Teach codex to test itself (#11531)

For fun and profit!

.codex/skills/test-tui/SKILL.md

@@ -0,0 +1,14 @@
+---
+name: test-tui
+description: Guide for testing Codex TUI interactively
+---
+
+You can start and use Codex TUI to verify changes. 
+
+Important notes:
+
+Start interactively.
+Always set RUST_LOG="trace" when starting the process.
+Pass `-c log_dir=<some_temp_dir>` argument to have logs written to a specific directory to help with debugging.
+When sending a test message programmatically, send text first, then send Enter in a separate write (do not send text + Enter in one burst).
+Use `just codex` target to run - `just codex -c ...`

codex-rs/tui/src/custom_terminal.rs

@@ -147,7 +147,12 @@ where
     /// Creates a new [`Terminal`] with the given [`Backend`] and [`TerminalOptions`].
     pub fn with_options(mut backend: B) -> io::Result<Self> {
         let screen_size = backend.size()?;
-        let cursor_pos = backend.get_cursor_position()?;
+        let cursor_pos = backend.get_cursor_position().unwrap_or_else(|err| {
+            // Some PTYs do not answer CPR (`ESC[6n`); continue with a safe default instead
+            // of failing TUI startup.
+            tracing::warn!("failed to read initial cursor position; defaulting to origin: {err}");
+            Position { x: 0, y: 0 }
+        });
         Ok(Self {
             backend,
             buffers: [Buffer::empty(Rect::ZERO), Buffer::empty(Rect::ZERO)],