Constant COMPLETION_PROTOCOL 

pub const COMPLETION_PROTOCOL: &str = "\
## Completion Protocol (REQUIRED)\n\
\n\
When all work is done, your FINAL message must be exactly:\n\
\n\
DEVFLOW_RESULT: {\"status\": \"success\"}\n\
\n\
If something prevents completion:\n\
\n\
DEVFLOW_RESULT: {\"status\": \"failed\", \"reason\": \"specific explanation\"}\n\
\n\
DevFlow reads this line to decide whether the stage succeeded. \
Output nothing after it.";

The completion contract every agent must honor as its final message.