test: build the surrogate-pair fixture from its code point

Author: elkaix

packages/agent-core/test/session/session-advisor.test.ts

@@ -208,8 +208,10 @@ describe('SessionAdvisor', () => {
   it('caps each advisory note at 500 code points', async () => {
     const fixture = await createFixture({ advisorAlias: 'advisor' });
     const steer = vi.spyOn(fixture.main.turn, 'steer').mockReturnValue(null);
-    // Keep this character as a surrogate pair to test code-point slicing.
-    const note = `  ${'a'.repeat(499)}𝐀extra  `;
+    // U+1D400 MATHEMATICAL BOLD CAPITAL A. Must stay a surrogate pair: this test
+    // proves the cap slices by code point rather than by UTF-16 code unit.
+    const surrogatePair = String.fromCodePoint(0x1d400);
+    const note = `  ${'a'.repeat(499)}${surrogatePair}extra  `;
     queueReview(fixture.scripted, note);
 
     await runMainTurn(fixture.main);
@@ -221,7 +223,7 @@ describe('SessionAdvisor', () => {
       [
         {
           type: 'text',
-          text: `<advisory>\nThe following notes are from a second reviewing model. Weigh them; do not blindly obey.\n- ${'a'.repeat(499)}𝐀\n</advisory>`,
+          text: `<advisory>\nThe following notes are from a second reviewing model. Weigh them; do not blindly obey.\n- ${'a'.repeat(499)}${surrogatePair}\n</advisory>`,
         },
       ],
       { kind: 'hook_result', event: 'advisor' },