Step 21: Lock/unlock toggle commands.

garden/lock.go: Lock() and Unlock() toggle the locked flag on
existing tracked entries. Errors on untracked paths. Persists
to manifest.

cmd/sgard/lock.go: sgard lock <path>..., sgard unlock <path>...

6 tests: lock/unlock existing entry, persistence, error on untracked,
checkpoint behavior changes after lock, status changes between
drifted and modified after unlock.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

garden/lock_test.go

@@ -0,0 +1,197 @@
+package garden
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLockExistingEntry(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	testFile := filepath.Join(root, "testfile")
+	if err := os.WriteFile(testFile, []byte("data"), 0o644); err != nil {
+		t.Fatalf("writing: %v", err)
+	}
+
+	// Add without lock.
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	if g.manifest.Files[0].Locked {
+		t.Fatal("should not be locked initially")
+	}
+
+	// Lock it.
+	if err := g.Lock([]string{testFile}); err != nil {
+		t.Fatalf("Lock: %v", err)
+	}
+
+	if !g.manifest.Files[0].Locked {
+		t.Error("should be locked after Lock()")
+	}
+
+	// Verify persisted.
+	g2, err := Open(repoDir)
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	if !g2.manifest.Files[0].Locked {
+		t.Error("locked state should persist")
+	}
+}
+
+func TestUnlockExistingEntry(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	testFile := filepath.Join(root, "testfile")
+	if err := os.WriteFile(testFile, []byte("data"), 0o644); err != nil {
+		t.Fatalf("writing: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}, AddOptions{Lock: true}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	if !g.manifest.Files[0].Locked {
+		t.Fatal("should be locked")
+	}
+
+	if err := g.Unlock([]string{testFile}); err != nil {
+		t.Fatalf("Unlock: %v", err)
+	}
+
+	if g.manifest.Files[0].Locked {
+		t.Error("should not be locked after Unlock()")
+	}
+}
+
+func TestLockUntrackedErrors(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	testFile := filepath.Join(root, "nottracked")
+	if err := os.WriteFile(testFile, []byte("data"), 0o644); err != nil {
+		t.Fatalf("writing: %v", err)
+	}
+
+	if err := g.Lock([]string{testFile}); err == nil {
+		t.Fatal("Lock on untracked path should error")
+	}
+}
+
+func TestLockChangesCheckpointBehavior(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	testFile := filepath.Join(root, "testfile")
+	if err := os.WriteFile(testFile, []byte("original"), 0o644); err != nil {
+		t.Fatalf("writing: %v", err)
+	}
+
+	// Add unlocked, checkpoint picks up changes.
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	origHash := g.manifest.Files[0].Hash
+
+	if err := os.WriteFile(testFile, []byte("changed"), 0o644); err != nil {
+		t.Fatalf("modifying: %v", err)
+	}
+
+	if err := g.Checkpoint(""); err != nil {
+		t.Fatalf("Checkpoint: %v", err)
+	}
+
+	if g.manifest.Files[0].Hash == origHash {
+		t.Fatal("unlocked file: checkpoint should update hash")
+	}
+
+	newHash := g.manifest.Files[0].Hash
+
+	// Now lock it and modify again — checkpoint should NOT update.
+	if err := g.Lock([]string{testFile}); err != nil {
+		t.Fatalf("Lock: %v", err)
+	}
+
+	if err := os.WriteFile(testFile, []byte("system overwrote"), 0o644); err != nil {
+		t.Fatalf("overwriting: %v", err)
+	}
+
+	if err := g.Checkpoint(""); err != nil {
+		t.Fatalf("Checkpoint: %v", err)
+	}
+
+	if g.manifest.Files[0].Hash != newHash {
+		t.Error("locked file: checkpoint should not update hash")
+	}
+}
+
+func TestUnlockChangesStatusBehavior(t *testing.T) {
+	root := t.TempDir()
+	repoDir := filepath.Join(root, "repo")
+
+	g, err := Init(repoDir)
+	if err != nil {
+		t.Fatalf("Init: %v", err)
+	}
+
+	testFile := filepath.Join(root, "testfile")
+	if err := os.WriteFile(testFile, []byte("original"), 0o644); err != nil {
+		t.Fatalf("writing: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}, AddOptions{Lock: true}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	if err := os.WriteFile(testFile, []byte("changed"), 0o644); err != nil {
+		t.Fatalf("modifying: %v", err)
+	}
+
+	// Locked: should be "drifted".
+	statuses, err := g.Status()
+	if err != nil {
+		t.Fatalf("Status: %v", err)
+	}
+	if statuses[0].State != "drifted" {
+		t.Errorf("locked: expected drifted, got %s", statuses[0].State)
+	}
+
+	// Unlock: should now be "modified".
+	if err := g.Unlock([]string{testFile}); err != nil {
+		t.Fatalf("Unlock: %v", err)
+	}
+
+	statuses, err = g.Status()
+	if err != nil {
+		t.Fatalf("Status: %v", err)
+	}
+	if statuses[0].State != "modified" {
+		t.Errorf("unlocked: expected modified, got %s", statuses[0].State)
+	}
+}