Feature Request: Escape key to interrupt a running agent turn #3196

Summary

Currently, the only way to stop the harness mid-run is Ctrl+C, which kills the entire process.
Claude Code supports pressing Escape to gracefully interrupt an in-progress agent turn
without exiting the session.

Current behavior

• input.rs binds Ctrl+C → ReadOutcome::Cancel / ReadOutcome::Exit
• No KeyCode::Esc binding exists during an active turn
• No in-flight request cancellation is wired up

Desired behavior

Press Escape while the agent is running to:

1. Cancel the active API request
2. Transition the worker state from Running → Interrupted
3. Return control to the REPL prompt without exiting the session

Implementation sketch

• Detect KeyCode::Esc in rusty-claude-cli/src/input.rs during an active turn
• Add an Interrupted state to the worker lifecycle in runtime/
• Cancel the in-flight HTTP request (e.g., via a CancellationToken)
• Emit a cancellation event for observability