fix(claude): forced tool_choice 400 on cc/ OAuth route

convertOpenAIToolChoice mapped {type:"function"} verbatim and cloakClaudeTools
left tool_choice.name unsuffixed, both rejected by Claude on the cc/ path.
Map forced-function to {type:"tool",name}, allowlist Claude-valid types, and
suffix tool_choice.name when it targets a renamed client tool.

Fixes #1592

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/openai-to-claude.test.js

@@ -122,6 +122,50 @@ describe("openaiToClaudeRequest", () => {
       expect(systemText).toContain("You must respond with valid JSON");
     });
   });
+
+  describe("tool_choice handling", () => {
+    const baseBody = {
+      messages: [{ role: "user", content: "add a todo" }],
+      tools: [{
+        type: "function",
+        function: { name: "todo_write", description: "write todos", parameters: { type: "object", properties: {} } }
+      }]
+    };
+
+    const choiceOf = (tc) =>
+      openaiToClaudeRequest("claude-sonnet-4.5", { ...baseBody, tool_choice: tc }, false).tool_choice;
+
+    it("converts OpenAI forced tool ({type:'function'}) to Claude {type:'tool'}", () => {
+      // Must NOT leak the OpenAI "function" type — Claude only accepts auto|any|tool|none.
+      expect(choiceOf({ type: "function", function: { name: "todo_write" } }))
+        .toEqual({ type: "tool", name: "todo_write" });
+    });
+
+    it("maps string tool_choice values", () => {
+      expect(choiceOf("auto")).toEqual({ type: "auto" });
+      expect(choiceOf("none")).toEqual({ type: "auto" });
+      expect(choiceOf("required")).toEqual({ type: "any" });
+    });
+
+    it("passes through Claude-native tool_choice objects unchanged", () => {
+      expect(choiceOf({ type: "tool", name: "todo_write" })).toEqual({ type: "tool", name: "todo_write" });
+      expect(choiceOf({ type: "any" })).toEqual({ type: "any" });
+      expect(choiceOf({ type: "none" })).toEqual({ type: "none" });
+    });
+
+    it("never leaks an invalid type (falls back to auto)", () => {
+      // Malformed forced choice with no tool name, and unknown types, must not
+      // pass an invalid `type` through to Claude.
+      expect(choiceOf({ type: "function", function: {} })).toEqual({ type: "auto" });
+      expect(choiceOf({ type: "function" })).toEqual({ type: "auto" });
+      expect(choiceOf({ type: "bogus" })).toEqual({ type: "auto" });
+    });
+
+    it("omits tool_choice entirely when the request has none", () => {
+      const result = openaiToClaudeRequest("claude-sonnet-4.5", baseBody, false);
+      expect(result.tool_choice).toBeUndefined();
+    });
+  });
 });
 
 describe("openaiToClaudeResponse", () => {