fix(gate): no admission lock in a tree without .mam; MAM_UPDATE_MONITOR_STOP_S in the knob table (Issue #72)

mam_update_admit created .mam/ to hold its lock, so a checkout running its
own run_loop.sh got a .mam (test_loop_marker_isolation L1, test_issue17 W1).
A tree without .mam is not an installed workspace, the only kind the update
runs in, so the gate admits there without a lock. The update's monitor-stop
wait is a normalised integer knob and is listed in INT_KNOBS
(test_issue26_ints B5).

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

.agents/skills/lib.sh

@@ -3264,11 +3264,15 @@ mam_control_plane_prefix() {
 # fd 7 (`7>&-` on such a child, as pane_lock's fd 9). The wait is bounded by
 # MAM_UPDATE_ADMISSION_WAIT_S (default 120).
 #
-# mam_update_admit [workspace]: rc 0 admitted (fd 7 held), 1 refused (stderr).
+# mam_update_admit [workspace]: rc 0 admitted (fd 7 held, unless the workspace
+# has no .mam), 1 refused (stderr).
 mam_update_admit() {
   local root="${1:-$WORKSPACE_ROOT}"
   local lock="$root/.mam/update-admission.lock" marker="$root/.mam/update-in-progress" st
-  if ! { mkdir -p "$root/.mam" && exec 7>>"$lock"; }; then
+  # No .mam: not an installed workspace, which is all the update runs in (and a
+  # checkout running its own scripts gets no .mam from this).
+  [ -d "$root/.mam" ] || return 0
+  if ! exec 7>>"$lock"; then
     echo "ERROR: cannot open the update admission lock $lock" >&2
     return 1
   fi

tests/test_issue26_ints.py

@@ -59,6 +59,8 @@ INT_KNOBS = {
     # once) and the wrapper's registry wait (0: decide at once - clear or busy)
     "MAM_ONBOARD_WAIT_S": (1, "600"),
     "MAM_DISPATCH_WAIT_S": (0, "600"),
+    # Issue #72: how long the update waits for the monitor to stop after SIGTERM
+    "MAM_UPDATE_MONITOR_STOP_S": (1, "30"),
     # delegate_wait_started's ack_s (MAM_ONBOARD_ACK_S / DELEGATE_JOB_ACK_S via create_session.sh)
     "delegate_wait_started:ack_s": (0, "180"),
     # wrapper flags