feat(storage): resolve portable workspace roots

harness/tht/config.py

@@ -254,6 +254,26 @@ def load_config(path: Path) -> Config:
         raise ConfigError(
             f"transport: rest richiede la sezione `rest` (base_url, api_key) in {path}."
         )
+    data_root = os.environ.get("THT_DATA_ROOT")
+    if data_root:
+        # Import locally: paths owns resolution, while ConfigError remains the public
+        # configuration exception callers already handle.
+        from tht.paths import resolve_workspace_paths
+
+        resolved = resolve_workspace_paths(path, cfg, Path(data_root))
+        cfg = cfg.model_copy(
+            update={
+                "paths": PathsConfig(
+                    sessions=resolved.sessions,
+                    artifacts=resolved.artifacts,
+                    indexes=resolved.indexes,
+                )
+            }
+        )
+    elif not used_legacy:
+        # Modern `roots` replace `paths`; without a mounted data root retain the old
+        # working-directory-relative behavior used by local development.
+        cfg = cfg.model_copy(update={"paths": PathsConfig(**cfg.roots.model_dump())})
     if used_legacy:
         warnings.warn(
             "DEPRECATION: legacy workspace resource keys are deprecated; "