fix(translator): strict Anthropic content-block compliance in antigravity→openai request (#5935)

Integrated into release/v3.8.44 — strict Anthropic content-block compliance in antigravity→openai (port upstream #2296). PR test green (9/9). UNSTABLE red is the pre-existing environmental setup-claude base-red (opencode-plugin dist not built in fast-path), not a regression from this PR.

CHANGELOG.md

@@ -12,7 +12,7 @@ _TBD_
 
 ### 🔧 Bug Fixes
 
-- **fix(sse):** strip ANSI/VT100 escape codes from gemini-cli stream frames so ANSI-prefixed `data:` lines are no longer silently dropped. (thanks @anki1kr)
+- **fix(translator):** antigravity→openai request now emits Anthropic-compliant content blocks — drops empty text blocks and preserves tool calls/text co-located with tool results. (thanks @SahrulRamadhanHardiansyah)
 
 ### 📝 Maintenance
 

open-sse/translator/request/antigravity-to-openai.ts

@@ -229,14 +229,17 @@ function convertContent(content) {
       continue;
     }
 
-    // Text with thoughtSignature = regular text after thinking
+    // Text with thoughtSignature = regular text after thinking.
+    // Skip empty text — Anthropic rejects empty content blocks with a 400.
     if (part.thoughtSignature && part.text !== undefined) {
-      textParts.push({ type: "text", text: part.text });
+      if (part.text) {
+        textParts.push({ type: "text", text: part.text });
+      }
       continue;
     }
 
-    // Regular text
-    if (part.text !== undefined) {
+    // Regular text — skip empty strings (Anthropic rejects empty content blocks).
+    if (part.text !== undefined && part.text !== "") {
       textParts.push({ type: "text", text: part.text });
     }
 
@@ -274,8 +277,26 @@ function convertContent(content) {
     }
   }
 
-  // Content with only functionResponses → return array of tool messages
+  // Function responses may be co-located with function calls / text / reasoning in
+  // the same content. Emit the tool messages AND the accompanying assistant message so
+  // nothing is dropped (previously only the tool messages survived).
   if (toolResults.length > 0) {
+    if (toolCalls.length > 0 || textParts.length > 0 || reasoningContent) {
+      const assistantMsg: JsonRecord = { role: "assistant" };
+      if (textParts.length > 0) {
+        assistantMsg.content =
+          textParts.length === 1 && textParts[0].type === "text"
+            ? textParts[0].text
+            : textParts;
+      }
+      if (reasoningContent) {
+        assistantMsg.reasoning_content = reasoningContent;
+      }
+      if (toolCalls.length > 0) {
+        assistantMsg.tool_calls = toolCalls;
+      }
+      return [...toolResults, assistantMsg];
+    }
     return toolResults;
   }
 

tests/unit/translator-antigravity-to-openai.test.ts

@@ -154,6 +154,74 @@ test("Antigravity -> OpenAI returns tool messages when content contains only fun
   ]);
 });
 
+test("Antigravity -> OpenAI keeps co-located function response, function call and text", () => {
+  const result = antigravityToOpenAIRequest(
+    "gpt-4o",
+    {
+      request: {
+        contents: [
+          {
+            role: "model",
+            parts: [
+              { text: "Let me look that up." },
+              { functionResponse: { id: "call_9", name: "lookup", response: { result: { ok: true } } } },
+              { functionCall: { id: "call_10", name: "lookup", args: { q: "weather" } } },
+            ],
+          },
+        ],
+      },
+    },
+    false
+  );
+
+  // Both the tool-result message AND the accompanying assistant message must survive.
+  const toolMsg = result.messages.find((m) => m.role === "tool");
+  const assistantMsg = result.messages.find((m) => m.role === "assistant");
+  assert.ok(toolMsg, "expected a role:tool message");
+  assert.equal(toolMsg.tool_call_id, "call_9");
+  assert.ok(assistantMsg, "expected a role:assistant message");
+  assert.equal(assistantMsg.content, "Let me look that up.");
+  assert.deepEqual(assistantMsg.tool_calls, [
+    {
+      id: "call_10",
+      type: "function",
+      function: { name: "lookup", arguments: '{"q":"weather"}' },
+    },
+  ]);
+});
+
+test("Antigravity -> OpenAI drops empty thoughtSignature text instead of emitting empty content", () => {
+  const result = antigravityToOpenAIRequest(
+    "gpt-4o",
+    {
+      request: {
+        contents: [
+          {
+            role: "model",
+            parts: [
+              { thoughtSignature: "sig", text: "" },
+              { functionCall: { id: "call_11", name: "noop", args: {} } },
+            ],
+          },
+        ],
+      },
+    },
+    false
+  );
+
+  const assistantMsg = result.messages.find((m) => m.role === "assistant");
+  assert.ok(assistantMsg, "expected a role:assistant message");
+  // No empty content block should be emitted (Anthropic rejects it with a 400).
+  assert.equal("content" in assistantMsg, false);
+  assert.deepEqual(assistantMsg.tool_calls, [
+    {
+      id: "call_11",
+      type: "function",
+      function: { name: "noop", arguments: "{}" },
+    },
+  ]);
+});
+
 test("Antigravity -> OpenAI lowers schema types recursively", () => {
   const result = antigravityToOpenAIRequest(
     "gpt-4o",