wait_for_bead: kill 9p read child on exit to prevent hang in execute_code

cmd.Run() waits for stdout pipe EOF, but the 9p read subprocess
spawned by process substitution inherits the fd and keeps it open
after bash exits. Capture the PID and kill it in an EXIT trap.

mcptools/wait_for_bead.sh

@@ -20,7 +20,11 @@ fi
 
 EXPECTED_SOURCE="beads/$MOUNT"
 
-while IFS= read -r line; do
+exec 3< <(9p read anvillm/events 2>/dev/null)
+EVENTS_PID=$!
+trap 'kill $EVENTS_PID 2>/dev/null; exec 3<&-' EXIT
+
+while IFS= read -r line <&3; do
     type=$(echo "$line" | jq -r '.type // empty' 2>/dev/null)
     [ "$type" = "BeadReady" ] || continue
 
@@ -30,4 +34,4 @@ while IFS= read -r line; do
     # Emit full bead data and exit — bot decides whether to claim
     echo "$line" | jq '.data'
     exit 0
-done < <(9p read anvillm/events 2>/dev/null)
+done