diff --git a/config/puma.rb b/config/puma.rb
index 6946840..5932fd5 100644
--- a/config/puma.rb
+++ b/config/puma.rb
@@ -32,17 +32,17 @@
 # Specifies the number of `workers` to boot in clustered mode.
 # Workers are forked web server processes. If using threads and workers together
 # the concurrency of the application would be max `threads` * `workers`.
-# Workers do not work on JRuby or Windows (both of which do not support
-# processes).
 #
-# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
-
-# Use the `preload_app!` method when specifying a `workers` number.
-# This directive tells Puma to first boot the application and load code
-# before forking the application. This takes advantage of Copy On Write
-# process behavior so workers use less memory.
-#
-# preload_app!
+# MRI executes Ruby on one core per process, so however many threads run above,
+# a single process caps the whole app at one core. Two workers in production;
+# development keeps single mode, where 0 means no cluster at all.
+default_workers = ENV.fetch('RAILS_ENV', 'development') == 'production' ? 2 : 0
+workers ENV.fetch('WEB_CONCURRENCY') { default_workers }.to_i
+
+# No preload_app!: phased restarts (SIGUSR1) replace workers one at a time with
+# the listener kept open — a restart without dropped requests — and they only
+# work when each worker can boot the app itself rather than inherit it from a
+# fork.
 
 # Allow puma to be restarted by `bin/rails restart` command.
 plugin :tmp_restart
diff --git a/deploy/purge-snapshots.sh b/deploy/purge-snapshots.sh
index 5fb461d..9673e36 100755
--- a/deploy/purge-snapshots.sh
+++ b/deploy/purge-snapshots.sh
@@ -14,6 +14,14 @@
 
 set -euo pipefail
 
+# One purge at a time. The container below carries a fixed name and the
+# cleanup after it removes whatever holds that name, so an overlapping run --
+# cron plus a manual invocation, say -- would kill the other's container and
+# then skip its own purge. The lock is released when the script exits and fd 9
+# closes.
+exec 9>/var/lock/openipc-purge-snapshots.lock
+flock -n 9 || { echo "another purge is already running; leaving it to finish"; exit 0; }
+
 COMPOSE_DIR=/srv/www/deploy-src/deploy
 BLOB_ROOT=/srv/www/shared/storage
 IMAGE_TAG=$(sed -n 's/^PROD_TAG=//p' "${COMPOSE_DIR}/.env" | tail -1)
@@ -36,13 +44,26 @@ log "purging snapshots past retention (image ${IMAGE_TAG:0:12})"
 # A one-off container rather than `docker exec` into web-prod: purging is IO
 # heavy and should not compete with request threads for the web process, and a
 # crash here must not take the site down.
-docker run --rm \
+# --name + timeout + rm -f: the runner can deadlock at process exit draining
+# the :async adapter's thread pool (ActiveStorage still enqueues PurgeJobs
+# during destroy despite the inline purge). When that happens the container
+# never exits, --rm never fires, one hung container accumulates per night
+# holding a MySQL connection, and set -e stops every later step of this script
+# from running. The purge work itself finishes in seconds, before the hang, so
+# a bounded lifetime loses nothing; ten minutes is generous.
+# A stale container from an interrupted run -- host reboot, script killed
+# after the timeout fired but before its own cleanup -- would make this run
+# fail on the name collision and cost a night's purge. Under the flock nothing
+# legitimate holds this name, so clear it first.
+docker rm -f openipc-purge-snapshots >/dev/null 2>&1 || true
+timeout 600 docker run --rm --name openipc-purge-snapshots \
   --env-file /srv/www/.env.prod \
   -v /run/mysqld:/run/mysqld \
   -v "$BLOB_ROOT":/rails/storage \
   "ghcr.io/openipc/website:${IMAGE_TAG}" \
   bundle exec rails runner 'puts "purged #{PurgeImagesJob.new.perform} snapshots"' \
-  || { log "FAILED: purge job errored"; exit 1; }
+  || log "WARNING: purge job errored or timed out, continuing"
+docker rm -f openipc-purge-snapshots >/dev/null 2>&1 || true
 
 # Download rows, past their window. A row is about 60 bytes and the site sends
 # roughly eighty images a day, so two years of them is a few megabytes -- the