# Control-plane DB substrate (#613)

**Status:** Implemented (SQLite single-writer MVP)

**ADR:** [`mcp-allocator-control-plane-observability-adr.md`](mcp-allocator-control-plane-observability-adr.md)

**Module:** `control_plane_db.py`

## Architecture statement

> **DB coordinates, Gitea records, Sentry/GlitchTip observe; the bridge is the only path that turns observations into Gitea work.**

## What this ships

| Capability | Notes |
|------------|--------|
| Schema | `sessions`, `work_items`, `leases`, `assignments`, `terminal_locks`, `events`, `incident_links` |
| Atomic assign+lease | `ControlPlaneDB.assign_and_lease` — one `BEGIN IMMEDIATE` transaction |
| Mutation gate | `require_valid_assignment` — live lease + allowed action + non-terminal work + non-stale head |
| Heartbeat / release / expire | Lease lifecycle helpers |
| Terminal-lock index | Routing signal for #600 (terminal path first) |
| `incident_links` | Provider-neutral link model for #612 — **not** assignable work; scope keys NULL-safe |

## Hard rules (enforced in code)

1. Assignable `work_items.kind` ∈ {`issue`, `pr`} only — **never** raw Sentry/GlitchTip incidents.
2. Two concurrent sessions cannot both receive an active assignment on the same open work item (second gets `wait`).
3. Merged/closed work items return `no_safe_work` at assign time, and `require_valid_assignment` fails closed if the work item becomes terminal later.
4. Assignments pin `expected_head_sha`; mutations fail closed if the work item head drifts.
5. SQLite path is the **single-writer MVP** (`GITEA_CONTROL_PLANE_DB`, default under `~/.cache/gitea-tools/control-plane/`). Multi-session multi-host production requires **Postgres** or a **single allocator daemon** (ADR §6).
6. `incident_links` optional scope fields are stored as empty strings (never NULL) so UNIQUE is canonical across minimal upserts.
7. Legacy `incident_links` migration collapses NULL-scope duplicates **only** when Gitea targets **and** all meaningful observation metadata agree (fingerprint, status, event_count, permalink, timestamps, linked PRs, etc.). Conflicting metadata fails closed — no silent discard.

## Dependency chain

```text
#613 control-plane DB (this)  →  #600 allocator API  →  #612 incident bridge
```

- **#600** must call this substrate (not file locks / comment-only leases alone) for completion.
- **#612** must write `incident_links` here and create **Gitea issues**; the allocator assigns those issues, not raw incidents.

## Allocator API (#600)

Module: `allocator_service.py` · MCP tool: `gitea_allocate_next_work`

- Workers call `gitea_allocate_next_work(apply=false|true)` instead of self-selecting work.
- `apply=false` returns a dry-run selection (`outcome=preview`) with skip reasons.
- `apply=true` reserves via `ControlPlaneDB.assign_and_lease` (atomic assignment+lease).
- Coordination source is **always** the control-plane DB — not file locks or comment-only leases.
- Routing follows ADR §5.3 (REQUEST_CHANGES → author, terminal path first, foreign lease → wait).
- Raw monitoring incidents are never candidates (#612 remains downstream).

## Non-goals (intentionally deferred)

- Sentry/GlitchTip provider adapters and auto-watchdog — **#612**
- Gitea comment/label mirror writers (may be added by allocator tooling later)

## Tests

```bash
python3 -m pytest tests/test_control_plane_db.py -q
```