pre-commit hook: Android tests through gradle-serial.sh with JDK 25 on PATH, JAVA_HOME untouched; installer replaces an older Kvitt hook

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

tools/install-git-hooks.sh

@@ -1,15 +1,24 @@
 #!/usr/bin/env bash
 # Installs the Kvitt pre-commit hook into this repository's hooks folder (shared by all worktrees).
 # The hook guards itself: on branches without android/ or server/ it only runs the secrets check.
+# An earlier version of the Kvitt hook (recognised by its first comment line) is replaced; any other hook is kept.
 set -euo pipefail
 here="$(cd "$(dirname "$0")" && pwd)"
+src="$here/git-hooks/pre-commit"
 hooks="$(git -C "$here" rev-parse --path-format=absolute --git-common-dir)/hooks"
 target="$hooks/pre-commit"
-if [[ -e "$target" ]] && ! cmp -s "$here/git-hooks/pre-commit" "$target"; then
-  echo "A different pre-commit hook already exists at $target; not overwriting. Merge them by hand." >&2
-  exit 1
+marker="# Kvitt pre-commit hook:"
+if [[ -e "$target" ]]; then
+  if cmp -s "$src" "$target"; then
+    echo "Up to date: $target"
+    exit 0
+  fi
+  if ! sed -n 2p "$target" | grep -qF "$marker"; then
+    echo "A different pre-commit hook already exists at $target; not overwriting. Merge them by hand." >&2
+    exit 1
+  fi
 fi
 mkdir -p "$hooks"
-cp "$here/git-hooks/pre-commit" "$target"
+cp "$src" "$target"
 chmod +x "$target"
 echo "Installed $target"