fix: keep Claude tool remap metadata off wire

open-sse/services/claudeCodeToolRemapper.ts

@@ -1,9 +1,8 @@
 /**
  * Claude Code tool name remapping.
  *
- * Anthropic uses tool name fingerprinting to detect third-party clients.
- * Real Claude Code uses TitleCase tool names (Bash, Read, Write, etc.)
- * while third-party clients like OpenCode use lowercase.
+ * Claude Code-compatible requests use TitleCase tool names (Bash, Read,
+ * Write, etc.) while OpenAI-compatible clients commonly use lowercase names.
  *
  * This module remaps tool names in both directions:
  * - Request path: lowercase → TitleCase (before sending to Anthropic)
@@ -38,17 +37,35 @@ for (const [k, v] of Object.entries(TOOL_RENAME_MAP)) {
   REVERSE_MAP[v] = k;
 }
 
+function attachToolNameMap(body: Record<string, unknown>, toolNameMap: Map<string, string>): void {
+  if (toolNameMap.size === 0) return;
+  Object.defineProperty(body, "_toolNameMap", {
+    value: toolNameMap,
+    enumerable: false,
+    configurable: true,
+    writable: true,
+  });
+}
+
 export function remapToolNamesInRequest(body: Record<string, unknown>): boolean {
   let hasLowercase = false;
   let hasTitleCase = false;
+  const existingToolNameMap = body._toolNameMap instanceof Map ? body._toolNameMap : null;
+  const toolNameMap = new Map<string, string>(existingToolNameMap ?? []);
+
+  const recordRemap = (upstreamName: string, originalName: string): void => {
+    toolNameMap.set(upstreamName, originalName);
+  };
 
   // Remap tool definitions
   const tools = body.tools as Array<Record<string, unknown>> | undefined;
   if (Array.isArray(tools)) {
     for (const tool of tools) {
       const name = String(tool.name || "");
-      if (TOOL_RENAME_MAP[name]) {
-        tool.name = TOOL_RENAME_MAP[name];
+      const mapped = TOOL_RENAME_MAP[name];
+      if (mapped) {
+        tool.name = mapped;
+        recordRemap(mapped, name);
         hasLowercase = true;
       } else if (REVERSE_MAP[name]) {
         hasTitleCase = true;
@@ -64,11 +81,13 @@ export function remapToolNamesInRequest(body: Record<string, unknown>): boolean
       if (!Array.isArray(content)) continue;
       for (const block of content) {
         if (block.type === "tool_use" && typeof block.name === "string") {
-          const mapped = TOOL_RENAME_MAP[block.name];
+          const name = block.name;
+          const mapped = TOOL_RENAME_MAP[name];
           if (mapped) {
             block.name = mapped;
+            recordRemap(mapped, name);
             hasLowercase = true;
-          } else if (REVERSE_MAP[block.name]) {
+          } else if (REVERSE_MAP[name]) {
             hasTitleCase = true;
           }
         }
@@ -79,27 +98,38 @@ export function remapToolNamesInRequest(body: Record<string, unknown>): boolean
   // Remap tool_choice
   const toolChoice = body.tool_choice as Record<string, unknown> | undefined;
   if (toolChoice?.type === "tool" && typeof toolChoice.name === "string") {
-    const mapped = TOOL_RENAME_MAP[toolChoice.name];
+    const name = toolChoice.name;
+    const mapped = TOOL_RENAME_MAP[name];
     if (mapped) {
       toolChoice.name = mapped;
+      recordRemap(mapped, name);
       hasLowercase = true;
-    } else if (REVERSE_MAP[toolChoice.name]) {
+    } else if (REVERSE_MAP[name]) {
       hasTitleCase = true;
     }
   }
 
-  if (hasLowercase && !hasTitleCase) {
-    body._claudeCodeRequiresLowercaseToolNames = true;
-  }
+  attachToolNameMap(body, toolNameMap);
 
   return hasLowercase && !hasTitleCase;
 }
 
-export function remapToolNamesInResponse(text: string, forceLowercase = true): string {
+export function remapToolNamesInResponse(
+  text: string,
+  forceLowercase = true,
+  toolNameMap: Map<string, string> | null = null
+): string {
   if (!forceLowercase) return text;
 
