wait_for_bead: fix pipe subshell exit leaving 9p read orphaned

Use process substitution instead of pipe so exit 0 terminates the
script and its file descriptor, killing the 9p read process cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcptools/wait_for_bead.sh

@@ -22,7 +22,7 @@ fi
 
 EXPECTED_SOURCE="beads/$MOUNT"
 
-9p read anvillm/events | while IFS= read -r line; do
+while IFS= read -r line; do
     type=$(echo "$line" | jq -r '.type // empty' 2>/dev/null)
     [ "$type" = "BeadReady" ] || continue
 
@@ -43,4 +43,4 @@ EXPECTED_SOURCE="beads/$MOUNT"
     # Emit full bead data and exit
     echo "$line" | jq '.data'
     exit 0
-done
+done < <(9p read anvillm/events)