docs: update CHANGELOG.md for v7.3.1

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

CHANGELOG.md

@@ -4,6 +4,44 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [7.3.1] - 2025-12-16
+
+## 🐛 Bug Fixes
+
+### Pending Messages Cleanup (Issue #353)
+
+Fixed unbounded database growth in the `pending_messages` table by implementing proper cleanup logic:
+
+- **Content Clearing**: `markProcessed()` now clears `tool_input` and `tool_response` when marking messages as processed, preventing duplicate storage of transcript data that's already saved in observations
+- **Count-Based Retention**: `cleanupProcessed()` now keeps only the 100 most recent processed messages for UI display, deleting older ones automatically
+- **Automatic Cleanup**: Cleanup runs automatically after processing messages in `SDKAgent.processSDKResponse()`
+
+### What This Fixes
+
+- Prevents database from growing unbounded with duplicate transcript content
+- Keeps metadata (tool_name, status, timestamps) for recent messages
+- Maintains UI functionality while optimizing storage
+
+### Technical Details
+
+**Files Modified:**
+- `src/services/sqlite/PendingMessageStore.ts` - Cleanup logic implementation
+- `src/services/worker/SDKAgent.ts` - Periodic cleanup calls
+
+**Database Behavior:**
+- Pending/processing messages: Keep full transcript data (needed for processing)
+- Processed messages: Clear transcript, keep metadata only (observations already saved)
+- Retention: Last 100 processed messages for UI feedback
+
+### Related
+
+- Fixes #353 - Observations not being saved
+- Part of the pending messages persistence feature (from PR #335)
+
+---
+
+**Full Changelog**: https://github.com/thedotmack/claude-mem/compare/v7.3.0...v7.3.1
+
 ## [7.3.0] - 2025-12-16
 
 ## Features