fix: stop spinner from spinning forever (#1440)

* fix: stop spinner from spinning forever due to orphaned DB messages

The activity spinner never stopped because isAnySessionProcessing() queried
ALL pending/processing messages in the database, including orphaned messages
from dead sessions that no generator would ever process.

Root cause: isAnySessionProcessing() used hasAnyPendingWork() which is a
global DB scan. Changed it to use getTotalQueueDepth() which only checks
sessions in the active in-memory Map.

Additional fixes:
- Add terminateSession() to enforce restart-or-terminate invariant
- Fix 3 zombie paths in .finally() handler that left sessions alive
- Clean up idle sessions from memory on successful completion
- Remove redundant bare isProcessing:true broadcast
- Replace inline require() with proper accessor
- Add 8 regression tests for session termination invariant

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: address review findings — idle-timeout race, double broadcast, query amplification

- Move pendingCount check before idle-timeout termination to prevent
  abandoning fresh messages that arrive between idle abort and .finally()
- Move broadcastProcessingStatus() inside restart branch only — the else
  branch already broadcasts via removeSessionImmediate callback
- Compute queueDepth once in broadcastProcessingStatus() and derive
  isProcessing from it, eliminating redundant double iteration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/worker/SessionManager.ts

@@ -350,7 +350,7 @@ export class SessionManager {
     this.sessions.delete(sessionDbId);
     this.sessionQueues.delete(sessionDbId);
 
-    logger.info('SESSION', 'Session removed (orphaned after SDK termination)', {
+    logger.info('SESSION', 'Session removed from active sessions', {
       sessionId: sessionDbId,
       project: session.project
     });
@@ -402,10 +402,11 @@ export class SessionManager {
   }
 
   /**
-   * Check if any session has pending messages (for spinner tracking)
+   * Check if any active session has pending messages (for spinner tracking).
+   * Scoped to in-memory sessions only.
    */
   hasPendingMessages(): boolean {
-    return this.getPendingStore().hasAnyPendingWork();
+    return this.getTotalQueueDepth() > 0;
   }
 
   /**
@@ -437,12 +438,12 @@ export class SessionManager {
   }
 
   /**
-   * Check if any session is actively processing (has pending messages OR active generator)
-   * Used for activity indicator to prevent spinner from stopping while SDK is processing
+   * Check if any active session has pending work.
+   * Scoped to in-memory sessions only — orphaned DB messages from dead
+   * sessions must not keep the spinner spinning forever.
    */
   isAnySessionProcessing(): boolean {
-    // hasAnyPendingWork checks for 'pending' OR 'processing'
-    return this.getPendingStore().hasAnyPendingWork();
+    return this.getTotalQueueDepth() > 0;
   }
 
   /**