feat(builder): SteamCMD first for Linux servers, and fall back to the next image

A draft built on a ready-made image whose files all live outside /server
(nodes keep only /server and /data) went round three times and ended as
WIP, although research had also verified the game's Steam app, which
SteamCMD installs straight into /server. The builder never tried it.

- research reads each Steam app's OS list. When it ships a Linux server,
  cm2network/steamcmd goes first in the variant's images and that variant
  is recommended. Windows-only servers keep images with Proton or Wine
  first. The research prompt says the same.
- build tries the variant's images in order: when no draft passes with one,
  the next image gets a fresh start. The first draft that boots wins; if
  none does, the PR gets the draft that got furthest, and its summary lists
  each image tried and how it went.

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

cmd/gbrgames/build.go

@@ -27,6 +27,7 @@ type buildResult struct {
 	Verified []string `json:"verified"`
 	Problems []string `json:"problems"`
 	Summary  string   `json:"summary"`
+	Tried    []string `json:"tried,omitempty"` // each image tried, and how it went
 }
 
 const defaultAgentImage = "www.gitea.gbreed.com/gbreed-public/gbr-node-agent:latest"
@@ -93,26 +94,81 @@ type buildOptions struct {
 	agentImage                    string
 }
 
+// build tries the variant's images in order (research puts SteamCMD first when the game ships a Linux
+// server) and keeps the first draft that boots. A draft that can't be made to work with one image is set
+// aside and the next image gets a fresh start; if none works, the draft that got furthest is returned.
 func build(o buildOptions) (*buildResult, error) {
-	if len(o.variant.Images) == 0 {
-		return nil, errors.New("the variant has no image to build from")
-	}
-	res := &buildResult{GameID: o.id, Dir: filepath.Join(o.gamesDir, o.id)}
-	res.Verified = append(res.Verified, o.variant.Verified...)
-
-	// 1. First boot of each candidate image until one runs as a non-root user
-	var report *bootReport
+	var candidates []string
 	for _, image := range o.variant.Images {
-		steam := isSteamCMDImage(image) && o.variant.SteamAppID != ""
-		if isSteamCMDImage(image) && !steam {
+		if isSteamCMDImage(image) && o.variant.SteamAppID == "" {
 			continue // the SteamCMD image alone runs nothing
 		}
-		res.Image = image
-		if steam && o.variant.StartupHint == "" {
-			fmt.Printf("[build] no startup command known for Steam app %s; drafting without a first boot\n", o.variant.SteamAppID)
-			report = nil
-			break
+		candidates = append(candidates, image)
+	}
+	if len(candidates) == 0 {
+		return nil, errors.New("the variant has no image to build from")
+	}
+	dir := filepath.Join(o.gamesDir, o.id)
+	setAside := filepath.Join("firstboot-out", o.id+"-best-draft")
+	var best *buildResult
+	var tried []string
+	for i, image := range candidates {
+		if i > 0 {
+			fmt.Printf("[build] trying the next image: %s\n", image)
 		}
+		res, err := buildWithImage(o, image)
+		if err != nil {
+			return res, err
+		}
+		tried = append(tried, attemptNote(res))
+		if res.Passed {
+			res.Tried = tried
+			res.Summary = buildSummary(o, res)
+			return res, nil
+		}
+		if _, err := os.Stat(filepath.Join(dir, "game.yaml")); err == nil {
+			// This one got a draft written: keep it in case no later image does better
+			os.RemoveAll(setAside)
+			if err := os.Rename(dir, setAside); err != nil {
+				return res, err
+			}
+			best = res
+		}
+	}
+	if best == nil {
+		return &buildResult{GameID: o.id, Dir: dir, Tried: tried, Problems: []string{"no image of this variant could be drafted"}},
+			errors.New("no image of this variant could be drafted: " + strings.Join(tried, "; "))
+	}
+	if err := os.Rename(setAside, dir); err != nil {
+		return best, err
+	}
+	best.Tried = tried
+	best.Summary = buildSummary(o, best)
+	return best, nil
+}
+
+func attemptNote(res *buildResult) string {
+	switch {
+	case res.Passed:
+		return res.Image + ": booted"
+	case len(res.Problems) > 0:
+		return res.Image + ": " + firstLine(res.Problems[0])
+	}
+	return res.Image + ": did not boot"
+}
+
+// buildWithImage drafts the template for one image: first boot, draft, then boots of the draft with
+// failures going back to the model.
+func buildWithImage(o buildOptions, image string) (*buildResult, error) {
+	res := &buildResult{GameID: o.id, Dir: filepath.Join(o.gamesDir, o.id), Image: image}
+	res.Verified = append(res.Verified, o.variant.Verified...)
+	steam := isSteamCMDImage(image)
+
+	// 1. First boot of the image untouched: its log, files and settings are the draft's facts
+	var report *bootReport
+	if steam && o.variant.StartupHint == "" {
+		fmt.Printf("[build] no startup command known for Steam app %s; drafting without a first boot\n", o.variant.SteamAppID)
+	} else {
 		fmt.Printf("[build] first boot of %s\n", image)
 		r, err := firstBoot(o.id+"-probe", image, o.variant.SteamAppID, steam, o.variant.StartupHint)
 		if err != nil {
@@ -120,18 +176,12 @@ func build(o buildOptions) (*buildResult, error) {
 		}
 		if why := imageUnusable(r); why != "" {
 			fmt.Printf("[build] %s can't be used: %s\n", image, why)
-			res.Problems = append(res.Problems, why)
-			res.Image = ""
-			continue
+			res.Problems = []string{why}
+			return res, nil
 		}
 		report = r
 		res.Verified = append(res.Verified, fmt.Sprintf("first boot of %s: %s", image, r.Outcome))
-		break
 	}
-	if res.Image == "" {
-		return res, errors.New("no image of this variant runs as a non-root user")
-	}
-	res.Problems = nil
 
