feat(mcp): implement graceful maintenance-drain mode (Closes #659)

Add durable per-repo drain state, allocator assignment stop, mutation deferral with a safety allowlist, observable status, and capability-gated enter/exit tools. Drain proof/restart gate remain #661. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
2026-07-25 17:02:12 -04:00
parent 76f293eb28
commit e91b94db56
7 changed files with 1056 additions and 1 deletions
@@ -31,8 +31,9 @@ from typing import Any, Iterator, Sequence

 import dependency_graph
 import gitea_audit
+import maintenance_drain

-SCHEMA_VERSION = 5
+SCHEMA_VERSION = 6

 # Assignable work kinds only — raw monitoring incidents are never work items.
 WORK_KINDS = frozenset({"issue", "pr"})
@@ -239,6 +240,31 @@ CREATE INDEX IF NOT EXISTS idx_session_checkpoints_session
 CREATE INDEX IF NOT EXISTS idx_session_checkpoints_work
    ON session_checkpoints(remote, org, repo, work_kind, work_number);

+-- Graceful maintenance-drain state (#659). One current row per repository
+-- scope — drain is a *state*, not a history, so entering and exiting update
+-- the same row and every transition is audited to ``events``. Creating the
+-- table is the v5->v6 migration: additive, idempotent, and it never touches
+-- prior tables. ``state`` is CHECK-constrained so an unknown value can never
+-- be written and later read as "not draining".
+CREATE TABLE IF NOT EXISTS maintenance_drain (
+    drain_id TEXT PRIMARY KEY,
+    remote TEXT NOT NULL,
+    org TEXT NOT NULL,
+    repo TEXT NOT NULL,
+    state TEXT NOT NULL DEFAULT 'inactive'
+        CHECK (state IN ('inactive', 'draining')),
+    reason TEXT NOT NULL DEFAULT '',
+    requested_by TEXT NOT NULL DEFAULT '',
+    requested_by_profile TEXT NOT NULL DEFAULT '',
+    session_id TEXT NOT NULL DEFAULT '',
+    entered_at TEXT NOT NULL DEFAULT '',
+    exited_at TEXT NOT NULL DEFAULT '',
+    drain_schema_version INTEGER NOT NULL DEFAULT 6,
+    created_at TEXT NOT NULL,
+    updated_at TEXT NOT NULL,
+    UNIQUE (remote, org, repo)
+);
+
 -- Model usage, token cost, latency, and performance events (#651)
 CREATE TABLE IF NOT EXISTS usage_events (
    usage_id INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -3025,3 +3051,170 @@ class ControlPlaneDB:
            "live_lease_id": None if live_lease_id is None else str(live_lease_id),
            "reconcile_action": "reconcile_required" if stale else "safe_to_resume",
        }
+
+    # ── Maintenance drain (#659) ─────────────────────────────────────────────
+
+    @staticmethod
+    def _maintenance_drain_row(row: sqlite3.Row | None) -> dict[str, Any] | None:
+        """Convert a ``maintenance_drain`` row to a plain record."""
+        if row is None:
+            return None
+        return {key: row[key] for key in row.keys()}
+
+    def read_maintenance_drain(
+        self, *, remote: str, org: str, repo: str
+    ) -> dict[str, Any] | None:
+        """Return the current drain record for a scope, or None if never set.
+
+        None and a stored ``inactive`` row mean the same thing to callers —
+        ``maintenance_drain.is_draining`` treats both as not draining — so the
+        read never has to invent a record to answer the gate.
+        """
+        with self._tx(immediate=False) as conn:
+            row = conn.execute(
+                """
+                SELECT * FROM maintenance_drain
+                 WHERE remote = ? AND org = ? AND repo = ?
+                """,
+                (str(remote or ""), str(org or ""), str(repo or "")),
+            ).fetchone()
+        return self._maintenance_drain_row(row)
+
+    def set_maintenance_drain(
+        self,
+        *,
+        remote: str,
+        org: str,
+        repo: str,
+        state: str,
+        reason: str = "",
+        requested_by: str = "",
+        requested_by_profile: str = "",
+        session_id: str = "",
+    ) -> dict[str, Any]:
+        """Enter or exit maintenance drain for one repository scope (AC1).
+
+        The state transition is audited to ``events`` — entering and exiting
+        are exactly the moments an operator has to be able to reconstruct
+        later. Re-entering an already-draining scope is idempotent: it refreshes
+        the reason/owner metadata, keeps the original ``entered_at``, and
+        records no duplicate transition event.
+
+        Capability authorization happens above this layer (the drain tasks
+        carry a non-``gitea.*`` permission in the task capability map); the DB
+        records who asked and why, and never grants the right itself.
+        """
+        state_norm = maintenance_drain.normalize_state(state)
+        raw = {
+            "reason": str(reason or ""),
+            "requested_by": str(requested_by or ""),
