fix: memory leaks and error handling improvements

- execution-bridge: track and cleanup retry timers to prevent memory leaks
- model-selector: add exhaustive type check for ModelTier
- ralph-tracker: fix division by zero when summary.total is 0
- respawn-controller: remove event listeners on stop to prevent memory leaks
- screen-manager: use Promise.allSettled for better error handling in stats
- session-manager: use Promise.allSettled for stopAllSessions resilience

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/execution-bridge.ts

@@ -211,6 +211,7 @@ export class ExecutionBridge extends EventEmitter {
 
   private _pollTimer: NodeJS.Timeout | null = null;
   private _groupTimeoutTimers: Map<number, NodeJS.Timeout> = new Map();
+  private _retryTimers: Map<string, NodeJS.Timeout> = new Map();
   private _runningTasks: Map<string, { startedAt: number; sessionId?: string }> = new Map();
 
   private _history: ExecutionHistoryEntry[] = [];
@@ -232,6 +233,12 @@ export class ExecutionBridge extends EventEmitter {
     });
 
     this._scheduler.on('groupCompleted', group => {
+      // Clear the group timeout timer to prevent memory leak
+      const timer = this._groupTimeoutTimers.get(group.groupNumber);
+      if (timer) {
+        clearTimeout(timer);
+        this._groupTimeoutTimers.delete(group.groupNumber);
+      }
       this.emit('groupCompleted', {
         groupNumber: group.groupNumber,
         status: group.status,
@@ -641,12 +648,14 @@ export class ExecutionBridge extends EventEmitter {
     });
 
     if (willRetry) {
-      // Schedule retry
-      setTimeout(() => {
+      // Schedule retry with tracked timer
+      const retryTimer = setTimeout(() => {
+        this._retryTimers.delete(task.id);
         task.status = 'pending';
         task.error = undefined;
         this._runningTasks.delete(task.id);
       }, TASK_RETRY_DELAY_MS);
+      this._retryTimers.set(task.id, retryTimer);
     } else {
       // Mark as permanently failed
       this._scheduler.updateTaskStatus(task.id, 'failed', error);
@@ -667,6 +676,13 @@ export class ExecutionBridge extends EventEmitter {
     const groupNum = this.findTaskGroup(taskId);
     if (groupNum === null) return;
 
+    // Clear any pending retry timer for this task
+    const retryTimer = this._retryTimers.get(taskId);
+    if (retryTimer) {
+      clearTimeout(retryTimer);
+      this._retryTimers.delete(taskId);
+    }
+
     this._scheduler.updateTaskStatus(taskId, 'completed');
     this._runningTasks.delete(taskId);
   }
@@ -790,6 +806,12 @@ export class ExecutionBridge extends EventEmitter {
     }
     this._groupTimeoutTimers.clear();
 
+    // Clear any pending retry timers
+    for (const timer of this._retryTimers.values()) {
+      clearTimeout(timer);
+    }
+    this._retryTimers.clear();
+
     this._scheduler.reset();
     this._runningTasks.clear();
     this._status = 'idle';

src/model-selector.ts

@@ -288,6 +288,12 @@ export class ModelSelector extends EventEmitter {
       case 'opus': return 5.0;    // ~5x more expensive
       case 'sonnet': return 1.0;  // baseline
       case 'haiku': return 0.04;  // ~25x cheaper
+      default: {
+        // Exhaustive check - if new ModelTier added, this will catch it
+        const _exhaustive: never = model;
+        console.warn(`[ModelSelector] Unknown model tier: ${_exhaustive}, using sonnet multiplier`);
+        return 1.0;
+      }
     }
   }
 }

src/ralph-tracker.ts

@@ -931,7 +931,7 @@ export class RalphTracker extends EventEmitter {
     // Prevent unbounded line buffer growth from very long lines
     if (this._lineBuffer.length > MAX_LINE_BUFFER_SIZE) {
       // Truncate to last portion to preserve recent data
-      this._lineBuffer = this._lineBuffer.slice(-MAX_LINE_BUFFER_SIZE / 2);
+      this._lineBuffer = this._lineBuffer.slice(-Math.floor(MAX_LINE_BUFFER_SIZE / 2));
     }
 
     // Process complete lines
@@ -2614,12 +2614,14 @@ export class RalphTracker extends EventEmitter {
       recommendations.push('More tasks have failed than completed. Review approach and consider plan adjustment.');
     }
 
-    const progressPercent = Math.round((summary.completed / summary.total) * 100);
+    const progressPercent = summary.total > 0
+      ? Math.round((summary.completed / summary.total) * 100)
+      : 0;
     if (progressPercent < 20 && this._loopState.cycleCount > 10) {
       recommendations.push('Progress is slow. Consider simplifying tasks or reviewing dependencies.');
     }
 
-    if (summary.blocked > summary.total / 3) {
+    if (summary.total > 0 && summary.blocked > summary.total / 3) {
       recommendations.push('Many tasks are blocked. Review dependency chain for bottlenecks.');
     }
 

src/respawn-controller.ts

@@ -1043,6 +1043,9 @@ export class RespawnController extends EventEmitter {
     this.log('Stopping respawn controller');
     this.aiChecker.cancel();
     this.planChecker.cancel();
+    // Remove event listeners from checkers to prevent memory leaks
+    this.aiChecker.removeAllListeners();
+    this.planChecker.removeAllListeners();
     this.clearTimers();
     this.stopDetectionUpdates();
     this.setState('stopped');

src/screen-manager.ts

@@ -717,10 +717,10 @@ export class ScreenManager extends EventEmitter {
     } catch {
       // Fall back to individual queries if batch fails
       const statsPromises = screens.map(screen => this.getProcessStats(screen.sessionId));
-      const allStats = await Promise.all(statsPromises);
+      const results = await Promise.allSettled(statsPromises);
       return screens.map((screen, i) => ({
         ...screen,
-        stats: allStats[i] || undefined
+        stats: results[i].status === 'fulfilled' ? (results[i].value ?? undefined) : undefined
       }));
     }
 
@@ -738,8 +738,13 @@ export class ScreenManager extends EventEmitter {
     }
 
     this.statsInterval = setInterval(async () => {
-      const screensWithStats = await this.getScreensWithStats();
-      this.emit('statsUpdated', screensWithStats);
+      try {
+        const screensWithStats = await this.getScreensWithStats();
+        this.emit('statsUpdated', screensWithStats);
+      } catch (err) {
+        // Log but don't crash - stats collection is non-critical
+        console.error('[ScreenManager] Stats collection error:', err);
+      }
     }, intervalMs);
   }
 

src/session-manager.ts

@@ -191,12 +191,19 @@ export class SessionManager extends EventEmitter {
 
   /**
    * Stops all active sessions.
+   * Uses Promise.allSettled to ensure all sessions are stopped even if some fail.
    */
   async stopAllSessions(): Promise<void> {
     const stopPromises = Array.from(this.sessions.keys()).map((id) =>
       this.stopSession(id)
     );
-    await Promise.all(stopPromises);
+    const results = await Promise.allSettled(stopPromises);
+    // Log any failures but don't throw - best effort cleanup
+    for (const result of results) {
+      if (result.status === 'rejected') {
+        console.error('[SessionManager] Failed to stop session:', result.reason);
+      }
+    }
   }
 
   /**