Missed Call Desk
A callback-only phone desk for the studio. A missed caller taps a few digits or leaves a voicemail and I get a clean, durable callback queue. Proven correct before it touches a phone.
A carrier reporting that a call ended looks exactly like a completed intake, and replayed or out-of-order webhooks quietly corrupt naive systems. I built the control plane first, against signed carrier-shaped fixtures instead of a paid number: exact raw-byte signature verification for three carriers, immutable raw events with idempotent projections, and caller confirmation gated on the durable write.
The owner desk shows the queue, each record's destination status, and one next action.
Screenshot coming
Stack
- TypeScript, React 19, Vite
- Cloudflare Workers and D1 with seven migrations
- Raw Web Crypto signature verification
- Vitest with 264 worker tests and 13 DOM tests, Biome, CI
Decisions
- Verify bytes first. Three carriers, three schemes, each verified on the exact raw request before parsing.
- Retry is not collision. A duplicate delivery is absorbed; the same event with different content is journaled as an integrity problem and never merged.
- The product cannot reach the lab. A static gate walks the owner desk's import graph and fails the build if it can reach fixture or simulation code.
Lessons
- Recovery is a hash. Export, isolated restore, SHA-256 comparison across every table, then deterministic replay rebuilds every projection from raw events alone; 2,500 events matched through restore.
- Removing one redundant read took the load p99 from 923 ms to 314 ms.