fix: Add endpoints to get/list artifact version metadata

This change introduces new FastAPI endpoints in adk_web_server.py and corresponding client methods in adk_web_server_client.py to allow fetching metadata for artifact versions without downloading the artifact content

Close #3710

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 868217569

src/google/adk/cli/adk_web_server.py

@@ -1347,6 +1347,24 @@ class AdkWebServer:
         raise HTTPException(status_code=404, detail="Artifact not found")
       return artifact
 
+    @app.get(
+        "/apps/{app_name}/users/{user_id}/sessions/{session_id}/artifacts/{artifact_name}/versions/metadata",
+        response_model=list[ArtifactVersion],
+        response_model_exclude_none=True,
+    )
+    async def list_artifact_versions_metadata(
+        app_name: str,
+        user_id: str,
+        session_id: str,
+        artifact_name: str,
+    ) -> list[ArtifactVersion]:
+      return await self.artifact_service.list_artifact_versions(
+          app_name=app_name,
+          user_id=user_id,
+          session_id=session_id,
+          filename=artifact_name,
+      )
+
     @app.get(
         "/apps/{app_name}/users/{user_id}/sessions/{session_id}/artifacts/{artifact_name}/versions/{version_id}",
         response_model_exclude_none=True,
@@ -1416,6 +1434,31 @@ class AdkWebServer:
         )
       return artifact_version
 
+    @app.get(
+        "/apps/{app_name}/users/{user_id}/sessions/{session_id}/artifacts/{artifact_name}/versions/{version_id}/metadata",
+        response_model=ArtifactVersion,
+        response_model_exclude_none=True,
+    )
+    async def get_artifact_version_metadata(
+        app_name: str,
+        user_id: str,
+        session_id: str,
+        artifact_name: str,
+        version_id: int,
+    ) -> ArtifactVersion:
+      artifact_version = await self.artifact_service.get_artifact_version(
+          app_name=app_name,
+          user_id=user_id,
+          session_id=session_id,
+          filename=artifact_name,
+          version=version_id,
+      )
+      if not artifact_version:
+        raise HTTPException(
+            status_code=404, detail="Artifact version not found"
+        )
+      return artifact_version
+
     @app.get(
         "/apps/{app_name}/users/{user_id}/sessions/{session_id}/artifacts",
         response_model_exclude_none=True,

src/google/adk/cli/conformance/adk_web_server_client.py

@@ -27,6 +27,7 @@ from typing import Optional
 
 import httpx
 
+from ...artifacts.base_artifact_service import ArtifactVersion
 from ...events.event import Event
 from ...sessions.session import Session
 from ..adk_web_server import RunAgentRequest
@@ -268,3 +269,38 @@ class AdkWebServerClient:
             yield Event.model_validate(event_data)
           else:
             logger.debug("Non data line received: %s", line)
+
+  async def get_artifact_version_metadata(
+      self,
+      *,
+      app_name: str,
+      user_id: str,
+      session_id: str,
+      artifact_name: str,
+      version: int,
+  ) -> ArtifactVersion:
+    """Retrieve metadata for a specific artifact version."""
+    async with self._get_client() as client:
+      response = await client.get((
+          f"/apps/{app_name}/users/{user_id}/sessions/{session_id}"
+          f"/artifacts/{artifact_name}/versions/{version}/metadata"
+      ))
+      response.raise_for_status()
+      return ArtifactVersion.model_validate(response.json())
+
+  async def list_artifact_versions_metadata(
+      self,
+      *,
+      app_name: str,
+      user_id: str,
+      session_id: str,
+      artifact_name: str,
+  ) -> list[ArtifactVersion]:
+    """List metadata for all versions of an artifact."""
+    async with self._get_client() as client:
+      response = await client.get((
+          f"/apps/{app_name}/users/{user_id}/sessions/{session_id}"
+          f"/artifacts/{artifact_name}/versions/metadata"
+      ))
+      response.raise_for_status()
+      return [ArtifactVersion.model_validate(item) for item in response.json()]