Previously when a user message was provided, cmd_continue would only
use the user message without the base agent workflow. Now both cases
build the full workflow and append the user message.
Changes:
- cmd_continue now always calls build_dev_agent_message even when
message is provided
- User message is appended at the end with 'Delegator's message:'
- Both with/without message cases now use the same workflow structure
Fixes#229
