — a leak
+  // that grows by one every time a browser adopts a session and then goes away.
+  session._sidecarUnsub = unsub;
 
   logger.info('Adopted orphaned chat session after restart', { sessionId, model });
   return session;
diff --git a/src/servers/channels/send-claude-code.ts b/src/servers/channels/send-claude-code.ts
index 3b2c5296..a6793c9a 100644
--- a/src/servers/channels/send-claude-code.ts
+++ b/src/servers/channels/send-claude-code.ts
@@ -45,7 +45,18 @@ type ClaudeCodeStreamingParams = {
 };
 
 type ClaudeCodeStreamingHandle = {
+  /** End the agent's session upstream and stop listening. For an explicit disconnect. */
   kill: () => void;
+  /**
+   * Stop listening and leave the agent running.
+   *
+   * These are separate because officer's idle GC and a user's "disconnect" want different things, and
+   * for a long time they could not have them: `unsub` was a closure reachable only through `kill`, so
+   * letting go of a session necessarily killed it. That is why an idle browser took a live agent down
+   * with it — including one the sidecar had deliberately protected because background work was still
+   * in flight.
+   */
+  detach: () => void;
 };
 
 export async function sendClaudeCodeStreaming(params: ClaudeCodeStreamingParams): Promise<ClaudeCodeStreamingHandle> {
@@ -67,5 +78,6 @@ export async function sendClaudeCodeStreaming(params: ClaudeCodeStreamingParams)
       sidecar.killClaude(params.sessionKey);
       unsub();
     },
+    detach: unsub,
   };
 }
diff --git a/src/servers/channels/send-opencode.ts b/src/servers/channels/send-opencode.ts
index 52f1ece9..4be73c23 100644
--- a/src/servers/channels/send-opencode.ts
+++ b/src/servers/channels/send-opencode.ts
@@ -25,7 +25,10 @@ type OpenCodeStreamingParams = {
 };
 
 type OpenCodeStreamingHandle = {
+  /** End the agent's session upstream and stop listening. For an explicit disconnect. */
   kill: () => void;
+  /** Stop listening and leave the agent running — see the same pair in `send-claude-code.ts`. */
+  detach: () => void;
 };
 
 export async function sendOpenCodeStreaming(params: OpenCodeStreamingParams): Promise<OpenCodeStreamingHandle> {
@@ -67,5 +70,6 @@ export async function sendOpenCodeStreaming(params: OpenCodeStreamingParams): Pr
       sidecar.killOpenCode(params.sessionKey);
       unsub();
     },
+    detach: unsub,
   };
 }