fix: per-handler claim lease in ledger, nats max_deliver, pin handler names

crates/adapters/sqlite/migrations/0101_outbox_identity.sql

@@ -1,5 +1,6 @@
--- Outbox identity: every queued event carries a stable id; handlers record
--- (event_id, handler) pairs so redeliveries are skipped.
+-- Outbox identity: every queued event carries a stable id; handlers claim
+-- (event_id, handler) pairs so redeliveries are skipped and concurrent
+-- deliveries never run the same handler twice.
 ALTER TABLE event_queue ADD COLUMN event_id TEXT;
 
 -- When the current claim started; a claim older than the lease is reclaimable.
@@ -21,6 +22,8 @@ CREATE UNIQUE INDEX idx_event_queue_event_id
 CREATE TABLE processed_events (
     event_id     TEXT NOT NULL,
     handler      TEXT NOT NULL,
+    status       TEXT NOT NULL CHECK (status IN ('in_progress', 'done')),
+    started_at   TEXT,
     processed_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
     PRIMARY KEY (event_id, handler)
 );