COD-118 feat: circuit breaker bounding repeated non-zero interactive-PTY exits

Defense-in-depth after COD-115. If the interactive PTY exits non-zero
repeatedly within a short window, recovery/reconnect paths recreate it
indefinitely (COD-115 saw 114 'exited with code: 1' events + orphans).

- New pure InteractivePtyExitBreaker (session-pty-exit-breaker.ts):
  injectable time, sliding window, clean-exit resets counter, stays
  tripped until reset(). Defaults: threshold 5, window 10s.
- Session records each interactive PTY exit in the breaker; on trip it
  flips _status to 'error', sets _respawnBlocked, emits
  respawnBreakerTripped. startInteractive() refuses to respawn while
  blocked, so all recovery/reconnect callers stop looping uniformly.
- Explicit user restart (POST /api/sessions/:id/interactive) calls
  resetRespawnBreaker() so intentional restarts are never blocked.
- New SSE event session:respawnBreakerTripped wired in sse-events.ts +
  constants.js (registries in sync) + session-listener-wiring.ts;
  minimal diagnostic toast in app.js.
- Tests: test/respawn-pty-breaker.test.ts (pure trip/reset/window +
  MockSession session-level trip/reset).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/session-pty-exit-breaker.ts

@@ -0,0 +1,102 @@
+/**
+ * @fileoverview Circuit breaker bounding repeated non-zero interactive-PTY exits (COD-118).
+ *
+ * Defense-in-depth after COD-115: if the interactive PTY exits non-zero repeatedly,
+ * external recovery/reconnect paths recreate it indefinitely (COD-115 observed 114
+ * `exited with code: 1` events + orphan sessions). This breaker tracks recent
+ * non-zero exits within a sliding window and "trips" once they exceed a threshold,
+ * so the Session can refuse to respawn and surface an error state instead of looping.
+ *
+ * Design notes:
+ * - PURE + dependency-free. Time is INJECTED (`nowMs` passed to `recordExit`); the
+ *   breaker never calls `Date.now()` itself, so trip/window logic is deterministically
+ *   unit-testable with no real timers.
+ * - A clean (exit code 0) exit resets the counter — a session that exited normally is
+ *   not on a crash-loop. (It does NOT clear an already-tripped breaker; only an explicit
+ *   `reset()` — e.g. a user-initiated restart — does that.)
+ * - Once tripped, stays tripped until `reset()`.
+ *
+ * @consumedby session (instantiates one per session; records exits in the interactive
+ *   PTY `onExit` handler; gates `startInteractive()` when tripped; `reset()` on restart)
+ * @module session-pty-exit-breaker
+ */
+
+/** Non-zero interactive-PTY exits within the window required to trip the breaker. */
+export const DEFAULT_BREAKER_THRESHOLD = 5;
+
+/** Sliding window (ms) over which non-zero exits accumulate toward the threshold. */
+export const DEFAULT_BREAKER_WINDOW_MS = 10_000;
+
+export interface InteractivePtyExitBreakerOptions {
+  /** Trip after this many non-zero exits within `windowMs` (default 5). */
+  threshold?: number;
+  /** Sliding window length in ms (default 10_000). */
+  windowMs?: number;
+}
+
+export interface RecordExitResult {
+  /** True once the breaker has tripped (stays true until `reset()`). */
+  tripped: boolean;
+  /** Number of non-zero exits currently inside the window. */
+  count: number;
+}
+
+/**
+ * Sliding-window counter that trips on rapid repeated non-zero exits.
+ *
+ * 5 within 10s safely clears normal usage (a single exit, an intentional restart)
+ * while tripping fast on a real loop — COD-115 saw 114 exits, far above 5.
+ */
+export class InteractivePtyExitBreaker {
+  private readonly _threshold: number;
+  private readonly _windowMs: number;
+
+  /** Timestamps (ms, injected) of recent non-zero exits, oldest first. */
+  private _exitTimes: number[] = [];
+
+  private _tripped = false;
+
+  constructor(opts: InteractivePtyExitBreakerOptions = {}) {
+    this._threshold = opts.threshold ?? DEFAULT_BREAKER_THRESHOLD;
+    this._windowMs = opts.windowMs ?? DEFAULT_BREAKER_WINDOW_MS;
+  }
+
+  /** Whether the breaker has tripped (respawn should be blocked). */
+  get tripped(): boolean {
+    return this._tripped;
+  }
+
+  /**
+   * Record a PTY exit. A zero (clean) exit resets the non-zero counter; a non-zero
+   * exit is added to the window, stale entries are evicted, and the breaker trips
+   * once the in-window count reaches the threshold.
+   *
+   * @param exitCode the PTY exit code (0 = clean)
+   * @param nowMs injected current time in ms (never read from a real clock)
+   */
+  recordExit(exitCode: number, nowMs: number): RecordExitResult {
+    if (exitCode === 0) {
+      // Clean exit: a normal stop, not a crash-loop. Clear accumulated non-zero
+      // exits. Does NOT un-trip an already-tripped breaker (only reset() does).
+      this._exitTimes = [];
+      return { tripped: this._tripped, count: 0 };
+    }
+
+    // Evict exits strictly older than the window, then record this one.
+    const cutoff = nowMs - this._windowMs;
+    this._exitTimes = this._exitTimes.filter((t) => t > cutoff);
+    this._exitTimes.push(nowMs);
+
+    if (this._exitTimes.length >= this._threshold) {
+      this._tripped = true;
+    }
+
+    return { tripped: this._tripped, count: this._exitTimes.length };
+  }
+
+  /** Clear the tripped state and the non-zero counter (e.g. on intentional restart). */
+  reset(): void {
+    this._exitTimes = [];
+    this._tripped = false;
+  }
+}

