After the runtime starts, DesktopLaunchGate calls applyServerBaseUrl() which reloads the
page with ?serverBaseUrl=… so the shell-host bootstrap can route API calls to the embedded
server. But main.tsx runs bootstrapShellHostContext() at module load — BEFORE the gate's
effect — and it strips every shell query param from the URL via history.replaceState. The
gate then checked window.location.search for serverBaseUrl (after an await), always missed
it, and re-ran the handoff → window.location.replace → reload → strip → an infinite reload
loop that renders as rapid "Starting local Fusion runtime…" flashing that never connects.
This was latent until the split-brain fix (78f0bc31) let the runtime actually start and
reach the handoff.
Fix: detect the completed handoff from the CACHED shell-host context
(getShellHostContext().serverUrl), which the bootstrap preserves, instead of the stripped
URL (URL param kept only as a fallback).
Adds a DesktopLaunchGate regression test: with serverUrl present in the cached context but
stripped from the URL, the gate renders children and does NOT reload; on first load it
performs the handoff exactly once. Verified the test fails against the pre-fix gate.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
04fd91f66b