diff --git a/scripts/worker.sh b/scripts/worker.sh
index 1511d7e..d0c57cf 100644
--- a/scripts/worker.sh
+++ b/scripts/worker.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 set -euo pipefail
 
-PLUGIN_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+PLUGIN_DIR="${PLUGIN_DIR:-$(cd "$(dirname "$0")/.." && pwd)}"
 DATA_DIR="$PLUGIN_DIR/data"
 JOB_DIR="$DATA_DIR/jobs/pending"
 PROCESSING_DIR="$DATA_DIR/jobs/processing"
@@ -10,15 +10,54 @@ WORKER_LOCK_DIR="$DATA_DIR/worker.lock"
 DB_LOCK_DIR="$DATA_DIR/lock"
 PID_DIR="$DATA_DIR/pids"
 CANCEL_DIR="$DATA_DIR/cancel"
+WORKER_LOCK_STALE_SECONDS="${WORKER_LOCK_STALE_SECONDS:-300}"
 
 mkdir -p "$JOB_DIR" "$PROCESSING_DIR" "$DONE_DIR" "$PID_DIR" "$CANCEL_DIR" "$DB_LOCK_DIR"
 
-if ! mkdir "$WORKER_LOCK_DIR" 2>/dev/null; then
+acquire_worker_lock() {
+  if mkdir "$WORKER_LOCK_DIR" 2>/dev/null; then
+    printf '%s' "$$" > "$WORKER_LOCK_DIR/pid" 2>/dev/null || true
+    return 0
+  fi
+
+  local existing_pid="" lock_mtime=0 now lock_age=0
+  if [ -r "$WORKER_LOCK_DIR/pid" ]; then
+    existing_pid="$(cat "$WORKER_LOCK_DIR/pid" 2>/dev/null || true)"
+  fi
+
+  if [ -n "$existing_pid" ]; then
+    if kill -0 "$existing_pid" 2>/dev/null; then
+      echo "alt-mysql worker: lock held by running pid $existing_pid, exiting" >&2
+      return 1
+    fi
+  else
+    lock_mtime="$(stat -c '%Y' "$WORKER_LOCK_DIR" 2>/dev/null || stat -f '%m' "$WORKER_LOCK_DIR" 2>/dev/null || echo 0)"
+    now="$(date +%s)"
+    if [ "$lock_mtime" -gt 0 ]; then
+      lock_age=$((now - lock_mtime))
+    fi
+    if [ "$lock_age" -lt "$WORKER_LOCK_STALE_SECONDS" ]; then
+      echo "alt-mysql worker: lock present without a live pid but younger than ${WORKER_LOCK_STALE_SECONDS}s (age ${lock_age}s), exiting" >&2
+      return 1
+    fi
+  fi
+
+  echo "alt-mysql worker: reclaiming stale lock (pid=${existing_pid:-none}, age=${lock_age}s)" >&2
+  rm -rf "$WORKER_LOCK_DIR"
+  if mkdir "$WORKER_LOCK_DIR" 2>/dev/null; then
+    printf '%s' "$$" > "$WORKER_LOCK_DIR/pid" 2>/dev/null || true
+    return 0
+  fi
+
+  return 1
+}
+
+if ! acquire_worker_lock; then
   exit 0
 fi
 
 cleanup() {
-  rmdir "$WORKER_LOCK_DIR" 2>/dev/null || true
+  rm -rf "$WORKER_LOCK_DIR" 2>/dev/null || true
 }
 trap cleanup EXIT
 
diff --git a/tests/worker_lock_test.sh b/tests/worker_lock_test.sh
new file mode 100755
index 0000000..d63100a
--- /dev/null
+++ b/tests/worker_lock_test.sh
@@ -0,0 +1,71 @@
+#!/bin/bash
+set -euo pipefail
+
+PLUGIN_DIR_REAL="$(cd "$(dirname "$0")/.." && pwd)"
+WORKER="$PLUGIN_DIR_REAL/scripts/worker.sh"
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+fail() {
+  echo "FAIL: $*" >&2
+  exit 1
+}
+
+backdate() {
+  local path="$1" seconds_ago="$2"
+  local ts
+  ts="$(date -v-"${seconds_ago}"S +%Y%m%d%H%M.%S 2>/dev/null || date -d "-${seconds_ago} seconds" +%Y%m%d%H%M.%S)"
+  touch -t "$ts" "$path"
+}
+
+run_worker() {
+  PLUGIN_DIR="$TMP_DIR" bash "$WORKER"
+}
+
+# --- Scenario 1: no existing lock - worker acquires it, runs, and cleans up normally ---
+OUTPUT1="$(run_worker 2>&1)"
+[ ! -e "$TMP_DIR/data/worker.lock" ] \
+  || fail "worker lock should be removed after a normal run with an empty queue, output: $OUTPUT1"
+
+# --- Scenario 2: lock genuinely held by a live process - worker must back off, not reclaim ---
+mkdir -p "$TMP_DIR/data"
+mkdir "$TMP_DIR/data/worker.lock"
+printf '%s' "$$" > "$TMP_DIR/data/worker.lock/pid"
+OUTPUT2="$(run_worker 2>&1)"
+echo "$OUTPUT2" | grep -qi "held by running pid" \
+  || fail "worker must log that the lock is held by a live pid, got: $OUTPUT2"
+[ -d "$TMP_DIR/data/worker.lock" ] \
+  || fail "worker must not remove a lock held by a genuinely live process"
+rm -rf "$TMP_DIR/data/worker.lock"
+
+# --- Scenario 3: lock left behind by a crashed worker (dead pid) - must be reclaimed ---
+mkdir -p "$TMP_DIR/data"
+mkdir "$TMP_DIR/data/worker.lock"
+printf '999999999' > "$TMP_DIR/data/worker.lock/pid"
+OUTPUT3="$(run_worker 2>&1)"
+echo "$OUTPUT3" | grep -qi "reclaiming stale lock" \
+  || fail "worker must log that it is reclaiming a stale lock (dead pid), got: $OUTPUT3"
+[ ! -e "$TMP_DIR/data/worker.lock" ] \
+  || fail "worker lock should be removed again after successfully reclaiming and running, output: $OUTPUT3"
+
+# --- Scenario 4: lock with no pid file but old enough to be considered abandoned ---
+mkdir -p "$TMP_DIR/data"
+mkdir "$TMP_DIR/data/worker.lock"
+backdate "$TMP_DIR/data/worker.lock" 301
+OUTPUT4="$(run_worker 2>&1)"
+echo "$OUTPUT4" | grep -qi "reclaiming stale lock" \
+  || fail "worker must reclaim an old lock with no pid file, got: $OUTPUT4"
+[ ! -e "$TMP_DIR/data/worker.lock" ] \
+  || fail "worker lock should be removed again after reclaiming an old pid-less lock, output: $OUTPUT4"
+
+# --- Scenario 5: lock with no pid file, but too young to be considered abandoned yet ---
+mkdir -p "$TMP_DIR/data"
+mkdir "$TMP_DIR/data/worker.lock"
+OUTPUT5="$(run_worker 2>&1)"
+echo "$OUTPUT5" | grep -qi "younger than" \
+  || fail "worker must back off on a young pid-less lock instead of reclaiming it, got: $OUTPUT5"
+[ -d "$TMP_DIR/data/worker.lock" ] \
+  || fail "worker must not remove a young pid-less lock (might just be mid-acquisition)"
+rm -rf "$TMP_DIR/data/worker.lock"
+
+echo "worker_lock_test: OK"