Fix letsencrypt auto-renew.

mise.toml

@@ -39,8 +39,10 @@ description = "Check the help output shapes and that every subcommand is documen
 run = "test/help-test.sh"
 
 [tasks.docker-build]
-description = "Build the auth service docker image"
-run = "docker build -t dokku-google-auth:latest ."
+description = "Build the auth service docker image, labelled the way the plugin does"
+# Via fn-ga-build-image so the image carries its source-hash label. A build
+# without it reads as permanently stale to the plugin.
+run = "bash -c 'source ./functions && fn-ga-build-image'"
 
 [tasks.check]
 description = "Run everything CI would run"