Add verify command to check blob store integrity.

Verify iterates manifest file entries, confirms each blob exists in the
store, and re-hashes the content to detect corruption. Includes unit
tests for the ok, hash-mismatch, and blob-missing cases, plus a thin
CLI wrapper that exits non-zero on any failure.

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

garden/verify_test.go

@@ -0,0 +1,126 @@
+package garden
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestVerifyAllOK(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("hello world\n"), 0o644); err != nil {
+		t.Fatalf("writing test file: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	results, err := g.Verify()
+	if err != nil {
+		t.Fatalf("Verify: %v", err)
+	}
+
+	if len(results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(results))
+	}
+
+	if !results[0].OK {
+		t.Errorf("expected OK, got %s", results[0].Detail)
+	}
+	if results[0].Detail != "ok" {
+		t.Errorf("expected detail 'ok', got %q", results[0].Detail)
+	}
+}
+
+func TestVerifyHashMismatch(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("hello world\n"), 0o644); err != nil {
+		t.Fatalf("writing test file: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	// Corrupt the blob on disk.
+	hash := g.manifest.Files[0].Hash
+	blobPath := filepath.Join(repoDir, "blobs", hash[:2], hash[2:4], hash)
+	if err := os.WriteFile(blobPath, []byte("corrupted data"), 0o644); err != nil {
+		t.Fatalf("corrupting blob: %v", err)
+	}
+
+	results, err := g.Verify()
+	if err != nil {
+		t.Fatalf("Verify: %v", err)
+	}
+
+	if len(results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(results))
+	}
+
+	if results[0].OK {
+		t.Error("expected not OK for corrupted blob")
+	}
+	if results[0].Detail != "hash mismatch" {
+		t.Errorf("expected detail 'hash mismatch', got %q", results[0].Detail)
+	}
+}
+
+func TestVerifyBlobMissing(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("hello world\n"), 0o644); err != nil {
+		t.Fatalf("writing test file: %v", err)
+	}
+
+	if err := g.Add([]string{testFile}); err != nil {
+		t.Fatalf("Add: %v", err)
+	}
+
+	// Delete the blob from disk.
+	hash := g.manifest.Files[0].Hash
+	blobPath := filepath.Join(repoDir, "blobs", hash[:2], hash[2:4], hash)
+	if err := os.Remove(blobPath); err != nil {
+		t.Fatalf("removing blob: %v", err)
+	}
+
+	results, err := g.Verify()
+	if err != nil {
+		t.Fatalf("Verify: %v", err)
+	}
+
+	if len(results) != 1 {
+		t.Fatalf("expected 1 result, got %d", len(results))
+	}
+
+	if results[0].OK {
+		t.Error("expected not OK for missing blob")
+	}
+	if results[0].Detail != "blob missing" {
+		t.Errorf("expected detail 'blob missing', got %q", results[0].Detail)
+	}
+}