fix(delegate): submit also takes the target workspace's update admission (Issue #72, review R1)

Decision 8: delegate submit uses the admission lock of the workspace the
target session belongs to. The wrapper resolved only its own
WORKSPACE_ROOT, so a job could be registered and delivered to an agent of
another installed workspace while that workspace was being updated.

lib_py.update target-workspace resolves a herdr:<name> row's workspace (the
.mam at or above its pane.cwd, else its control_plane.workspace_root);
mam_update_admit takes an fd, and submit holds the caller root on fd 7 and
the target on fd 8 until the record is written. Rowless and remote targets
keep the caller-root gate.

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

.agents/skills/lib_py/update.py

@@ -16,6 +16,11 @@ this module what needs parsing. Standard library only, Python 3.9.
   python -m lib_py.update monitor --workspace W
       JSON {"pids": [...], "lock": "free"|"held"}: the monitor daemons
       daemon.find_running recognises, and whether .mam/monitor.lock is held.
+  python -m lib_py.update target-workspace --workspace W --agent-session S
+      The installed workspace a delegate target `herdr:<name>` belongs to
+      (decision 8), when it is not W: the nearest directory holding a .mam
+      at or above its row's pane.cwd, else the row's control_plane
+      workspace_root. Nothing for a rowless or non-herdr target.
   python -m lib_py.update backup-registry --workspace W --dest D
       Copies the registry into D under the registry's own write lock
       (agent-sessions.db.lock, as atomic_yaml takes it): the DB through the
@@ -231,6 +236,31 @@ def precheck(workspace: str, state: dict, herdr: str, env: Mapping[str, str]) ->
     return blockers
 
 
+# --------------------------------------------------------------------------- delegate target
+
+def target_workspace(workspace: str, state: dict, agent_session: str) -> str:
+    if not agent_session.startswith("herdr:"):
+        return ""
+    name = agent_session[len("herdr:"):]
+    row = next((s for s in state.get("herdr_sessions") or []
+                if isinstance(s, dict) and s.get("name") == name), None)
+    if row is None:
+        return ""
+    found = ""
+    cwd = (row.get("pane") or {}).get("cwd") or ""
+    d = _real(cwd) if cwd else ""
+    while d and not found:
+        if os.path.isdir(os.path.join(d, ".mam")):
+            found = d
+        elif os.path.dirname(d) == d:
+            break
+        d = os.path.dirname(d)
+    if not found:
+        root = (row.get("control_plane") or {}).get("workspace_root") or ""
+        found = _real(root) if root else ""
+    return "" if found == _real(workspace) else found
+
+
 # --------------------------------------------------------------------------- monitor
 
 def monitor_state(workspace: str) -> dict:
@@ -288,6 +318,9 @@ def main(argv: Optional[List[str]] = None) -> int:
     s.add_argument("--herdr", required=True)
     s = sub.add_parser("monitor")
     s.add_argument("--workspace", required=True)
+    s = sub.add_parser("target-workspace")
+    s.add_argument("--workspace", required=True)
+    s.add_argument("--agent-session", required=True)
     s = sub.add_parser("backup-registry")
     s.add_argument("--workspace", required=True)
     s.add_argument("--dest", required=True)
@@ -303,6 +336,13 @@ def main(argv: Optional[List[str]] = None) -> int:
         for line in lines:
             print(line)
         return 1 if lines else 0
+    if a.cmd == "target-workspace":
+        try:
+            state = _state()
+        except ValueError:
+            state = {}
+        print(target_workspace(ws, state, a.agent_session))
+        return 0
     if a.cmd == "monitor":
         print(json.dumps(monitor_state(ws)))
         return 0