feat(api+dash): wire MCP page to real backend (closes #206)

[thinmintdev]

Summary

Replaces the v3 dashboard's HAL0_DATA-driven /agents/mcp page with live queries against new /api/mcp/* routes. Closes #206.

Backend (new — src/hal0/api/routes/mcp.py)

• GET /api/mcp/servers — introspects app.state.mcp_servers (FastMCP instances) for tool/resource/prompt counts; returns connect_url + audit-derived activity.rpm and connected clients
• GET /api/mcp/clients — derives connected clients from the hal0.mcp.audit journald stream (grouped by client_id, with role heuristic)
• GET /api/mcp/catalog — static module-level installable list (ADR-0013 will swap to live registry)
• GET /api/mcp/stream — SSE tail of mcp.tool.* audit events; backfills last 60 s on subscribe
• GET /api/mcp/{id}/logs — per-server audit rows for the LogsDrawer
• POST /api/mcp/install + DELETE /api/mcp/{id} + POST /api/mcp/{id}/{action} + PATCH /api/mcp/{id}/config — STUB 501 with code mcp.not_implemented pending ADR-0013 mcp_client.py work

mcp_mount.py now stashes the live FastMCP instances on app.state.mcp_servers so the introspection route can call server.list_tools() etc. without re-importing the builders. This is the only new export from the existing MCP infrastructure.

Frontend (new — ui/src/api/hooks/useMcp.ts)

• useMcpServers / useMcpClients / useMcpCatalog — TanStack Query hooks with 404 → mock fallback
• useMcpCallStream — EventSource against /api/mcp/stream, returns {calls, now} matching the existing useLiveCallStream shape so the LiveTimeline render is unchanged
• useMcpInstall / useMcpUninstall / useMcpRestart / useMcpConfigPatch / useMcpServerLogs — mutations that catch 501 and surface the ADR-0013 toast

Page wiring (mcp.jsx + mcp-modals.jsx)

• McpView reads useMcpServers / useMcpClients; falls back to HAL0_DATA mock when live returns empty so the prototype demo + skip-marked specs keep rendering
• LiveTimeline driven by useMcpCallStream (the local random stream is only used against the HAL0_DATA mock)
• InstallDrawer catalog reads useMcpCatalog; Install button fires useMcpInstall mutation (501 → toast)
• LogsDrawer reads useMcpServerLogs; sample lines remain as a fresh-install fallback
• EditConfigModal Save fires useMcpConfigPatch (501 → toast)

Sidebar (chrome.jsx)

• Adds the MCP nav item so the page is reachable without typing the URL fragment

STUB list (pending ADR-0013 mcp_client.py)

• POST /api/mcp/install
• DELETE /api/mcp/{id}
• POST /api/mcp/{id}/{action} (start/stop/restart)
• PATCH /api/mcp/{id}/config

All return 501 with envelope {error: {code: "mcp.not_implemented", message: "... pending ADR-0013 follow-up (#206)"}}. Follow-up issue will track the actual lifecycle work.

Test plan

• uv run pytest tests/api/test_mcp_routes.py -v — 11 pass
• uv run pytest tests/api/ --tb=short — 338 pass, 3 pre-existing skips
• uv run ruff format --check && uv run ruff check — clean
• npx tsc --noEmit — clean
• npm run build — clean
• npx playwright test — 38 pass, 15 pre-existing skips
• npx playwright test specs/mcp-v3-wired.spec.ts — 5/5 pass (new spec)

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