fix(tests): handle the cancelled token-sealing run's rejection before polling for its backend

The operator-cancel test started migrate() and only attached a handler after
its pg_cancel_backend polling loop. When the cancellation reached the run's
connection before the loop broke, Node saw an unhandled rejection and Vitest
failed the whole db shard even though every test passed. Attach the rejection
assertion when the run starts and await it after the loop.

Author: waleedlatif1

packages/db/script-migrations/0037_seal_account_tokens.integration.ts

@@ -358,7 +358,8 @@ describe('sealing stored account tokens in PostgreSQL', () => {
       await insertAccount('cancelled-access', 'cancelled-refresh')
       await onAccountUpdate('PERFORM pg_sleep(20)')
 
-      const run = migrate()
+      /** Handled from the start: the cancel can fail the run before the polling loop sees it. */
+      const failed = expect(migrate()).rejects.toThrow('canceling statement due to user request')
       for (let attempt = 0; attempt < 100; attempt++) {
         const [cancelled] = await admin<{ cancelled: boolean }[]>`
           SELECT pg_cancel_backend(pid) AS cancelled FROM pg_stat_activity
@@ -368,7 +369,7 @@ describe('sealing stored account tokens in PostgreSQL', () => {
         await sleep(50)
       }
 
-      await expect(run).rejects.toThrow('canceling statement due to user request')
+      await failed
       expect(await isRecorded()).toBe(false)
       expect((await storedRows())[0].access_token).toBe('cancelled-access')
     }, 30_000)