feat: add macOS desktop notification Stop hook

Add a new Stop hook that sends a native macOS notification with the
task summary (first line of last_assistant_message) when Claude finishes
responding. Uses osascript via spawnSync for shell injection safety.
Supports run-with-flags fast require() path. Only active on standard
and strict profiles; silently skips on non-macOS platforms.

hooks/README.md

@@ -48,6 +48,7 @@ User request → Claude picks a tool → PreToolUse hook runs → Tool executes
 | **Session summary** | `Stop` | Persists session state when transcript path is available |
 | **Pattern extraction** | `Stop` | Evaluates session for extractable patterns (continuous learning) |
 | **Cost tracker** | `Stop` | Emits lightweight run-cost telemetry markers |
+| **Desktop notify** | `Stop` | Sends macOS desktop notification with task summary (standard+) |
 | **Session end marker** | `SessionEnd` | Lifecycle marker and cleanup log |
 
 ## Customizing Hooks

hooks/hooks.json

@@ -289,6 +289,18 @@
           }
         ],
         "description": "Track token and cost metrics per session"
+      },
+      {
+        "matcher": "*",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "node \"${CLAUDE_PLUGIN_ROOT}/scripts/hooks/run-with-flags.js\" \"stop:desktop-notify\" \"scripts/hooks/desktop-notify.js\" \"standard,strict\"",
+            "async": true,
+            "timeout": 5
+          }
+        ],
+        "description": "Send macOS desktop notification with task summary when Claude responds"
       }
     ],
     "SessionEnd": [

scripts/hooks/desktop-notify.js

@@ -0,0 +1,88 @@
+#!/usr/bin/env node
+/**
+ * Desktop Notification Hook (Stop)
+ *
+ * Sends a native desktop notification with the task summary when Claude
+ * finishes responding.  Currently supports macOS (osascript); other
+ * platforms exit silently.  Windows (PowerShell) and Linux (notify-send)
+ * support is planned.
+ *
+ * Hook ID : stop:desktop-notify
+ * Profiles: standard, strict
+ */
+
+'use strict';
+
+const { spawnSync } = require('child_process');
+const { isMacOS, log } = require('../lib/utils');
+
+const TITLE = 'Claude Code';
+const MAX_BODY_LENGTH = 100;
+
+/**
+ * Extract a short summary from the last assistant message.
+ * Takes the first non-empty line and truncates to MAX_BODY_LENGTH chars.
+ */
+function extractSummary(message) {
+  if (!message || typeof message !== 'string') return 'Done';
+
+  const firstLine = message
+    .split('\n')
+    .map(l => l.trim())
+    .find(l => l.length > 0);
+
+  if (!firstLine) return 'Done';
+
+  return firstLine.length > MAX_BODY_LENGTH
+    ? `${firstLine.slice(0, MAX_BODY_LENGTH)}...`
+    : firstLine;
+}
+
+/**
+ * Send a macOS notification via osascript.
+ * Uses spawnSync with an argument array to avoid shell injection.
+ */
+function notifyMacOS(title, body) {
+  const script = `display notification ${JSON.stringify(body)} with title ${JSON.stringify(title)}`;
+  spawnSync('osascript', ['-e', script], { stdio: 'ignore', timeout: 5000 });
+}
+
+// TODO: future platform support
+// function notifyWindows(title, body) { ... }
+// function notifyLinux(title, body) { ... }
+
+/**
+ * Fast-path entry point for run-with-flags.js (avoids extra process spawn).
+ */
+function run(raw) {
+  try {
+    if (!isMacOS) return raw;
+
+    const input = raw.trim() ? JSON.parse(raw) : {};
+    const summary = extractSummary(input.last_assistant_message);
+    notifyMacOS(TITLE, summary);
+  } catch (err) {
+    log(`[DesktopNotify] Error: ${err.message}`);
+  }
+
+  return raw;
+}
+
+module.exports = { run };
+
+// Legacy stdin path (when invoked directly rather than via run-with-flags)
+if (require.main === module) {
+  const MAX_STDIN = 1024 * 1024;
+  let data = '';
+
+  process.stdin.setEncoding('utf8');
+  process.stdin.on('data', chunk => {
+    if (data.length < MAX_STDIN) {
+      data += chunk.substring(0, MAX_STDIN - data.length);
+    }
+  });
+  process.stdin.on('end', () => {
+    const output = run(data);
+    if (output) process.stdout.write(output);
+  });
+}