feat(04-03): register plugin mail layouts and publish the mailer at boot

- Map short layout names onto dotted layout files and wrap text/HTML
- party.Activate publishes postcard.Mailer before Boot and names missing files
- Hello plugin sends through the app-scoped mailer

Co-authored-by: Cursor <cursoragent@cursor.com>

party/registry.go

@@ -8,6 +8,7 @@ import (
 	"git.golem15.com/golem15/summercms/backpack"
 	"git.golem15.com/golem15/summercms/pact"
 	"git.golem15.com/golem15/summercms/phrasebook"
+	"git.golem15.com/golem15/summercms/postcard"
 )
 
 // Plugin is the required descriptor every compiled plugin implements.
@@ -120,7 +121,13 @@ func activate(registered []Plugin, app *backpack.App, ids []string) ([]Plugin, e
 	if err := phrasebook.Activate(app, ordered); err != nil {
 		return nil, fmt.Errorf("party: lang: %w", err)
 	}
+	if err := postcard.Activate(app, ordered); err != nil {
+		return nil, fmt.Errorf("party: mail: %w", err)
+	}
 	for _, p := range ordered {
+		if err := postcard.BootPlugin(app, p); err != nil {
+			return nil, fmt.Errorf("party: boot %s: %w", p.ID(), err)
+		}
 		if err := p.Boot(app); err != nil {
 			return nil, fmt.Errorf("party: boot %s: %w", p.ID(), err)
 		}

party/registry_test.go

@@ -14,6 +14,7 @@ import (
 	"git.golem15.com/golem15/summercms/compass"
 	"git.golem15.com/golem15/summercms/pact"
 	"git.golem15.com/golem15/summercms/phrasebook"
+	"git.golem15.com/golem15/summercms/postcard"
 )
 
 type tracePlugin struct {
@@ -455,3 +456,65 @@ func TestActivateMalformedLangFailsWithPluginContext(t *testing.T) {
 		t.Fatalf("error %q should name the plugin and path problem", msg)
 	}
 }
+
+type mailPlugin struct {
+	id        string
+	fsys      fs.FS
+	templates []string
+	layouts   map[string]string
+	sawMailer *bool
+}
+
+func (p *mailPlugin) ID() string                           { return p.id }
+func (p *mailPlugin) Requires() []string                   { return nil }
+func (p *mailPlugin) Register(*backpack.App) error         { return nil }
+func (p *mailPlugin) MailTemplatesFS() fs.FS               { return p.fsys }
+func (p *mailPlugin) MailTemplates() []string              { return p.templates }
+func (p *mailPlugin) MailLayouts() map[string]string       { return p.layouts }
+
+func (p *mailPlugin) Boot(app *backpack.App) error {
+	if p.sawMailer == nil {
+		return nil
+	}
+	_, ok := app.Lookup[postcard.Mailer]()
+	*p.sawMailer = ok
+	return nil
+}
+
+func TestActivatePublishesMailerBeforeBoot(t *testing.T) {
+	var saw bool
+	p := &mailPlugin{
+		id:        "golem15.hello",
+		sawMailer: &saw,
+		templates: []string{"golem15.hello::mail.hello"},
+		layouts:   map[string]string{"hello": "golem15.hello::mail.layouts.hello"},
+		fsys: fstest.MapFS{
+			"views/mail/hello.htm": {Data: []byte("subject = \"Hi\"\nlayout = \"hello\"\n==\nHi.\n")},
+			"views/mail/layouts/hello.htm": {Data: []byte("name = \"Hello\"\n==\n{{ .Content }}\n==\n<div>{{ .Content }}</div>\n")},
+		},
+	}
+	app := backpack.New(&compass.Config{})
+	if _, err := activate([]Plugin{p}, app, []string{"golem15.hello"}); err != nil {
+		t.Fatalf("activate: %v", err)
+	}
+	if !saw {
+		t.Fatal("mailer must be published before Boot")
+	}
+}
+
+func TestActivateMissingMailTemplateFailsBootWithName(t *testing.T) {
+	p := &mailPlugin{
+		id:        "golem15.hello",
+		templates: []string{"golem15.hello::mail.hello"},
+		fsys:      fstest.MapFS{},
+	}
+	app := backpack.New(&compass.Config{})
+	_, err := activate([]Plugin{p}, app, []string{"golem15.hello"})
+	if err == nil {
+		t.Fatal("expected missing template error")
+	}
+	msg := err.Error()
+	if !strings.Contains(msg, "party: boot golem15.hello") || !strings.Contains(msg, "golem15.hello::mail.hello") {
+		t.Fatalf("error %q should name the boot plugin and missing template", msg)
+	}
+}