fix(google): steer Google models away from unrendered LaTeX math formatting (carry of #3480)

src/adapters/google.ts

@@ -52,6 +52,7 @@ const GOOGLE_BREVITY_INSTRUCTION = [
   "- Do detailed reasoning internally, not as visible intermediate output.",
   "- Prefer taking the next tool action over explaining; keep calling tools until the task is complete.",
   "- This applies only to intermediate progress text. Your final answer after the work is done is exempt: write it in full and at whatever length the task requires.",
+  "- Formatting: The client environment renders standard Markdown and does not support LaTeX math delimiters ($...$, $$...$$, \\(...\\), \\[...\\]). Do not use LaTeX math delimiters or LaTeX markup (such as \\text{}, \\times, \\le, \\ge, etc.) for variables, formulas, dimensions, or units. Use clean plain text, Markdown, and Unicode symbols (e.g. 180°, 2560 × 1920 px, ≤, ≥, Δ, ±) instead.",
 ].join("\n");
 
 const ANTIGRAVITY_REJECTED_CLAUDE_SDK_PARAGRAPH =

tests/adapters/google/google-adapter.test.ts

@@ -174,6 +174,16 @@ describe("google adapter — tool-call ids on the wire", () => {
     expect(instruction.parts[0].text).toContain("Valid tool names for this turn are exactly `exec_command`.");
   });
 
+  test("systemInstruction includes formatting guidance against unrendered LaTeX math", async () => {
+    const body = await geminiBody(parsedWith(
+      [{ role: "user", content: "inspect results" }],
+      [],
+    ));
+    const instruction = body.systemInstruction as { parts: Array<{ text: string }> };
+    expect(instruction.parts[0].text).toContain(String.raw`does not support LaTeX math delimiters ($...$, $$...$$, \(...\), \[...\])`);
+    expect(instruction.parts[0].text).toContain(String.raw`\text{}, \times, \le, \ge`);
+  });
+
   test("functionCall and functionResponse carry the matching tool-call id", async () => {
     const contents = await geminiContents(parsedWith([
       { role: "assistant", content: [{ type: "toolCall", id: "call_abc", name: "bash", arguments: { cmd: "ls" } }] },