feat: codeless plugin repos (plugin.mod, no Go) exempt from go.mod checks (WO-WZ-020)

A codeless .bnp repo has no go.mod by design — mirror the ninja CLI
classifier (core bnp.IsCodelessRepo) and skip both the standalone-plugin
go.mod checks and the backend replace-directive parse for such roots.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

check_sdkboundaries.go

@@ -31,7 +31,9 @@ func init() {
 				}
 			}
 			for _, target := range ctx.backendTargets {
-				if samePath(target.root, ctx.backendDir) {
+				// A codeless plugin repo (plugin.mod, no Go) has no go.mod by
+				// design — nothing for the replace-directive check to parse.
+				if samePath(target.root, ctx.backendDir) && !isCodelessPluginRepo(target.root) {
 					for _, v := range checkCMSCoreSDKGoMod(target.root) {
 						v.file = prefixDisplayPath(target.displayOrRoot(), v.file)
 						cmsGoModViolations = append(cmsGoModViolations, v)

plugin_sdk_versions.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"golang.org/x/mod/modfile"
 )
@@ -121,7 +122,30 @@ func checkCMSCoreSDKGoMod(root string) []pluginGoModViolation {
 	return checkGoModForModuleReplaceDirective(filepath.Join(root, "go.mod"), blockCoreImportPrefix)
 }
 
+// isCodelessPluginRepo mirrors the ninja CLI classifier (core
+// cmd/ninja/internal/bnp.IsCodelessRepo): a plugin.mod with no Go source at
+// the repo root is a codeless plugin (WO-WZ-020) — declarative-only, no
+// go.mod and no SDK version to pin.
+func isCodelessPluginRepo(root string) bool {
+	if !fileExists(filepath.Join(root, "plugin.mod")) {
+		return false
+	}
+	entries, err := os.ReadDir(root)
+	if err != nil {
+		return false
+	}
+	for _, e := range entries {
+		if !e.IsDir() && strings.HasSuffix(e.Name(), ".go") {
+			return false
+		}
+	}
+	return true
+}
+
 func checkStandalonePluginGoMod(root, requiredSDKVersion string) []pluginGoModViolation {
+	if isCodelessPluginRepo(root) {
+		return nil
+	}
 	goModPath := filepath.Join(root, "go.mod")
 	parsed, violations := parseGoModForSafety(goModPath)
 	if parsed == nil {

plugin_sdk_versions_test.go

@@ -102,3 +102,31 @@ require git.dev.alexdunmow.com/block/core v0.2.1
 		t.Fatalf("checkStandalonePluginGoMod() returned %d violations, want 0: %#v", len(violations), violations)
 	}
 }
+
+func TestCheckStandalonePluginGoModSkipsCodelessRepo(t *testing.T) {
+	root := t.TempDir()
+	writeTestFile(t, filepath.Join(root, "plugin.mod"), "[plugin]\nname = \"fixture\"\nversion = \"0.1.0\"\n", 0644)
+	writeTestFile(t, filepath.Join(root, "blocks", "blocks.yaml"), "blocks: []\n", 0644)
+
+	if !isCodelessPluginRepo(root) {
+		t.Fatal("isCodelessPluginRepo() = false, want true for plugin.mod with no root Go source")
+	}
+	violations := checkStandalonePluginGoMod(root, "v0.2.1")
+	if len(violations) != 0 {
+		t.Fatalf("checkStandalonePluginGoMod() returned %d violations, want 0 for codeless repo: %#v", len(violations), violations)
+	}
+}
+
+func TestCheckStandalonePluginGoModStillRequiresGoModWithRootGoSource(t *testing.T) {
+	root := t.TempDir()
+	writeTestFile(t, filepath.Join(root, "plugin.mod"), "[plugin]\nname = \"fixture\"\nversion = \"0.1.0\"\n", 0644)
+	writeTestFile(t, filepath.Join(root, "main.go"), "package main\nfunc main() {}\n", 0644)
+
+	if isCodelessPluginRepo(root) {
+		t.Fatal("isCodelessPluginRepo() = true, want false with root Go source")
+	}
+	violations := checkStandalonePluginGoMod(root, "v0.2.1")
+	if len(violations) != 1 || violations[0].rule != "missing-go-mod" {
+		t.Fatalf("checkStandalonePluginGoMod() = %#v, want single missing-go-mod violation", violations)
+	}
+}