fix(vt): Ctrl+letter keys not forwarded to child processes under kitty kb protocol

[michaellukashov]

fix(vt): Ctrl+letter keys not forwarded to child processes under kitty keyboard protocol

Problem

When kitty keyboard protocol is active in the VT shell, Ctrl+letter combinations (A-Z) generate kitty escape sequences (ESC[4;5u for Ctrl+D) instead of raw control bytes (0x04). Non-far2l child processes — like any terminal application that doesn't implement kitty keyboard protocol — receive nothing for these keypresses. This breaks Ctrl+D, Ctrl+K, Ctrl+U, Ctrl+A, Ctrl+E in editors, shells, and TUI applications running inside far2l's VT panels.

Root Cause

TranslateKeyEvent in far2l/src/vt/vtshell.cpp checks _kitty_kb_flags first. When set (child negotiated kitty keyboard protocol), VT_TranslateKeyToKitty always wins — even for keys that have trivial legacy encodings. The kitty escape sequences are only understood by terminals implementing that protocol, not by arbitrary child processes.

Fix

In TranslateKeyEvent, after kitty translation produces a result for Ctrl+letter keys (ctrl only, no alt/shift, VK between A-Z), fall through to the legacy VT_TranslateSpecialKey path which correctly maps Ctrl+D→\x04, Ctrl+K→\x0b, etc. All other keys (arrows, F-keys, modifiers, multi-modifier combos) continue to use kitty protocol unchanged.

// Ctrl+letter falls through to legacy translation
if (!(ctrl && !alt && !shift
    && KeyEvent.wVirtualKeyCode >= 'A'
    && KeyEvent.wVirtualKeyCode <= 'Z')) {
    return as_kitty;
}

Additional changes

• TTYRawMode enhancement — explicit termios flag clearing beyond cfmakeraw (CREAD|CLOCAL, VMIN=1/VTIME=0, defensive clearing of IUTF8/IXOFF/IUCLC/ECHOCTL). Added dup() failure check. Previously, raw mode could fail silently.
• FAR2L_TTY_DIAG — runtime diagnostic (env var, no recompile) prints actual terminal flags after raw mode setup
• Build fix — g_tty_profiler pointer access (g_tty_profiler.frames → g_tty_profiler->frames) in TTYBackend.cpp WriterThread

Files changed

File	Lines	Purpose
far2l/src/vt/vtshell.cpp	+7/-2	Main fix: kitty kb Ctrl+letter fallthrough

Verification

Tested under WindowsTerminal → SSH → far2l running oh-my-pi (a TUI application). Before: Ctrl+D/K/U/A/E produce no effect. After: all Ctrl+letter keys work correctly (confirmed with FAR2L_TTY_DIAG=1 and byte-level tracing).

[unxed]

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