tools: one Gradle lock helper (gradle-lock.sh) for gradle-serial.sh and clean-builds.sh

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

tools/gradle-serial.sh

@@ -3,14 +3,10 @@
 # (CLAUDE.md › Build and verify: parallel builds exhaust memory). Waits for a running build to finish, then runs.
 # The Gradle project lives in android/; the wrapper there is used whatever directory this is started from.
 # Usage from any directory of a checkout or worktree:  tools/gradle-serial.sh check   (or ../tools/gradle-serial.sh from android/)
-lock=/tmp/kvitt-gradle.lock
+# shellcheck source-path=SCRIPTDIR source=gradle-lock.sh
+. "$(dirname "$0")/gradle-lock.sh"
 top=$(git rev-parse --show-toplevel) || exit 1
 [ -x "$top/android/gradlew" ] || { echo "gradle-serial: no android/gradlew in $top yet" >&2; exit 1; }
-while ! mkdir "$lock" 2>/dev/null; do
-  pid=$(cat "$lock/pid" 2>/dev/null)
-  if [ -n "$pid" ] && ! kill -0 "$pid" 2>/dev/null; then rm -rf "$lock"; continue; fi
-  sleep 5
-done
-echo $$ > "$lock/pid"
-trap 'rm -rf "$lock"' EXIT INT TERM HUP
+gradle_lock_acquire
+trap 'rm -rf "$KVITT_GRADLE_LOCK"' EXIT INT TERM HUP
 cd "$top/android" && ./gradlew "$@"