decision(firestore-send-email): kit/extension parity – event source is per function, not per instance #3298

firestore-send-email kit/extension parity. Priority: medium. Event consumers that filter on source stop receiving the kit's events.

Difference

• Extension: source is the instance, //firebaseextensions.googleapis.com/extensions/projects/<project>/instances/<instance>.
• Kit: the CLI sets source to the function's Cloud Run service, projects/<project>/locations/<region>/services/kit-<instance>-processQueue. That uses the camelCase function id, which doesn't match the real lowercase service name. .env can't override it, because EVENTARC_CLOUD_EVENT_SOURCE is a reserved key. Event types, subject and data are otherwise the same.

Reproduced

Both instances published to the same channel and a recorder captured the events:

• Extension: //firebaseextensions.googleapis.com/extensions/projects/corie-testing/instances/sepext
• Kit: projects/corie-testing/locations/us-central1/services/kit-sepkit-processQueue

Code

• Kit: channel setup events.ts#L23-L30. The source comes from firebase-tools (deploy/functions/prepare.js, EVENTARC_CLOUD_EVENT_SOURCE).

Resolution

Same call as #3255 and #3272:

• either set a stable, instance-based source on published events;
• or record this as an accepted difference under "Decisions" in firestore-send-email kit tracking issue #3290 and document it in the README's Events section.