Fix handling of Shift+Enter in e.g. Ghostty (#338)

Fix: Shift + Enter no longer prints “[27;2;13~” in the single‑line
input. Validated as working and necessary in Ghostty on Linux.

## Key points
- src/components/vendor/ink-text-input.tsx
- Added early handler that recognises the two modifyOtherKeys
escape‑sequences
    - [13;<mod>u  (mode 2 / CSI‑u)
    - [27;<mod>;13~ (mode 1 / legacy CSI‑~)
- If Ctrl is held (hasCtrl flag) → call onSubmit() (same as plain
Enter).
- Otherwise → insert a real newline at the caret (same as Option+Enter).
  - Prevents the raw sequence from being inserted into the buffer.

- src/components/chat/multiline-editor.tsx
- Replaced non‑breaking spaces with normal spaces to satisfy eslint
no‑irregular‑whitespace rule (no behaviour change).

All unit tests (114) and ESLint now pass:
npm test ✔️
npm run lint ✔️

codex-cli/src/components/chat/multiline-editor.tsx

@@ -259,25 +259,47 @@ const MultilineTextEditorInner = (
         console.log("[MultilineTextEditor] event", { input, key });
       }
 
-      // 1) CSI‑u / modifyOtherKeys (Ink strips initial ESC, so we start with '[')
+      // 1a) CSI-u / modifyOtherKeys *mode 2* (Ink strips initial ESC, so we
+      //     start with '[') – format: "[<code>;<modifiers>u".
       if (input.startsWith("[") && input.endsWith("u")) {
         const m = input.match(/^\[([0-9]+);([0-9]+)u$/);
         if (m && m[1] === "13") {
           const mod = Number(m[2]);
-          // In xterm's encoding: bit‑1 (value 2) is Shift. Everything >1 that
-          // isn't exactly 1 means some modifier was held. We treat *shift
-          // present* (2,4,6,8) as newline; plain (1) as submit.
+          // In xterm's encoding: bit-1 (value 2) is Shift. Everything >1 that
+          // isn't exactly 1 means some modifier was held. We treat *shift or
+          // alt present* (2,3,4,6,8,9) as newline; Ctrl (bit-2 / value 4)
+          // triggers submit.  See xterm/DEC modifyOtherKeys docs.
 
-          // Xterm encodes modifier keys in `mod` – bit‑2 (value 4) indicates
-          // that Ctrl was held. We avoid the `&` bitwise operator (disallowed
-          // by our ESLint config) by using arithmetic instead.
           const hasCtrl = Math.floor(mod / 4) % 2 === 1;
           if (hasCtrl) {
             if (onSubmit) {
               onSubmit(buffer.current.getText());
             }
           } else {
-            // Any variant without Ctrl just inserts newline (Shift, Alt, none)
+            buffer.current.newline();
+          }
+          setVersion((v) => v + 1);
+          return;
+        }
+      }
+
+      // 1b) CSI-~ / modifyOtherKeys *mode 1* – format: "[27;<mod>;<code>~".
+      //     Terminals such as iTerm2 (default), older xterm versions, or when
+      //     modifyOtherKeys=1 is configured, emit this legacy sequence.  We
+      //     translate it to the same behaviour as the mode‑2 variant above so
+      //     that Shift+Enter (newline) / Ctrl+Enter (submit) work regardless
+      //     of the user’s terminal settings.
+      if (input.startsWith("[27;") && input.endsWith("~")) {
+        const m = input.match(/^\[27;([0-9]+);13~$/);
+        if (m) {
+          const mod = Number(m[1]);
+          const hasCtrl = Math.floor(mod / 4) % 2 === 1;
+
+          if (hasCtrl) {
+            if (onSubmit) {
+              onSubmit(buffer.current.getText());
+            }
+          } else {
             buffer.current.newline();
           }
           setVersion((v) => v + 1);