fix(gateway): stamp Responses tool strictness only for Anthropic conversions

Native /v1/responses clients omit strict as API semantics; forcing false opted them out of strict tool schemas.

packages/core/src/gateway/core-runtime/responses-tool-strictness.ts

@@ -9,6 +9,8 @@ type UpstreamRequest = {
 };
 
 export type ResponsesToolStrictnessInput = {
+  sourceAdapterKey?: string;
+  sourceProvider?: string;
   targetProviderConfig?: {
     type?: string;
   };
@@ -18,6 +20,8 @@ export type ResponsesToolStrictnessInput = {
 /**
  * OpenAI Responses treats omitted `strict` as "try to make this schema strict".
  * Claude Code tools leave `strict` unset, so optional fields get forced on.
+ * Only converted Anthropic/Claude Code requests are stamped. Native
+ * `/v1/responses` pass-through keeps omitted `strict` as API semantics.
  * Explicit boolean strictness is left alone. Other protocols pass through.
  */
 export function applyResponsesToolStrictness(input: ResponsesToolStrictnessInput): UpstreamRequest {
@@ -26,6 +30,11 @@ export function applyResponsesToolStrictness(input: ResponsesToolStrictnessInput
   if (providerType !== "openai_responses") {
     return upstreamRequest;
   }
+  const sourceKey = input.sourceAdapterKey?.trim().toLowerCase();
+  const sourceProvider = input.sourceProvider?.trim().toLowerCase();
+  if (sourceKey !== "anthropic_messages" && sourceProvider !== "anthropic") {
+    return upstreamRequest;
+  }
   const body = upstreamRequest.body;
   if ((upstreamRequest.bodyEncoding ?? "json") !== "json" || !isRecord(body) || !Array.isArray(body.tools)) {
     return upstreamRequest;

packages/core/test/unit/gateway/responses-tool-strictness.test.mjs

@@ -42,6 +42,8 @@ function readTool(overrides = {}) {
 
 function responsesInput(overrides = {}) {
   return {
+    sourceAdapterKey: "anthropic_messages",
+    sourceProvider: "anthropic",
     targetProviderConfig: {
       name: "multi-channel::openai_responses",
       type: "openai_responses"
@@ -147,6 +149,49 @@ test("requests without tools pass through untouched", () => {
   assert.equal(result, input.upstreamRequest);
 });
 
+test("native Responses requests leave omitted strict unchanged", () => {
+  const tool = monitorTool();
+  const body = {
+    input: [],
+    model: "gpt-5.1-codex",
+    stream: true,
+    tools: [tool]
+  };
+
+  const input = responsesInput({
+    sourceAdapterKey: undefined,
+    sourceProvider: undefined,
+    request: {
+      body,
+      headers: { "content-type": "application/json" }
+    },
+    upstreamRequest: {
+      body,
+      bodyEncoding: "json",
+      headers: { "content-type": "application/json" },
+      method: "POST",
+      url: "https://provider.example/v1/responses"
+    }
+  });
+
+  const result = applyResponsesToolStrictness(input);
+
+  assert.equal(result, input.upstreamRequest);
+  assert.equal(result.body.tools[0].strict, undefined);
+});
+
+test("Chat Completions conversions leave omitted strict unchanged", () => {
+  const input = responsesInput({
+    sourceAdapterKey: "openai_chat",
+    sourceProvider: "openai"
+  });
+
+  const result = applyResponsesToolStrictness(input);
+
+  assert.equal(result, input.upstreamRequest);
+  assert.equal(result.body.tools[0].strict, undefined);
+});
+
 test("gateway boundary plugin registers the tool strictness hook", async () => {
   const hooks = createGatewayPlugin().providerHooks;
   assert.equal(hooks[0].key, "ccr-upstream-header-sanitizer");