+            "requested_by_profile": str(requested_by_profile or ""),
+            "session_id": str(session_id or ""),
+        }
+        clean = gitea_audit.redact(raw)
+        remote_s, org_s, repo_s = str(remote or ""), str(org or ""), str(repo or "")
+        now_s = _ts()
+
+        with self._tx() as conn:
+            existing = conn.execute(
+                """
+                SELECT * FROM maintenance_drain
+                 WHERE remote = ? AND org = ? AND repo = ?
+                """,
+                (remote_s, org_s, repo_s),
+            ).fetchone()
+
+            prior_state = (
+                maintenance_drain.normalize_state(existing["state"])
+                if existing is not None
+                else maintenance_drain.STATE_INACTIVE
+            )
+            transitioned = prior_state != state_norm
+
+            prior_entered = (
+                str(existing["entered_at"] or "") if existing is not None else ""
+            )
+            prior_exited = (
+                str(existing["exited_at"] or "") if existing is not None else ""
+            )
+            if state_norm == maintenance_drain.STATE_DRAINING:
+                # A re-entry keeps the original entry time (the drain never
+                # stopped); a fresh entry stamps now and clears the old exit.
+                entered_at = prior_entered if (not transitioned and prior_entered) else now_s
+                exited_at = ""
+            else:
+                entered_at = prior_entered
+                exited_at = now_s if (transitioned or not prior_exited) else prior_exited
+
+            if existing is None:
+                drain_id = uuid.uuid4().hex
+                conn.execute(
+                    """
+                    INSERT INTO maintenance_drain(
+                        drain_id, remote, org, repo, state, reason,
+                        requested_by, requested_by_profile, session_id,
+                        entered_at, exited_at, drain_schema_version,
+                        created_at, updated_at
+                    ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+                    """,
+                    (
+                        drain_id, remote_s, org_s, repo_s, state_norm,
+                        clean["reason"], clean["requested_by"],
+                        clean["requested_by_profile"], clean["session_id"],
+                        entered_at, exited_at,
+                        maintenance_drain.DRAIN_SCHEMA_VERSION, now_s, now_s,
+                    ),
+                )
+            else:
+                drain_id = str(existing["drain_id"])
+                conn.execute(
+                    """
+                    UPDATE maintenance_drain
+                       SET state = ?, reason = ?, requested_by = ?,
+                           requested_by_profile = ?, session_id = ?,
+                           entered_at = ?, exited_at = ?,
+                           drain_schema_version = ?, updated_at = ?
+                     WHERE drain_id = ?
+                    """,
+                    (
+                        state_norm, clean["reason"], clean["requested_by"],
+                        clean["requested_by_profile"], clean["session_id"],
+                        entered_at, exited_at,
+                        maintenance_drain.DRAIN_SCHEMA_VERSION, now_s, drain_id,
+                    ),
+                )
+
+            if transitioned:
+                event_type = (
+                    "maintenance_drain_enter"
+                    if state_norm == maintenance_drain.STATE_DRAINING
+                    else "maintenance_drain_exit"
+                )
+                conn.execute(
+                    """
+                    INSERT INTO events(work_item_id, event_type, message, created_at)
+                    VALUES (NULL, ?, ?, ?)
+                    """,
+                    (
+                        event_type,
+                        f"drain {drain_id} scope {remote_s}/{org_s}/{repo_s} "
+                        f"{prior_state} -> {state_norm} by "
+                        f"{clean['requested_by'] or '(unknown)'} "
+                        f"({clean['requested_by_profile'] or 'no profile'}); "
+                        f"reason: {clean['reason'] or '(none)'}",
+                        now_s,
+                    ),
+                )
+
+            row = conn.execute(
+                "SELECT * FROM maintenance_drain WHERE drain_id = ?", (drain_id,)
+            ).fetchone()
+
+        record = self._maintenance_drain_row(row) or {}
+        return {
+            "record": record,
+            "drain_id": drain_id,
+            "state": state_norm,
+            "prior_state": prior_state,
+            "transitioned": transitioned,
+        }