Fix Windows terminal background rendering and add /debug command

- Strip carriage return characters from bash tool output to fix background padding on Windows
- Add hidden /debug command to write rendered lines to debug log for TUI debugging
- Document /debug command in README.md development section

packages/coding-agent/README.md

@@ -1156,6 +1156,19 @@ import { getPackageDir, getThemeDir, getPackageJsonPath, getReadmePath, getChang
 
 **Never use `__dirname` directly** for resolving package assets. The `paths.ts` module handles the differences between execution modes automatically.
 
+### Debug Command
+
+The `/debug` command is a hidden development feature (not shown in autocomplete) that writes all currently rendered lines with their visible widths and ANSI escape sequences to `~/.pi/agent/pi-debug.log`. This is useful for debugging TUI rendering issues, especially when lines don't extend to the terminal edge or contain unexpected invisible characters.
+
+```
+/debug
+```
+
+The debug log includes:
+- Terminal width at time of capture
+- Total number of rendered lines
+- Each line with its index, visible width, and JSON-escaped content showing all ANSI codes
+
 ## License
 
 MIT