Show a live preview of the header on the Design tab's Menu card

The menu options had grown to a dozen switches with nothing to look at
but the blog after a save. A new POST /b/{sub}/design/preview reads the
form as a save would and renders the header alone — the real blog.css
and theme CSS, the modules in their order, the menu as edited — into a
sandboxed frame that refreshes shortly after every change, with a Wide
screen / Phone toggle. Nothing is stored.

The frame keeps the dashboard's origin (allow-same-origin, no scripts)
so the blog's logo and fonts, linked through /b/<sub>/media since the
root host's /media is the root blog's, get the session cookie; that is
safe because no header module is owner HTML. The frame runs no scripts,
so the page's own script folds the menu in it the way the blog does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sd8UPWrvyYCLj97JexNw3A

1 files changed, 3 insertions, 3 deletions

diff --git a/internal/web/templates/layouts/blog.html b/internal/web/templates/layouts/blog.html
index d55512a..71a62b0 100644
--- a/internal/web/templates/layouts/blog.html
+++ b/internal/web/templates/layouts/blog.html
@@ -48,7 +48,7 @@
      which drops nav-auto, the no-script fallback blog.css folds on phones. */}}
 {{define "siteheader"}}{{$l := .Data.layout}}{{$t := .Data.theme}}<div class="site-header{{if $l.Fold}} nav-fold nav-auto{{end}}{{if eq $t.HeaderAlign "center"}} header-center{{end}}">
   {{if $l.Fold}}<input type="checkbox" id="nav-toggle" class="nav-toggle" aria-label="{{t "Menu"}}">{{end}}
-  {{if $t.HeaderImage}}<div class="header-image"><a href="/"><img src="/media/{{$t.HeaderImage}}" alt=""></a></div>{{end}}
+  {{if $t.HeaderImage}}<div class="header-image"><a href="/"><img src="{{$.Media}}/{{$t.HeaderImage}}" alt=""></a></div>{{end}}
   {{range $i, $m := $l.Header}}{{template "module" (dict "m" $m "root" $ "burger" (and $l.Fold (eq $i $l.BurgerAt)))}}{{end}}
 </div>{{if $l.Fold}}<script>(function () {
   var h = document.querySelector && document.querySelector(".site-header.nav-fold"), cb = document.getElementById("nav-toggle");
@@ -86,8 +86,8 @@
   <h1 class="site-title"><a href="/">{{$r.Blog.Title}}</a></h1>
   {{if $r.Blog.Tagline}}<p class="tagline">{{$r.Blog.Tagline}}</p>{{end}}
 </div>{{template "rule" (dict "before" false "rc" $rc "theme" $t)}}{{if $b}}{{template "burger" $t}}{{end}}</div>
-{{- else if eq $m.Kind "logo"}}{{if $t.Logo}}{{if eq $m.Area "header"}}<div class="wrap header-logo{{with $rc}} {{.}}{{end}}{{if $b}} has-burger{{end}}">{{template "rule" (dict "before" true "rc" $rc "theme" $t)}}<div class="brand"><a href="/"><img class="logo" src="/media/{{$t.Logo}}" alt="{{$r.Blog.Title}}"></a></div>{{template "rule" (dict "before" false "rc" $rc "theme" $t)}}{{if $b}}{{template "burger" $t}}{{end}}</div>
-{{else}}<div class="mod mod-logo"><a href="/"><img class="logo" src="/media/{{$t.Logo}}" alt="{{$r.Blog.Title}}"></a></div>{{end}}{{end}}
+{{- else if eq $m.Kind "logo"}}{{if $t.Logo}}{{if eq $m.Area "header"}}<div class="wrap header-logo{{with $rc}} {{.}}{{end}}{{if $b}} has-burger{{end}}">{{template "rule" (dict "before" true "rc" $rc "theme" $t)}}<div class="brand"><a href="/"><img class="logo" src="{{$r.Media}}/{{$t.Logo}}" alt="{{$r.Blog.Title}}"></a></div>{{template "rule" (dict "before" false "rc" $rc "theme" $t)}}{{if $b}}{{template "burger" $t}}{{end}}</div>
+{{else}}<div class="mod mod-logo"><a href="/"><img class="logo" src="{{$r.Media}}/{{$t.Logo}}" alt="{{$r.Blog.Title}}"></a></div>{{end}}{{end}}
 {{- else if eq $m.Kind "menu"}}{{if eq $m.Area "header"}}<div class="site-nav{{if $b}} has-burger{{end}}"><div class="wrap nav-inner">{{if $b}}{{template "burger" $t}}{{end}}{{if $r.Data.layout.HeaderSearch}}{{template "searchform" $r}}{{end}}{{template "menulinks" $r}}</div></div>
 {{else}}<div class="mod site-nav mod-menu">{{template "modtitle" $m}}<div class="nav-inner">{{template "menulinks" $r}}</div></div>{{end}}
 {{- else if eq $m.Kind "recent"}}<div class="mod mod-recent">{{template "modtitle" $m}}