 	// 2. Draft until validation and the image checks pass
 	steamApp := ""
@@ -411,6 +461,12 @@ func buildSummary(o buildOptions, res *buildResult) string {
 		fmt.Fprintf(&b, ", Steam app %s", o.variant.SteamAppID)
 	}
 	fmt.Fprintf(&b, "\n- Model rounds: %d\n", res.Rounds)
+	if len(res.Tried) > 1 {
+		b.WriteString("\n**Images tried, in order**\n")
+		for _, t := range res.Tried {
+			fmt.Fprintf(&b, "- %s\n", firstLine(t))
+		}
+	}
 	if len(res.Verified) > 0 {
 		b.WriteString("\n**Checked for real**\n")
 		for _, v := range res.Verified {

cmd/gbrgames/research.go

@@ -173,9 +173,10 @@ const researchPrompt = "You research how to host a game's dedicated server for G
 	"in Docker on Linux, as a non-root user, with a volume at /server. From the search results and pages given, list " +
 	"the ways this game's dedicated server can be run (variants): separate editions of the game with their own server, " +
 	"crossplay builds, or notably different server images. For each variant give:\n" +
-	"- images: Docker Hub images that run this server, best first (prefer images that run as a non-root user, and the " +
-	"plain SteamCMD route cm2network/steamcmd when the game ships a Linux dedicated server on Steam). Only images that " +
-	"appear in the pages.\n" +
+	"- images: how to run this server, best first. When the game has a dedicated server on Steam that runs on Linux, " +
+	"cm2network/steamcmd (the plain SteamCMD route, installing the server into /server) always comes first and that " +
+	"variant is the recommended one. Then Docker Hub images that appear in the pages and run as a non-root user " +
+	"(needed for servers that only exist for Windows).\n" +
 	"- steamAppId: the Steam app id of the DEDICATED SERVER (not the game itself), if installed via SteamCMD; else \"\".\n" +
 	"- startupHint: the command that starts the server from its install folder /server, with the launch options " +
 	"for name, port, world and save location exactly as the pages document them; \"\" if unknown.\n" +
@@ -299,13 +300,13 @@ func trimToJSON(answer string) string {
 // Steam apps must exist and be readable anonymously (what SteamCMD installs need). What fails is dropped
 // and noted; a variant left with nothing runnable can't be recommended.
 func verifyVariants(res *researchResult) {
-	var apps []string
+	var appIDs []string
 	for _, v := range res.Variants {
 		if v.SteamAppID != "" {
-			apps = append(apps, v.SteamAppID)
+			appIDs = append(appIDs, v.SteamAppID)
 		}
 	}
-	names := steamAppNames(apps)
+	apps := steamApps(appIDs)
 	anyRunnable := false
 	for i := range res.Variants {
 		v := &res.Variants[i]
@@ -324,10 +325,11 @@ func verifyVariants(res *researchResult) {
 		}
 		v.Images = images
 		if v.SteamAppID != "" {
-			if name, ok := names[v.SteamAppID]; ok {
