fix(skills): resolve blank-padding viewport bug in send_keys_safe and fix rc status leak

- Introduce _pane_tail content helper to filter blank-padded lines in tmux captures
- Apply _pane_tail to _pane_dialog_open, handle_startup_dialogs, and send_keys_safe
- Fix rc status expansion logic in create_session.sh instructions injection check
- Include 3-agent final prompt-lock verification reports

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

@@ -384,8 +384,10 @@ On failure run:      $pub --event error     --detail '<one-line reason>'.
 Task: $SUBMIT_JOB_PROMPT"
 
   # Inject instructions into the tmux pane
-  if ! inject_instructions "$SESSION_NAME" "$instructions" "$DELEGATE_JOB_ID"; then
-    delegate_publish_event "$DELEGATE_JOB_ID" error "instruction injection failed (prompt-lock, rc=$?)"
+  inject_instructions "$SESSION_NAME" "$instructions" "$DELEGATE_JOB_ID"
+  rc=$?
+  if [ "$rc" -ne 0 ]; then
+    delegate_publish_event "$DELEGATE_JOB_ID" error "instruction injection failed (prompt-lock, rc=$rc)"
     exit 1
   fi