feat: control-plane DB substrate for atomic assign/lease (Closes #613)

Add SQLite single-writer MVP control plane per the allocator ADR: sessions, work_items (issue/pr only), atomic assign+lease, mutation gates, terminal-lock index, and provider-neutral incident_links. DB coordinates concurrency; Gitea remains assignable work; raw Sentry/GlitchTip incidents are never work items. #600 and #612 build on this substrate.
2026-07-09 22:27:51 -04:00
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+# 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` — workers need a live assignment/lease |
+| 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 |
+
+## 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`.
+4. 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).
+
+## 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.
+
+## Non-goals (intentionally deferred)
+
+- Full `gitea_allocate_next_work` routing policy (REQUEST_CHANGES → author, etc.) — **#600**
+- 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
+```