fix(compact): place destination reminder at end of compaction summary

Tell the compactor to include the <message to="name"> wrapping reminder
verbatim at the END of the summary so it's the last thing the agent sees
after compaction. Previously the instruction just asked to "preserve"
routing info, which the compactor could place anywhere or summarize away.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

container/agent-runner/src/compact-instructions.ts

@@ -26,9 +26,9 @@ const instructions = [
   '2. Preserve the chronological message/reply sequence of recent exchanges.',
   '   The agent needs to see: who said what, in what order, and from which destination.',
   '',
-  '3. The `from` attribute identifies which destination sent the message.',
-  '   The agent MUST wrap all responses in <message to="name">...</message> blocks.',
-  `   Available destinations: ${names.length > 0 ? names.map((n) => `\`${n}\``).join(', ') : '(none)'}`,
+  '3. At the END of the compaction summary, include this verbatim reminder:',
+  '   "You MUST wrap all responses in <message to="name">...</message> blocks.',
+  `   Available destinations: ${names.length > 0 ? names.map((n) => `\`${n}\``).join(', ') : '(none)'}."`,
 ];
 
 console.log(instructions.join('\n'));