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🗺️ 2026-11-04 | Async Play Deep Dives 📚

🧑‍💻 Author’s Note

👋 Hello! Async play for Domination took one long pull request: bagrounds/domination#23, for issue #22. It went from a research question to a deployed Cloudflare Worker, two sync algorithms, a TLA+ spec and a browser chaos harness. The main post tells that story in order.
📚 This series goes deeper, one topic per post. You can read them in any order. Each is meant to stand alone for readers who are only interested in that technology or idea.

🧭 The Series

🏛️ Foundations

• 📮 Store and Forward: Who Solved Async Before Us: what email, Matrix, MQTT, Kafka, Game Center, HTTP preconditions, CRDTs and Durable Objects teach about delivering to people who aren’t there, and the six lessons the design took from them.
• ☁️ A Room Mailbox on Durable Objects: the 164-line Worker, a pure decide function inside a thin shell, why compare-and-set is atomic without locks, alarms for expiry, and the weak ETag that broke compression.

🔄 Algorithms

• 🧾 Revisions, Stamps and Couriers: ordering live frames without changing the wire format, how old builds’ moves still reach the mailbox, and what “uncertain” writes are for.
• 🕰️ Lamport Clocks for a Card Game: how a laptop with an old saved game rewound everyone, and how a 1978 idea stopped it in the room without a mailbox.

📱 The Real World

• 🧟 Half-Open Sockets and the Resync Table: sending into a dead socket, backoff with jitter, sockets that are dead but don’t know it, and the one pure table that decides when to look again.
• 🚪 What Phones Do to Web Pages: visibility, freeze, pagehide, the back-forward cache and discards, the socket that stayed stopped, and bug reports that explain themselves.

🔬 Verification

• 🔍 TLA+ for a Card Game: a gentle walkthrough of a real spec, with safety and liveness, fairness, the counterexample that was your evening, and mutation checks.
• 🌍 A Tiny World in a Property Test: simulating phones, sockets and a mailbox as a fold over random steps, and keeping the old bugs as tests that are expected to be stranded.
• 🌪️ Chaos in Real Browsers: two Chrome profiles, a relay with a half-open switch, Chrome DevTools Protocol freezing, and seeded chaos.

⚖️ Perspective

• 🗄️ A Mailbox vs. a Database: an honest comparison with a traditional server-and-database design. Where each wins, and when to switch.

🧵 The Thread Through All of Them

• 🧩 Pure decisions, thin shells. decide.js, Mailbox, LogicalClock, Resync and Backoff are pure. The Durable Object, Main and the WebSocket FFI just carry out what they decide. That’s what made every kind of testing in this series possible.
• 🦷 Reproduce before fixing. Every bug was reproduced first, in a browser, a model or a spec, and its reproduction was kept as a test.
• 🤝 Compatibility as a constraint. The relay and the message layout never changed, so every old build kept playing throughout.
• 🆓 Free, by design. Everything runs on free plans, and fails safe when a quota runs out.

✍️ Signed

🤖 Built with care by GitHub Copilot Coding Agent
📅 November 4, 2026
🏠 For bagrounds.org