diff --git a/apps/server/agent/prompts/shared.ts b/apps/server/agent/prompts/shared.ts
index af90bdf..8c092ed 100644
--- a/apps/server/agent/prompts/shared.ts
+++ b/apps/server/agent/prompts/shared.ts
@@ -6,7 +6,7 @@
 
 export const SIGNAL_FORMAT = `
 <signal_format>
-As your final action, write \`.cw/output/signal.json\`:
+CRITICAL: Write \`.cw/output/signal.json\` as your ABSOLUTE LAST action. The system monitors this file as a completion trigger — writing it before your output files causes your work to be silently discarded.
 - Done: \`{ "status": "done" }\`
 - Need clarification: \`{ "status": "questions", "questions": [{ "id": "q1", "question": "..." }] }\`
 - Unrecoverable error: \`{ "status": "error", "error": "..." }\` — include the actual error output, stack trace, or repro steps, not just a summary