feat: implement --onboard flag in multi-agent-mux-create and update AGENT.md onboarding handshake protocol

.agents/skills/lib.sh

@@ -826,4 +826,67 @@ start_watchdog() {
   echo "$pid"
 }
 
+# wait_for_tui_ready <session_name> <agent>
+# Gated wait to ensure that the agent's TUI is fully loaded and responsive
+# before injecting any keyboard instructions.
+wait_for_tui_ready() {
+  local sess="$1" agent="$2"
+  local local_tmux="tmux"
+  if [ -n "${TMUX_SERVER_NAME:-}" ] && [ "$TMUX_SERVER_NAME" != "default" ]; then
+    local_tmux="tmux -L $TMUX_SERVER_NAME"
+  fi
+  
+  echo "🔍 Waiting for $agent TUI to become ready..."
+  for i in {1..15}; do
+    local content
+    content=$($local_tmux capture-pane -p -t "$sess" 2>/dev/null || echo "")
+    if [ -n "$content" ]; then
+      case "$agent" in
+        claude)
+          if echo "$content" | grep -E -q "Anthropic|Assistant|Chat|Dangerously|dangerously|Enter|Welcome|projects" 2>/dev/null; then
+            echo "✅ Claude TUI detected ready."
+            return 0
+          fi
+          ;;
+        agy)
+          if echo "$content" | grep -q "Antigravity" 2>/dev/null; then
+            echo "✅ Antigravity TUI detected ready."
+            return 0
+          fi
+          ;;
+        hermes)
+          if echo "$content" | grep -q "Hermes" 2>/dev/null; then
+            echo "✅ Hermes TUI detected ready."
+            return 0
+          fi
+          ;;
+        cline)
+          if echo "$content" | grep -E -q "Cline|history|Chat" 2>/dev/null; then
+            echo "✅ Cline TUI detected ready."
+            return 0
+          fi
+          ;;
+      esac
+    fi
+    sleep 1
+  done
+  echo "⚠️ Warning: TUI readiness check timed out. Proceeding anyway..."
+}
+
+# inject_instructions <session_name> <instructions> [job_id]
+# Injects instructions into the tmux session using paste-buffer and C-m.
+inject_instructions() {
+  local sess="$1" instructions="$2" job_id="${3:-onboard}"
+  local local_tmux="tmux"
+  if [ -n "${TMUX_SERVER_NAME:-}" ] && [ "$TMUX_SERVER_NAME" != "default" ]; then
+    local_tmux="tmux -L $TMUX_SERVER_NAME"
+  fi
+  
+  $local_tmux set-buffer -b "job_buf_$job_id" "$instructions"
+  $local_tmux paste-buffer -b "job_buf_$job_id" -t "$sess"
+  sleep 0.5
+  $local_tmux send-keys -t "$sess" C-m
+  $local_tmux delete-buffer -b "job_buf_$job_id"
+}
+