src/session.ts

@@ -82,6 +82,7 @@ import {
 import { SessionAutoOps } from './session-auto-ops.js';
 import { detectUsageLimitPause } from './usage-limit-patterns.js';
 import { SessionTaskCache } from './session-task-cache.js';
+import { InteractivePtyExitBreaker } from './session-pty-exit-breaker.js';
 import { parseAttachmentMagicLinks } from './attachment-magic.js';
 import {
   sanitizeAttachmentHistory,
@@ -288,6 +289,13 @@ export class Session extends EventEmitter {
   private _pid: number | null = null;
   private _status: SessionStatus = 'idle';
   private _currentTaskId: string | null = null;
+
+  // COD-118: bound repeated non-zero interactive-PTY exits. Recorded in the
+  // interactive PTY onExit handler; when it trips, the session flips to 'error'
+  // and startInteractive() refuses to respawn until an explicit user restart
+  // calls resetRespawnBreaker(). Defense-in-depth over the COD-115 crash-loop.
+  private readonly _ptyExitBreaker = new InteractivePtyExitBreaker();
+  private _respawnBlocked = false;
   // Use BufferAccumulator for hot-path buffers to reduce GC pressure
   private _terminalBuffer = new BufferAccumulator(MAX_TERMINAL_BUFFER_SIZE, TERMINAL_BUFFER_TRIM_SIZE);
   private _textOutput = new BufferAccumulator(MAX_TEXT_OUTPUT_SIZE, TEXT_OUTPUT_TRIM_SIZE);
@@ -1256,6 +1264,16 @@ export class Session extends EventEmitter {
       throw new Error('Session already has a running process');
     }
 
+    // COD-118: if the PTY exit breaker has tripped (repeated non-zero exits in a
+    // short window), refuse to respawn. This is the uniform choke point that stops
+    // automatic recovery/reconnect callers from re-creating a crash-looping PTY.
+    // An explicit user restart clears it via resetRespawnBreaker().
+    if (this._respawnBlocked) {
+      throw new Error(
+        'Respawn blocked: interactive PTY exited non-zero too many times in a short window (circuit breaker tripped). Restart the session to clear it.'
+      );
+    }
+
     this._resetBuffers();
 
     const modeLabel = getModeLabel(this.mode);
@@ -1496,6 +1514,9 @@ export class Session extends EventEmitter {
 
