feat: grade open answers through a grader registry in the background

- graders registry collected at boot from every HasGraders plugin,
  manual first; a duplicate or reserved code fails boot
- grading job on queue quizzes_grading with three attempts; a stale
  or reviewed answer is never touched; the last failure marks it failed
- learning answers enqueue at once, tests at close; a grade
  recalculates a finished attempt and fires AnswerGradedEvent after
  commit

plugin.go

@@ -3,16 +3,21 @@ package quizzes
 import (
 	"context"
 	"embed"
+	"errors"
 	"io/fs"
 	"net/http"
 	"strconv"
 	"time"
 
+	"git.golem15.com/golem15/sm-quizzes-plugin/classes"
 	"git.golem15.com/golem15/sm-quizzes-plugin/console"
+	"git.golem15.com/golem15/sm-quizzes-plugin/graders"
+	"git.golem15.com/golem15/sm-quizzes-plugin/jobs"
 	"git.golem15.com/golem15/sm-quizzes-plugin/models"
 	"git.golem15.com/golem15/summercms/modules/backpack"
 	"git.golem15.com/golem15/summercms/modules/bonfire"
 	"git.golem15.com/golem15/summercms/modules/bouncer"
+	"git.golem15.com/golem15/summercms/modules/conga"
 	"git.golem15.com/golem15/summercms/modules/lagoon"
 	"git.golem15.com/golem15/summercms/modules/pact"
 	"git.golem15.com/golem15/summercms/modules/party"
@@ -53,6 +58,8 @@ var adminFS embed.FS
 // Plugin is the golem15.quizzes plugin.
 type Plugin struct {
 	app *backpack.App
+	// graders is the grader registry built at Boot.
+	graders *graders.Registry
 }
 
 func (p *Plugin) ID() string { return "golem15.quizzes" }
@@ -68,10 +75,17 @@ func (p *Plugin) Register(app *backpack.App) error {
 	return nil
 }
 
-// Boot keeps the application and points the admin filter choices at its
-// database.
+// Boot keeps the application, collects the grader registry and points the
+// admin filter choices at its database.
+//
+// Grading plugins never register themselves: golem15.quizzes pulls their
+// graders through graders.HasGraders, as golem15.paymentgateway pulls
+// payment operators.
 func (p *Plugin) Boot(app *backpack.App) error {
 	p.app = app
+	if err := bootGraders(p, app); err != nil {
+		return err
+	}
 	models.FilterDB = func() *gorm.DB {
 		if app == nil {
 			return nil
@@ -82,6 +96,35 @@ func (p *Plugin) Boot(app *backpack.App) error {
 	return nil
 }
 
+// bootGraders builds the grader registry: manual first, then the graders of
+// every other activated plugin that implements graders.HasGraders, in
+// activation order. A duplicate or reserved code fails boot. The registry
+// is kept on p and published on the app as *graders.Registry.
+func bootGraders(p *Plugin, app *backpack.App) error {
+	reg := graders.NewRegistry()
+	if app == nil {
+		p.graders = reg
+		return nil
+	}
+	activated, _ := app.Lookup[party.Activated]()
+	for _, plugin := range activated {
+		if plugin == nil || plugin.ID() == p.ID() {
+			continue
+		}
+		hg, ok := plugin.(graders.HasGraders)
+		if !ok {
+			continue
+		}
+		for _, g := range hg.QuizGraders() {
+			if err := reg.Add(plugin.ID(), g); err != nil {
+				return err
+			}
+		}
+	}
+	p.graders = reg
+	return app.Publish(reg)
+}
+
 func (p *Plugin) ConfigFS() fs.FS { return configFS }
 func (p *Plugin) LangFS() fs.FS   { return langFS }
 
@@ -91,7 +134,27 @@ func (p *Plugin) MailLayouts() map[string]string { return nil }
 
 func (p *Plugin) Models() []any                       { return generatedModels() }
 func (p *Plugin) Migrations() []*gormigrate.Migration { return generatedMigrations() }
-func (p *Plugin) Jobs() []pact.Job                    { return generatedJobs() }
+
+// Jobs returns the generated jobs plus the grading job: one open answer per
+// job on its own queue, GradeMaxAttempts attempts, each with GradeTimeout.
+func (p *Plugin) Jobs() []pact.Job {
+	return append(generatedJobs(), conga.Job(p.gradeAnswer,
+		conga.OnQueue(jobs.Queue),
+		conga.MaxAttempts(classes.GradeMaxAttempts),
+		conga.Timeout(classes.GradeTimeout)))
+}
+
+// gradeAnswer runs one grading job on the application's database.
+func (p *Plugin) gradeAnswer(ctx context.Context, args jobs.GradeAnswerArgs) error {
+	var gdb *gorm.DB
+	if p.app != nil {
+		gdb, _ = p.app.Lookup[*gorm.DB]()
+	}
+	if gdb == nil {
+		return errors.New("quizzes: database unavailable")
+	}
+	return classes.ForApp(p.app, gdb).GradeAnswer(ctx, args.AnswerID, args.Seq)
+}
 func (p *Plugin) AdminControllers() []pact.AdminController {
 	return generatedAdminControllers()
 }