Subagent "x to kill" keybinding types into prompt instead of killing agent

When a subagent is running and selected via arrow-down in the agent list, the UI displays x to kill, but pressing x inserts the character into the input prompt rather than terminating the agent. There is no functional way to kill a subagent from the UI.

Steps to reproduce:

1. Start a long-running subagent (e.g. a background agent task)
2. Press arrow-down to select it in the agent list
3. Press x as indicated by the UI hint

Expected: The subagent is killed
Actual: x is typed into the input prompt; the agent continues running

Version: 2.1.133 / macOS 24.6.0