restore the activity stamp across restarts: the quiet ordering no longer flattens on deploy

Root cause of the reviewer's mass-bump measurement (17 of 17 sessions with an
identical lastActivityAt): every restart restamps all sessions in the
constructor loop, and the boot auto-attach's repaint re-bumps the rest within
the same second. A 12-minute steady-state sample shows NO ambient mass bump,
so restarts are the whole story, and Codeman restarts on every deploy.

The stamp now has a display twin: recovery threads the previous run's
lastActivityAt from state.json into the wire-visible stamp (getter + toState),
and a 15s settle window keeps the attach repaint from overwriting it. Real
actions (input, task assignment, respawn) always write through. The private
stamp keeps its boot-anchored semantics untouched, because the idle
confirmation reads it as how long the pane has been quiet.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/session.ts

@@ -135,6 +135,14 @@ const MUX_STARTUP_DELAY_MS = 300;
 /** Delay before declaring session idle after last output (2 seconds) */
 const IDLE_DETECTION_DELAY_MS = 2000;
 
+// How long after construction a RECOVERED session's wire activity stamp keeps
+// its restored previous-run value. Recovery attaches every pane at boot and the
+// attach repaint arrives as ordinary PTY output; without this window that
+// repaint would overwrite every restored stamp within the same second, which is
+// exactly the restart flattening the restore exists to prevent. Real actions
+// (input, task assignment, respawn) always stamp through it.
+const WIRE_ACTIVITY_SETTLE_MS = 15_000;
+
 // Note: Auto-compact/clear timing constants moved to session-auto-ops.ts
 
 /** Graceful shutdown delay when stopping session (100ms) */
@@ -392,6 +400,12 @@ export class Session extends EventEmitter {
   private _textOutput = new BufferAccumulator(MAX_TEXT_OUTPUT_SIZE, TEXT_OUTPUT_TRIM_SIZE);
   private _errorBuffer: string = '';
   private _lastActivityAt: number;
+  // Display twin of _lastActivityAt, reported by toState()/the getter. It can
+  // lag behind on recovery: the restored previous-run stamp survives the attach
+  // repaint (see _markActivity), so a restart does not flatten the home
+  // screens' quiet ordering. Idle detection never reads it.
+  private _wireActivityAt: number;
+  private _wireActivitySettleUntil: number;
   private _claudeSessionId: string | null = null;
   private _totalCost: number = 0;
   private _messages: ClaudeMessage[] = [];
@@ -592,6 +606,8 @@ export class Session extends EventEmitter {
       attachmentHistory?: SessionAttachmentHistoryItem[];
       /** Restored wall-clock ms of the pane's last Enter (see `lastSubmitAt`). */
       lastSubmitAt?: number;
+      /** Restored wall-clock ms of the pane's last output (recovery only; see `_wireActivityAt`). */
+      lastActivityAt?: number;
       /** Remote execution metadata for sessions launched through SSH inside local tmux. */
       remote?: SessionRemote;
       /** Docker execution metadata for sessions launched inside a container via local tmux. */
@@ -620,9 +636,18 @@ export class Session extends EventEmitter {
     // NOW, not `createdAt`: recovery passes the ORIGINAL creation time of a
     // days-old tmux session, and seeding last-activity from it would report a
     // freshly re-attached pane as having been silent for days, which the idle
-    // confirmation reads as "already quiet" and the home screens print as its
-    // idle duration. For a genuinely new session the two are the same instant.
+    // confirmation reads as "already quiet". For a genuinely new session the
+    // two are the same instant.
     this._lastActivityAt = Date.now();
+    // The WIRE copy of the stamp is allowed to be older: recovery threads the
+    // previous run's value so a restart does not flatten the home screens'
+    // most-recently-quiet ordering (every stamp otherwise resets to boot time,
+    // and the attach repaint re-bumps the rest within the same second). The
+    // settle window in _markActivity() carries the restored value through that
+    // repaint; the private stamp above stays boot-anchored because the idle
+    // confirmation reads it as "how long has the pane been quiet".
+    this._wireActivityAt = config.lastActivityAt || Date.now();
+    this._wireActivitySettleUntil = config.lastActivityAt ? Date.now() + WIRE_ACTIVITY_SETTLE_MS : 0;
     // Set claudeSessionId — when resuming, the Claude conversation ID is the resumed one.
     this._claudeSessionId = config.resumeSessionId || this.id;
     // Restored from state.json on boot recovery. start() resets _claudeSessionId
@@ -794,7 +819,21 @@ export class Session extends EventEmitter {
   }
 
