fix(reset): refuse every registration during a reset and purge only ids owned by the row's folder (#78)

Review round 2 (codex):
- R1: register_job reads .mam/reset-in-progress under the registry lock and
  refuses while a reset of the workspace owning <ws>/.mam/jobs is live, so the
  public registry.py register CLI and the API no longer bypass the gate. The
  reset's precheck takes that lock once after publishing its marker, so a
  registration is either seen by it or refused. The reset's own create passes
  MAM_RESET_OWNER_PID; the remote runner refuses the dispatch.
- R2: before each purge the reset re-runs stop's revalidate check
  (verify_session_uuid) for a post-discovered id against the row's folder and
  skips the target (id not verified) when it does not verify.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/lib_py/delegation/remote.py

@@ -221,6 +221,9 @@ def mirror_job(d: Dict[str, Any], registry_dir: str, session: str) -> Optional[s
     except FileExistsError as exc:  # lost the race to a newer (or equal) attempt under the lock
         logger.warning("refusing dispatch for %s: %s", jid, exc)
         return None
+    except registry.ResetInProgressError as exc:  # Issue #78: this workspace is being reset
+        logger.warning("refusing dispatch for %s: %s", jid, exc)
+        return None
     brief_dir = os.path.join(registry_dir, jid)
     os.makedirs(brief_dir, exist_ok=True)
     with open(os.path.join(brief_dir, "brief.md"), "w", encoding="utf-8") as fh: