Chat request duplication/splitting during slow responses

[chubes4]

Problem

Single chat requests sometimes create multiple duplicate sessions when AI processing is slow.

Root Cause Analysis

• Race conditions in session creation during long AI loops
• Pending session reuse logic may fail under load
• Transient caching might not prevent parallel processing
• Session state updates during processing cause conflicts

Steps to Reproduce

1. Send single message triggering slow AI processing
2. Check database - multiple sessions created from one request

Expected Behavior

• One request = one session, regardless of processing time
• Robust deduplication prevents any duplication

Technical Details

• Backend checks for pending sessions but may have race conditions
• Request ID caching exists but timing issues possible
• Database: wp_datamachine_chat_sessions table updates

Proposed Solutions

• Fix race conditions in Chat::handle_chat() session creation
• Improve pending session detection logic
• Add database-level uniqueness constraints
• Better atomic session state management
• Add comprehensive logging for duplication tracking