Merge pull request #2442 from Koshkoshinsk/fix/core-instructions-message-wrapping

fix(core-instructions): require message wrapping for single-destination agents

Author: gabi-simons

container/agent-runner/src/mcp-tools/core.instructions.md

@@ -1,6 +1,6 @@
 ## Sending messages
 
-Your final response is delivered via the `## Sending messages` rules in your runtime system prompt (single-destination: just write; multi-destination: use `<message to="name">...</message>` blocks). See that section for the current destination list.
+**Every response** must be wrapped in `<message to="name">...</message>` blocks — even if you only have one destination. Bare text outside of `<message>` blocks is scratchpad (logged but never sent). See the `## Sending messages` section in your runtime system prompt for the current destination list and names.
 
 ### Mid-turn updates (`send_message`)