-				v.Verified = append(v.Verified, fmt.Sprintf("Steam app %s is %q", v.SteamAppID, name))
-				if !hasImage(v.Images, "cm2network/steamcmd") {
-					v.Images = append(v.Images, "cm2network/steamcmd")
+			if app, ok := apps[v.SteamAppID]; ok {
+				v.Verified = append(v.Verified, fmt.Sprintf("Steam app %s is %q", v.SteamAppID, app.name))
+				v.Images = withSteamCMD(v.Images, app.linux)
+				if app.linux {
+					v.Verified = append(v.Verified, "it ships a Linux server, so SteamCMD (installing it into /server) is tried first")
 				}
 			} else {
 				v.Problems = append(v.Problems, "Steam app "+v.SteamAppID+" not found for anonymous SteamCMD")
@@ -346,44 +348,56 @@ func verifyVariants(res *researchResult) {
 		res.Reason = "unknown"
 		res.Message = "No variant has a Docker image or Steam app that could be confirmed. " + res.Message
 	}
-	// Exactly one recommendation, among the runnable ones
+	recommend(res.Variants)
+}
+
+// recommend marks exactly one variant recommended, among the runnable ones. A variant that installs a Linux
+// server with SteamCMD comes before the model's choice: it keeps everything under /server, as nodes need.
+func recommend(variants []variant) {
+	runnable := func(v variant) bool { return len(v.Images) > 0 }
+	steamFirst := func(v variant) bool { return runnable(v) && isSteamCMDImage(v.Images[0]) }
 	rec := -1
-	for i, v := range res.Variants {
-		if v.Recommended && rec < 0 && len(v.Images) > 0 {
-			rec = i
-		}
-		res.Variants[i].Recommended = false
-	}
-	if rec < 0 {
-		for i, v := range res.Variants {
-			if len(v.Images) > 0 {
+	for _, want := range []func(variant) bool{
+		func(v variant) bool { return v.Recommended && steamFirst(v) },
+		steamFirst,
+		func(v variant) bool { return v.Recommended && runnable(v) },
+		runnable,
+	} {
+		for i, v := range variants {
+			if rec < 0 && want(v) {
 				rec = i
-				break
 			}
 		}
 	}
-	if rec >= 0 {
-		res.Variants[rec].Recommended = true
+	for i := range variants {
+		variants[i].Recommended = i == rec
 	}
 }
 
-func hasImage(images []string, name string) bool {
-	for _, i := range images {
-		if i == name || strings.HasPrefix(i, name+":") {
-			return true
-		}
-	}
-	return false
+var (
+	appName  = regexp.MustCompile(`"common"\s*\{[^}]*?"name"\s+"([^"]+)"`)
+	appLinux = regexp.MustCompile(`"oslist"\s+"[^"]*linux`)
+)
+
+type steamApp struct {
+	name  string
+	linux bool // ships a Linux server: SteamCMD installs it straight into /server
 }
 
-var appName = regexp.MustCompile(`"common"\s*\{[^}]*?"name"\s+"([^"]+)"`)
+func parseAppInfo(out string) (steamApp, bool) {
+	m := appName.FindStringSubmatch(out)
+	if m == nil {
+		return steamApp{}, false
+	}
+	return steamApp{name: m[1], linux: appLinux.MatchString(out)}, true
+}
 
