[BUG] Prompt is not always returned after agents receive messages

When using inter-agent messaging extensively it often happens that the message gets printed to the agent prompt, but return isn't sent or received correctly, leading the agent to hang and needing human tmux intervention to send the return to get the agent processing the message.

Provider: Kiro_CLI

Start by reproducing the issue with extensive inter-agent messaging through the Kiro_CLI provider and observe the associated tmux session. Trace where the message reaches the prompt and where return handling stops; done means messages consistently trigger agent processing without human tmux intervention.

Written by the indexing model from the issue text.