fix(kitty): read file permissions correctly where stat is GNU

`chezmoi apply` on Linux printed "could not regenerate kitty theme
files" every run. GNU stat reads -f as --file-system, so
`stat -f '%Lp' file` prints a block of filesystem info to stdout and
exits non-zero. The `|| stat -c '%a'` fallback then appended the real
answer to that block, and chmod rejected the result, failing the script
under set -e.

Replace the chain with a file_mode() helper in both scripts: try the GNU
form first, since BSD rejects -c cleanly without printing anything, and
accept the answer only if it is octal. Covered by a new case in
tests/test_theme_mode.sh using a stat stub that reproduces GNU's
behaviour; it fails against the old chain.

private_dot_config/kitty/private_executable_apply-theme-mode.sh

@@ -14,6 +14,22 @@
 
 set -eu
 
+# Permission bits of a file, or 600 if they cannot be read. GNU stat spells this
+# `-c %a` while BSD/macOS spells it `-f %Lp`, and each mis-parses the other's
+# form -- GNU treats `-f` as --file-system and prints a block of filesystem info
+# before failing -- so try one at a time and only accept an octal answer.
+file_mode() {
+    _m=$(stat -c '%a' "$1" 2>/dev/null) || _m=''
+    case "$_m" in
+        [0-7][0-7][0-7] | [0-7][0-7][0-7][0-7]) printf '%s\n' "$_m"; return 0 ;;
+    esac
+    _m=$(stat -f '%Lp' "$1" 2>/dev/null) || _m=''
+    case "$_m" in
+        [0-7][0-7][0-7] | [0-7][0-7][0-7][0-7]) printf '%s\n' "$_m"; return 0 ;;
+    esac
+    printf '600\n'
+}
+
 script_dir="$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"
 config_dir=${1:-"$script_dir"}
 canonical_dir="$config_dir/themes"
@@ -54,12 +70,9 @@ for appearance in dark light no-preference; do
     [ -f "$canonical" ] || continue
 
     generated="$config_dir/$appearance-theme.auto.conf"
-    # stat -f is BSD/macOS, stat -c is GNU; this also runs on Linux boxes.
     mode_bits=600
     if [ -f "$generated" ]; then
-        mode_bits=$(stat -f '%Lp' "$generated" 2>/dev/null \
-            || stat -c '%a' "$generated" 2>/dev/null \
-            || echo 600)
+        mode_bits=$(file_mode "$generated")
     fi
 
     tmp=$(mktemp "$generated.tmp.XXXXXX")

private_dot_config/kitty/private_executable_repair-auto-themes.sh

@@ -2,6 +2,22 @@
 
 set -eu
 
+# Permission bits of a file, or 600 if they cannot be read. GNU stat spells this
+# `-c %a` while BSD/macOS spells it `-f %Lp`, and each mis-parses the other's
+# form -- GNU treats `-f` as --file-system and prints a block of filesystem info
+# before failing -- so try one at a time and only accept an octal answer.
+file_mode() {
+    _m=$(stat -c '%a' "$1" 2>/dev/null) || _m=''
+    case "$_m" in
+        [0-7][0-7][0-7] | [0-7][0-7][0-7][0-7]) printf '%s\n' "$_m"; return 0 ;;
+    esac
+    _m=$(stat -f '%Lp' "$1" 2>/dev/null) || _m=''
+    case "$_m" in
+        [0-7][0-7][0-7] | [0-7][0-7][0-7][0-7]) printf '%s\n' "$_m"; return 0 ;;
+    esac
+    printf '600\n'
+}
+
 config_dir=${1:-"$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"}
 
 for appearance in dark light no-preference; do
@@ -22,10 +38,7 @@ for appearance in dark light no-preference; do
     trap 'rm -f "$tmp"' EXIT HUP INT TERM
     awk '$1 != "macos_titlebar_color"' "$config_file" > "$tmp"
     printf '\nmacos_titlebar_color background\n' >> "$tmp"
-    # stat -f is BSD/macOS, stat -c is GNU; this also runs on Linux boxes.
-    chmod "$(stat -f '%Lp' "$config_file" 2>/dev/null \
-        || stat -c '%a' "$config_file" 2>/dev/null \
-        || echo 600)" "$tmp"
+    chmod "$(file_mode "$config_file")" "$tmp"
     mv -f "$tmp" "$config_file"
     trap - EXIT HUP INT TERM
 done

private_dot_config/kitty/private_tests/private_executable_test_theme_mode.sh

@@ -149,4 +149,36 @@ run_fish dark 'theme >/dev/null'
 
 "$root/tests/verify_auto_themes.sh" "$config_dir"
 
+# --- the scripts must work where stat is GNU, not BSD ---------------------
+# GNU stat reads -f as --file-system, so `stat -f '%Lp' file` prints a block of
+# filesystem info to stdout *and* exits non-zero. Chaining it into `|| stat -c`
+# concatenates that block with the real answer and chmod then rejects it, which
+# broke `chezmoi apply` on Linux with "could not regenerate kitty theme files".
+cat >"$fake_bin/stat" <<'EOF'
+#!/bin/sh
+case "$1" in
+    -c) shift; [ "$1" = "%a" ] && shift; /usr/bin/stat -f '%Lp' "$1" ;;
+    -f) shift
+        echo "  File: \"$2\""
+        echo "Block size: 4096       Fundamental block size: 4096"
+        exit 1 ;;
+    *) exec /usr/bin/stat "$@" ;;
+esac
+EOF
+chmod +x "$fake_bin/stat"
+
+echo auto >"$config_dir/theme-mode"
+if ! PATH="$fake_bin:/usr/bin:/bin" "$root/apply-theme-mode.sh" "$config_dir" \
+        >/dev/null 2>&1; then
+    echo "not ok - apply-theme-mode.sh fails where stat is GNU" >&2
+    exit 1
+fi
+for appearance in dark light no-preference; do
+    [ -f "$config_dir/$appearance-theme.auto.conf" ] || {
+        echo "not ok - GNU stat run did not produce $appearance theme" >&2
+        exit 1
+    }
+done
+rm -f "$fake_bin/stat"
+
 echo "PASS: theme mode is remembered, survives kitten themes, and collapses to auto"