Route async task mode through TaskExecutionService

[vybe]

Problem

The async mode path in chat.py (_execute_task_background(), lines 376-567) does NOT use TaskExecutionService. It implements its own parallel logic for slot management, activity tracking, error handling, and credential sanitization — inline.

/api/task (async=true)  → _execute_task_background()    ← INLINE, NOT TaskExecutionService
/api/task (sync)        → TaskExecutionService.execute_task()  ← Unified path

Impact

• Any fix applied to TaskExecutionService (status values, sanitization, slot logic) does NOT apply to async mode
• Async mode has its own slot acquire/release that could diverge
• Async mode has its own error handling with potentially different status values
• Async mode may miss credential sanitization steps added to the service
• Two maintenance surfaces for the same logical operation

Current Async Flow (chat.py)

1. Create execution record early (db.create_task_execution())
2. Acquire slot inline (slot_service.acquire_slot())
3. Track activity inline (activity_service.track_activity())
4. Spawn asyncio.create_task(_execute_task_background())
5. Background function: call agent, update records, release slot in finally

Required Changes

1. Add async support to TaskExecutionService (e.g., execute_task_async() that spawns background and returns immediately)
2. Move all inline logic from _execute_task_background() into the service
3. Chat router's async path should only create execution record + call service
4. Ensure identical slot, activity, sanitization, and error handling between sync and async

Files to Change

• src/backend/services/task_execution_service.py — Add async execution mode
• src/backend/routers/chat.py — Remove _execute_task_background(), delegate to service
• src/backend/routers/public.py — Also has _execute_public_chat_background() that should use service

[vybe]

Actualization (2026-03-30)

Current state: Still valid. _execute_task_background() in chat.py still has inline slot/activity/error handling that bypasses TaskExecutionService.

Quick verification:

• chat.py still contains _execute_task_background() with inline slot_service.acquire_slot(), activity_service.track_activity(), and custom error handling
• public.py has similar inline logic in _execute_public_chat_background()
• The sync path correctly uses TaskExecutionService.execute_task()

Impact remains: Fixes to TaskExecutionService (status values, sanitization, slot logic) don't apply to async mode. Two maintenance surfaces for the same operation.

Recommendation: Still needs implementation. This is a code quality / reliability issue that will cause divergence bugs over time.