     this.ptyProcess.onExit(({ exitCode }) => {
       console.log('[Session] Interactive PTY exited with code:', exitCode);
+      // COD-118: record the exit in the circuit breaker BEFORE status bookkeeping.
+      // A clean (0) exit resets the counter; rapid non-zero repeats trip it.
+      const breakerResult = this._ptyExitBreaker.recordExit(exitCode, Date.now());
       this.ptyProcess = null;
       this._pid = null;
       this._status = 'idle';
@@ -1523,10 +1544,38 @@ export class Session extends EventEmitter {
       if (this._muxSession && this._mux) {
         this._mux.setAttached(this.id, false);
       }
+      // COD-118: if the breaker tripped, surface an error state and block the NEXT
+      // respawn so recovery/reconnect callers stop looping. Still emit 'exit' below
+      // for normal cleanup. Cleared by an explicit user restart (resetRespawnBreaker()).
+      if (breakerResult.tripped && !this._respawnBlocked) {
+        this._respawnBlocked = true;
+        this._status = 'error';
+        console.error(
+          `[Session] PTY exit circuit breaker tripped for ${this.id} (${breakerResult.count} non-zero exits within window); blocking respawn.`
+        );
+        this.emit('respawnBreakerTripped', { count: breakerResult.count });
+      }
       this.emit('exit', exitCode);
     });
   }
 
+  /**
+   * Clear the interactive-PTY exit circuit breaker (COD-118).
+   *
+   * Called on an EXPLICIT, user-initiated (re)start so an intentional restart is
+   * never blocked by a prior crash-loop trip. Automatic recovery/reconnect paths
+   * must NOT call this — that's the whole point of the breaker.
+   */
+  resetRespawnBreaker(): void {
+    this._ptyExitBreaker.reset();
+    this._respawnBlocked = false;
+  }
+
+  /** Whether the interactive-PTY exit circuit breaker is currently tripped (COD-118). */
+  get respawnBlocked(): boolean {
+    return this._respawnBlocked;
+  }
+
   /**
    * Process expensive parsers (ANSI strip, Ralph, bash tool, token, CLI info, task descriptions).
    * Called on a throttled schedule (every EXPENSIVE_PROCESS_INTERVAL_MS) instead of on every

src/web/public/app.js

@@ -156,6 +156,7 @@ const _SSE_HANDLER_MAP = [
   [SSE_EVENTS.SESSION_LIMIT_PAUSE_SCHEDULED, '_onSessionLimitPauseScheduled'],
   [SSE_EVENTS.SESSION_LIMIT_RESUME, '_onSessionLimitResume'],
   [SSE_EVENTS.SESSION_LIMIT_RESUME_CANCELLED, '_onSessionLimitResumeCancelled'],
+  [SSE_EVENTS.SESSION_RESPAWN_BREAKER_TRIPPED, '_onSessionRespawnBreakerTripped'],
   [SSE_EVENTS.SESSION_CLI_INFO, '_onSessionCliInfo'],
   [SSE_EVENTS.SESSION_STATUS_TELEMETRY, '_onSessionStatusTelemetry'],
 
@@ -1852,6 +1853,15 @@ class CodemanApp {
     this.updateAutoResumeStatus(data.sessionId);
   }
 
+  // COD-118: the interactive PTY exit circuit breaker tripped (repeated non-zero exits).
+  // The errored status itself arrives via session:updated; this just surfaces a toast for
+  // diagnostic clarity so a silently-looping session is obvious. Restart clears the breaker.
+  _onSessionRespawnBreakerTripped(data) {
+    const session = this.sessions.get(data.sessionId);
+    const label = session?.name || 'Session';
+    this.showToast?.(`${label} stopped: repeated crashes detected. Restart to retry.`, 'error');
+  }
+
   _onSessionCliInfo(data) {
     const session = this.sessions.get(data.sessionId);
     if (session) {

src/web/public/constants.js

@@ -262,6 +262,7 @@ const SSE_EVENTS = {
   SESSION_LIMIT_PAUSE_SCHEDULED: 'session:limitPauseScheduled',
   SESSION_LIMIT_RESUME: 'session:limitResume',
   SESSION_LIMIT_RESUME_CANCELLED: 'session:limitResumeCancelled',
+  SESSION_RESPAWN_BREAKER_TRIPPED: 'session:respawnBreakerTripped',
   SESSION_CLI_INFO: 'session:cliInfo',
   SESSION_MESSAGE: 'session:message',
   SESSION_INTERACTIVE: 'session:interactive',

src/web/routes/session-routes.ts

@@ -633,6 +633,9 @@ export function registerSessionRoutes(
         }
       }
 
+      // COD-118: an explicit user-initiated start clears any tripped PTY-exit
+      // circuit breaker so an intentional restart is never blocked by a prior crash-loop.
+      session.resetRespawnBreaker();
       await session.startInteractive();
       getLifecycleLog().log({
         event: 'started',

