Truncate tool summaries by code point

Claude-Session: https://claude.ai/code/session_01JtuZTCMW9TyogEmBgGf8JT

src/agent/events.test.ts

@@ -23,4 +23,10 @@ describe("summarizeToolCall", () => {
     expect(long).toHaveLength(80);
     expect(long.endsWith("...")).toBe(true);
   });
+  it("truncates by code point so a non-BMP character at the cut is not split", () => {
+    const s = summarizeToolCall("bash", { command: "x".repeat(70) + "😀" + "y".repeat(20) });
+    expect(s.endsWith("...")).toBe(true);
+    expect(Array.from(s)).toHaveLength(80);
+    expect(s).not.toMatch(/[\uD800-\uDBFF](?![\uDC00-\uDFFF])/);
+  });
 });

src/agent/events.ts

@@ -51,5 +51,6 @@ export function summarizeToolCall(toolName: string, args: unknown): string {
       break;
   }
   const summary = detail ? `${toolName}: ${detail}` : toolName;
-  return summary.length > SUMMARY_MAX ? `${summary.slice(0, SUMMARY_MAX - 3)}...` : summary;
+  const chars = Array.from(summary);
+  return chars.length > SUMMARY_MAX ? `${chars.slice(0, SUMMARY_MAX - 3).join("")}...` : summary;
 }