feat: create OpenSpec proposal for enhanced memory management

- Create comprehensive proposal addressing OOM crashes and memory leaks
- Define 6 core areas: model lifecycle, service pooling, monitoring
- Add 58 implementation tasks across 8 sections
- Design ModelManager with reference counting and idle timeout
- Plan OCRServicePool for singleton service pattern
- Specify MemoryGuard for proactive memory monitoring
- Include concurrency controls and cleanup hooks
- Add spec deltas for ocr-processing and task-management
- Create detailed design document with architecture diagrams
- Define performance targets: 75% memory reduction, 4x concurrency

Critical improvements:
- Remove PP-StructureV3 permanent exemption from unloading
- Replace per-task OCRService instantiation with pooling
- Add real GPU memory monitoring (currently always returns True)
- Implement semaphore-based concurrency limits
- Add proper resource cleanup on task completion

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

openspec/changes/enhance-memory-management/tasks.md

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+# Tasks for Enhanced Memory Management
+
+## Section 1: Model Lifecycle Management (Priority: Critical)
+
+### 1.1 Create ModelManager class
+- [ ] Design ModelManager interface with load/unload/get methods
+- [ ] Implement reference counting for model instances
+- [ ] Add idle timeout tracking with configurable thresholds
+- [ ] Create teardown() method for explicit cleanup
+- [ ] Add logging for model lifecycle events
+
+### 1.2 Integrate PP-StructureV3 with ModelManager
+- [ ] Remove permanent exemption from unloading (lines 255-267)
+- [ ] Wrap PP-StructureV3 in managed model wrapper
+- [ ] Implement lazy loading on first access
+- [ ] Add unload capability with cache clearing
+- [ ] Test model reload after unload
+
+## Section 2: Service Singleton Pattern (Priority: Critical)
+
+### 2.1 Create OCRServicePool
+- [ ] Design pool interface with acquire/release methods
+- [ ] Implement per-device instance management
+- [ ] Add queue-based task distribution
+- [ ] Implement concurrency limits via semaphores
+- [ ] Add health check for pooled instances
+
+### 2.2 Refactor task router
+- [ ] Replace OCRService() instantiation with pool.acquire()
+- [ ] Add proper release in finally blocks
+- [ ] Handle pool exhaustion gracefully
+- [ ] Add metrics for pool utilization
+- [ ] Update error handling for pooled services
+
+## Section 3: Enhanced Memory Monitoring (Priority: High)
+
+### 3.1 Create MemoryGuard class
+- [ ] Implement paddle.device.cuda memory queries
+- [ ] Add pynvml integration as fallback
+- [ ] Add torch memory query support
+- [ ] Create configurable threshold system
+- [ ] Implement memory prediction for operations
+
+### 3.2 Integrate memory checks
+- [ ] Replace existing check_gpu_memory implementation
+- [ ] Add pre-operation memory checks
+- [ ] Implement CPU fallback when memory low
+- [ ] Add memory usage logging
+- [ ] Create memory pressure alerts
+
+## Section 4: Concurrency Control (Priority: High)
+
+### 4.1 Implement prediction semaphores
+- [ ] Add semaphore for PP-StructureV3.predict
+- [ ] Configure max concurrent predictions
+- [ ] Add queue for waiting predictions
+- [ ] Implement timeout handling
+- [ ] Add metrics for queue depth
+
+### 4.2 Add selective processing
+- [ ] Create config for disabling chart/formula/table
+- [ ] Implement batch processing for large documents
+- [ ] Add progressive loading for multi-page docs
+- [ ] Create priority queue for operations
+- [ ] Test memory savings with selective processing
+
+## Section 5: Active Memory Management (Priority: Medium)
+
+### 5.1 Create memory monitor thread
+- [ ] Implement background monitoring loop
+- [ ] Add periodic memory metrics collection
+- [ ] Create threshold-based triggers
+- [ ] Implement automatic cache clearing
+- [ ] Add LRU-based model unloading
+
+### 5.2 Add recovery mechanisms
+- [ ] Implement emergency memory release
+- [ ] Add worker process restart capability
+- [ ] Create memory dump for debugging
+- [ ] Add cooldown period after recovery
+- [ ] Test recovery under various scenarios
+
+## Section 6: Cleanup Hooks (Priority: Medium)
+
+### 6.1 Implement shutdown handlers
+- [ ] Add FastAPI shutdown event handler
+- [ ] Create signal handlers (SIGTERM, SIGINT)
+- [ ] Implement graceful model unloading
+- [ ] Add connection draining
+- [ ] Test shutdown sequence
+
+### 6.2 Add task cleanup
+- [ ] Wrap background tasks with cleanup
+- [ ] Add success/failure callbacks
+- [ ] Implement resource release on completion
+- [ ] Add cleanup verification logging
+- [ ] Test cleanup in error scenarios
+
+## Section 7: Configuration & Settings (Priority: Low)
+
+### 7.1 Add memory settings to config
+- [ ] Define memory threshold parameters
+- [ ] Add model timeout settings
+- [ ] Configure pool sizes
+- [ ] Add feature flags for new behavior
+- [ ] Document all settings
+
+### 7.2 Create monitoring dashboard
+- [ ] Add memory metrics endpoint
+- [ ] Create pool status endpoint
+- [ ] Add model lifecycle stats
+- [ ] Implement health check endpoint
+- [ ] Add Prometheus metrics export
+
+## Section 8: Testing & Documentation (Priority: High)
+
+### 8.1 Create comprehensive tests
+- [ ] Unit tests for ModelManager
+- [ ] Integration tests for OCRServicePool
+- [ ] Memory leak detection tests
+- [ ] Stress tests with concurrent requests
+- [ ] Performance benchmarks
+
+### 8.2 Documentation
+- [ ] Document memory management architecture
+- [ ] Create tuning guide
+- [ ] Add troubleshooting section
+- [ ] Document monitoring setup
+- [ ] Create migration guide
+
+---
+
+**Total Tasks**: 58
+**Estimated Effort**: 3-4 weeks
+**Critical Path**: Sections 1-2 must be completed first as they form the foundation