   get lastActivityAt(): number {
-    return this._lastActivityAt;
+    return this._wireActivityAt;
+  }
+
+  /**
+   * Stamp activity NOW. The private stamp (idle detection's "how long has the
+   * pane been quiet") always moves; the wire stamp holds its restored value
+   * through the post-recovery attach-repaint window unless the activity is a
+   * real action (input, task assignment, respawn), which always writes through.
+   */
+  private _markActivity(realAction = false): void {
+    this._lastActivityAt = Date.now();
+    if (realAction || Date.now() >= this._wireActivitySettleUntil) {
+      this._wireActivityAt = this._lastActivityAt;
+      this._wireActivitySettleUntil = 0;
+    }
   }
 
   get claudeSessionId(): string | null {
@@ -1219,7 +1258,9 @@ export class Session extends EventEmitter {
       parentSessionId: this._parentSessionId,
       currentTaskId: this._currentTaskId,
       createdAt: this.createdAt,
-      lastActivityAt: this._lastActivityAt,
+      // The wire twin, not the private stamp: it survives the post-recovery
+      // attach repaint, so the home screens' quiet ordering survives a restart.
+      lastActivityAt: this._wireActivityAt,
       name: this._name,
       mode: this.mode,
       autoClearEnabled: this._autoOps.autoClearEnabled,
@@ -1585,7 +1626,7 @@ export class Session extends EventEmitter {
 
     // BufferAccumulator handles auto-trimming when max size exceeded
     this._terminalBuffer.append(data);
-    this._lastActivityAt = Date.now();
+    this._markActivity();
     this.emit('terminal', data);
     this.emit('output', data);
   }
@@ -2484,7 +2525,7 @@ export class Session extends EventEmitter {
     this._messages = [];
     this._lineBuffer = '';
     this._altScreenSeqCarry = '';
-    this._lastActivityAt = Date.now();
+    this._markActivity(true);
   }
 
   private _clearAllTimers(): void {
@@ -3083,7 +3124,7 @@ export class Session extends EventEmitter {
   // Legacy method for sending input - wraps runPrompt
   async sendInput(input: string): Promise<void> {
     this._status = 'busy';
-    this._lastActivityAt = Date.now();
+    this._markActivity(true);
     this.runPrompt(input).catch((err) => {
       const errorMsg = getErrorMessage(err);
       // Clean up task state so the task queue doesn't get stuck
@@ -3091,7 +3132,7 @@ export class Session extends EventEmitter {
         const taskId = this._currentTaskId;
         this._currentTaskId = null;
         this._status = 'idle';
-        this._lastActivityAt = Date.now();
+        this._markActivity(true);
         this.emit('taskError', taskId, errorMsg);
       } else {
         this._status = 'idle';
@@ -3252,13 +3293,13 @@ export class Session extends EventEmitter {
     this._textOutput.clear();
     this._errorBuffer = '';
     this._messages = [];
-    this._lastActivityAt = Date.now();
+    this._markActivity(true);
   }
 
   clearTask(): void {
     this._currentTaskId = null;
     this._status = 'idle';
-    this._lastActivityAt = Date.now();
+    this._markActivity(true);
   }
 
   getOutput(): string {

src/web/server.ts

@@ -2657,6 +2657,11 @@ export class WebServer extends EventEmitter {
               // the launch conversation until the user types again, even though
               // the re-attached CLI is on a post-`/clear` one.
               lastSubmitAt: savedState?.lastSubmitAt,
+              // The pane's last output, previous run's value. Without it every
+              // restart restamped all sessions "now" (constructor + the attach
+              // repaint within the same second), flattening the home screens'
+              // most-recently-quiet ordering to tab order after each deploy.
+              lastActivityAt: savedState?.lastActivityAt,
               // Remote SSH metadata must round-trip on recovery: without it the
               // attach cwd falls back to the (nonexistent-locally) remote path and
               // respawn rebuilds a LOCAL command, breaking the pane and silently