Threaded gunicorn workers so a retry storm cannot starve the UI

docker-compose.yml

@@ -79,10 +79,26 @@ services:
       - gunicorn
       - --bind
       - 0.0.0.0:5001
+      # Threaded workers, not the blocking sync default. An agent that fails
+      # the TLS handshake retries in a loop, and with 4 sync workers a handful
+      # of those pinned every worker: real UI requests queued 20+ seconds while
+      # the CPU sat idle. A stuck connection now holds one THREAD, and 32
+      # (4 x 8) have to be exhausted before a person waits.
+      #
+      # Found in production at the other site (their commit db75ca7). Their
+      # server, our agent - so the same client behaviour will reach any site
+      # running the endpoint agent, and the fix belongs in the product rather
+      # than on one branch.
+      - --worker-class
+      - gthread
       - --workers
       - "4"
+      - --threads
+      - "8"
+      # 30, not 60: a hung connection frees its thread in half the time, which
+      # is what decides whether a retry storm is absorbed or queues.
       - --timeout
-      - "60"
+      - "30"
       - --access-logfile
       - "-"
       - --error-logfile