feat(builder): pinpoint settings a server can't start without

Booting drafts as deployed catches a server that stops when a setting is
empty, but the server's own output rarely says why, so the model guessed
(more memory) for three rounds and the draft ended as WIP.

When a draft fails with its defaults and has blank password-like settings
without x-generate, the builder boots it once more with those filled. If
that boot passes, the cause is certain, and the model is told exactly that:
these settings stop the server when empty; give them x-generate (a password
per server) or a working default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/gbrgames/build.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sort"
 	"strings"
 )
 
@@ -232,46 +233,26 @@ func firstBoot(name, image, steamApp string, steam bool, startup string) (*bootR
 // bootCheck deploys the template with the node-agent's BootTest, the same check CI runs, and when the
 // game wrote files outside its volume on the first boot, boots it once more to see that it no longer does.
 func bootCheck(gamesDir, id, agentImage string, wantOutside bool) (problems, verified []string, err error) {
-	self, err := os.Executable()
-	if err != nil {
-		return nil, nil, err
-	}
-	// A boot test that was killed (worker restarted mid-build) leaves its container and volume behind,
-	// and the next deploy under the same name would trip over them
-	runCmd("docker", "rm", "-f", "boottest-"+id)
-	runCmd("docker", "volume", "rm", "-f", "boottest-"+id+"-data")
-	payloadCmd := exec.Command(self, "boottest-payload", "-as-deployed", "-games", gamesDir, id)
-	var stderr bytes.Buffer
-	payloadCmd.Stderr = &stderr
-	payload, err := payloadCmd.Output()
-	if err != nil {
-		var exitErr *exec.ExitError
-		if errors.As(err, &exitErr) && exitErr.ExitCode() == exitMissingSecret {
-			// The builder has no CI secrets: that's the template's problem to fix, not a reason to stop
-			return []string{"the boot test can't run: " + strings.TrimSpace(stderr.String()) + ". Remove 'secrets' from " +
-				"test.yaml; boot tests fill password settings with a throwaway value"}, nil, nil
-		}
-		return nil, nil, fmt.Errorf("boottest-payload: %v: %s", err, strings.TrimSpace(stderr.String()))
-	}
 	if out, err := runCmd("docker", "pull", "-q", agentImage); err != nil {
 		return nil, nil, fmt.Errorf("docker pull %s: %v: %s", agentImage, err, out)
 	}
-	cmd := exec.Command("docker", "run", "--rm", "-i", "-v", "/var/run/docker.sock:/var/run/docker.sock",
-		"--entrypoint", "java", agentImage, "-Dloader.main=com.gbreed.gbr.nodeagent.BootTest", "-cp", "app.jar",
-		"org.springframework.boot.loader.launch.PropertiesLauncher")
-	cmd.Stdin = bytes.NewReader(payload)
-	var output bytes.Buffer
-	cmd.Stdout = &teeWriter{&output}
-	cmd.Stderr = cmd.Stdout
-	runErr := cmd.Run()
-	if runErr != nil {
-		var exitErr *exec.ExitError
-		if !errors.As(runErr, &exitErr) {
-			return nil, nil, runErr
+	output, passed, problems, err := agentBoot(gamesDir, id, agentImage, true)
+	if err != nil || problems != nil {
+		return problems, nil, err
 	}
-		return []string{bootFailure(output.String())}, nil, nil
+	if !passed {
+		// The server's own output rarely says it stopped because a setting was empty. Booting once more
+		// with the blank ones filled tells for certain whether they are the cause.
+		if blank := blankRequiredLooking(gamesDir, id); len(blank) > 0 {
+			fmt.Printf("[build] it failed with the defaults; booting again with %s filled to see whether empty settings are the cause\n",
+				strings.Join(blank, ", "))
+			if _, filledPassed, _, err := agentBoot(gamesDir, id, agentImage, false); err == nil && filledPassed {
+				return []string{emptySettingsProblem(blank, bootVerdict(output))}, nil, nil
 			}
-	verified = append(verified, "boot test with the node-agent: "+bootVerdict(output.String()))
+		}
+		return []string{bootFailure(output)}, nil, nil
+	}
+	verified = append(verified, "boot test with the node-agent: "+bootVerdict(output))
 
 	if wantOutside {
 		fmt.Println("[build] first boot wrote saves outside the volume; booting the draft to see that it no longer does")
@@ -290,6 +271,82 @@ func bootCheck(gamesDir, id, agentImage string, wantOutside bool) (problems, ver
 	return nil, verified, nil
 }
 
