feat(backend): add chat session listing API and wire selector

[locke69321]

Summary by CodeRabbit

Release Notes

• New Features

  • Chat sessions listing: View and access your previously created conversations.
  • Agent status tracking: Monitor agent activity and operational status.

• Bug Fixes

  • Improved error handling for chat operations with meaningful feedback when sessions are unavailable.

• Improvements

  • Chat initialization now automatically loads existing sessions instead of creating new ones by default.

[coderabbitai]

Walkthrough

This PR introduces agent status monitoring and chat session management capabilities with new /agent/status and /chat/sessions endpoints. It adds supporting service and repository layers, refactors FastAPI startup using an async lifespan context manager, enhances error handling for chat operations, and updates the frontend to retrieve and load chat sessions.

Changes

Cohort / File(s)	Summary
Agent Status Feature router.py, schemas.py, dtos.py, agent_service.py	Introduces /agent/status endpoint with AgentStatusResponse model, AgentStatusData DTO, and new AgentService class that aggregates active runs and subagent data to report status as "active" or "idle" with lastRunAt timestamp.
Chat Session Management router.py, chat_service.py, sqlalchemy_repo.py	Adds /chat/sessions listing endpoint, list_sessions() service method, and repository methods get_chat_session() and list_chat_sessions() ordered by descending creation date.
Chat Service Validation chat_service.py	Adds input validation to add_message() and list_messages() with ValueError("Session not found") for missing sessions; refactors prompt construction to use prior message history.
Repository Query Methods sqlalchemy_repo.py	Adds list_runs_by_status() and latest_run() methods to support agent status aggregation and run tracking.
Application Lifecycle Refactor main.py	Replaces explicit startup event hook with async lifespan() context manager for deterministic DB initialization via FastAPI's lifecycle management.
Frontend Session Integration client.ts, chat.tsx, -index.smoke.test.tsx	Adds listChatSessions() API client method; refactors chat route with loadSessions() callback to fetch existing sessions on mount, set active session, or create default; adds mock responses for sessions endpoint in tests.
Test Infrastructure conftest.py, test_chat_memory_api.py, test_db_repo_and_types.py	Updates DB environment configuration to always set SQLite paths deterministically; expands integration and unit test coverage for session listing, message history validation, and agent status behavior in idle/active states.

Sequence Diagram

sequenceDiagram
    participant Client
    participant API as /agent/status
    participant AgentService
    participant SqlAlchemyRepository
    participant Database

    Client->>API: GET /agent/status
    API->>AgentService: get_status()
    AgentService->>SqlAlchemyRepository: list_runs_by_status(RUNNING)
    SqlAlchemyRepository->>Database: Query Run records<br/>where status=RUNNING
    Database-->>SqlAlchemyRepository: [Run, ...]
    SqlAlchemyRepository-->>AgentService: [Run, ...]
    AgentService->>SqlAlchemyRepository: latest_run()
    SqlAlchemyRepository->>Database: Query Run ordered<br/>by created_at DESC
    Database-->>SqlAlchemyRepository: Run | None
    SqlAlchemyRepository-->>AgentService: Run | None
    AgentService-->>API: AgentStatusData<br/>(status, subagents,<br/>activeRuns, lastRunAt)
    API-->>Client: AgentStatusResponse

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sequenceDiagram
    participant Client
    participant API as /chat/sessions
    participant ChatService
    participant SqlAlchemyRepository
    participant Database

    Client->>API: GET /chat/sessions
    API->>ChatService: list_sessions()
    ChatService->>SqlAlchemyRepository: list_chat_sessions()
    SqlAlchemyRepository->>Database: Query ChatSession<br/>ordered by created_at DESC
    Database-->>SqlAlchemyRepository: [ChatSession, ...]
    SqlAlchemyRepository-->>ChatService: [ChatSession, ...]
    ChatService-->>API: [ChatSessionData, ...]
    API-->>Client: [ChatSessionResponse, ...]

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• locke69321/elara-assistant#12: Frontend implementation of agent status panel and session listing UI that integrates with the backend endpoints and repository methods introduced in this PR.

Poem

🐰 A rabbit hops through agent paths,
Listing sessions, checking status graphs,
Lifecycle managed with context care,
New endpoints bloom in the spring air! 🌱
Sessions dance, runs now tracked so clear,
Our burrow's smarter, year by year! 🎉

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main changes: adding a chat session listing API and wiring a selector, which aligns with the primary objectives and commits in the PR.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch codex/backend-chat-session-listing

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[locke69321]

• feat(backend): add chat session listing API and wire selector #13 👈 (View in Graphite)
• feat(frontend): redesign dashboard IA and dark-mode UI #12
• main

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[locke69321]

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[locke69321]

Merge activity

• Feb 7, 2:01 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Feb 7, 2:01 PM UTC: @locke69321 merged this pull request with Graphite.