[push][EPIC] FCM push activation

[cestercian]

EPIC — FCM push activation. Broken into 5 dependency-ordered phases. Push is currently inactive; the app works fully over realtime chat, users just get no background notifications. Full runbook: docs/PUSH_SETUP.md.

Derived scope (from the iOS app)

Firebase for Android == FCM push only (iOS uses APNs directly; analytics is PostHog, crash is Sentry — no other Firebase surface). The event/payload contract is fixed and reused verbatim from send-push + iOS PushService:

• Events: message, gig_request, booking_confirmed_client, booking_confirmed_artist, booking_reminder_24h, booking_review_request.
• Data keys: artistant_event, artistant_thread_id, artistant_request_id, artistant_booking_id.
• The message preview is already server-redacted (left(NEW.body,140), NEW.body redacted by the order-proofed BEFORE-INSERT trigger) → safe on a lockscreen; the anti-leakage moat holds with no client-side redaction.
• Transport: data-only FCM messages + android.priority=high, so onMessageReceived fires foreground + background (client owns the channel, foreground-suppression, and routing).
• Schema change is additive: device_tokens.fcm_token (nullable, unique) + apns_token becomes nullable + a one-token CHECK. iOS is unaffected (it selects explicit columns and always writes apns_token).

Phases

Phase	Issue	Where	Depends on
P1 Backend — send-push FCM transport + device_tokens.fcm_token	#37	cestercian/Artistant (iOS/Supabase)	P3 for live delivery (merges inert)
P2a Android — deep-link producer seam + channels + DeviceTokenRepository (no Firebase)	#38	this repo	—
P2b Android — Firebase Messaging + token lifecycle	#39	this repo	#38, #40
P3 Operator — Firebase project + google-services.json + FCM secrets	#40	Firebase + Supabase dashboards	—
P4 On-device verification + rollout	#41	physical device	#37, #39, #40

Dependency graph

P3 #40 (operator) ─┬─► P1 #37 (backend, live delivery)
                   └─► P2b #39 (build) ◄── P2a #38 (seam)
P1 #37 + P2b #39 + P3 #40 ─► P4 #41 (device verify) ─► close this epic

Critical path: P3 (operator, ~15 min) is the unblocker — both the backend (P1) and the Android Firebase code (P2b) can be written now but only go live once P3 lands. P2a has no blockers and can land immediately.

[cestercian]

Status update — the whole code + backend chain is DONE

• P1 (backend) ✅ merged (cestercian/Artistant#94) + applied/deployed to dev AND prod (migration 0069 + send-push FCM v9, verify_jwt=false).
• P2a (seam) ✅ merged ([push][P2a] Android — deep-link producer seam + notification channels + DeviceTokenRepository (no Firebase) #38).
• P2b (FCM receiver + token lifecycle + the deferred deep-stack nav fix) ✅ merged (feat(push): P2b — FCM receiver + token lifecycle + deep-stack nav fix (#39) #43). All gates green incl. R8; 228 unit tests.
• P3 (operator): Firebase project artistant-2a53f created, Android app in.artistant.app registered, google-services.json placed (gitignored), migration + function deployed. Only the FCM secrets remain (owner, with a FRESH key — the first-generated one was exposed and must be rotated): FCM_PROJECT_ID=artistant-2a53f + FCM_SERVICE_ACCOUNT on both projects.
• P4 ([push][P4] On-device verification + rollout #41): on-device verification — blocked only on the secrets + a physical device.

Net: Android FCM push is code-complete and backend-live. The only things between here and working push are the two secrets and a device smoke-test.