feat: add structured prompt invocation backend

- parse prompt tools metadata and carry structured promptInvocation payloads
- store prompt invocation metadata on trigger messages for replay-safe reruns
- route prompt agents through per-turn plan or Copilot agent overrides
- restrict prompt-scoped tools in sidecar session configuration
- auto-rescan project customization files with debounced watchers
- document the new customization watcher and prompt invocation flow

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/main/projectCustomizationWatcher.test.ts

@@ -0,0 +1,80 @@
+import { afterEach, describe, expect, mock, test } from 'bun:test';
+import { mkdir, mkdtemp, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+import {
+  collectProjectCustomizationWatchPaths,
+  ProjectCustomizationWatcher,
+} from '@main/services/projectCustomizationWatcher';
+
+const temporaryPaths: string[] = [];
+
+afterEach(async () => {
+  await Promise.all(
+    temporaryPaths.splice(0).map((path) => rm(path, { recursive: true, force: true })),
+  );
+});
+
+async function createTempDirectory(): Promise<string> {
+  const directory = await mkdtemp(join(tmpdir(), 'aryx-customization-watcher-'));
+  temporaryPaths.push(directory);
+  return directory;
+}
+
+describe('ProjectCustomizationWatcher', () => {
+  test('collects the project root plus existing customization directories recursively', async () => {
+    const projectPath = await createTempDirectory();
+    await mkdir(join(projectPath, '.claude', 'rules'), { recursive: true });
+    await mkdir(join(projectPath, '.github', 'prompts', 'docs'), { recursive: true });
+
+    expect(await collectProjectCustomizationWatchPaths(projectPath)).toEqual([
+      projectPath,
+      join(projectPath, '.claude'),
+      join(projectPath, '.claude', 'rules'),
+      join(projectPath, '.github'),
+      join(projectPath, '.github', 'prompts'),
+      join(projectPath, '.github', 'prompts', 'docs'),
+    ]);
+  });
+
+  test('debounces change notifications and closes watches when projects are removed', async () => {
+    const changeCalls: string[] = [];
+    const closeByPath = new Map<string, ReturnType<typeof mock>>();
+    const listenersByPath = new Map<string, () => void>();
+    const watcher = new ProjectCustomizationWatcher(
+      async (projectId) => {
+        changeCalls.push(projectId);
+      },
+      {
+        debounceMs: 20,
+        resolveWatchPaths: async (projectPath) => [projectPath, `${projectPath}\\.github`],
+        watchFactory: (directoryPath, onChange) => {
+          const close = mock(() => undefined);
+          closeByPath.set(directoryPath, close);
+          listenersByPath.set(directoryPath, onChange);
+          return { close };
+        },
+      },
+    );
+
+    await watcher.syncProjects([
+      {
+        id: 'project-alpha',
+        path: 'C:\\workspace\\alpha',
+      },
+    ]);
+
+    listenersByPath.get('C:\\workspace\\alpha')?.();
+    listenersByPath.get('C:\\workspace\\alpha\\.github')?.();
+
+    await new Promise((resolve) => setTimeout(resolve, 60));
+
+    expect(changeCalls).toEqual(['project-alpha']);
+
+    await watcher.syncProjects([]);
+
+    expect(closeByPath.get('C:\\workspace\\alpha')).toHaveBeenCalled();
+    expect(closeByPath.get('C:\\workspace\\alpha\\.github')).toHaveBeenCalled();
+  });
+});