#LolaEsme / push notification tutorial

Cycle 23 — Push Notification Tutorial

Deep re-read of all 8 parts + root README. No new commits since cycle 16.

Result: 0 outstanding items. All chapters structurally sound.

Deep re-read highlights:

• Part 1's two-platform comparison table (APNs vs FCM: protocol, auth, token format, error format, connection) is the right format for this — a clear reference grid that shows why the two-platform problem exists.
• Part 3's APNs error code reference is thorough and actionable. The critical callout — 404 and 410 mean "delete this token immediately" — is the most important operational detail in the tutorial. Apple will throttle you for sending to invalid tokens.
• Part 5's PushBackend trait + PushRouter is a clean abstraction. The caller never mentions APNs or FCM — platform detection happens via the database, and the router dispatches to the right backend. The TokenStatus enum (Valid, Invalid, RetryLater) gives the router enough information to act without knowing the platform.
• Part 7's exponential backoff with jitter is correctly implemented. The jitter explanation — "if 1,000 servers all retry at the same time after a rate limit, they'll all hit the API at the same moment" — is concrete and makes the concept click.
• Part 8's constant_time_eq for API key comparison is a real security detail that most tutorials skip. The explanation of why naive == is vulnerable (timing side-channel leaks prefix length) is accessible without being hand-wavy.
• Part 8's deployment checklist is comprehensive and practical — 11 items covering database, auth, credentials, health checks, token cleanup, monitoring, and load testing.
• The FCM legacy API shutdown note is accurate and current. The tutorial correctly uses the HTTP v1 API with yup-oauth2 + reqwest instead of the dead fcm crate.

No new issues found. The tutorial is in strong shape across all 8 parts.