feat(coding-agent): add message copy shortcut

packages/coding-agent/docs/keybindings.md

@@ -119,6 +119,7 @@ Modifier combinations: `ctrl+shift+x`, `alt+ctrl+x`, `ctrl+shift+alt+x`, `ctrl+1
 | Keybinding id | Default | Description |
 |--------|---------|-------------|
 | `app.tools.expand` | `ctrl+o` | Collapse or expand tool output |
+| `app.message.copy` | `ctrl+x` | Copy the last assistant message, or the selected message in `/tree` |
 | `app.message.followUp` | `alt+enter` | Queue follow-up message |
 | `app.message.dequeue` | `alt+up` | Restore queued messages to editor |
 

packages/coding-agent/docs/usage.md

@@ -22,6 +22,7 @@ The editor can be replaced temporarily by built-in UI such as `/settings` or by
 | File reference | Type `@` to fuzzy-search project files |
 | Path completion | Press Tab to complete paths |
 | Multi-line input | Shift+Enter, or Ctrl+Enter on Windows Terminal |
+| Copy response | Ctrl+X copies the last assistant message; in `/tree`, it copies the selected message |
 | Images | Paste with Ctrl+V, Alt+V on Windows, or drag into the terminal |
 | Shell command | `!command` runs and sends output to the model |
 | Hidden shell command | `!!command` runs without sending output to the model |