✨ Add ScheduledTaskTool with global scheduler and frontend polling

[2862282695gjh-afk]

Summary

Add a ScheduledTaskTool that enables Nexent agents to create, list, and cancel cron-based or one-shot scheduled tasks.

Architecture

ScheduledTaskTool (thin CRUD)
  ├── create → write to scheduled_tasks_t
  ├── list   → read by agent_id + tenant_id
  └── cancel → update status

Global SchedulerService (singleton, survives agent runs)
  └── 10s DB poll → find due tasks → new agent run → save messages

Frontend Polling
  ├── Layer 1: 5s poll active conversation (refresh + scroll)
  └── Layer 2: 10s batch-poll background conversations (silent cache update)

Why not just a tool module?

Nexent creates a new agent instance per message — tools, scheduler threads, and all state are GCd after each run. A scheduled task tool needs to survive beyond a single agent run, which requires:

1. DB persistence — task data outlives any agent instance
2. Global scheduler — independent singleton thread, started at runtime_service startup
3. Frontend polling — SSE is request-response only, no persistent connection for push

Key Design Decisions

Decision	Rationale
Global scheduler, not per-tool	Agent instances are ephemeral — per-tool schedulers die with the agent
Scheduler strips ScheduledTaskTool from triggered agent	Prevents recursive task creation (agent sees the prompt and tries to create another task)
message_idx from DB max()	Original save_messages computes idx from history=[] → always 0, causing collisions
Two-layer frontend polling	Active conversation gets fast updates; background conversations get silent cache refresh
Ownership check in polling API	get_new_messages_service validates conversation.created_by == user_id

Multi-Tenant Compatibility

• ScheduledTaskRecord includes tenant_id and user_id fields
• query_tasks_by_agent and cancel_task filter by tenant_id
• Scheduler is global (polls all pending tasks) but uses each tasks own tenant_id/user_id for agent runs
• Frontend polling API validates conversation ownership

Files Changed (15 files, +877 lines, all additive)

New files (3):

• backend/database/scheduled_task_db.py — 5 CRUD functions
• backend/services/scheduled_task_scheduler.py — global scheduler singleton
• sdk/nexent/core/tools/scheduled_task_tool.py — tool with cron parser

Modified files (12, no existing logic changed):

• backend/database/db_models.py — ScheduledTaskRecord model
• backend/database/conversation_db.py — get_max_message_index()
• backend/services/conversation_management_service.py — get_new_messages_service()
• backend/apps/conversation_management_app.py — polling endpoints
• backend/apps/runtime_app.py — scheduler lifecycle
• backend/agents/create_agent_info.py — conversation_id passthrough
• sdk/nexent/core/agents/nexent_agent.py — ScheduledTaskTool metadata injection
• sdk/nexent/core/tools/__init__.py — export ScheduledTaskTool
• docker/init.sql — scheduled_tasks_t table
• frontend/services/api.ts — new endpoints
• frontend/services/conversationService.ts — polling methods
• frontend/app/[locale]/chat/internal/chatInterface.tsx — polling useEffect

Testing

Tested with Docker (v2.2.0 image + bind mounts):

• Created "remind me every 5 minutes" task → agent created task in DB ✅
• Scheduler detected due task → triggered agent run → wrote messages to DB ✅
• Frontend polling detected new messages → refreshed display ✅
• Switched conversation → background polling updated cache ✅
• No ScheduledTaskTool not found errors ✅
• No recursive task creation ✅