test: extract MODE_RE + optionsSignature into PTY runner exports

Refactor prep for the upcoming per-finding AskUserQuestion count test
across plan-{ceo,eng,design,devex}-review. Both new tests and the existing
mode-routing test need the same mode regex and the same option-list
fingerprint dedupe — pulling them into one source of truth in
test/helpers/claude-pty-runner.ts so a fifth mode (or a tweak to the
fingerprint shape) updates everywhere instead of drifting per-test.

Mechanical: no behavior change in the mode-routing test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/skill-e2e-plan-ceo-mode-routing.test.ts

@@ -37,6 +37,8 @@ import {
   isPermissionDialogVisible,
   parseNumberedOptions,
   isPlanReadyVisible,
+  MODE_RE,
+  optionsSignature,
   TAIL_SCAN_BYTES,
   type ClaudePtySession,
 } from './helpers/claude-pty-runner';
@@ -44,8 +46,6 @@ import {
 const shouldRun = !!process.env.EVALS && process.env.EVALS_TIER === 'periodic';
 const describeE2E = shouldRun ? describe : describe.skip;
 
-const MODE_RE = /HOLD SCOPE|SCOPE EXPANSION|SELECTIVE EXPANSION|SCOPE REDUCTION/i;
-
 interface ModeCase {
   mode: 'HOLD SCOPE' | 'SCOPE EXPANSION';
   /** Regex applied to visible-since-mode-pick text. At least one must match. */
@@ -96,8 +96,8 @@ async function navigateToModeAskUserQuestion(
 
     // Has the rendered list changed since last poll? If not, we're seeing
     // the same prompt and shouldn't double-press.
-    const sig = opts.map(o => `${o.index}:${o.label}`).join('|');
-    const lastSig = lastSeenList.map(o => `${o.index}:${o.label}`).join('|');
+    const sig = optionsSignature(opts);
+    const lastSig = optionsSignature(lastSeenList);
     if (sig === lastSig) continue;
     lastSeenList = opts;