feat: delegate plugin protocols in get_store_spec()

When a store config uses an unrecognised protocol, settings.py now
queries the adapter registry before raising an error. Registered
plugin adapters are validated and default keys are applied; unknown
protocols surface a clear message directing users to install a plugin
package. Includes new test class TestGetStoreSpecPluginDelegation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kushalbakshi

src/datajoint/settings.py

@@ -434,10 +434,31 @@ def get_store_spec(self, store: str | None = None, *, use_filepath_default: bool
         protocol = spec.get("protocol", "").lower()
         supported_protocols = ("file", "s3", "gcs", "azure")
         if protocol not in supported_protocols:
-            raise DataJointError(
-                f'Missing or invalid protocol in config.stores["{store}"]. '
-                f"Supported protocols: {', '.join(supported_protocols)}"
+            from .storage_adapter import get_storage_adapter
+
+            adapter = get_storage_adapter(protocol)
+            if adapter is None:
+                raise DataJointError(
+                    f'Unknown protocol "{protocol}" in config.stores["{store}"]. '
+                    f"Built-in: {', '.join(supported_protocols)}. "
+                    f"Install a plugin package for additional protocols."
+                )
+            # Apply common defaults for plugin protocols
+            spec.setdefault("subfolding", None)
+            spec.setdefault("partition_pattern", None)
+            spec.setdefault("token_length", 8)
+            spec.setdefault("hash_prefix", "_hash")
+            spec.setdefault("schema_prefix", "_schema")
+            spec.setdefault("filepath_prefix", None)
+            spec.setdefault("location", "")
+            adapter.validate_spec(spec)
+            self._validate_prefix_separation(
+                store_name=store,
+                hash_prefix=spec.get("hash_prefix"),
+                schema_prefix=spec.get("schema_prefix"),
+                filepath_prefix=spec.get("filepath_prefix"),
             )
+            return spec
 
         # Set protocol-specific defaults
         if protocol == "s3":

tests/unit/test_storage_adapter.py

@@ -103,3 +103,43 @@ def setup_method(self):
 
     def test_default_url_format(self):
         assert self.adapter.get_url({}, "data/file.dat") == "dummy://data/file.dat"
+
+
+import datajoint as dj
+
+
+class TestGetStoreSpecPluginDelegation:
+    """Tests for plugin protocol handling in Config.get_store_spec()."""
+
+    def setup_method(self):
+        import datajoint.storage_adapter as sa_mod
+
+        sa_mod._adapter_registry["dummy"] = _DummyAdapter()
+        self._original_stores = dj.config.stores.copy()
+
+    def teardown_method(self):
+        import datajoint.storage_adapter as sa_mod
+
+        sa_mod._adapter_registry.pop("dummy", None)
+        dj.config.stores = self._original_stores
+
+    def test_plugin_protocol_accepted(self):
+        """Plugin protocol passes validation via adapter."""
+        dj.config.stores["test_store"] = {
+            "protocol": "dummy",
+            "endpoint": "https://example.com",
+            "location": "",
+            "hash_prefix": "_hash",
+            "schema_prefix": "_schema",
+        }
+        spec = dj.config.get_store_spec("test_store")
+        assert spec["protocol"] == "dummy"
+
+    def test_unknown_protocol_error_message(self):
+        """Unknown protocol gives clear error mentioning plugin installation."""
+        dj.config.stores["bad_store"] = {
+            "protocol": "nonexistent_xyz",
+            "location": "",
+        }
+        with pytest.raises(DataJointError, match="Install a plugin"):
+            dj.config.get_store_spec("bad_store")