zit serve rebuilt its whole in-memory snapshot from the log on every request, and classified held-vs-phantom by calling content on every rid, forcing a full inflate of the entire repository per request. A clone cost O(rounds x store) of server work; past a few thousand artifacts one round outran the connection deadline and the server answered nothing at all.

ArtifactStore grows heldCount, the aggregate of the existing non-inflating held predicate, and serve counts with it rather than re-deriving a worse predicate caller-side. ServeCtx caches the snapshot and rebuilds only when a stat shows the append-only log grew, so a commit made alongside a live server is still advertised on the next request.

Reuse needs isolation: the responder interns phantoms and upgrades entries as it answers, and that would change what later rounds serve. A new OverlayStore answers each request over a per-request write overlay, reads falling through, writes confined to the overlay. The persist pass now takes an ArtifactStore.

On 67,499 artifacts: unfixed, no round completes; fixed, one snapshot build then sub-millisecond rounds. check-in: 2874978461 user: dmestas tags: fix9-serve-stall