Check-in [e88fa2b9ed]

zit serve built its whole in-memory snapshot of the repository before it opened the listener socket. The build is O(store), so past a few thousand artifacts it outlasted the client's readiness probe and the client reported the server never came up — the store could be served, just never reached.

Bring-up now binds first: listen, announce, then prime, then accept. A client that connects during the prime queues in the kernel accept backlog instead of being refused, so the readiness window starts at the bind rather than after the scans. The listener open moves ahead of BOTH O(store) reads on the path — the config read and the prime. The connection deadline is armed only on accept, so priming never falls inside it. On a 254k-artifact store a connect now completes in ~2 ms against a ~5 s prime.

A push made the snapshot stale, and the old code rebuilt it inside the pushing round's own reply deadline — an O(store) rebuild charged to the request that caused it. The rebuild moves to a maintain hook the accept loop runs between connections, with no connection open to charge it to; the append-only stat gate makes the stale snapshot self-correcting until then.

The reorder is inherently a large-corpus latency property: reverting it leaves every unit test green, because the failure only shows when prime latency exceeds the readiness window. It is pinned in the milestone tier instead, where smoke already lives: zig build bench -- serve synthesizes a store, spawns the real server, and asserts time-to-first-connect is a small fraction of the prime (fixed order ~0.1; reverted order jumps past 1.0). The de-race and the accept-loop hook are pinned by ordinary unit tests. check-in: de218fa6f6 user: dmestas tags: trunk