diff --git a/src/responses/parser.ts b/src/responses/parser.ts
index 72204ea4d..8c263e689 100644
--- a/src/responses/parser.ts
+++ b/src/responses/parser.ts
@@ -112,6 +112,11 @@ function mapToolChoice(value: unknown): OcxRequestOptions["toolChoice"] {
     if (t === "image_generation" || t === "image_gen") {
       return { name: IMAGE_GEN_TOOL_NAME };
     }
+    // Hosted web-search choices force the synthetic routed search tool. Treating this shape as
+    // `auto` would also advertise unrelated client tools when the sidecar injects web_search.
+    if (t === "web_search" || t === "web_search_preview") {
+      return { name: WEB_SEARCH_TOOL_NAME };
+    }
     if (t === "allowed_tools" && Array.isArray(value.tools)) {
       const names = value.tools
         .map(allowedToolName)
diff --git a/tests/responses-parser.test.ts b/tests/responses-parser.test.ts
index 5b35e8b10..ef130d20e 100644
--- a/tests/responses-parser.test.ts
+++ b/tests/responses-parser.test.ts
@@ -161,6 +161,20 @@ describe("Responses parser", () => {
     expect(parsed.options.toolChoice).toEqual({ allowedTools: ["web_search"], mode: "required" });
   });
 
+  test("maps a forced hosted web_search choice to the synthetic routed tool", () => {
+    const parsed = parseRequest({
+      model: "umans/umans-kimi-k2.7",
+      input: "search",
+      tools: [
+        { type: "web_search" },
+        { type: "function", name: "run_shell", parameters: { type: "object" } },
+      ],
+      tool_choice: { type: "web_search" },
+    });
+
+    expect(parsed.options.toolChoice).toEqual({ name: "web_search" });
+  });
+
   test("maps type-only hosted image_generation tool_choice to required image_gen", () => {
     const parsed = parseRequest({
       model: "claude-opus-4-6",