Merge pull request #506 from koic/cover_json_schema_2020_12_preservation_scenario

[Conformance] Cover the JSON Schema 2020-12 preservation scenario

Author: koic

conformance/client.rb

@@ -182,6 +182,14 @@ def build_provider_for(scenario, context)
   case scenario
   when "initialize"
     client.tools
+  when "json-schema-2020-12-preservation"
+    # SEP-1613/SEP-2106: echo the focal tool's observed inputSchema verbatim so the harness
+    # can diff what the client preserved. Preservation holds because `Client::Tool#input_schema`
+    # is the parsed response untouched.
+    tools = client.tools
+    focal = tools.find { |t| t.name == "json_schema_2020_12_tool" }
+    abort("Tool json_schema_2020_12_tool not found") unless focal
+    client.call_tool(name: "json_schema_echo", arguments: { "schema" => focal.input_schema })
   when "tools_call"
     tools = client.tools
     add_numbers = tools.find { |t| t.name == "add_numbers" }

conformance/expected_failures.yml

@@ -8,9 +8,9 @@ client:
   # are not implemented in `MCP::Client::HTTP` yet.
   - http-custom-headers
   - http-invalid-tool-headers
-  # Client-side JSON Schema preservation gaps: `$ref` values must reach the caller unresolved.
+  # Client-side JSON Schema handling: `$ref` values must reach the caller unresolved,
+  # and the conformance client does not run the scenario over the modern lifecycle yet.
   - json-schema-ref-no-deref
-  - json-schema-2020-12-preservation
   # Unimplemented authorization extensions.
   - auth/dpop
   - auth/dpop-nonce