fix(contrib/mark3labs/mcp-go): preserve raw input schema fields on intent injection

Tools defined with NewToolWithRawSchema may declare JSON Schema keywords
that mcp.ToolInputSchema doesn't model (additionalProperties, oneOf, allOf,
patternProperties, pattern, enum, minimum, etc.). The previous intent-
capture unmarshal-into-ToolInputSchema path silently dropped those fields,
causing tools/list to advertise a more permissive schema than the tool
author specified whenever intent capture was enabled.

Inject telemetry into the raw JSON via a generic map[string]any so unknown
top-level keywords pass through verbatim. The struct-based path is kept
for tools that don't use RawInputSchema.

Same bug existed in dd-source #413963 and is now fixed in dd-trace-go.

Reported by chatgpt-codex-connector on PR #4939.

Author: jboolean

contrib/mark3labs/mcp-go/intent_capture.go

@@ -44,13 +44,15 @@ func injectTelemetryListToolsHook(ctx context.Context, id any, message *mcp.List
 	for i := range result.Tools {
 		t := &result.Tools[i]
 
+		// mcp.ToolInputSchema only models type/properties/required/$defs;
+		// for tools defined with NewToolWithRawSchema we mutate the raw
+		// JSON via a generic map so keywords like additionalProperties,
+		// oneOf, or patternProperties pass through verbatim.
 		if t.RawInputSchema != nil {
-			var schema mcp.ToolInputSchema
-			if err := json.Unmarshal(t.RawInputSchema, &schema); err != nil {
-				continue
+			if newRaw, ok := injectTelemetryIntoRawSchema(t.RawInputSchema); ok {
+				t.RawInputSchema = newRaw
 			}
-			t.InputSchema = schema
-			t.RawInputSchema = nil
+			continue
 		}
 
 		if t.InputSchema.Type == "" {
@@ -72,6 +74,38 @@ func injectTelemetryListToolsHook(ctx context.Context, id any, message *mcp.List
 	}
 }
 
+// injectTelemetryIntoRawSchema mutates a raw JSON Schema document to add the
+// telemetry property and require it. Unknown top-level keywords pass through
+// verbatim. Returns false when the input can't be parsed as a JSON object.
+func injectTelemetryIntoRawSchema(raw json.RawMessage) (json.RawMessage, bool) {
+	var schema map[string]any
+	if json.Unmarshal(raw, &schema) != nil || schema == nil {
+		return nil, false
+	}
+	if _, ok := schema["type"]; !ok {
+		schema["type"] = "object"
+	}
+	props, _ := schema["properties"].(map[string]any)
+	props = maps.Clone(props)
+	if props == nil {
+		props = map[string]any{}
+	}
+	props[instrmcp.TelemetryKey] = telemetrySchema()
+	schema["properties"] = props
+
+	required, _ := schema["required"].([]any)
+	if !slices.Contains(required, any(instrmcp.TelemetryKey)) {
+		required = append(slices.Clone(required), instrmcp.TelemetryKey)
+	}
+	schema["required"] = required
+
+	out, err := json.Marshal(schema)
+	if err != nil {
+		return nil, false
+	}
+	return out, true
+}
+
 // Removing tracing parameters from the tool call request so its not sent to the tool.
 // This must be registered after the tool handler middleware (mcp-go runs middleware in registration order).
 // This removes the telemetry parameter before user-defined middleware or tool handlers can see it.

contrib/mark3labs/mcp-go/intent_capture_test.go

@@ -92,6 +92,34 @@ func TestIntentCapture(t *testing.T) {
 	assert.Equal(t, "test intent description", toolSpan.Meta["intent"])
 }
 
+func TestIntentCaptureRawInputSchemaPreservesUnknownFields(t *testing.T) {
+	// mcp.ToolInputSchema doesn't model additionalProperties/oneOf/etc;
+	// intent capture must not silently strip those when injecting telemetry.
+	tt := testTracer(t)
+	defer tt.Stop()
+
+	srv := server.NewMCPServer("test-server", "1.0.0", WithMCPServerTracing(&TracingConfig{IntentCaptureEnabled: true}))
+	srv.AddTool(mcp.NewToolWithRawSchema("raw_tool", "raw", json.RawMessage(`{
+		"type": "object",
+		"properties": {"app_id": {"type": "string"}},
+		"required": ["app_id"],
+		"additionalProperties": false,
+		"oneOf": [{"required": ["app_id"]}]
+	}`)), func(ctx context.Context, _ mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		return mcp.NewToolResultText("ok"), nil
+	})
+
+	listResp := srv.HandleMessage(context.Background(), []byte(`{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}`))
+	var listResult map[string]interface{}
+	require.NoError(t, json.Unmarshal(mustMarshal(listResp), &listResult))
+	schema := listResult["result"].(map[string]interface{})["tools"].([]interface{})[0].(map[string]interface{})["inputSchema"].(map[string]interface{})
+
+	assert.Contains(t, schema["properties"].(map[string]interface{}), "telemetry")
+	assert.Contains(t, schema["required"].([]interface{}), "telemetry")
+	assert.Equal(t, false, schema["additionalProperties"])
+	assert.NotNil(t, schema["oneOf"])
+}
+
 func TestIntentCaptureRawInputSchema(t *testing.T) {
 	tt := testTracer(t)
 	defer tt.Stop()