+// agentBoot runs one boot test with the node-agent's BootTest: with the settings a new server gets
+// (asDeployed), or with blank password-like settings filled with throwaway values as CI's boot test does.
+// problems is set when the template can't be boot-tested at all.
+func agentBoot(gamesDir, id, agentImage string, asDeployed bool) (output string, passed bool, problems []string, err error) {
+	self, err := os.Executable()
+	if err != nil {
+		return "", false, nil, err
+	}
+	// A boot test that was killed (worker restarted mid-build) leaves its container and volume behind,
+	// and the next deploy under the same name would trip over them
+	runCmd("docker", "rm", "-f", "boottest-"+id)
+	runCmd("docker", "volume", "rm", "-f", "boottest-"+id+"-data")
+	args := []string{"boottest-payload", "-games", gamesDir, id}
+	if asDeployed {
+		args = []string{"boottest-payload", "-as-deployed", "-games", gamesDir, id}
+	}
+	payloadCmd := exec.Command(self, args...)
+	var stderr bytes.Buffer
+	payloadCmd.Stderr = &stderr
+	payload, err := payloadCmd.Output()
+	if err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) && exitErr.ExitCode() == exitMissingSecret {
+			// The builder has no CI secrets: that's the template's problem to fix, not a reason to stop
+			return "", false, []string{"the boot test can't run: " + strings.TrimSpace(stderr.String()) + ". Remove 'secrets' from " +
+				"test.yaml; boot tests fill password settings with a throwaway value"}, nil
+		}
+		return "", false, nil, fmt.Errorf("boottest-payload: %v: %s", err, strings.TrimSpace(stderr.String()))
+	}
+	cmd := exec.Command("docker", "run", "--rm", "-i", "-v", "/var/run/docker.sock:/var/run/docker.sock",
+		"--entrypoint", "java", agentImage, "-Dloader.main=com.gbreed.gbr.nodeagent.BootTest", "-cp", "app.jar",
+		"org.springframework.boot.loader.launch.PropertiesLauncher")
+	cmd.Stdin = bytes.NewReader(payload)
+	var out bytes.Buffer
+	cmd.Stdout = &teeWriter{&out}
+	cmd.Stderr = cmd.Stdout
+	if runErr := cmd.Run(); runErr != nil {
+		var exitErr *exec.ExitError
+		if !errors.As(runErr, &exitErr) {
+			return "", false, nil, runErr
+		}
+		return out.String(), false, nil, nil
+	}
+	return out.String(), true, nil, nil
+}
+
+// blankRequiredLooking lists the settings a new server gets empty that CI's boot test would fill with a
+// throwaway value: password-like keys with an empty default and no x-generate.
+func blankRequiredLooking(gamesDir, id string) []string {
+	g, err := loadMap(filepath.Join(gamesDir, id, "game.yaml"))
+	if err != nil {
+		return nil
+	}
+	defaults, _ := g["defaultConfig"].(map[string]any)
+	var keys []string
+	for key, p := range schemaProperties(g) {
+		prop, _ := p.(map[string]any)
+		if prop["x-generate"] != nil || !passwordKey.MatchString(key) {
+			continue
+		}
+		if v, ok := defaults[key]; !ok || v == nil || v == "" {
+			keys = append(keys, key)
+		}
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+func emptySettingsProblem(keys []string, verdict string) string {
+	return fmt.Sprintf("the server stops when %s is empty, as it is for every new server: booted with your defaults it "+
+		"failed (%s), and booted again with a value in %s it ran. A new server must start without the owner typing "+
+		"anything: give %s \"x-generate\": {\"type\": \"password\"} in configSchema (the panel then makes a password for "+
+		"each server; keep the default \"\"), or a default value that works. Keep the setting so owners can change it",
+		strings.Join(keys, ", "), verdict, strings.Join(keys, ", "), strings.Join(keys, ", "))
+}
+
 func firstBootGame(gamesDir, id string) (*bootReport, error) {
 	outDir := filepath.Join("firstboot-out", id+"-draft")
 	if err := runFirstBoot([]string{"-games", gamesDir, "-game", id, "-out", outDir}); err != nil {

cmd/gbrgames/build_test.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -48,3 +50,30 @@ func TestVariantNotes(t *testing.T) {
 		}
 	}
 }
+
+func TestBlankRequiredLookingSettings(t *testing.T) {
+	dir := t.TempDir()
+	game := filepath.Join(dir, "example")
+	os.MkdirAll(game, 0o755)
+	os.WriteFile(filepath.Join(game, "game.yaml"), []byte(`id: example
+defaultConfig:
+  JoinPassword: ""
+  AdminPassword: ""
+  ServerPassword: set-by-default
+  ServerName: x
+configSchema:
+  properties:
+    JoinPassword: {type: string}
+    AdminPassword: {type: string, x-generate: {type: password}}
+    ServerPassword: {type: string}
+    ServerName: {type: string}
+`), 0o644)
+	got := blankRequiredLooking(dir, "example")
+	if len(got) != 1 || got[0] != "JoinPassword" {
+		t.Errorf("got %v, want only JoinPassword (AdminPassword is generated, ServerPassword has a default)", got)
+	}
+	msg := emptySettingsProblem(got, "FAILED: server crashed")
+	if !strings.Contains(msg, "stops when JoinPassword is empty") || !strings.Contains(msg, `"x-generate": {"type": "password"}`) {
+		t.Errorf("message: %s", msg)
+	}
+}