fix(issue-34): a pane caller reaches an agent of another workspace on its own server; an unseen target is not recorded as busy

- mam_herdr: for name lookups (agent / has-session / kill-session) a
  HERDR_WORKSPACE_ID that is the caller pane's own workspace (it matches
  the HERDR_PANE_ID prefix) is dropped. Live agent names are unique per
  server (herdr --skill), so this cannot address a same-named agent of
  another workspace; an id the caller chose, or one set outside a pane,
  still scopes (H-18/H-21/H-23). The generated shim is unchanged (S11).
- wrapper: a preflight that cannot see the target closes the job
  cancelled with detail target_not_found instead of session_busy; the
  loop's sub-job table counts it as NOT-DISPATCHED.
- tests: T10-T12 with the measured pane env (same-server socket, caller
  w6, target w2); T8 follows the sub-job-armed guard.

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

.agents/skills/multi-agent-mux-delegate-job/multi-agent-mux-delegate-job

@@ -892,6 +892,8 @@ finalize_unfinished() {
   if [ "$phase" = "preflight" ] || [ "$phase" = "idle_wait" ]; then
     close_req="cancelled"
     detail="session_busy"
+    # Issue #34: a target the preflight could not see was never busy
+    [ "$phase" = "preflight" ] && [ -n "${PREFLIGHT_REASON:-}" ] && detail="$PREFLIGHT_REASON"
   fi
 
   local close_args=(--job "$job_id" --request "$close_req")
@@ -921,7 +923,7 @@ finalize_unfinished() {
     local disp_arg=()
     [ -n "${_disp_tok:-}" ] && disp_arg=(--expect-dispatch-token "$_disp_tok")
     if [ "$close_req" = "cancelled" ]; then
-      "$PY" "$SCRIPT_DIR/scripts/publish_event.py" --registry-dir "$REGISTRY_DIR" --job "$job_id" --event cancelled --detail "session_busy" ${disp_arg[@]+"${disp_arg[@]}"} 2>/dev/null || true
+      "$PY" "$SCRIPT_DIR/scripts/publish_event.py" --registry-dir "$REGISTRY_DIR" --job "$job_id" --event cancelled --detail "$detail" ${disp_arg[@]+"${disp_arg[@]}"} 2>/dev/null || true
     elif [ "$sub_rc" -ne 1 ] || [ "$phase" = "inject" ]; then
       local err_detail="deadline_timeout"
       [ "$phase" = "inject" ] && err_detail="agent_blocked"
@@ -947,6 +949,7 @@ preflight_agent() {
   export HERDR_SESSION_NAME="$(resolve_herdr_session "$sess" "$WORKDIR")"
 
   if ! herdr has-session -t "$sess" 2>/dev/null; then
+    PREFLIGHT_REASON="target_not_found"  # Issue #34: not a busy session
     echo "ERROR: 에이전트 세션 '$sess'이 존재하지 않습니다. 작업을 위임하기 전에 먼저 에이전트 세션을 기동해 주세요." >&2
     echo "       팁: 'multi-agent-mux-resume' 또는 'multi-agent-mux-create'를 통해 에이전트를 먼저 생성할 수 있습니다." >&2
     return 1