fix: fix background color detection printing stuff into terminal on wsl boot

bin/executable_term-background

@@ -13,19 +13,43 @@
 #   export TERM_BACKGROUND=light   # or dark
 # in ~/.environment.local on that machine.
 #
-# Tune the response wait via TERM_BACKGROUND_TIMEOUT (tenths of a second).
+# Tune the per-attempt wait via TERM_BACKGROUND_TIMEOUT (tenths of a second)
+# and the number of attempts via TERM_BACKGROUND_ATTEMPTS. We poll rather than
+# do a single fixed-length read because on a freshly booted WSL instance the
+# very first terminal's OSC 11 reply can arrive well after a short window
+# closes; if we restored cooked/echo mode by then, the late reply leaks onto
+# the screen (and into the shell's input buffer) as literal text. Staying in
+# raw/no-echo mode across multiple short attempts lets a slow first reply
+# still be captured silently instead of leaking.
 
 # Need a controlling terminal to talk to.
 [ -t 0 ] || { echo dark; exit 0; }
 exec 3<>/dev/tty || { echo dark; exit 0; }
 
-# Raw mode with a short read timeout (min 0 time N = up to N*0.1s) so an
-# unresponsive terminal costs us at most that long.
 saved=$(stty -g <&3 2>/dev/null) || { echo dark; exit 0; }
 stty raw -echo min 0 time "${TERM_BACKGROUND_TIMEOUT:-4}" <&3 2>/dev/null
 
 printf '\033]11;?\033\\' >&3            # OSC 11 query
-answer=$(dd bs=64 count=1 <&3 2>/dev/null)
+
+answer=""
+attempts="${TERM_BACKGROUND_ATTEMPTS:-3}"
+i=0
+while [ "$i" -lt "$attempts" ]; do
+    answer="$answer$(dd bs=64 count=1 <&3 2>/dev/null)"
+    # A full "rgb:RRRR/GGGG/BBBB" reply has two '/' separators; stop as soon
+    # as we have them instead of waiting out every remaining attempt.
+    rest=${answer#*rgb:}
+    if [ "$rest" != "$answer" ]; then
+        tmp=$rest
+        count=0
+        while [ "$tmp" != "${tmp#*/}" ]; do
+            count=$((count + 1))
+            tmp=${tmp#*/}
+        done
+        [ "$count" -ge 2 ] && break
+    fi
+    i=$((i + 1))
+done
 
 stty "$saved" <&3 2>/dev/null           # restore before anything else
 exec 3>&-