* fix(branch): slice fork transcript in GET /api/session merged-view coordinates
keep_count sent by forkFromMessage is an index into the merged display
view (sidecar lineage stitched across compression snapshots, append-only
merged with state.db rows, parent backfill). The branch handler sliced the
raw sidecar instead, which diverges from that view in both length and
content after compactions: forks from the final conclusion landed rows
too early, ending the fork mid tool-run and dropping the conclusion.
Build source_messages through the exact same pipeline as the
GET /api/session load_messages path for non-messaging sessions.
Regression test: test_branch_route_slices_merged_display_view_not_raw_sidecar
(fails on the old code with the fork ending on a tool row).
* fix(branch): align fork source with display bounds
---------
Co-authored-by: Anthony Ruiz <ruizanthony@users.noreply.github.com>
Co-authored-by: nesquena-hermes <nesquena+hermes@gmail.com>
