Accept absolute paths in reindent.sh --check

`--check` prefixed every path with the repository root unconditionally, so
passing an absolute path produced a bogus `$root//abs/path`, cp failed, and
the subsequent cmp reported the file as non-conforming. The exit status
happened to be 1, which looked correct while being reached for the wrong
reason.

In-place mode was unaffected -- it cds to the root and hands the list
straight to Emacs, where absolute paths resolve normally, which is why the
pre-commit hook worked.

Normalize both the copy and the compare through an abspath helper so
relative and absolute paths behave identically in either mode.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/reindent.sh

@@ -68,10 +68,19 @@ fi
 tmp=$(mktemp -d)
 trap 'rm -rf "$tmp"' EXIT INT TERM
 
+# Accept both repo-relative and absolute paths: the default file list is
+# relative, but callers (including the pre-commit hook) pass absolute ones.
+abspath() {
+    case "$1" in
+        /*) printf '%s' "$1" ;;
+        *)  printf '%s/%s' "$root" "$1" ;;
+    esac
+}
+
 copies=''
 for f in $files; do
     dest="$tmp/$(printf '%s' "$f" | tr '/' '_')"
-    cp "$root/$f" "$dest"
+    cp "$(abspath "$f")" "$dest"
     copies="$copies $dest"
 done
 
@@ -84,7 +93,7 @@ emacs --batch -Q -l "$elisp" -- $copies >/dev/null || {
 status=0
 for f in $files; do
     dest="$tmp/$(printf '%s' "$f" | tr '/' '_')"
-    if ! cmp -s "$root/$f" "$dest"; then
+    if ! cmp -s "$(abspath "$f")" "$dest"; then
         echo "$f"
         status=1
     fi