v3.6.121

Fix false completion signal preventing worker retries

output_has_completion_signal() was grepping raw tee output including file
contents workers READ. full-loop.md contains FULL_LOOP_COMPLETE as doc text —
workers that read it and died mid-turn were falsely classified as 'success',
preventing the continuation retry from ever firing.

Now parses the OpenCode JSON stream and only checks model text events, not
tool output content.