Add symlink watcher support with tests

- syncCreate: remove existing file before creating symlink
- syncWrite: handle symlink target changes (remove + recreate)
- Added 4 new tests:
  - CreateSymlink: new symlink synced to /data
  - UpdateSymlinkTarget: symlink target change updates /data
  - RemoveSymlink: symlink removal synced
  - ModifySymlinkTargetFile: target file change preserves symlink
- 39 tests passing

2 files changed, 165 insertions, 0 deletions

diff --git a/watcher.go b/watcher.go
index 192b61b..d2a98e9 100644
--- a/watcher.go
+++ b/watcher.go
@@ -138,6 +138,7 @@ func syncCreate(srcPath, destPath, relPath string, manifest *Manifest, stack *Gi
 	}
 
 	os.MkdirAll(filepath.Dir(destPath), 0755)
+	os.Remove(destPath)
 
 	if linkTarget != "" {
 		if err := os.Symlink(linkTarget, destPath); err != nil {
@@ -166,10 +167,16 @@ func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun, ve
 		return
 	}
 
+	linkTarget := ""
+	if info.Mode()&os.ModeSymlink != 0 {
+		linkTarget, _ = os.Readlink(srcPath)
+	}
+
 	manifest.Files[relPath] = FileMeta{
 		Size:    info.Size(),
 		Mode:    info.Mode(),
 		ModTime: info.ModTime(),
+		Symlink: linkTarget,
 	}
 
 	if dryRun {
@@ -177,6 +184,15 @@ func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun, ve
 		return
 	}
 
+	os.Remove(destPath)
+
+	if linkTarget != "" {
+		if err := os.Symlink(linkTarget, destPath); err != nil {
+			log.Printf("error creating symlink %s: %v", relPath, err)
+		}
+		return
+	}
+
 	if err := copyFile(srcPath, destPath, info.Mode()); err != nil {
 		log.Printf("error copying %s: %v", relPath, err)
 	}
diff --git a/watcher_test.go b/watcher_test.go
index db0defb..8fac419 100644
--- a/watcher_test.go
+++ b/watcher_test.go
@@ -318,6 +318,155 @@ func TestWatcher_NestedGitignore_CreateUnignore(t *testing.T) {
 	assertFileEventually(t, data, "sub/important.txt", "keep me", 2*time.Second)
 }
 
+func TestWatcher_CreateSymlink(t *testing.T) {
+	host := t.TempDir()
+	data := t.TempDir()
+
+	writeFile(t, host, "target.txt", "target content")
+
+	stack := NewGitignoreStack(host)
+	manifest, err := initialSync(host, data, stack, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go watch(ctx, host, data, manifest, stack, false, false)
+
+	time.Sleep(100 * time.Millisecond)
+
+	if err := os.Symlink("target.txt", filepath.Join(host, "link.txt")); err != nil {
+		t.Fatal(err)
+	}
+
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		info, err := os.Lstat(filepath.Join(data, "link.txt"))
+		if err == nil && info.Mode()&os.ModeSymlink != 0 {
+			target, _ := os.Readlink(filepath.Join(data, "link.txt"))
+			if target == "target.txt" {
+				return
+			}
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	t.Error("symlink not created in /data within timeout")
+}
+
+func TestWatcher_UpdateSymlinkTarget(t *testing.T) {
+	host := t.TempDir()
+	data := t.TempDir()
+
+	writeFile(t, host, "v1.txt", "version 1")
+	writeFile(t, host, "v2.txt", "version 2")
+	if err := os.Symlink("v1.txt", filepath.Join(host, "link.txt")); err != nil {
+		t.Fatal(err)
+	}
+
+	stack := NewGitignoreStack(host)
+	manifest, err := initialSync(host, data, stack, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Verify initial symlink
+	linkInfo, err := os.Lstat(filepath.Join(data, "link.txt"))
+	if err != nil || linkInfo.Mode()&os.ModeSymlink == 0 {
+		t.Fatal("initial symlink not created")
+	}
+	target, _ := os.Readlink(filepath.Join(data, "link.txt"))
+	if target != "v1.txt" {
+		t.Fatalf("initial symlink target = %q, want %q", target, "v1.txt")
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go watch(ctx, host, data, manifest, stack, false, false)
+
+	time.Sleep(100 * time.Millisecond)
+
+	// Update symlink to point to v2.txt
+	os.Remove(filepath.Join(host, "link.txt"))
+	os.Symlink("v2.txt", filepath.Join(host, "link.txt"))
+
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		info, err := os.Lstat(filepath.Join(data, "link.txt"))
+		if err == nil && info.Mode()&os.ModeSymlink != 0 {
+			tgt, _ := os.Readlink(filepath.Join(data, "link.txt"))
+			if tgt == "v2.txt" {
+				return
+			}
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	t.Error("symlink target not updated within timeout")
+}
+
+func TestWatcher_RemoveSymlink(t *testing.T) {
+	host := t.TempDir()
+	data := t.TempDir()
+
+	writeFile(t, host, "target.txt", "content")
+	if err := os.Symlink("target.txt", filepath.Join(host, "link.txt")); err != nil {
+		t.Fatal(err)
+	}
+
+	stack := NewGitignoreStack(host)
+	manifest, err := initialSync(host, data, stack, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go watch(ctx, host, data, manifest, stack, false, false)
+
+	time.Sleep(100 * time.Millisecond)
+
+	os.Remove(filepath.Join(host, "link.txt"))
+
+	assertFileRemovedEventually(t, data, "link.txt", 2*time.Second)
+}
+
+func TestWatcher_ModifySymlinkTargetFile(t *testing.T) {
+	host := t.TempDir()
+	data := t.TempDir()
+
+	writeFile(t, host, "target.txt", "original")
+	if err := os.Symlink("target.txt", filepath.Join(host, "link.txt")); err != nil {
+		t.Fatal(err)
+	}
+
+	stack := NewGitignoreStack(host)
+	manifest, err := initialSync(host, data, stack, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go watch(ctx, host, data, manifest, stack, false, false)
+
+	time.Sleep(100 * time.Millisecond)
+
+	// Modify the target file, not the symlink itself
+	writeFile(t, host, "target.txt", "modified")
+
+	// The symlink should still exist and point to the target
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		info, err := os.Lstat(filepath.Join(data, "link.txt"))
+		if err == nil && info.Mode()&os.ModeSymlink != 0 {
+			// Symlink still exists, which is correct
+			return
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	t.Error("symlink lost after target file modification")
+}
+
 // Helpers
 
 func assertFileEventually(t *testing.T, dir, path, expectedContent string, timeout time.Duration) {