Bump ttimeoutlen to 50ms on SSH/TTY (#75)

* Bump ttimeoutlen to 50ms on SSH/TTY

ttimeoutlen=10 fragments multi-byte key codes (F-keys, arrows, Alt-
prefixes) when one-way latency exceeds 10ms, which is normal on SSH.
Vim then sees ESC followed by a literal letter and either returns to
Normal mode mid-insert or treats the trailing byte as a separate
keypress (so <F4> inserts "4").

50ms is the standard "slow link" value: well below perceptible <Esc>
delay locally and big enough for typical residential/long-haul SSH.
g:is_tty already gates several other terminal accommodations; reuse
it here.

Closes #74

* Pin TERM in ttimeoutlen test (env-hermetic)

CHANGELOG.md

@@ -26,6 +26,10 @@
 - README badge and `install.sh` recommend Vim 8.1+ instead of 8.0+ —
   the runtime conditionally relies on patches `8.1.0360` (diffopt) and
   `8.1.1517` (completeopt+=popup), so 8.0 users hit option errors
+- `ttimeoutlen` is now 50ms when `g:is_tty` (was 10ms unconditionally);
+  fixes F-keys, arrow keys, and Alt-prefixes fragmenting on SSH where
+  one-way latency exceeds 10ms. Local terminals keep the 10ms snappy
+  default
 - `install.sh` no longer silently `PlugClean!`s user-added plugins from
   `~/.vim/plugged`; it now lists undeclared plugin directories first and
   asks before removing them (`--yes` skips the removal entirely)

modules/core.vim

@@ -42,7 +42,10 @@ set noerrorbells
 set novisualbell
 set t_vb=
 set ttimeout
-set ttimeoutlen=10
+" Wait long enough on SSH/TTY for multi-byte key codes to arrive intact —
+" 10ms fragments F-keys, arrows, and Alt-prefixes when one-way latency > 10ms.
+" 50ms is well under perceptible <Esc>→Normal delay locally.
+let &ttimeoutlen = g:is_tty ? 50 : 10
 
 if $COLORTERM ==# 'gnome-terminal'
     set t_Co=256

scripts/test.sh

@@ -257,6 +257,14 @@ check_vim() {
         -c 'if maparg(",F", "n") !~# "gg=G" | cquit | endif' \
         -c 'qa!' 2>&1
 
+    TERM=xterm-256color XDG_CONFIG_HOME="$EMPTY_XDG" vim -u .vimrc -i NONE -es -N \
+        -c 'if g:is_tty || &ttimeoutlen != 10 | cquit | endif' \
+        -c 'qa!' 2>&1
+
+    TERM=linux XDG_CONFIG_HOME="$EMPTY_XDG" vim -u .vimrc -i NONE -es -N \
+        -c 'if !g:is_tty || &ttimeoutlen != 50 | cquit | endif' \
+        -c 'qa!' 2>&1
+
     XDG_CONFIG_HOME="$EMPTY_XDG" vim -u .vimrc -i NONE -es -N \
         -c 'silent! delcommand LspStatus' \
         -c 'silent! delcommand LspInstallServer' \