Make object recovery settlement-safe

sql/003_recovery_settlement.sql

@@ -0,0 +1,33 @@
+ALTER TABLE mutations
+    ADD COLUMN IF NOT EXISTS dispatch_started_at TIMESTAMPTZ,
+    ADD COLUMN IF NOT EXISTS request_deadline_at TIMESTAMPTZ,
+    ADD COLUMN IF NOT EXISTS worker_lease_until TIMESTAMPTZ,
+    ADD COLUMN IF NOT EXISTS settled_at TIMESTAMPTZ;
+
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1
+        FROM mutations
+        WHERE external_state = 'pending'
+    ) THEN
+        RAISE EXCEPTION
+            'recovery settlement migration requires no pending mutations';
+    END IF;
+END
+$$;
+
+ALTER TABLE mutations
+    ADD CONSTRAINT mutations_dispatch_timing_check CHECK (
+        (external_state <> 'pending') OR
+        (dispatch_started_at IS NOT NULL AND
+         request_deadline_at IS NOT NULL AND
+         worker_lease_until IS NOT NULL)
+    ) NOT VALID;
+
+ALTER TABLE mutations
+    VALIDATE CONSTRAINT mutations_dispatch_timing_check;
+
+CREATE INDEX IF NOT EXISTS mutations_recovery_idx
+    ON mutations (worker_lease_until, request_deadline_at, updated_at)
+    WHERE state IN ('prepared', 'applying');