Steps 10 & 11: Garden accessors and proto-manifest conversion.

Step 10: GetManifest, BlobExists, ReadBlob, WriteBlob, ReplaceManifest
accessor methods on Garden. 5 tests.

Step 11: ManifestToProto/ProtoToManifest conversion functions in
server package with time.Time <-> timestamppb handling. Round-trip
test covering all 3 entry types.

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

server/convert.go

@@ -0,0 +1,62 @@
+package server
+
+import (
+	"github.com/kisom/sgard/manifest"
+	"github.com/kisom/sgard/sgardpb"
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+// ManifestToProto converts a manifest.Manifest to its protobuf representation.
+func ManifestToProto(m *manifest.Manifest) *sgardpb.Manifest {
+	files := make([]*sgardpb.ManifestEntry, len(m.Files))
+	for i, e := range m.Files {
+		files[i] = EntryToProto(e)
+	}
+	return &sgardpb.Manifest{
+		Version: int32(m.Version),
+		Created: timestamppb.New(m.Created),
+		Updated: timestamppb.New(m.Updated),
+		Message: m.Message,
+		Files:   files,
+	}
+}
+
+// ProtoToManifest converts a protobuf Manifest to a manifest.Manifest.
+func ProtoToManifest(p *sgardpb.Manifest) *manifest.Manifest {
+	pFiles := p.GetFiles()
+	files := make([]manifest.Entry, len(pFiles))
+	for i, e := range pFiles {
+		files[i] = ProtoToEntry(e)
+	}
+	return &manifest.Manifest{
+		Version: int(p.GetVersion()),
+		Created: p.GetCreated().AsTime(),
+		Updated: p.GetUpdated().AsTime(),
+		Message: p.GetMessage(),
+		Files:   files,
+	}
+}
+
+// EntryToProto converts a manifest.Entry to its protobuf representation.
+func EntryToProto(e manifest.Entry) *sgardpb.ManifestEntry {
+	return &sgardpb.ManifestEntry{
+		Path:    e.Path,
+		Hash:    e.Hash,
+		Type:    e.Type,
+		Mode:    e.Mode,
+		Target:  e.Target,
+		Updated: timestamppb.New(e.Updated),
+	}
+}
+
+// ProtoToEntry converts a protobuf ManifestEntry to a manifest.Entry.
+func ProtoToEntry(p *sgardpb.ManifestEntry) manifest.Entry {
+	return manifest.Entry{
+		Path:    p.GetPath(),
+		Hash:    p.GetHash(),
+		Type:    p.GetType(),
+		Mode:    p.GetMode(),
+		Target:  p.GetTarget(),
+		Updated: p.GetUpdated().AsTime(),
+	}
+}