forkBranch called session.create without a profile, so in app-global
remote mode (one backend serving every profile) a branch of a
non-default-profile chat silently landed on the launch profile — the
"session jumps between profiles after branching" bug. New chats already
carry their profile (desktopSessionCreateParams, #39993); branching was
the remaining create callsite without it.
Thread the parent's owning profile through both branch entry points:
branchStoredSession already resolved it (#67603) but dropped it before
the create; branchCurrentSession now resolves the open chat's profile
via the same cache → active → cross-profile ladder as resume. forkBranch
swaps the live gateway onto that profile and passes it on session.create,
which also makes the optimistic sidebar row's profile stamp correct.
Supersedes #40788 — same invariant, rebuilt for the current forkBranch/
branchStoredSession split.
Co-authored-by: Dusk1e <yusufalweshdemir@gmail.com>
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