beads: add wait_for_bead.sh event-driven work discovery

Blocks on anvillm/events, filters BeadReady for matching mount and role,
emits full bead JSON (including comments) and exits. Zero polling, zero
context cost, no supervisor needed for work assignment.

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

mcptools/wait_for_bead.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+# capabilities: beads
+# description: Block until a bead matching --mount and --role is ready, then print its full JSON (including comments) and exit. Uses the anvillm/events stream — no polling.
+# Usage: wait_for_bead.sh --mount <mount> [--role <role>]
+set -euo pipefail
+
+MOUNT=""
+ROLE="${AGENT_ROLE:-developer}"
+
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --mount) MOUNT="$2"; shift 2 ;;
+        --role)  ROLE="$2";  shift 2 ;;
+        *) echo "unknown argument: $1" >&2; exit 1 ;;
+    esac
+done
+
+if [ -z "$MOUNT" ]; then
+    echo "usage: wait_for_bead.sh --mount <mount> [--role <role>]" >&2
+    exit 1
+fi
+
+EXPECTED_SOURCE="beads/$MOUNT"
+
+9p read anvillm/events | while IFS= read -r line; do
+    type=$(echo "$line" | jq -r '.type // empty' 2>/dev/null)
+    [ "$type" = "BeadReady" ] || continue
+
+    source=$(echo "$line" | jq -r '.source // empty' 2>/dev/null)
+    [ "$source" = "$EXPECTED_SOURCE" ] || continue
+
+    # Check role label matches (format: "role:<role>")
+    bead_role=$(echo "$line" | jq -r '
+        .data.labels // [] |
+        map(select(startswith("role:"))) |
+        first // "" |
+        ltrimstr("role:")
+    ' 2>/dev/null)
+    # Default to "developer" if no role label
+    [ -z "$bead_role" ] && bead_role="developer"
+    [ "$bead_role" = "$ROLE" ] || continue
+
+    # Emit full bead data and exit
+    echo "$line" | jq '.data'
+    exit 0
+done

skills/beads/SKILL.md

@@ -38,6 +38,14 @@ Tool: execute_code
 tool: list_mounts.sh
 ```
 
+Wait for a bead matching your mount and role (blocks until one is ready, returns full bead JSON including comments, then exits):
+```
+Tool: execute_code
+tool: wait_for_bead.sh
+args: ["--mount", "<mount>"]
+```
+`--role <role>` is optional; defaults to `$AGENT_ROLE` or `developer`.
+
 List ready beads (open, unblocked):
 ```
 Tool: execute_code