Replace the two salvaged per-command test files with a single suite that drives
the real /branch, /resume and /sessions <id> handlers against a real SessionDB
and asserts the invariant that matters: while a turn is running, the session id
(CLI and agent) is unchanged and the current row is not ended; when idle,
/branch still proceeds. Red on origin/main (3 busy cases), green with the guards.
The /branch MagicMock fixture gains an explicit `_agent_running = False`: a bare
MagicMock attribute is truthy and would trip the new guard.
Docs: /branch and /resume rows in the slash-command reference say they are
refused mid-turn in the classic CLI and why.
Co-authored-by: sonderhq <144971773+sonderhq@users.noreply.github.com>
Co-authored-by: MohamadKanso <91088196+MohamadKanso@users.noreply.github.com>
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