# Queue System Simplification Implementation

I have successfully implemented the queue system simplification plan.

## Changes Implemented

### 1. Database Layer Hardening
- **Added `claimNextMessage(sessionDbId)` to `PendingMessageStore`:**
  - Implements an atomic transaction (SELECT oldest pending + UPDATE to processing).
  - Ensures a message can only be claimed by one worker at a time.
  - Eliminates race conditions between "peeking" and "marking".
- **Removed `peekPending()`:**
  - No longer needed as `claimNextMessage` handles retrieval and locking in one step.

### 2. Unified "Pump" Architecture
- **Created `src/services/queue/SessionQueueProcessor.ts`:**
  - Implements a robust `AsyncIterableIterator` that yields messages.
  - Encapsulates the "Claim -> Yield -> Wait" loop.
  - Replaces fragile polling/recursive logic with event-driven `waitForMessage`.
  - Handles empty queues gracefully by waiting for signals.

### 3. SessionManager Refactoring
- **Updated `getMessageIterator`:**
  - Now delegates to `SessionQueueProcessor`.
  - Removes complex manual synchronization logic.
- **Removed In-Memory Queue State:**
  - `queueObservation` and `queueSummarize` now only write to DB and emit events.
  - `pendingMessages` array is no longer used for logic (kept deprecated for type compatibility).
  - `getTotalActiveWork`, `hasPendingMessages`, etc., now query `PendingMessageStore` directly (counting both 'pending' and 'processing' states).

### 4. Logic Cleanup
- **Removed Recursive Restarts:**
  - Refactored `startGeneratorWithProvider` in `SessionRoutes.ts` and `startSessionProcessor` in `WorkerService.ts`.
  - Removed logic that deleted sessions when queue emptied (sessions now wait for new work).
  - Removed "auto-restart" logic for normal completion (only kept for crash recovery).

## Benefits
- **Reliability:** Atomic DB operations prevent stuck or duplicate messages.
- **Simplicity:** Removed complex "peek-then-mark" and recursive restart chains.
- **Performance:** Zero-latency event notification with efficient DB queries.
- **Maintainability:** Clear separation of concerns (Store vs Processor vs Manager).

## Verification
- Ran static analysis (`tsc`) to verify type safety of new components.
- Verified removal of dead code (`peekPending`).
- Confirmed integration points in `SessionManager` and `SessionRoutes`.