feat: add /update skill for pulling upstream changes (#372)

Interactive skill that guides Claude through fetching upstream NanoClaw,
previewing changes, merging with customizations, running migrations, and
verifying the result. Includes:

- SKILL.md with 9-step update flow
- fetch-upstream.sh: detects remote, fetches, extracts tracked paths
- run-migrations.ts: discovers and runs version-ordered migrations
- post-update.ts: clears backup after conflict resolution
- update-core.ts: adds --json and --preview-only flags
- BASE_INCLUDES moved to constants.ts as single source of truth
- 16 new tests covering fetch, migrations, and CLI flags

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

skills-engine/__tests__/update-core-cli.test.ts

@@ -0,0 +1,131 @@
+import { execFileSync } from 'child_process';
+import fs from 'fs';
+import path from 'path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { stringify } from 'yaml';
+
+import { cleanup, createTempDir, initGitRepo, setupNanoclawDir } from './test-helpers.js';
+
+describe('update-core.ts CLI flags', () => {
+  let tmpDir: string;
+  const scriptPath = path.resolve('scripts/update-core.ts');
+  const tsxBin = path.resolve('node_modules/.bin/tsx');
+
+  beforeEach(() => {
+    tmpDir = createTempDir();
+    setupNanoclawDir(tmpDir);
+    initGitRepo(tmpDir);
+
+    // Write state file
+    const statePath = path.join(tmpDir, '.nanoclaw', 'state.yaml');
+    fs.writeFileSync(
+      statePath,
+      stringify({
+        skills_system_version: '0.1.0',
+        core_version: '1.0.0',
+        applied_skills: [],
+      }),
+    );
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  function createNewCore(files: Record<string, string>): string {
+    const dir = path.join(tmpDir, 'new-core');
+    fs.mkdirSync(dir, { recursive: true });
+    for (const [relPath, content] of Object.entries(files)) {
+      const fullPath = path.join(dir, relPath);
+      fs.mkdirSync(path.dirname(fullPath), { recursive: true });
+      fs.writeFileSync(fullPath, content);
+    }
+    return dir;
+  }
+
+  it('--json --preview-only outputs JSON preview without applying', () => {
+    const baseDir = path.join(tmpDir, '.nanoclaw', 'base');
+    fs.mkdirSync(path.join(baseDir, 'src'), { recursive: true });
+    fs.writeFileSync(path.join(baseDir, 'src/index.ts'), 'original');
+
+    fs.mkdirSync(path.join(tmpDir, 'src'), { recursive: true });
+    fs.writeFileSync(path.join(tmpDir, 'src/index.ts'), 'original');
+
+    const newCoreDir = createNewCore({
+      'src/index.ts': 'updated',
+      'package.json': JSON.stringify({ version: '2.0.0' }),
+    });
+
+    const stdout = execFileSync(
+      tsxBin,
+      [scriptPath, '--json', '--preview-only', newCoreDir],
+      { cwd: tmpDir, encoding: 'utf-8', stdio: 'pipe', timeout: 30_000 },
+    );
+
+    const preview = JSON.parse(stdout);
+
+    expect(preview.currentVersion).toBe('1.0.0');
+    expect(preview.newVersion).toBe('2.0.0');
+    expect(preview.filesChanged).toContain('src/index.ts');
+
+    // File should NOT have been modified (preview only)
+    expect(fs.readFileSync(path.join(tmpDir, 'src/index.ts'), 'utf-8')).toBe(
+      'original',
+    );
+  });
+
+  it('--preview-only without --json outputs human-readable text', () => {
+    const newCoreDir = createNewCore({
+      'src/new-file.ts': 'export const x = 1;',
+      'package.json': JSON.stringify({ version: '2.0.0' }),
+    });
+
+    const stdout = execFileSync(
+      tsxBin,
+      [scriptPath, '--preview-only', newCoreDir],
+      { cwd: tmpDir, encoding: 'utf-8', stdio: 'pipe', timeout: 30_000 },
+    );
+
+    expect(stdout).toContain('Update Preview');
+    expect(stdout).toContain('2.0.0');
+    // Should NOT contain JSON (it's human-readable mode)
+    expect(stdout).not.toContain('"currentVersion"');
+  });
+
+  it('--json applies and outputs JSON result', () => {
+    fs.mkdirSync(path.join(tmpDir, 'src'), { recursive: true });
+    fs.writeFileSync(path.join(tmpDir, 'src/index.ts'), 'original');
+
+    const newCoreDir = createNewCore({
+      'src/index.ts': 'original',
+      'package.json': JSON.stringify({ version: '2.0.0' }),
+    });
+
+    const stdout = execFileSync(
+      tsxBin,
+      [scriptPath, '--json', newCoreDir],
+      { cwd: tmpDir, encoding: 'utf-8', stdio: 'pipe', timeout: 30_000 },
+    );
+
+    const result = JSON.parse(stdout);
+
+    expect(result.success).toBe(true);
+    expect(result.previousVersion).toBe('1.0.0');
+    expect(result.newVersion).toBe('2.0.0');
+  });
+
+  it('exits with error when no path provided', () => {
+    try {
+      execFileSync(tsxBin, [scriptPath], {
+        cwd: tmpDir,
+        encoding: 'utf-8',
+        stdio: 'pipe',
+        timeout: 30_000,
+      });
+      expect.unreachable('Should have exited with error');
+    } catch (err: any) {
+      expect(err.status).toBe(1);
+      expect(err.stderr).toContain('Usage');
+    }
+  });
+});