plex: move the watchtower ntfy URL out of compose into a gitignored .env, and sync the opt-in watchtower changes that were only on the host

plex/docker-compose.yml

@@ -9,6 +9,12 @@ services:
     container_name: plex
     restart: unless-stopped
 
+    # Watchtower runs in OPT-IN mode (WATCHTOWER_LABEL_ENABLE below), so this
+    # label is what keeps Plex auto-updating. Remove it and Plex silently
+    # stops getting updates.
+    labels:
+      com.centurylinklabs.watchtower.enable: "true"
+
     # NOT OPTIONAL. Plex's local discovery (GDM) and client auto-detection rely
     # on broadcast traffic that a bridge network silently eats. (DLNA is off on
     # this server, so discovery — not DLNA — is the reason.) This is also why
@@ -111,13 +117,24 @@ services:
   watchtower:
     # Auto-updater — checks daily at 05:00 local, pulls newer images,
     # recreates the container with identical settings, prunes old images,
-    # and ntfys arrsstack-alerts about anything it did. Local builds
+    # and ntfys arrsstack-alerts about anything it did.
-    # (shell-mcp) have no registry to compare against and are ignored.
+    #
+    # OPT-IN MODE (WATCHTOWER_LABEL_ENABLE=true). Watchtower touches ONLY
+    # containers carrying com.centurylinklabs.watchtower.enable=true.
+    # Locally-built images (gamelab, shell-mcp) exist in no registry, so under
+    # the old opt-out mode Watchtower HEAD-requested Docker Hub for them,
+    # got a 401, and ntfyd a failure every single morning. Opt-in makes the
+    # safe thing the default: a new local build is ignored unless someone
+    # deliberately labels it. Anything added here that SHOULD auto-update
+    # needs enable=true, same as Plex above.
     image: containrrr/watchtower
     container_name: watchtower
     restart: unless-stopped
+    labels:
+      com.centurylinklabs.watchtower.enable: "true"
     environment:
       - TZ=${TZ:-America/New_York}
+      - WATCHTOWER_LABEL_ENABLE=true
       # Watchtower v1.7.1's bundled docker client defaults to API 1.25 and
       # its version negotiation fails against Engine 29 (min API 1.40),
       # leaving the container in a crash loop. Pinning the API version is
@@ -127,7 +144,11 @@ services:
       - WATCHTOWER_SCHEDULE=0 0 5 * * *
       - WATCHTOWER_CLEANUP=true
       - WATCHTOWER_NOTIFICATIONS=shoutrrr
-      - WATCHTOWER_NOTIFICATION_URL=ntfy://ntfy.thewichersfamily.com/arrsstack-alerts
+      # Carries ntfy credentials, so it lives in /srv/plex/.env (gitignored,
+      # 0600) and NEVER in this file. See .env.example. ntfy went deny-all on
+      # 2026-08-03; before that this URL was anonymous and publishing to
+      # arrsstack-alerts with no auth at all.
+      - WATCHTOWER_NOTIFICATION_URL=${WATCHTOWER_NOTIFICATION_URL}
       - WATCHTOWER_NOTIFICATION_TEMPLATE={{range .}}{{.Message}}{{println}}{{end}}
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock