The boot-time MEMFS staging fetched one file per round-trip, serially, so a
many-file project (an uploaded repo) paid full request latency per file before
the editor could open anything — the dominant cost of opening such a project.
Fetch with a bounded pool (8, same as the lib presync) and write as each
lands; the writes are synchronous FS calls on distinct paths, so completion
order does not matter. A failed fetch still rejects the stage, after the
in-flight siblings settle so none can write into MEMFS behind the caller.
Tests cover all three properties: every file lands under reverse-staggered
fetch delays, the overlap is >1 and <=8, and a failing fetch rejects.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H8jo7zz1ZwzYpjJ64UZKN4
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