tag claim flow: scanned code auto-fills Add Tag field (?code=), unclaimed tag page shows 'Add this tag to my account' when logged in, login honors next= so code survives the login step

frontend/internal/handlers/auth.go

@@ -64,7 +64,11 @@ func (a *App) Register(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
-	http.Redirect(w, r, "/account", http.StatusSeeOther)
+	next := r.FormValue("next")
+	if next == "" || !strings.HasPrefix(next, "/") || strings.HasPrefix(next, "//") {
+		next = "/account"
+	}
+	http.Redirect(w, r, next, http.StatusSeeOther)
 }
 
 func (a *App) LoginPage(w http.ResponseWriter, r *http.Request) {
@@ -93,7 +97,11 @@ func (a *App) Login(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
-	http.Redirect(w, r, "/account", http.StatusSeeOther)
+	next := r.FormValue("next")
+	if next == "" || !strings.HasPrefix(next, "/") || strings.HasPrefix(next, "//") {
+		next = "/account"
+	}
+	http.Redirect(w, r, next, http.StatusSeeOther)
 }
 
 func (a *App) Logout(w http.ResponseWriter, r *http.Request) {

frontend/internal/handlers/tag_page.go

@@ -13,6 +13,7 @@ import (
 type publicData struct {
 	UpdatedAt   pgtype.Timestamptz
 	Preview     bool
+	Authed      bool
 	ID          int64
 	TagCode     string
 	Status      string
@@ -48,8 +49,10 @@ func (a *App) PublicTag(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	_, authed := auth.GetUserID(r)
 	pd := publicData{
 		Preview:     r.URL.Query().Get("preview") == "1",
+		Authed:      authed,
 		UpdatedAt:   tag.UpdatedAt,
 		ID:          tag.ID,
 		TagCode:     tag.TagCode,

frontend/internal/handlers/tags.go

@@ -18,8 +18,9 @@ import (
 const maxTagsPerAccount = 20
 
 type accountData struct {
-	Tags     []db.Tag
-	AddError string
+	Tags       []db.Tag
+	AddError   string
+	AddTagCode string
 }
 
 func ownerID(uid int64) pgtype.Int8 {
@@ -33,7 +34,7 @@ func (a *App) Account(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "internal error", http.StatusInternalServerError)
 		return
 	}
-	a.render(w, r, "account", "My Tags", accountData{Tags: tags}, "")
+	a.render(w, r, "account", "My Tags", accountData{Tags: tags, AddTagCode: r.URL.Query().Get("code")}, "")
 }
 
 // AddTag binds a tag code to the current account (HTMX: returns account-panel).
@@ -44,6 +45,7 @@ func (a *App) AddTag(w http.ResponseWriter, r *http.Request) {
 	oid := ownerID(uid)
 	data := accountData{}
 
+	data.AddTagCode = code
 	if code == "" {
 		data.AddError = "Enter a tag code."
 	} else {