fix(mcp): make resources/read and resources/templates/list work

Two bugs made the Resources tab unusable in any MCP client.

read_resource returned mcp.types.TextContent, but the low-level
Server.read_resource decorator expects str, bytes or an iterable of
ReadResourceContents and reads .content / .mime_type off each item.
TextContent carries .text, so every resources/read failed at
serialisation with "'TextContent' object has no attribute 'content'".
The handler itself runs, so the error only ever reached the client and
never showed up in the server log.

No list_resource_templates handler was registered either, so the SDK
answered resources/templates/list with "Method not found". That hid the
homelable://nodes/{node_id} template read_resource already serves — it
is absent from RESOURCE_LIST because it is a template, not a concrete
URI, so nothing advertised it at all.

ha-relevant: no

mcp/app/resources.py

@@ -1,6 +1,7 @@
 import json
 from mcp.server import Server
-from mcp.types import Resource, TextContent
+from mcp.server.lowlevel.helper_types import ReadResourceContents
+from mcp.types import Resource, ResourceTemplate
 from .backend_client import backend
 
 RESOURCE_LIST = [
@@ -19,8 +20,26 @@ ROUTES = {
     "homelable://scan/runs":    "/api/v1/scan/runs",
 }
 
+# read_resource() also serves homelable://nodes/<id>, which is not in
+# RESOURCE_LIST because it is a template, not a concrete URI. Without a
+# list_resource_templates handler the SDK answers resources/templates/list with
+# "Method not found" and the template stays invisible to every client.
+RESOURCE_TEMPLATES = [
+    ResourceTemplate(
+        uriTemplate="homelable://nodes/{node_id}",
+        name="Node",
+        description="A single node by id",
+        mimeType="application/json",
+    ),
+]
 
-async def read_resource(uri: str) -> list[TextContent]:
+
+# The low-level Server.read_resource decorator expects str, bytes or an
+# iterable of ReadResourceContents, and reads .content / .mime_type off each
+# item. Returning mcp.types.TextContent instead fails at serialisation time with
+# "'TextContent' object has no attribute 'content'" — the handler runs, so the
+# error only surfaces to the client, never in the server log.
+async def read_resource(uri: str) -> list[ReadResourceContents]:
     # The MCP framework hands us a pydantic AnyUrl, not a plain str, so string
     # ops like .startswith / dict lookups blow up with
     # "'AnyUrl' object has no attribute 'startswith'". Coerce to str first.
@@ -28,13 +47,20 @@ async def read_resource(uri: str) -> list[TextContent]:
     if uri.startswith("homelable://nodes/") and uri != "homelable://nodes/":
         node_id = uri.split("/")[-1]
         data = await backend.get(f"/api/v1/nodes/{node_id}")
-        return [TextContent(type="text", text=json.dumps(data, indent=2))]
+        return [_json_contents(data)]
 
     if uri not in ROUTES:
         raise ValueError(f"Unknown resource URI: {uri}")
 
     data = await backend.get(ROUTES[uri])
-    return [TextContent(type="text", text=json.dumps(data, indent=2))]
+    return [_json_contents(data)]
+
+
+def _json_contents(data) -> ReadResourceContents:
+    return ReadResourceContents(
+        content=json.dumps(data, indent=2),
+        mime_type="application/json",
+    )
 
 
 def register_resources(server: Server):
@@ -42,6 +68,10 @@ def register_resources(server: Server):
     async def _list():
         return RESOURCE_LIST
 
+    @server.list_resource_templates()
+    async def _list_templates():
+        return RESOURCE_TEMPLATES
+
     @server.read_resource()
     async def _read(uri: str):
         return await read_resource(uri)

mcp/tests/test_resources.py

@@ -1,3 +1,4 @@
+import json
 import pytest
 from pydantic import AnyUrl
 from unittest.mock import AsyncMock, patch
@@ -67,3 +68,46 @@ async def test_read_edges_anyurl(mock_backend):
 async def test_read_single_node_anyurl(mock_backend):
     await read_resource(AnyUrl("homelable://nodes/abc123"))
     mock_backend.get.assert_called_once_with("/api/v1/nodes/abc123")
+
+
+@pytest.mark.anyio
+async def test_read_returns_read_resource_contents(mock_backend):
+    """Regression: returning mcp.types.TextContent made every resources/read
+    fail client-side with "'TextContent' object has no attribute 'content'".
+    The low-level Server reads .content / .mime_type off each item."""
+    from mcp.server.lowlevel.helper_types import ReadResourceContents
+
+    result = await read_resource("homelable://canvas")
+
+    assert isinstance(result[0], ReadResourceContents)
+    assert result[0].mime_type == "application/json"
+    assert json.loads(result[0].content) == {"data": "ok"}
+
+
+@pytest.mark.anyio
+async def test_read_node_returns_read_resource_contents(mock_backend):
+    from mcp.server.lowlevel.helper_types import ReadResourceContents
+
+    result = await read_resource("homelable://nodes/abc123")
+
+    assert isinstance(result[0], ReadResourceContents)
+    assert result[0].mime_type == "application/json"
+
+
+@pytest.mark.anyio
+async def test_resource_templates_are_registered():
+    """Regression: no list_resource_templates handler meant
+    resources/templates/list answered "Method not found", hiding the
+    homelable://nodes/{node_id} template read_resource already serves."""
+    from mcp.server import Server
+    from mcp.types import ListResourceTemplatesRequest
+    from app.resources import register_resources
+
+    server = Server("test")
+    register_resources(server)
+
+    handler = server.request_handlers[ListResourceTemplatesRequest]
+    result = await handler(None)
+
+    templates = result.root.resourceTemplates
+    assert [t.uriTemplate for t in templates] == ["homelable://nodes/{node_id}"]