Carry forward the arbiter verdict too, not just the owner final

When a paired task ends on an arbiter ESCALATE (asking the user to choose), the
user's next reply was carried into the fresh task with the owner's earlier final
as context — not the arbiter message they were actually responding to. Generalize
the carry-forward to the latest user-facing final (owner final OR arbiter
verdict, whichever the task ended on), so the user can choose based on the last
arbiter message without the new turn re-reading the whole prior conversation.
The carried-forward guidance marker is now matched by a shared prefix so it
triggers for both. Adds tests for the arbiter-escalation carry and the prefix
guidance.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/message-runtime-prompts.test.ts

@@ -96,6 +96,28 @@ describe('message-runtime-prompts carry-forward guidance', () => {
     );
   });
 
+  it('prepends the carry-forward warning for a carried arbiter verdict too', () => {
+    const prompt = buildPairedTurnPrompt({
+      taskId: 'task-1',
+      chatJid: 'group@test',
+      timezone: 'UTC',
+      missedMessages: [makeHumanMessage('1번 선택할게')],
+      labeledFallbackMessages: [makeHumanMessage('1번 선택할게')],
+      turnOutputs: [
+        makeTurnOutput(
+          '[Carried forward context from the previous task: latest arbiter verdict]\nESCALATE\n1) A 2) B',
+        ),
+      ],
+    });
+
+    expect(
+      prompt.startsWith('System note:\nIf you see a message beginning with'),
+    ).toBe(true);
+    expect(prompt).toContain(
+      'Respond only to the latest human request and the current task.',
+    );
+  });
+
   it('prepends a carry-forward warning to reviewer pending prompts', () => {
     const prompt = buildReviewerPendingPrompt({
       chatJid: 'group@test',