Log the error when Postgres closes an idle pool connection

[anurag]

Problem

db() in app/store.ts made a pg.Pool with no "error" listener. Postgres can close an idle connection of the pool, for example in a restart, a failover, or maintenance, or with pg_terminate_backend. Then pg-pool emits "error" on the pool. With no listener, Node stops the process with exit code 1:

node:events:496
      throw er; // Unhandled 'error' event
error: terminating connection due to administrator command
Emitted 'error' event on BoundPool instance at:
    at Client.idleListener (node_modules/pg-pool/index.js:62:10)
  severity: 'FATAL',
  code: '57P01',

The gateway (app/server.ts) and the workflows host (app/host.ts) both use this pool. Thus a maintenance restart of Render Postgres can stop both processes.

Change

• db() attaches an "error" listener to the pool. The listener logs the error with console.error and does not throw it. pg-pool removes the client before it emits the event, so the next query gets a new connection. The node-postgres documentation tells an application to always listen for this event.
• tests/store.test.ts emits "error" on the pool. It expects no throw and one log entry. Without the listener, the emit throws and the test fails. The test opens no connection to Postgres.
• AGENTS.md adds store to the list of tests.

Verification

• npm run check passes: lint, typecheck, and 394 tests.
• I used a throwaway local Postgres 18, and the gateway polled GET /ui/apps each second:
  • Before the change, pg_ctl -m fast stop stopped the gateway with exit code 1 and the stack above.
  • After the change, the gateway logs Lost an idle Postgres connection: error: terminating connection due to administrator command and continues. GET /ui/apps gives 503 while Postgres is stopped, and 200 after Postgres starts again. pg_terminate_backend on the idle connection gives the same result.
  • With a password in DATABASE_URL, the logged error does not contain the password. pg keeps the password in a property that is not enumerable.
• Each log entry is about 120 lines. pg-pool attaches the client object to the error, and console.error prints it.

Not in this change

A client that withAppLock() checks out has no "error" listener until it goes back to the pool. If Postgres closes its connection during the transaction, the query fails, and then the client emits Connection terminated unexpectedly. Node then stops the process. A local check shows this: pg_terminate_backend during select pg_sleep(5) in a transaction of the same shape. This change does not fix that path.

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