feat: support metta://policy/<short_name_or_class_path> URIs for built-in policies

Author: daveey

CLAUDE.md

@@ -54,3 +54,7 @@ Internal `metta/` folder dependencies are enforced by `import-linter`. Run `uv r
 ```
 
 See `common/src/metta/common/tool/README.md` for details.
+
+## Git Hub Integration
+
+Use graphite ("gt") to create PRs. Name the branch $user-short-issue-name

metta/rl/metta_scheme_resolver.py

@@ -7,6 +7,8 @@
 from metta.app_backend.clients.stats_client import StatsClient
 from metta.app_backend.metta_repo import PolicyVersionWithName
 from metta.common.util.constants import PROD_STATS_SERVER_URI
+from mettagrid.policy.loader import discover_and_register_policies
+from mettagrid.policy.policy_registry import get_policy_registry
 from mettagrid.util.uri_resolvers.base import MettaParsedScheme, SchemeResolver
 from mettagrid.util.uri_resolvers.schemes import resolve_uri
 
@@ -112,7 +114,40 @@ def get_policy_version(self, uri: str) -> PolicyVersionWithName:
 
         return policy_version
 
+    def _resolve_builtin_policy_class_path(self, identifier: str) -> str | None:
+        """Resolve a policy identifier to a full class path.
+
+        Supports:
+          - Short names (e.g., "noop", "random") via the policy registry
+          - Full class paths (e.g., "mettagrid.policy.noop.NoopPolicy")
+
+        Returns the full class path if valid, None otherwise.
+        """
+        discover_and_register_policies()
+        registry = get_policy_registry()
+
+        # First check if it's a registered short name
+        if identifier in registry:
+            return registry[identifier]
+
+        # Otherwise, check if it looks like a full class path (contains dots)
+        if "." in identifier:
+            return identifier
+
+        return None
+
     def get_path_to_policy_spec_or_mpt(self, uri: str) -> str:
+        parsed = self.parse(uri)
+        path = parsed.path
+
+        # Check for built-in policy: metta://policy/<short_name_or_class_path>
+        if path.startswith("policy/"):
+            policy_identifier = path[len("policy/") :]
+            class_path = self._resolve_builtin_policy_class_path(policy_identifier)
+            if class_path:
+                logger.info(f"Metta scheme resolver: {uri} resolved to builtin policy: {class_path}")
+                return f"builtin://{class_path}"
+
         policy_version = self.get_policy_version(uri)
         # By default we send you to the s3 path that contains the policy spec
         if policy_version.s3_path:

packages/mettagrid/python/src/mettagrid/util/uri_resolvers/base.py

@@ -75,7 +75,23 @@ def checkpoint_info(self) -> tuple[str, int] | None:
         return _extract_run_and_epoch(self.path)
 
 
-ParsedScheme = Union[FileParsedScheme, S3ParsedScheme, MockParsedScheme, MettaParsedScheme]
+class BuiltinParsedScheme(BaseModel, frozen=True):
+    """Parsed scheme for built-in policies loaded by class path."""
+
+    scheme: Literal["builtin"] = "builtin"
+    canonical: str
+    class_path: str
+
+    @property
+    def local_path(self) -> None:
+        return None
+
+    @property
+    def checkpoint_info(self) -> tuple[str, int] | None:
+        return None
+
+
+ParsedScheme = Union[FileParsedScheme, S3ParsedScheme, MockParsedScheme, MettaParsedScheme, BuiltinParsedScheme]
 
 
 class SchemeResolver(ABC):

packages/mettagrid/python/src/mettagrid/util/uri_resolvers/schemes.py

@@ -9,6 +9,7 @@
 
 from mettagrid.util.module import load_symbol
 from mettagrid.util.uri_resolvers.base import (
+    BuiltinParsedScheme,
     CheckpointMetadata,
     FileParsedScheme,
     MockParsedScheme,
@@ -198,12 +199,34 @@ def parse(self, uri: str) -> MockParsedScheme:
         return MockParsedScheme(canonical=canonical, path=path)
 
 
+class BuiltinSchemeResolver(SchemeResolver):
+    """Resolves builtin:// URIs for built-in policies loaded by class path.
+
+    Supported formats:
+      - builtin://full.class.path.PolicyClass
+    """
+
+    @property
+    def scheme(self) -> str:
+        return "builtin"
+
+    def parse(self, uri: str) -> BuiltinParsedScheme:
+        if not uri.startswith("builtin://"):
+            raise ValueError(f"Expected builtin:// URI, got: {uri}")
+        class_path = uri[len("builtin://") :]
+        if not class_path:
+            raise ValueError("builtin:// URIs must include a class path")
+        canonical = f"builtin://{class_path}"
+        return BuiltinParsedScheme(canonical=canonical, class_path=class_path)
+
+
 _SCHEME_RESOLVERS: list[str] = [
     "mettagrid.util.uri_resolvers.schemes.FileSchemeResolver",
     "mettagrid.util.uri_resolvers.schemes.S3SchemeResolver",
     "mettagrid.util.uri_resolvers.schemes.HttpSchemeResolver",
     "mettagrid.util.uri_resolvers.schemes.HttpSchemeResolver",
     "mettagrid.util.uri_resolvers.schemes.MockSchemeResolver",
+    "mettagrid.util.uri_resolvers.schemes.BuiltinSchemeResolver",
     "metta.rl.metta_scheme_resolver.MettaSchemeResolver",
 ]
 
@@ -272,6 +295,10 @@ def policy_spec_from_uri(
 
     parsed = resolve_uri(uri)
 
+    # Handle built-in policies (e.g., builtin://mettagrid.policy.noop.NoopPolicy)
+    if parsed.scheme == "builtin":
+        return PolicySpec(class_path=parsed.class_path)
+
     if parsed.canonical.endswith(".mpt"):
         checkpoint_path = str(parsed.local_path) if parsed.local_path else parsed.canonical
         return PolicySpec(