Skip non-regular files when detecting pasted image paths (#57774)

## Why

Probing a pasted serial device or FIFO path for image dimensions can block the TUI input loop.

## What changed

Only probe regular files for image dimensions, leaving pasted device and FIFO paths as literal text.

## Testing

Add a Unix regression test that pastes a FIFO path and verifies it remains editable with Backspace.

GitOrigin-RevId: c9ae3479f8b14920232e75fe6d2cee86c3300bda

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -283,6 +283,7 @@
 //!   [`ChatComposer::handle_paste`], which first commits buffered typing before classifying the
 //!   pasted text. This preserves the order when a paste arrives before the next burst-flush tick;
 //!   buffered keys have already been classified and go directly through `apply_paste`.
+//!   Image detection probes only regular files. Pasted device and FIFO paths stay literal.
 //! - Startup recovery previews held keys with the live Vim Replace policy without consuming them.
 //!   Buffered pastes remain literal in recovery so large-paste and image classification stays with
 //!   the live paste path.
@@ -1267,8 +1268,11 @@ impl ChatComposer {
             return false;
         };
 
-        // normalize_pasted_path already handles Windows → WSL path conversion,
-        // so we can directly try to read the image dimensions.
+        // Opening a serial device or FIFO can block the input loop.
+        if !path_buf.is_file() {
+            return false;
+        }
+
         match image::image_dimensions(&path_buf) {
             Ok((width, height)) => {
                 tracing::info!("OK: {pasted}");

codex-rs/tui/src/bottom_pane/chat_composer/paste_tests.rs

@@ -1,4 +1,4 @@
-//! Raw paste tabs remain draft text until the user explicitly submits or queues it.
+//! Composer paste handling for literal paths and raw tabs.
 
 use super::tests::new_test_composer;
 use super::*;
@@ -6,6 +6,27 @@ use pretty_assertions::assert_eq;
 use ratatui::Terminal;
 use ratatui::backend::TestBackend;
 
+#[cfg(unix)]
+#[test]
+fn pasting_fifo_path_keeps_it_editable() {
+    let dir = tempfile::tempdir().unwrap();
+    let name = "tty.usbserial-110";
+    let status = std::process::Command::new("mkfifo")
+        .arg(dir.path().join(name))
+        .status()
+        .unwrap();
+    assert!(status.success());
+
+    let (mut composer, _rx) = new_test_composer();
+    let prefix = shlex::try_quote(dir.path().to_str().unwrap()).unwrap();
+    composer.handle_paste(format!("{prefix}/{name}"));
+    composer.handle_key_event(KeyEvent::from(KeyCode::Backspace));
+    insta::assert_snapshot!(
+        composer.current_text().strip_prefix(prefix.as_ref()).unwrap(),
+        @"/tty.usbserial-11"
+    );
+}
+
 #[test]
 fn paste_burst_tabs_preserve_multiline_draft() {
     for running in [false, true] {