fix(issue-50): review findings of PR #56 on macOS

- admission: a `submit --dry-run` record is marked dry_run and is not an
  open job of its session (review 1e25cf2f F1)
- create: the monitor-row adoption requires the row's server to be the one
  this create spawned on (review 1e25cf2f F2)
- pane lock: retry only on contention (BlockingIOError); the docs say the
  flock lasts while any fd-9 holder (the claim shell and the shim) lives
  (review 66680d9d)
- tests on macOS: real-herdr box HOMEs under /tmp (sun_path is 104 bytes),
  resolved paths, the fake claude reads non-canonical input (MAX_CANON 1024)
  and the pane is read unwrapped; lock holders exec their sleep so killing
  them frees the lock; the adoption tests name the server

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/multi-agent-mux-create/scripts/create_session.sh

@@ -533,9 +533,13 @@ running_same = [s for s in sessions if s.get('name') == name and s.get('status')
 # registered, with no job, for a pane created after this create began, is
 # this create's own pane - herdr keeps live names unique per server and the
 # preflight refused an older session of this name - so it is replaced, not
-# refused as a second live session.
+# refused as a second live session. Names are unique per server only, so the
+# row must be this server's (review 1e25cf2f F2: another server's row of the
+# name was replaced). The pane pid is no identity: it is the pane's foreground
+# process at the time it was read.
 def _adopted_own(s):
     return (s.get('last_visible_note') == 'auto-registered by monitor' and not s.get('delegate_job_id')
+            and (s.get('herdr_server') or s.get('herdr_session') or 'default') == server_name
             and epoch.isdigit() and int(s.get('herdr_session_epoch') or 0) >= int(epoch) - 1)
 if running_same and all(_adopted_own(s) for s in running_same):
     print(f"NOTE: the monitor registered {name} while it was being created; that row is replaced by this one", flush=True)