Subagents run in unfocused Orca terminal tabs in the current worktree,
selected automatically between Herdr, Orca (ORCA_TERMINAL_HANDLE), and tmux.
- Tabs are created against ORCA_WORKTREE_ID since pi's cwd may live outside
any Orca worktree, and start in pi's cwd via the startup command
- createSurface blocks on two-phase readiness (startup marker, then a
verified probe echo) because input typed during shell init is swallowed
by the initial shell's exec or flushed during bash startup
- terminal read reports ok with status exited for closed terminals, so
reads throw on non-running status to match herdr/tmux semantics
- Integration harness gains Orca focus support via terminal switch and
visual-layout active-pane lookup
jb