fix(cli): skip Kitty keyboard protocol push for Ghostty, use modifyOtherKeys only

Ghostty's Kitty disambiguate-mode implementation strips the Alt modifier
from the Backspace key — Option+Backspace arrives as bare \x7f instead of
the expected \x1b[27;3;127~, breaking backward-kill-word.  This was a
regression introduced when PR #87630 re-added the CSI >1u Kitty protocol
push for all allowlisted terminals including Ghostty.

Under modifyOtherKeys mode (CSI >4;2m), Ghostty correctly sends
\x1b[27;3;127~ for Option+Backspace, which the alias table in
pt_input_extras already maps to (Escape, ControlH) = backward-kill-word.

Fix: for Ghostty only, push just modifyOtherKeys and skip the Kitty
protocol push.  All other terminals (iTerm2, WezTerm, kitty, tmux, VS Code)
still get the full dual-protocol push.

Ghostty upstream tracking: discussion #9560, issue #9895 (cmd+backspace
variant of the same root cause).

cli.py

@@ -4095,6 +4095,13 @@ _TERMINAL_INPUT_MODE_RESET_SEQ = (
     "\x1b[?25h"    # ensure cursor visible
 )
 _EXTENDED_ENTER_KEYS_SEQ = "\x1b[>1u\x1b[>4;2m"
+# Ghostty: push ONLY modifyOtherKeys, not the Kitty keyboard protocol.
+# Ghostty's Kitty disambiguate-mode implementation strips the Alt modifier
+# from the Backspace key — Option+Backspace arrives as bare \x7f instead of
+# the expected \x1b[27;3;127~, breaking backward-kill-word (#87630
+# regression).  modifyOtherKeys mode works correctly on Ghostty and covers
+# every modified key combo the alias table handles.
+_GHOSTTY_EXTENDED_ENTER_KEYS_SEQ = "\x1b[>4;2m"
 
 
 _BACKSLASH_LINE_CONTINUATION_RE = re.compile(r"\\[ \t]*$")
@@ -4148,20 +4155,37 @@ def _enable_extended_enter_keys(output=None, env: Optional[Mapping[str, str]] =
     Ctrl+C, which is handled by prompt_toolkit's ``c-c`` binding (raw mode
     clears ISIG, so the kernel INTR path was never in play for the CLI).
 
+    Ghostty exception: Ghostty's Kitty disambiguate mode strips the Alt
+    modifier from the Backspace key, so Option+Backspace arrives as bare
+    \x7f instead of \x1b[27;3;127~, breaking backward-kill-word.  Ghostty
+    implements modifyOtherKeys correctly, so for Ghostty we push only
+    modifyOtherKeys and skip the Kitty protocol push.
+
     The exit reset sequence pops/resets both modes, so this is safe across
     normal exits, Ctrl+C, and SIGTERM cleanup.
     """
     if not _terminal_supports_extended_enter_keys(env):
         return False
     try:
+        # Ghostty: skip Kitty protocol, use only modifyOtherKeys.
+        if env is None:
+            env = os.environ
+        term_program = (env.get("TERM_PROGRAM") or "").strip()
+        term = (env.get("TERM") or "").strip().lower()
+        is_ghostty = (
+            term_program == "ghostty"
+            or term == "xterm-ghostty"
+        )
+        seq = _GHOSTTY_EXTENDED_ENTER_KEYS_SEQ if is_ghostty else _EXTENDED_ENTER_KEYS_SEQ
+
         target = output
         if target is not None and hasattr(target, "write_raw"):
-            target.write_raw(_EXTENDED_ENTER_KEYS_SEQ)
+            target.write_raw(seq)
             target.flush()
             return True
         stream = sys.stdout
         if stream is not None and stream.isatty():
-            stream.write(_EXTENDED_ENTER_KEYS_SEQ)
+            stream.write(seq)
             stream.flush()
             return True
     except Exception:

tests/cli/test_ctrl_enter_newline.py

@@ -153,6 +153,66 @@ def test_unknown_terminal_does_not_enable_extended_enter_keys():
     assert cli_mod._terminal_supports_extended_enter_keys({"TERM_PROGRAM": "unknown"}) is False
 
 
+# ---------------------------------------------------------------------------
+# Ghostty: must push ONLY modifyOtherKeys, not the Kitty keyboard protocol.
+# Ghostty's Kitty disambiguate mode strips the Alt modifier from Backspace,
+# so Option+Backspace arrives as bare \x7f instead of \x1b[27;3;127~,
+# breaking backward-kill-word.  modifyOtherKeys mode works correctly.
+# ---------------------------------------------------------------------------
+class _FakeOutput:
+    """Minimal output object with write_raw + flush for _enable_extended_enter_keys."""
+    def __init__(self):
+        self.written = b""
+    def write_raw(self, data):
+        self.written += data.encode() if isinstance(data, str) else data
+    def flush(self):
+        pass
+
+
+def test_ghostty_uses_modify_other_keys_only():
+    """Ghostty must NOT push the Kitty keyboard protocol (CSI >1u)."""
+    import cli as cli_mod
+
+    out = _FakeOutput()
+    result = cli_mod._enable_extended_enter_keys(
+        output=out,
+        env={"TERM_PROGRAM": "ghostty", "TERM": "xterm-ghostty"},
+    )
+    assert result is True
+    # Must contain modifyOtherKeys push ...
+    assert b"\x1b[>4;2m" in out.written
+    # ... but NOT the Kitty protocol push.
+    assert b"\x1b[>1u" not in out.written
+
+
+def test_ghostty_via_term_var_uses_modify_other_keys_only():
+    """xterm-ghostty TERM (without TERM_PROGRAM) also skips Kitty protocol."""
+    import cli as cli_mod
+
+    out = _FakeOutput()
+    result = cli_mod._enable_extended_enter_keys(
+        output=out,
+        env={"TERM": "xterm-ghostty"},
+    )
+    assert result is True
+    assert b"\x1b[>4;2m" in out.written
+    assert b"\x1b[>1u" not in out.written
+
+
+def test_non_ghostty_terminals_still_push_kitty_protocol():
+    """iTerm2 and others still get the full dual-protocol push."""
+    import cli as cli_mod
+
+    out = _FakeOutput()
+    result = cli_mod._enable_extended_enter_keys(
+        output=out,
+        env={"TERM_PROGRAM": "iTerm.app", "TERM": "xterm-256color"},
+    )
+    assert result is True
+    assert b"\x1b[>1u" in out.written
+    assert b"\x1b[>4;2m" in out.written
+
+
 @pytest.mark.linux_only
 def test_proc_version_microsoft_marker_preserves_newline():
     """WSL detection via /proc when env vars are scrubbed (sudo etc.).