Exit with the shutdown's code and wait for image processing (closes #86)

fx alone handles SIGINT and SIGTERM; the server's own handler, which
only cancelled a context that fx's stop did not wait for, is gone.
runApp starts the fx app, waits for a signal or a shutdown request,
stops the app and returns the exit code, which main passes to os.Exit.
A listen error asks fx to shut down with exit code 1. A Sentry DSN that
cannot be used fails the server's start hook, so fx stops what had
already started. The server's stop hook stops the HTTP server, then
waits for the images still being processed, both within
ShutdownTimeout; images still being processed after that are logged and
fail the stop, so the exit code is 1.

Model: opus-5-5

internal/server/http.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"net/http"
 	"time"
+
+	"go.uber.org/fx"
 )
 
 // HTTP server configuration constants.
@@ -36,19 +38,19 @@ func (s *Server) newHTTPServer() *http.Server {
 	}
 }
 
+// serveUntilShutdown serves on s.httpServer until it is shut down. When it
+// stops for any other reason, such as its port being in use, it asks fx to
+// shut down with exit code 1.
 func (s *Server) serveUntilShutdown() {
-	s.httpServer = s.newHTTPServer()
-
-	s.SetupRoutes()
-
 	s.log.Info("http begin listen", "listenaddr", s.httpServer.Addr)
 
 	err := s.httpServer.ListenAndServe()
 	if err != nil && !errors.Is(err, http.ErrServerClosed) {
 		s.log.Error("listen error", "error", err)
 
-		if s.cancelFunc != nil {
-			s.cancelFunc()
+		err = s.shutdowner.Shutdown(fx.ExitCode(1))
+		if err != nil {
+			s.log.Error("shutdown request failed", "error", err)
 		}
 	}
 }