Feat v0.8.0 files sandbox module

Bridge ObjectStore (PVC/S3) into the Starlark sandbox with extension-scoped
key namespacing. New files module with put/get/meta/list/delete/exists
builtins gated by files.read and files.write permissions.

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

server/storage/pvc.go

@@ -211,6 +211,78 @@ func (s *PVCStore) Exists(ctx context.Context, key string) (bool, error) {
 	return false, fmt.Errorf("storage/pvc: exists %q: %w", key, err)
 }
 
+// List returns objects under the given prefix, up to limit entries.
+func (s *PVCStore) List(ctx context.Context, prefix string, limit int) ([]ObjectEntry, error) {
+	if prefix != "" {
+		if err := validateKey(prefix); err != nil {
+			return nil, err
+		}
+	}
+	if limit <= 0 {
+		limit = 100
+	}
+
+	absPrefix := s.resolve(prefix)
+
+	// If the prefix path doesn't exist, return empty.
+	info, err := os.Stat(absPrefix)
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("storage/pvc: list %q: %w", prefix, err)
+	}
+
+	var entries []ObjectEntry
+
+	if !info.IsDir() {
+		// Prefix points to a single file — return it.
+		s.mu.RLock()
+		ct := s.mimeMap[prefix]
+		s.mu.RUnlock()
+		if ct == "" {
+			ct = "application/octet-stream"
+		}
+		return []ObjectEntry{{Key: prefix, Size: info.Size(), ContentType: ct}}, nil
+	}
+
+	// Walk the directory tree under the prefix.
+	walkRoot := absPrefix
+	err = filepath.Walk(walkRoot, func(path string, fi os.FileInfo, walkErr error) error {
+		if walkErr != nil {
+			return nil // skip inaccessible entries
+		}
+		if fi.IsDir() {
+			return nil
+		}
+		if len(entries) >= limit {
+			return filepath.SkipAll
+		}
+
+		// Recover the storage key by stripping basePath + "/".
+		rel, relErr := filepath.Rel(s.basePath, path)
+		if relErr != nil {
+			return nil
+		}
+		key := filepath.ToSlash(rel)
+
+		s.mu.RLock()
+		ct := s.mimeMap[key]
+		s.mu.RUnlock()
+		if ct == "" {
+			ct = "application/octet-stream"
+		}
+
+		entries = append(entries, ObjectEntry{Key: key, Size: fi.Size(), ContentType: ct})
+		return nil
+	})
+	if err != nil {
+		return entries, fmt.Errorf("storage/pvc: list walk %q: %w", prefix, err)
+	}
+
+	return entries, nil
+}
+
 // Healthy verifies the storage path is writable.
 func (s *PVCStore) Healthy(ctx context.Context) error {
 	probe := filepath.Join(s.basePath, ".health-probe")