diff --git a/scripts/lib/storage.sh b/scripts/lib/storage.sh
index 8b629182c..104cc632f 100644
--- a/scripts/lib/storage.sh
+++ b/scripts/lib/storage.sh
@@ -346,7 +346,12 @@ agmsg_runtime_lock_acquire() {
   resource="$1"; owner_pid="$2"; expected_owner="${3:-}"
   case "$owner_pid:$expected_owner" in *[!0-9:]*) return 1 ;; esac
   db="$(_agmsg_runtime_db_path)"
-  _agmsg_runtime_db_exists "$db" || return 1
+  if ! _agmsg_runtime_db_exists "$db"; then
+    # Leave a diagnostic (#424). The status stays 1. Keep the words busy and
+    # locked out of this line: actas-lock.sh retries stderr that matches them.
+    printf 'agmsg_runtime_lock_acquire: runtime db missing: %s\n' "$db" >&2
+    return 1
+  fi
   resource_sql="$(_agmsg_runtime_lock_resource_sql "$resource")"
   sql=".bail on
 BEGIN IMMEDIATE;
diff --git a/tests/test_storage.bats b/tests/test_storage.bats
index 1ad921813..1d1c347f9 100644
--- a/tests/test_storage.bats
+++ b/tests/test_storage.bats
@@ -213,6 +213,36 @@ SH
   [ ! -e "$AGMSG_STORAGE_PATH/messages.db" ]
 }
 
+@test "storage: runtime lock acquire on an absent store says why on stderr and keeps status 1" {
+  # #424: the refusal used to be silent.
+  export AGMSG_STORAGE_PATH="$BATS_TEST_TMPDIR/silent-lock-store"
+  source "$SCRIPTS/lib/storage.sh"
+  local err="$BATS_TEST_TMPDIR/lock-acquire.stderr" out rc=0 db
+  db="$(_agmsg_runtime_db_path)"
+
+  out="$(agmsg_runtime_lock_acquire codex-dispatcher:test 111 2>"$err")" || rc=$?
+
+  [ "$rc" -eq 1 ]
+  [ -z "$out" ]
+  [ "$(wc -l < "$err" | tr -d ' ')" -eq 1 ]
+  [ "$(cat "$err")" = "agmsg_runtime_lock_acquire: runtime db missing: $db" ]
+  [ ! -e "$db" ]
+}
+
+@test "storage: runtime lock acquire on a present store writes nothing to stderr" {
+  # Negative control for #424: the diagnostic belongs to the absent-store path only.
+  export AGMSG_STORAGE_PATH="$BATS_TEST_TMPDIR/present-lock-store"
+  source "$SCRIPTS/lib/storage.sh"
+  agmsg_storage_ensure_initialized
+  local err="$BATS_TEST_TMPDIR/lock-acquire-present.stderr" out rc=0
+
+  out="$(agmsg_runtime_lock_acquire codex-dispatcher:test 111 2>"$err")" || rc=$?
+
+  [ "$rc" -eq 0 ]
+  [ "$out" = 111 ]
+  [ ! -s "$err" ]
+}
+
 @test "storage: every runtime lock entrypoint refuses an absent store" {
   export AGMSG_STORAGE_PATH="$BATS_TEST_TMPDIR/absent-lock-store"
   source "$SCRIPTS/lib/storage.sh"