-// steamAppNames asks SteamCMD (anonymously, in its official image) for each app's info: an app that
+// steamApps asks SteamCMD (anonymously, in its official image) for each app's info: an app that
 // anonymous SteamCMD can't see can't be installed by the node-agent either.
-func steamAppNames(apps []string) map[string]string {
-	names := map[string]string{}
+func steamApps(apps []string) map[string]steamApp {
+	found := map[string]steamApp{}
 	if len(apps) == 0 {
-		return names
+		return found
 	}
 	for _, app := range apps {
 		if !regexp.MustCompile(`^\d+$`).MatchString(app) {
@@ -395,9 +409,25 @@ func steamAppNames(apps []string) map[string]string {
 			fmt.Printf("[research] steamcmd for app %s: %v\n", app, err)
 			continue
 		}
-		if m := appName.FindStringSubmatch(out); m != nil {
-			names[app] = m[1]
+		if info, ok := parseAppInfo(out); ok {
+			found[app] = info
 		}
 	}
-	return names
+	return found
+}
+
+// withSteamCMD adds the plain SteamCMD route to a variant's images. When the Steam app ships a Linux server
+// it goes first: it installs into /server, which nodes keep, while ready-made images often keep their
+// files elsewhere. For Windows-only servers it stays last, behind images that bring Proton or Wine.
+func withSteamCMD(images []string, linux bool) []string {
+	var others []string
+	for _, i := range images {
+		if !isSteamCMDImage(i) {
+			others = append(others, i)
+		}
+	}
+	if linux {
+		return append([]string{"cm2network/steamcmd"}, others...)
+	}
+	return append(others, "cm2network/steamcmd")
 }

cmd/gbrgames/research_test.go

@@ -39,3 +39,52 @@ func TestAppNameFromAppInfo(t *testing.T) {
 		t.Errorf("got %v", m)
 	}
 }
+
+func TestParseAppInfoFindsLinuxServers(t *testing.T) {
+	linux, ok := parseAppInfo(`"1000000"
+{
+	"common"
+	{
+		"name"		"Example Dedicated Server"
+		"oslist"		"windows,linux"
+	}
+}`)
+	if !ok || linux.name != "Example Dedicated Server" || !linux.linux {
+		t.Errorf("got %+v %v", linux, ok)
+	}
+	// A server that only exists for Windows (needs Proton or Wine)
+	windows, _ := parseAppInfo(`"common" { "name" "Example Server" "oslist" "windows" }`)
+	if windows.linux {
+		t.Error("windows-only app reported as linux")
+	}
+}
+
+func TestWithSteamCMDGoesFirstOnlyForLinuxServers(t *testing.T) {
+	images := []string{"someone/example-server", "cm2network/steamcmd", "other/example"}
+	got := withSteamCMD(images, true)
+	if len(got) != 3 || got[0] != "cm2network/steamcmd" || got[1] != "someone/example-server" {
+		t.Errorf("linux: %v", got)
+	}
+	got = withSteamCMD([]string{"someone/proton-example"}, false)
+	if len(got) != 2 || got[1] != "cm2network/steamcmd" {
+		t.Errorf("windows-only: %v", got)
+	}
+}
+
+func TestRecommendPrefersTheSteamCMDVariant(t *testing.T) {
+	v := []variant{
+		{ID: "image", Recommended: true, Images: []string{"someone/example-server"}},
+		{ID: "steam", Images: []string{"cm2network/steamcmd", "someone/example-server"}},
+		{ID: "broken", Recommended: true},
+	}
+	recommend(v)
+	if v[0].Recommended || !v[1].Recommended || v[2].Recommended {
+		t.Errorf("got %+v", v)
+	}
+	// Without a SteamCMD variant, the model's runnable choice stands
+	v = []variant{{ID: "a", Images: []string{"x/a"}}, {ID: "b", Recommended: true, Images: []string{"x/b"}}}
+	recommend(v)
+	if v[0].Recommended || !v[1].Recommended {
+		t.Errorf("got %+v", v)
+	}
+}