fix(gemini): parse prefixed textual tool calls

open-sse/handlers/responseTranslator.ts

@@ -36,7 +36,15 @@ function firstPositiveNumber(...values: unknown[]): number {
 
 function parseTextualToolCall(text: unknown): { name: string; args: unknown } | null {
   if (typeof text !== "string") return null;
-  const match = text.match(/^\s*\[Tool call:\s*([^\]\n]+)\]\s*\nArguments:\s*([\s\S]+?)\s*$/);
+
+  // Gemini/Antigravity sometimes imitates the request-side fallback with small
+  // variations, e.g. a leading "(empty)" marker or zero-width chars inserted
+  // into argument strings. Normalize those variants before parsing so the
+  // response is still surfaced as a structured OpenAI tool call.
+  const normalized = text.replace(/[\u200B-\u200D\uFEFF]/g, "");
+  const match = normalized.match(
+    /^[\s\S]*?\[Tool call:\s*([^\]\n]+)\]\s*\nArguments:\s*([\s\S]+?)\s*$/
+  );
   if (!match) return null;
   const name = match[1]?.trim();
   const rawArgs = match[2]?.trim();

open-sse/translator/response/gemini-to-openai.ts

@@ -25,7 +25,15 @@ type GeminiFunctionCallPart = {
 
 function parseTextualToolCall(text: unknown): { name: string; args: unknown } | null {
   if (typeof text !== "string") return null;
-  const match = text.match(/^\s*\[Tool call:\s*([^\]\n]+)\]\s*\nArguments:\s*([\s\S]+?)\s*$/);
+
+  // Gemini/Antigravity sometimes imitates the request-side fallback with small
+  // variations, e.g. a leading "(empty)" marker or zero-width chars inserted
+  // into argument strings. Normalize those variants before parsing so the
+  // response is still surfaced as a structured OpenAI tool call.
+  const normalized = text.replace(/[\u200B-\u200D\uFEFF]/g, "");
+  const match = normalized.match(
+    /^[\s\S]*?\[Tool call:\s*([^\]\n]+)\]\s*\nArguments:\s*([\s\S]+?)\s*$/
+  );
   if (!match) return null;
   const name = match[1]?.trim();
   const rawArgs = match[2]?.trim();

tests/unit/translator-resp-gemini-to-openai.test.ts

@@ -381,6 +381,45 @@ test("Gemini stream: converts textual Tool call block to structured tool_calls",
   assert.equal(result.at(-1).choices[0].finish_reason, "tool_calls");
 });
 
+test("Gemini stream: converts prefixed textual Tool call block with zero-width chars", () => {
+  const state = createStreamingState();
+  const result = geminiToOpenAIResponse(
+    {
+      responseId: "resp-textual-tool-prefixed",
+      modelVersion: "gemini-3.5-flash-low",
+      candidates: [
+        {
+          content: {
+            parts: [
+              {
+                text: '(empty)[Tool call: terminal]\nArguments: {"command":"sqlite3 ~/.o\u200dmniroute/storage.sqlite"}',
+              },
+            ],
+          },
+          finishReason: "STOP",
+        },
+      ],
+    },
+    state
+  );
+
+  const toolCall = result.find((event: any) => event.choices?.[0]?.delta?.tool_calls)?.choices[0]
+    .delta.tool_calls[0];
+  assert.ok(toolCall.id.startsWith("terminal-"));
+  assert.equal(toolCall.function.name, "terminal");
+  assert.equal(
+    toolCall.function.arguments,
+    JSON.stringify({
+      command: "sqlite3 ~/.omniroute/storage.sqlite",
+    })
+  );
+  assert.equal(
+    result.some((event: any) => event.choices?.[0]?.delta?.content?.includes("[Tool call:")),
+    false
+  );
+  assert.equal(result.at(-1).choices[0].finish_reason, "tool_calls");
+});
+
 test("Gemini stream: tool calls without native IDs keep deterministic fallback shape", () => {
   const state = createStreamingState();
   const result = geminiToOpenAIResponse(