fix: handle duplicate message ID in session DB insert

Use INSERT OR IGNORE and escalate trigger 0→1 when the row already
exists. Prevents approval replays from failing when the message was
already accumulated by a duplicate platform event.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db/session-db.ts

@@ -8,6 +8,7 @@
 import Database from 'better-sqlite3';
 
 import { INBOUND_SCHEMA, OUTBOUND_SCHEMA } from './schema.js';
+import { log } from '../log.js';
 
 /** Apply the inbound or outbound schema to a DB file. Idempotent. */
 export function ensureSchema(dbPath: string, schema: 'inbound' | 'outbound'): void {
@@ -102,14 +103,23 @@ export function insertMessage(
     trigger?: 0 | 1;
   },
 ): void {
-  db.prepare(
-    `INSERT INTO messages_in (id, seq, kind, timestamp, status, platform_id, channel_type, thread_id, content, process_after, recurrence, series_id, trigger)
+  const trigger = message.trigger ?? 1;
+  const result = db
+    .prepare(
+      `INSERT OR IGNORE INTO messages_in (id, seq, kind, timestamp, status, platform_id, channel_type, thread_id, content, process_after, recurrence, series_id, trigger)
      VALUES (@id, @seq, @kind, @timestamp, 'pending', @platformId, @channelType, @threadId, @content, @processAfter, @recurrence, @id, @trigger)`,
-  ).run({
-    ...message,
-    trigger: message.trigger ?? 1,
-    seq: nextEvenSeq(db),
-  });
+    )
+    .run({
+      ...message,
+      trigger,
+      seq: nextEvenSeq(db),
+    });
+  if (result.changes === 0) {
+    log.warn('Duplicate message ID ignored', { id: message.id });
+    if (trigger === 1) {
+      db.prepare(`UPDATE messages_in SET trigger = 1 WHERE id = ? AND trigger = 0`).run(message.id);
+    }
+  }
 }
 
 export function countDueMessages(db: Database.Database): number {