Print a startup or shutdown error once, without fx's event log (closes #359)

pixad builds its fx app with fx.NopLogger and runs start, wait and stop
itself, so that it can print a start or stop error to stderr once.
dig.RootCause strips the frames fx and dig wrap around the error, which
leaves the line that names the setting. The exit status is as before.

Model: opus-5-5

.gitignore

@@ -70,4 +70,3 @@ vendor/
 # Local dev configs
 config.yml
 config.yaml
-config.dev.yml

Makefile

@@ -79,12 +79,15 @@ docker-versioned:
 docker-test:
 	@script/test
 
-# Run local dev server in Docker
+# Run local dev server in Docker, with debug on and a new random signing
+# key each run. Log in to the page with the key it prints.
 devserver: docker-versioned devserver-stop
+	@key="$$(head -c 32 /dev/urandom | base64)" && \
 	docker run -d --name pixad-dev -p 8080:8080 \
-		-v $(CURDIR)/config.dev.yml:/etc/pixa/config.yml:ro \
-		pixa:latest
-	@echo "pixad running at http://localhost:8080"
+		-e PIXA_SIGNING_KEY="$$key" -e PIXA_DEBUG=true \
+		pixa:latest >/dev/null && \
+	echo "pixad running at http://localhost:8080" && \
+	echo "signing key: $$key"
 
 # Stop dev server
 devserver-stop:

internal/app/app_test.go

@@ -98,7 +98,7 @@ func TestRunWritesNothingToStderrOnStartAndStop(t *testing.T) {
 		t.Fatalf("starting pixad: %v", err)
 	}
 
-	waitForHealthCheck(t, port)
+	waitForHealthCheck(t, cmd, port, stderr)
 
 	err = cmd.Process.Signal(syscall.SIGTERM)
 	if err != nil {
@@ -127,19 +127,23 @@ func freePort(t *testing.T) int {
 		t.Fatalf("finding a free port: %v", err)
 	}
 
-	port := listener.Addr().(*net.TCPAddr).Port //nolint:forcetypeassert // a TCP listener
+	addr, ok := listener.Addr().(*net.TCPAddr)
+	if !ok {
+		t.Fatalf("listener address %v is not a TCP address", listener.Addr())
+	}
 
 	err = listener.Close()
 	if err != nil {
 		t.Fatalf("closing listener: %v", err)
 	}
 
-	return port
+	return addr.Port
 }
 
-// waitForHealthCheck waits up to 30 seconds for pixad to answer its
-// health check on port.
-func waitForHealthCheck(t *testing.T, port int) {
+// waitForHealthCheck waits up to 30 seconds for pixad, started as cmd, to
+// answer its health check on port. If it does not, it stops pixad and
+// fails the test with what pixad wrote to stderr.
+func waitForHealthCheck(t *testing.T, cmd *exec.Cmd, port int, stderr *bytes.Buffer) {
 	t.Helper()
 
 	url := fmt.Sprintf("http://127.0.0.1:%d/.well-known/healthcheck.json", port)
@@ -163,5 +167,11 @@ func waitForHealthCheck(t *testing.T, port int) {
 		time.Sleep(100 * time.Millisecond)
 	}
 
-	t.Fatalf("pixad did not answer its health check on port %d", port)
+	// Stop pixad first: stderr is complete, and safe to read, only once
+	// cmd.Wait has returned.
+	_ = cmd.Process.Kill()
+	_ = cmd.Wait()
+
+	t.Fatalf("pixad did not answer its health check on port %d; stderr:\n%s",
+		port, stderr)
 }