src/web/session-listener-wiring.ts

@@ -48,6 +48,7 @@ export interface SessionListenerRefs {
   limitPauseScheduled: (data: { resetAt: number; resumeAt: number; matched: string }) => void;
   limitResume: (data: { attempt: number }) => void;
   limitResumeCancelled: (data: { reason: string }) => void;
+  respawnBreakerTripped: (data: { count: number }) => void;
   cliInfoUpdated: (data: { version?: string; model?: string; accountType?: string; latestVersion?: string }) => void;
   ralphLoopUpdate: (state: RalphTrackerState) => void;
   ralphTodoUpdate: (todos: RalphTodoItem[]) => void;
@@ -270,6 +271,27 @@ export function createSessionListeners(session: Session, deps: SessionListenerDe
       deps.persistSessionState(session);
     },
 
+    /**
+     * Broadcasts `session:respawnBreakerTripped` (COD-118) — repeated non-zero PTY exits
+     * tripped the circuit breaker; the session is now errored and respawn is blocked.
+     * Also pushes the errored state (`session:updated`) so the tab renders the error,
+     * persists it, and notifies for diagnostic visibility.
+     */
+    respawnBreakerTripped: (data: { count: number }) => {
+      deps.broadcast(SseEvent.SessionRespawnBreakerTripped, { sessionId: session.id, ...data });
+      deps.broadcast(SseEvent.SessionUpdated, deps.getSessionStateWithRespawn(session));
+      deps.persistSessionState(session);
+      deps.sendPushNotifications(SseEvent.SessionRespawnBreakerTripped, {
+        sessionId: session.id,
+        sessionName: session.name,
+        count: data.count,
+      });
+      const tracker = deps.getRunSummaryTracker(session.id);
+      if (tracker) {
+        tracker.recordError('Respawn circuit breaker tripped', `${data.count} non-zero PTY exits within window`);
+      }
+    },
+
     // ─── CLI Info ────────────────────────────────────────────
 
     /** Broadcasts `session:cliInfo` — Claude Code version, model, account type parsed from terminal */
@@ -387,6 +409,7 @@ export function attachSessionListeners(session: Session, refs: SessionListenerRe
   session.on('limitPauseScheduled', refs.limitPauseScheduled);
   session.on('limitResume', refs.limitResume);
   session.on('limitResumeCancelled', refs.limitResumeCancelled);
+  session.on('respawnBreakerTripped', refs.respawnBreakerTripped);
   session.on('cliInfoUpdated', refs.cliInfoUpdated);
   session.on('ralphLoopUpdate', refs.ralphLoopUpdate);
   session.on('ralphTodoUpdate', refs.ralphTodoUpdate);
@@ -420,6 +443,7 @@ export function detachSessionListeners(session: Session, refs: SessionListenerRe
   session.off('limitPauseScheduled', refs.limitPauseScheduled);
   session.off('limitResume', refs.limitResume);
   session.off('limitResumeCancelled', refs.limitResumeCancelled);
+  session.off('respawnBreakerTripped', refs.respawnBreakerTripped);
   session.off('cliInfoUpdated', refs.cliInfoUpdated);
   session.off('ralphLoopUpdate', refs.ralphLoopUpdate);
   session.off('ralphTodoUpdate', refs.ralphTodoUpdate);

src/web/sse-events.ts

@@ -80,6 +80,8 @@ export const SessionLimitPauseScheduled = 'session:limitPauseScheduled' as const
 export const SessionLimitResume = 'session:limitResume' as const;
 /** Pending usage-limit auto-resume cancelled (session resumed or feature disabled). */
 export const SessionLimitResumeCancelled = 'session:limitResumeCancelled' as const;
+/** Interactive-PTY exit circuit breaker tripped (COD-118): repeated non-zero exits; respawn blocked, session errored. */
+export const SessionRespawnBreakerTripped = 'session:respawnBreakerTripped' as const;
 /** CLI version/model info detected from session output. */
 export const SessionCliInfo = 'session:cliInfo' as const;
 /** General session message (e.g. status text). */
@@ -384,6 +386,7 @@ export const SseEvent = {
   SessionLimitPauseScheduled,
   SessionLimitResume,
   SessionLimitResumeCancelled,
+  SessionRespawnBreakerTripped,
   SessionCliInfo,
   SessionMessage,
   SessionInteractive,