+  const replacements = new Map<string, string>(Object.entries(REVERSE_MAP));
+  if (toolNameMap instanceof Map) {
+    for (const [upstreamName, originalName] of toolNameMap.entries()) {
+      replacements.set(upstreamName, originalName);
+    }
+  }
+
   // Replace TitleCase tool names back to lowercase in SSE chunks
-  for (const [titleCase, lower] of Object.entries(REVERSE_MAP)) {
+  for (const [titleCase, lower] of replacements.entries()) {
     // Match in "name":"ToolName" patterns
     text = text.replaceAll(`"name":"${titleCase}"`, `"name":"${lower}"`);
     text = text.replaceAll(`"name": "${titleCase}"`, `"name": "${lower}"`);

tests/unit/claude-code-parity.test.ts

@@ -23,7 +23,10 @@ import {
 } from "../../open-sse/services/claudeCodeFingerprint.ts";
 
 // ── Tool remapper ─────────────────────────────────────────────────────────────
-import { remapToolNamesInRequest } from "../../open-sse/services/claudeCodeToolRemapper.ts";
+import {
+  remapToolNamesInRequest,
+  remapToolNamesInResponse,
+} from "../../open-sse/services/claudeCodeToolRemapper.ts";
 
 // ── Constraints ───────────────────────────────────────────────────────────────
 import {
@@ -165,6 +168,61 @@ describe("remapToolNamesInRequest", () => {
     assert.ok(Array.isArray(body.tools), "tools array must still be present after remap");
   });
 
+  it("tracks remapped tool names without leaking helper fields into the wire payload", () => {
+    const body = {
+      tools: [
+        { name: "bash", description: "Run bash commands" },
+        { name: "glob", description: "Search files" },
+      ],
+      tool_choice: { type: "tool", name: "glob" },
+      messages: [
+        {
+          role: "assistant",
+          content: [{ type: "tool_use", name: "read", input: { file_path: "README.md" } }],
+        },
+      ],
+    };
+
+    remapToolNamesInRequest(body);
+
+    const mappedBody = body as Record<string, unknown> & {
+      _toolNameMap?: Map<string, string>;
+      _claudeCodeRequiresLowercaseToolNames?: boolean;
+    };
+
+    assert.equal(body.tools[0].name, "Bash");
+    assert.equal(body.tools[1].name, "Glob");
+    assert.equal(body.tool_choice.name, "Glob");
+    assert.equal(body.messages[0].content[0].name, "Read");
+    assert.equal(mappedBody._toolNameMap?.get("Bash"), "bash");
+    assert.equal(mappedBody._toolNameMap?.get("Glob"), "glob");
+    assert.equal(mappedBody._toolNameMap?.get("Read"), "read");
+    assert.equal(Object.keys(body).includes("_toolNameMap"), false);
+    assert.equal(mappedBody._claudeCodeRequiresLowercaseToolNames, undefined);
+
+    const wirePayload = JSON.stringify(body);
+    assert.equal(wirePayload.includes("_toolNameMap"), false);
+    assert.equal(wirePayload.includes("_claudeCodeRequiresLowercaseToolNames"), false);
+    assert.match(wirePayload, /"name":"Bash"/);
+    assert.match(wirePayload, /"name":"Glob"/);
+  });
+
+  it("merges an existing in-memory tool name map and keeps it non-enumerable", () => {
+    const body: Record<string, unknown> = {
+      tools: [{ name: "bash", description: "Run bash commands" }],
+      messages: [],
+    };
+    body._toolNameMap = new Map([["proxy_read_file", "read_file"]]);
+
+    remapToolNamesInRequest(body);
+
+    const toolNameMap = body._toolNameMap as Map<string, string>;
+    assert.equal(toolNameMap.get("proxy_read_file"), "read_file");
+    assert.equal(toolNameMap.get("Bash"), "bash");
+    assert.equal(Object.keys(body).includes("_toolNameMap"), false);
+    assert.equal(JSON.stringify(body).includes("_toolNameMap"), false);
+  });
+
   it("handles body without tools without throwing", () => {
     const body = { messages: [{ role: "user", content: "hello" }] };
     assert.doesNotThrow(() => remapToolNamesInRequest(body));
@@ -172,6 +230,24 @@ describe("remapToolNamesInRequest", () => {
   // Note: remapToolNamesInRequest requires a non-null body (callers always provide one)
 });
 
+describe("remapToolNamesInResponse", () => {
+  it("restores response tool names from the request-side map", () => {
+    const text = 'data: {"name":"Bash","other":{"name": "Glob"}}\n\n';
+    const restored = remapToolNamesInResponse(
+      text,
+      true,
+      new Map([
+        ["Bash", "shell"],
+        ["Glob", "glob"],
+      ])
+    );
+
+    assert.match(restored, /"name":"shell"/);
+    assert.match(restored, /"name": "glob"/);
+    assert.equal(remapToolNamesInResponse(text, false), text);
+  });
+});
+
 // ─────────────────────────────────────────────────────────────────────────────
 // API constraints tests
 // ─────────────────────────────────────────────────────────────────────────────