fix: address medium severity issues from code review

- Fix inconsistent null handling in state-store (use ?? instead of ||)
- Add JSON.stringify error handling with specific messages
- Add error handling for SSE init event in app.js
- Fix spawn orchestrator silent failures (add logging)
- Fix statSync race condition in subagent-watcher
- Fix unbounded _taskNumberToContent Map in ralph-tracker
- Fix YAML pattern case sensitivity in ralph-config

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

src/session.ts

@@ -1250,6 +1250,9 @@ export class Session extends EventEmitter {
   }
 
   private processOutput(data: string): void {
+    // Early return if session is stopped to prevent any processing or timer creation
+    if (this._isStopped) return;
+
     // Try to extract JSON from output (Claude may output JSON in stream mode)
     this._lineBuffer += data;
 
@@ -1391,8 +1394,12 @@ export class Session extends EventEmitter {
     }
   }
 
+  /** Maximum number of task descriptions to keep */
+  private static readonly MAX_TASK_DESCRIPTIONS = 100;
+
   /**
    * Remove task descriptions older than TASK_DESCRIPTION_MAX_AGE_MS.
+   * Also enforces MAX_TASK_DESCRIPTIONS size limit.
    */
   private cleanupOldTaskDescriptions(): void {
     const cutoff = Date.now() - Session.TASK_DESCRIPTION_MAX_AGE_MS;
@@ -1401,6 +1408,15 @@ export class Session extends EventEmitter {
         this._recentTaskDescriptions.delete(timestamp);
       }
     }
+
+    // Enforce size limit by removing oldest entries
+    if (this._recentTaskDescriptions.size > Session.MAX_TASK_DESCRIPTIONS) {
+      const sortedKeys = Array.from(this._recentTaskDescriptions.keys()).sort((a, b) => a - b);
+      const keysToRemove = sortedKeys.slice(0, this._recentTaskDescriptions.size - Session.MAX_TASK_DESCRIPTIONS);
+      for (const key of keysToRemove) {
+        this._recentTaskDescriptions.delete(key);
+      }
+    }
   }
 
   /**