fix(responses): sanitize empty string placeholders from tool-call optional arguments in stream delta accumulation (#1674)

CHANGELOG.md

@@ -15,6 +15,9 @@
 
 ### 🐛 Bug Fixes
 
+- **fix(responses):** sanitize empty string placeholders from tool-call optional arguments in stream delta accumulation to avoid breaking strict clients (#1674)
+- **fix(codex):** prevent unexpected protocol leakage and fabricated instructions on bare chat completion requests without tools (#1686)
+- **fix(executors):** truncate tools array to 128 items max in GitHub Copilot and OpenCode executors to mitigate 400 Bad Request errors from upstream (#1687)
 - **fix(chatgpt-web):** bound tls-client native deadlocks so requests never hang forever (#1664)
 - **fix(codex):** default gpt-5.5 to HTTP transport instead of WebSocket (#1660)
 - **fix(codex):** [urgent] fix gpt-5.5 websocket transport and model labels (#1656)

open-sse/transformer/responsesTransformer.ts

@@ -221,7 +221,27 @@ export function createResponsesApiTransformStream(logger = null) {
   const closeToolCall = (controller, idx) => {
     const callId = state.funcCallIds[idx];
     if (callId && !state.funcItemDone[idx]) {
-      const args = state.funcArgsBuf[idx] || "{}";
+      let args = state.funcArgsBuf[idx] || "{}";
+
+      // Fix #1674: Final cleanup of empty string placeholders that might have been split across delta chunks
+      try {
+        const parsed = JSON.parse(args);
+        if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) {
+          let modified = false;
+          for (const [k, v] of Object.entries(parsed)) {
+            if (v === "") {
+              delete parsed[k];
+              modified = true;
+            }
+          }
+          if (modified) {
+            args = JSON.stringify(parsed);
+            state.funcArgsBuf[idx] = args;
+          }
+        }
+      } catch (e) {
+        // Ignore malformed JSON
+      }
 
       emit(controller, "response.function_call_arguments.done", {
         type: "response.function_call_arguments.done",
@@ -484,15 +504,25 @@ export function createResponsesApiTransformStream(logger = null) {
 
             if (tc.function?.arguments) {
               const refCallId = state.funcCallIds[tcIdx] || newCallId;
+              let deltaStr = tc.function.arguments;
+
+              // Fix #1674: cx/gpt-5.5 injects empty strings for optional parameters.
+              // We strip these directly from the streaming deltas to avoid breaking strict clients like Claude Code.
+              if (deltaStr.includes('""')) {
+                deltaStr = deltaStr
+                  .replace(/,"[a-zA-Z0-9_]+":""/g, "")
+                  .replace(/"[a-zA-Z0-9_]+":"",/g, "");
+              }
+
               if (refCallId) {
                 emit(controller, "response.function_call_arguments.delta", {
                   type: "response.function_call_arguments.delta",
                   item_id: `fc_${refCallId}`,
                   output_index: tcIdx,
-                  delta: tc.function.arguments,
+                  delta: deltaStr,
                 });
               }
-              state.funcArgsBuf[tcIdx] += tc.function.arguments;
+              state.funcArgsBuf[tcIdx] += deltaStr;
             }
           }
         }

tests/unit/executor-codex.test.ts

@@ -174,6 +174,7 @@ test("CodexExecutor.transformRequest injects default instructions, clamps reason
   const body = {
     model: "gpt-5-mini",
     messages: [{ role: "user", content: "hello" }],
+    tools: [{ type: "function", function: { name: "test_tool" } }],
     prompt: "legacy",
     stream_options: { include_usage: true },
     instructions: "",