fix(fastmcp): propagate mimeType in resource template listing and add test

- Fix resource template list did not include the mimeType attribute.
- Propagate mimeType from template metadata to the list output in FastMCP.
- Add test_resource_template_includes_mime_type to verify that listed resource templates include the correct mimeType and the resource is still accessible via the client.

Author: pchoudhury22

src/mcp/server/fastmcp/server.py

@@ -296,6 +296,7 @@ async def list_resource_templates(self) -> list[MCPResourceTemplate]:
                 name=template.name,
                 title=template.title,
                 description=template.description,
+                mimeType=template.mime_type,
             )
             for template in templates
         ]

tests/server/fastmcp/test_server.py

@@ -739,6 +739,27 @@ def get_data(name: str) -> str:
         result = await resource.read()
         assert result == "Data for test"
 
+    @pytest.mark.anyio
+    async def test_resource_template_includes_mime_type(self):
+        """Test that list resource templates includes the correct mimeType."""
+        mcp = FastMCP()
+
+        @mcp.resource("resource://{user}/csv", mime_type="text/csv")
+        def get_csv(user: str) -> str:
+            return f"csv for {user}"
+
+        templates = await mcp.list_resource_templates()
+        assert len(templates) == 1
+        template = templates[0]
+
+        assert hasattr(template, "mimeType")
+        assert template.mimeType == "text/csv"
+        
+        async with client_session(mcp._mcp_server) as client:
+            result = await client.read_resource(AnyUrl("resource://bob/csv"))
+            assert isinstance(result.contents[0], TextResourceContents)
+            assert result.contents[0].text == "csv for bob"
+
 
 class TestContextInjection:
     """Test context injection in tools."""