diff --git a/src/server.test.ts b/src/server.test.ts
index 59bcc5d37..bedc1bfd0 100644
--- a/src/server.test.ts
+++ b/src/server.test.ts
@@ -470,6 +470,92 @@ test("open_workspace scopes checkout reuse to OpenAI session metadata", async (t
   assert.ok(Array.isArray(structuredContent(unscoped).agents_files));
 });
 
+test("HTTP cached workspaceId arguments preserve canonical schemas and validation", async (t) => {
+  const { root, localBaseUrl, accessToken } = await httpServerFixture(t, "devspace-cached-arguments-test-");
+  await writeFile(join(root, "note.txt"), "cached argument regression\n");
+  const opened = await postModernMcp(localBaseUrl, accessToken, "tools/call", {
+    name: "open_workspace", arguments: { path: root },
+  });
+  const workspaceId = (await opened.json()).result.structuredContent.workspace_id as string;
+  assert.equal(typeof workspaceId, "string");
+
+  for (const argumentsValue of [
+    { workspaceId, path: "note.txt" },
+    { workspaceId, workspace_id: workspaceId, path: "note.txt" },
+    { workspace_id: workspaceId, path: "note.txt" },
+  ]) {
+    const response = await postModernMcp(localBaseUrl, accessToken, "tools/call", {
+      name: "read", arguments: argumentsValue,
+    });
+    const body = await response.json();
+    assert.equal(response.status, 200, JSON.stringify(body));
+    assert.equal(body.error, undefined, JSON.stringify(body));
+    assert.notEqual(body.result?.isError, true, JSON.stringify(body));
+    assert.match(JSON.stringify(body.result), /cached argument regression/);
+  }
+
+  const conflict = await postModernMcp(localBaseUrl, accessToken, "tools/call", {
+    name: "read", arguments: { workspaceId, workspace_id: "different", path: "note.txt" },
+  });
+  assert.equal(conflict.status, 400);
+  assert.equal((await conflict.json()).error.code, -32602);
+
+  for (const workspaceId of [null, 42, {}, []]) {
+    const invalid = await postModernMcp(localBaseUrl, accessToken, "tools/call", {
+      name: "read", arguments: { workspaceId, path: "note.txt" },
+    });
+    const body = await invalid.json();
+    assert.ok(body.error || body.result?.isError, JSON.stringify(body));
+    assert.notEqual(invalid.status, 500);
+  }
+
+  const unauthorized = await postModernMcp(localBaseUrl, undefined, "tools/call", {
+    name: "read", arguments: { workspaceId, workspace_id: "different", path: "note.txt" },
+  });
+  assert.equal(unauthorized.status, 401);
+  const outside = await postModernMcp(localBaseUrl, accessToken, "tools/call", {
+    name: "read", arguments: { workspaceId, path: "../outside.txt" },
+  });
+  assert.equal((await outside.json()).result.isError, true);
+
+  const listed = await postModernMcp(localBaseUrl, accessToken, "tools/list", {});
+  const tools = (await listed.json()).result.tools as Array<{ name: string; inputSchema: { properties?: Record<string, unknown> } }>;
+  const read = tools.find((tool) => tool.name === "read");
+  assert.ok(read?.inputSchema.properties?.workspace_id);
+  assert.equal(read?.inputSchema.properties?.workspaceId, undefined);
+});
+
+test("HTTP conflicting workspace aliases preserve request IDs and notification semantics", async (t) => {
+  const { localBaseUrl, accessToken } = await httpServerFixture(t, "devspace-cached-id-test-");
+  for (const id of ["cached-request", 37, null, undefined]) {
+    await t.test(id === undefined ? "notification" : `request ID ${JSON.stringify(id)}`, async () => {
+      const response = await fetch(`${localBaseUrl}/mcp`, {
+        method: "POST",
+        headers: {
+          authorization: `Bearer ${accessToken}`,
+          "content-type": "application/json",
+          "mcp-method": "tools/call",
+          "mcp-name": "read",
+          "mcp-protocol-version": "2026-07-28",
+        },
+        body: JSON.stringify({
+          jsonrpc: "2.0", ...(id === undefined ? {} : { id }), method: "tools/call",
+          params: { name: "read", arguments: { workspaceId: "old", workspace_id: "new", path: "note.txt" } },
+        }),
+      });
+      if (id === undefined) {
+        assert.equal(response.status, 202);
+        assert.equal(await response.text(), "");
+      } else {
+        assert.equal(response.status, 400);
+        const body = await response.json();
+        assert.equal(body.error.code, -32602);
+        assert.equal(body.id, id);
+      }
+    });
+  }
+});
+
 test("HTTP endpoint serves modern MCP and stateless legacy clients", async (t) => {
   const { root, localBaseUrl, accessToken } = await httpServerFixture(
     t,
diff --git a/src/server.ts b/src/server.ts
index 0a2792f3f..5dbac7315 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -199,14 +199,35 @@ function sendJsonRpcError(
   status: number,
   code: number,
   message: string,
+  id: string | number | null = null,
 ): void {
   res.status(status).json({
     jsonrpc: "2.0",
     error: { code, message },
-    id: null,
+    id,
   });
 }
 
+// ChatGPT may retain the pre-snake_case workspace argument in cached tool calls.
+// Normalize only that known alias at the HTTP edge; the public schema remains canonical.
+function normalizeCachedWorkspaceArgument(body: unknown): boolean {
+  if (!body || typeof body !== "object" || Array.isArray(body)) return true;
+  const request = body as Record<string, unknown>;
+  if (request.method !== "tools/call") return true;
+  const params = request.params;
+  if (!params || typeof params !== "object" || Array.isArray(params)) return true;
+  const args = (params as Record<string, unknown>).arguments;
+  if (!args || typeof args !== "object" || Array.isArray(args)) return true;
+  const values = args as Record<string, unknown>;
+  if (!Object.hasOwn(values, "workspaceId")) return true;
+  if (Object.hasOwn(values, "workspace_id") && values.workspace_id !== values.workspaceId) {
+    return false;
+  }
+  if (!Object.hasOwn(values, "workspace_id")) values.workspace_id = values.workspaceId;
+  delete values.workspaceId;
+  return true;
+}
+
 function requestLogFields(req: Request, config: ServerConfig): Record<string, unknown> {
   return {
     ip: requestIp(req, config.logging.trustProxy),
@@ -946,6 +967,17 @@ export function createServer(
       method: req.method,
     });
 
+    if (!normalizeCachedWorkspaceArgument(req.body)) {
+      const body = req.body as Record<string, unknown>;
+      if (!Object.hasOwn(body, "id")) {
+        res.status(202).end();
+        return;
+      }
+      const id = typeof body.id === "string" || typeof body.id === "number" ? body.id : null;
+      sendJsonRpcError(res, 400, -32602, "Conflicting workspaceId and workspace_id arguments", id);
+      return;
+    }
+
     try {
       await mcpNodeHandler(req, res, req.body);
     } catch (error) {