Crawlers

Single-player games usually keep gameplay logic on the client — it's the path of least resistance. I went the other way. The ASP.NET Core server owns every truth: movement legality, line-of-sight, dice rolls, item drops, even which tiles each player is allowed to see. Fog of war is filtered server-side; the client never receives data the player shouldn't see. The React + Pixi.js client sends intent and renders state diffs over SignalR.

That decision compounded. When I added 1-4 player co-op, the gameplay layer barely changed — the same room broadcast that drove single-player now fanned out to multiple connections. Fog of war was already per-player. The animation pipeline already consumed structured combat events. Persistence (corpses, world stats) was already isolated. The shape of the system absorbed multiplayer instead of resisting it.

Floors are generated by BSP partitioning, deterministic per seed. The Generation project is a pure function of (seed, config) — no I/O, no DI, no hidden state. That's what made the system testable end-to-end: 161 server tests covering BSP layout, field-of-view, movement legality, engagement, combat, item interactions, and descent.

Combat uses a `ScriptedDice` test double, so non-deterministic outcomes are deterministic on demand. A flaky test is a real bug, not noise. And the same seed produces the same dungeon every time, which means bug reports are reproducible and runs are shareable.

Combat could have been the boring thing — server changes HP, client re-renders. Instead it emits a structured event stream: Hit, Crit, Miss, Fumble, Heal, each carrying target, magnitude, and timing. The client consumes this stream as an animation queue.

Hits get a lunge plus a red flash. Crits add camera shake. Misses sidestep. Heals pulse green. Killing-blow sprites defer destruction until pending animations drain, so death looks final because the animation that earned the kill finishes first. The result: combat *feel* lives entirely in the client, combat *truth* never leaves the server. Two concerns, cleanly separated.

EF Core + Postgres for run history, player identity, corpses, and aggregate world stats. Configuration is environment-driven (`ConnectionStrings__DefaultConnection` and friends) — if no DB is present in dev, every persistence service falls back to a Null implementation and the game still runs. Postgres is optional in dev, required in prod.

The whole thing ships as a multi-stage Dockerfile + compose stack: server, Postgres, and the Vite client behind a single LAN-bound port. From clone to playable on another machine takes one command.