fix: syncDirectory — guard same-path copy and skip nested .git dirs

Two bugs causing 'EACCES: permission denied, copyfile' when source
and target are the same path (e.g. wizard with sourceDir == mosaicHome):

1. No same-path guard — syncDirectory tried to copy every file onto
   itself; git pack files are read-only (0444) so copyFileSync fails.
2. excludeGit only matched top-level .git — nested .git dirs like
   sources/agent-skills/.git were copied, hitting the same permission
   issue.

Fixes:
- Early return when resolve(source) === resolve(target)
- Match .git dirs at any depth via dirName and relPath checks
- Skip files inside .git/ paths

Added file-ops.test.ts with 4 tests covering all cases.

packages/mosaic/__tests__/platform/file-ops.test.ts

@@ -0,0 +1,88 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import {
+  mkdtempSync,
+  mkdirSync,
+  writeFileSync,
+  readFileSync,
+  existsSync,
+  chmodSync,
+  rmSync,
+} from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+import { syncDirectory } from '../../src/platform/file-ops.js';
+
+describe('syncDirectory', () => {
+  let tmpDir: string;
+
+  beforeEach(() => {
+    tmpDir = mkdtempSync(join(tmpdir(), 'mosaic-file-ops-'));
+  });
+
+  afterEach(() => {
+    rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('is a no-op when source and target are the same path', () => {
+    const dir = join(tmpDir, 'same');
+    mkdirSync(dir, { recursive: true });
+    writeFileSync(join(dir, 'file.txt'), 'hello');
+    // Should not throw even with read-only files
+    const gitDir = join(dir, '.git', 'objects', 'pack');
+    mkdirSync(gitDir, { recursive: true });
+    const packFile = join(gitDir, 'pack-abc.idx');
+    writeFileSync(packFile, 'data');
+    chmodSync(packFile, 0o444);
+
+    expect(() => syncDirectory(dir, dir)).not.toThrow();
+  });
+
+  it('skips nested .git directories when excludeGit is true', () => {
+    const src = join(tmpDir, 'src');
+    const dest = join(tmpDir, 'dest');
+
+    // Create source with a nested .git
+    mkdirSync(join(src, 'sources', 'skills', '.git', 'objects'), { recursive: true });
+    writeFileSync(join(src, 'sources', 'skills', '.git', 'objects', 'pack.idx'), 'git-data');
+    writeFileSync(join(src, 'sources', 'skills', 'SKILL.md'), 'skill content');
+    writeFileSync(join(src, 'README.md'), 'readme');
+
+    syncDirectory(src, dest, { excludeGit: true });
+
+    // .git contents should NOT be copied
+    expect(existsSync(join(dest, 'sources', 'skills', '.git'))).toBe(false);
+    // Normal files should be copied
+    expect(readFileSync(join(dest, 'sources', 'skills', 'SKILL.md'), 'utf-8')).toBe(
+      'skill content',
+    );
+    expect(readFileSync(join(dest, 'README.md'), 'utf-8')).toBe('readme');
+  });
+
+  it('copies nested .git directories when excludeGit is false', () => {
+    const src = join(tmpDir, 'src');
+    const dest = join(tmpDir, 'dest');
+
+    mkdirSync(join(src, 'sub', '.git'), { recursive: true });
+    writeFileSync(join(src, 'sub', '.git', 'HEAD'), 'ref: refs/heads/main');
+
+    syncDirectory(src, dest, { excludeGit: false });
+
+    expect(readFileSync(join(dest, 'sub', '.git', 'HEAD'), 'utf-8')).toBe('ref: refs/heads/main');
+  });
+
+  it('respects preserve option', () => {
+    const src = join(tmpDir, 'src');
+    const dest = join(tmpDir, 'dest');
+
+    mkdirSync(src, { recursive: true });
+    mkdirSync(dest, { recursive: true });
+    writeFileSync(join(src, 'SOUL.md'), 'new soul');
+    writeFileSync(join(dest, 'SOUL.md'), 'old soul');
+    writeFileSync(join(src, 'README.md'), 'new readme');
+
+    syncDirectory(src, dest, { preserve: ['SOUL.md'] });
+
+    expect(readFileSync(join(dest, 'SOUL.md'), 'utf-8')).toBe('old soul');
+    expect(readFileSync(join(dest, 'README.md'), 'utf-8')).toBe('new readme');
+  });
+});