fix(codex): reassemble chunk-split sequences before the strip; mouse parity on replay

Review fixes:

- Hold back a trailing partial CSI (digit-only intro, ≤7 chars) in
  _handleTerminalOutput and prepend it to the next chunk. PTY chunk
  boundaries are arbitrary, so '\x1b[?1049h' can arrive as '\x1b[?104' +
  '9h' — the per-chunk strip misses it, xterm obeys the reassembled toggle,
  and (with the matching ?1049l stripped) stays stuck in the scrollback-less
  alt buffer until the next replay. Complete sequences are never held; the
  carry resets with the other buffers in _resetBuffers.

- Replay path now also strips mouse-tracking enables (?1000-?1007), matching
  the live strip: buffers persisted BEFORE the live strip existed can still
  carry them, and a replayed ?1006h re-hijacks the scroll wheel.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/session.ts

@@ -258,6 +258,9 @@ export class Session extends EventEmitter {
   private _messages: ClaudeMessage[] = [];
   private _lineBuffer: string = '';
   private _lineBufferFlushTimer: NodeJS.Timeout | null = null;
+  // Codex only: trailing partial CSI held back so sequences split across PTY
+  // chunks can't slip past the alt-screen/scrollback strip (see _handleTerminalOutput)
+  private _codexSeqCarry: string = '';
   private resolvePromise: ((value: { result: string; cost: number }) => void) | null = null;
   private rejectPromise: ((reason: Error) => void) | null = null;
   private _promptResolved: boolean = false; // Guard against race conditions in runPrompt
@@ -1069,6 +1072,21 @@ export class Session extends EventEmitter {
     // scrollback intact. Codex's cursor-positioned redraws overwrite only the
     // cells they actually target, so the non-erased rows keep their content.
     if (this.mode === 'codex') {
+      // Reassemble sequences split across PTY chunk boundaries first: a chunk
+      // ending mid-sequence ('\x1b[?104' now, '9h' next) would slip past the
+      // strip below and leave xterm stuck in the scrollback-less alt buffer
+      // until the next buffer replay. Hold back an incomplete digit-only CSI
+      // tail (≤7 chars — the longest strippable intro is '\x1b[?1049') and
+      // prepend it to the next chunk; complete sequences are never held.
+      data = this._codexSeqCarry + data;
+      this._codexSeqCarry = '';
+      // eslint-disable-next-line no-control-regex
+      const splitTail = data.match(/\x1b(?:\[\??[0-9]{0,4})?$/);
+      if (splitTail) {
+        this._codexSeqCarry = splitTail[0];
+        data = data.slice(0, -splitTail[0].length);
+        if (!data) return;
+      }
       data = data
         // eslint-disable-next-line no-control-regex
         .replace(/\x1b\[\?(?:47|1047|1049)[hl]/g, '')
@@ -1691,6 +1709,7 @@ export class Session extends EventEmitter {
     this._errorBuffer = '';
     this._messages = [];
     this._lineBuffer = '';
+    this._codexSeqCarry = '';
     this._lastActivityAt = Date.now();
   }
 

src/web/routes/session-routes.ts

@@ -83,6 +83,12 @@ const LEADING_WHITESPACE_PATTERN = /^[\s\r\n]+/;
 const ALT_SCREEN_TOGGLE_PATTERN = /\x1b\[\?(?:47|1047|1049)[hl]/g;
 // eslint-disable-next-line no-control-regex
 const ERASE_SCROLLBACK_PATTERN = /\x1b\[3J/g;
+// Mouse-tracking enables (X10/button/any-event/UTF-8/SGR/alt-scroll) — once on,
+// xterm.js forwards wheel events to the app instead of scrolling the viewport.
+// Live streams are stripped at the source, but buffers persisted BEFORE that
+// strip existed can still carry them; strip on replay for parity.
+// eslint-disable-next-line no-control-regex
+const MOUSE_TRACKING_PATTERN = /\x1b\[\?(?:1000|1001|1002|1003|1005|1006|1007)[hl]/g;
 
 /**
  * Strip redundant Ink spinner/status-bar redraw frames from the terminal buffer.
@@ -941,7 +947,10 @@ export function registerSessionRoutes(
     // xterm.js obeys them by switching to its scrollback-less alt buffer and
     // wiping saved lines, so conversation history disappears on tab switch.
     if (session.mode === 'codex') {
-      strippedBuffer = strippedBuffer.replace(ALT_SCREEN_TOGGLE_PATTERN, '').replace(ERASE_SCROLLBACK_PATTERN, '');
+      strippedBuffer = strippedBuffer
+        .replace(ALT_SCREEN_TOGGLE_PATTERN, '')
+        .replace(ERASE_SCROLLBACK_PATTERN, '')
+        .replace(MOUSE_TRACKING_PATTERN, '');
     }
 
     if (tailBytes > 0 && strippedBuffer.length > tailBytes) {