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/claude-cloaking.test.js

@@ -0,0 +1,76 @@
+/**
+ * Unit tests for open-sse/utils/claudeCloaking.js
+ *
+ * Tests cover:
+ *  - cloakClaudeTools() - tool renaming and forced tool_choice suffixing
+ */
+
+import { describe, it, expect } from "vitest";
+import { cloakClaudeTools } from "../../open-sse/utils/claudeCloaking.js";
+import { CLAUDE_TOOL_SUFFIX } from "../../open-sse/config/appConstants.js";
+
+describe("cloakClaudeTools", () => {
+  const baseBody = {
+    tools: [{ name: "todo_write", description: "write todos", input_schema: { type: "object", properties: {} } }],
+    messages: [{ role: "user", content: [{ type: "text", text: "add a todo" }] }]
+  };
+
+  it("suffixes client tool names and maps them back", () => {
+    const { body, toolNameMap } = cloakClaudeTools(baseBody);
+    const suffixed = `todo_write${CLAUDE_TOOL_SUFFIX}`;
+    expect(body.tools.find(t => t.name === suffixed)).toBeDefined();
+    expect(toolNameMap.get(suffixed)).toBe("todo_write");
+  });
+
+  it("suffixes a forced tool_choice to match the renamed tool", () => {
+    const { body } = cloakClaudeTools({
+      ...baseBody,
+      tool_choice: { type: "tool", name: "todo_write" }
+    });
+    // Without this, Claude rejects: "Tool 'todo_write' not found in provided tools".
+    expect(body.tool_choice).toEqual({ type: "tool", name: `todo_write${CLAUDE_TOOL_SUFFIX}` });
+  });
+
+  it("suffixes only the chosen tool when several are present", () => {
+    const { body } = cloakClaudeTools({
+      tools: [
+        { name: "search", input_schema: { type: "object", properties: {} } },
+        { name: "todo_write", input_schema: { type: "object", properties: {} } }
+      ],
+      tool_choice: { type: "tool", name: "todo_write" }
+    });
+    expect(body.tool_choice).toEqual({ type: "tool", name: `todo_write${CLAUDE_TOOL_SUFFIX}` });
+  });
+
+  it("leaves non-forced tool_choice untouched", () => {
+    const auto = cloakClaudeTools({ ...baseBody, tool_choice: { type: "auto" } });
+    expect(auto.body.tool_choice).toEqual({ type: "auto" });
+
+    const none = cloakClaudeTools({ ...baseBody });
+    expect(none.body.tool_choice).toBeUndefined();
+  });
+
+  it("does not suffix a forced choice that targets a non-client (decoy/built-in) tool", () => {
+    // "Bash" is an injected decoy sent unsuffixed; forcing it must stay as-is.
+    const { body } = cloakClaudeTools({ ...baseBody, tool_choice: { type: "tool", name: "Bash" } });
+    expect(body.tool_choice).toEqual({ type: "tool", name: "Bash" });
+  });
+
+  it("renames tool_use names in message history", () => {
+    const { body } = cloakClaudeTools({
+      ...baseBody,
+      messages: [
+        { role: "assistant", content: [{ type: "tool_use", id: "t1", name: "todo_write", input: {} }] }
+      ]
+    });
+    const block = body.messages[0].content[0];
+    expect(block.name).toBe(`todo_write${CLAUDE_TOOL_SUFFIX}`);
+  });
+
+  it("returns the body unchanged when there are no tools", () => {
+    const input = { messages: [{ role: "user", content: "hi" }], tool_choice: { type: "tool", name: "x" } };
+    const { body, toolNameMap } = cloakClaudeTools(input);
+    expect(body).toBe(input);
+    expect(toolNameMap).toBeNull();
+  });
+});

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", () => {