Branching the open chat calls navigate(child) and then resumeSession(child)
in the same tick. resumeSession captures the route token at entry, but
the router only publishes the new pathname on the next render, so the
token it captured still named the PARENT. When that render landed while
resume was awaiting resolveStoredSession/gateway, isCurrentResume() saw
the token change and returned, abandoning the resume before it bound the
warm branch runtime. The pane was left with the child selected, no
active runtime, an empty transcript and a loader for a row with history;
use-route-resume saw nothing to heal (selection already matched the
route, creatingSessionRef had suppressed the pathname edge), so the
child stayed on the spinner with no composer until the user switched
away and back.
isCurrentResume now treats the route arriving at the session being
resumed as still current (resumeRouteStillCurrent in
session-context-drift.ts); a route to any other chat still supersedes
the resume exactly as before.
De-flakes Desktop core E2E lineage-sidebar ("a branch child is titled
and is its own row"), which hit this ~2 in 10 runs.
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