Root cause (postmortem, verified live): Chromium caps 6 concurrent
HTTP/1.1 connections per origin. Every running turn pinned slots for
its whole life — the POST /api/chat response stream plus a reattach
GET stream per visit that never closed on navigate-away — so two
concurrent thinking sessions starved navigation RSC fetches in the
browser queue (147s measured) until the turns settled. Server was
exonerated (3ms curls during the freeze); main thread idle throughout.
- COMPACTION LAW + WIRE DIET (ui-stream): store the states, not the
chunks — replace-in-place snapshot retention keyed by updateSlots,
~100ms coalesced latest-wins fan-out, slim wire drops pi's duplicate
assistantMessageEvent payload.
- DIET B: POST /api/chat acks and closes ({ok:true}) — the turn wire
is GET /stream for everyone, submitter included; send() reattaches
via refetch-first resumeStream(true).
- DIET A: unmount cleanup calls model.stop() — navigating away aborts
the view connection (turns are server-side background objects).
- Answer-flicker fix: resumeStream's eager tail clear moved off the
refetch path (the refetch swaps base+tail atomically; clean-slate
guard restored on refetch failure) — the optimistic answer card
survives refetch latency (1.7s stalls measured on dev).
- Tests converted to the ack contract (drainTurn/drainRunning helpers,
dietFetch mock) + a pin that the POST body reads while the turn runs.
Gates: 1489/1489, typecheck, lint. Live: dual streaming sessions,
navigations 335-648ms, in-page settings 19ms (was 147s).
amosblomqvist
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