Add post tags, with a tag page and two side-column modules

Posts can now carry tags, set on the post form as a checklist of the
blog's existing tags plus a comma-separated box for new ones (no JS).
A tag is a name and a unique slug, so "Go" and "go" are one tag and
Greek tags get readable URLs; tags no post uses any more are deleted.

On the blog, tags appear under the post date and link to /tag/<slug>,
which lists the published posts from every page, paginated like a page.
Two new layout modules show them: a Tags list (with counts, by use) and
a Tag cloud (alphabetical, sized by use). Both are only fetched when a
visible module needs them.

The article loop and pager move to a shared postlist partial; while
there, the pager stops adding a trailing slash — /news/?p=2 was a 404
because a {page} wildcard never matches one.

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

1 files changed, 47 insertions, 5 deletions

diff --git a/internal/web/handlers_blog.go b/internal/web/handlers_blog.go
index f2e7713..c6030f2 100644
--- a/internal/web/handlers_blog.go
+++ b/internal/web/handlers_blog.go
@@ -51,10 +51,26 @@ func (s *Server) blogView(r *http.Request) (map[string]any, error) {
 		}
 		v["recent"] = recent
 	}
+	if layout.NeedsTags() {
+		counts, err := blogStore(r).TagCounts(ctx)
+		if err != nil {
+			return nil, err
+		}
+		v["tags"], v["tagcloud"] = topTags(counts), cloudSizes(counts)
+	}
 	v["notices"] = placeNotices(sections, layout)
 	return v, nil
 }
 
+// pageNum reads the ?p= of a paginated listing (1 when absent or silly).
+func pageNum(r *http.Request) int {
+	n, _ := strconv.Atoi(r.URL.Query().Get("p"))
+	if n < 1 {
+		n = 1
+	}
+	return n
+}
+
 func (s *Server) handleBlogHome(w http.ResponseWriter, r *http.Request) {
 	page, err := blogStore(r).HomePage(r.Context())
 	if err != nil {
@@ -83,10 +99,7 @@ func (s *Server) renderPage(w http.ResponseWriter, r *http.Request, page *store.
 		s.serverError(w, err)
 		return
 	}
-	n, _ := strconv.Atoi(r.URL.Query().Get("p"))
-	if n < 1 {
-		n = 1
-	}
+	n := pageNum(r)
 	posts, total, err := blogStore(r).PublishedPosts(r.Context(), page.ID, postsPerPage, (n-1)*postsPerPage)
 	if err != nil {
 		s.serverError(w, err)
@@ -94,13 +107,42 @@ func (s *Server) renderPage(w http.ResponseWriter, r *http.Request, page *store.
 	}
 	last := (total + postsPerPage - 1) / postsPerPage
 	v["page"], v["posts"], v["pageNum"], v["lastPage"] = page, posts, n, last
+	// The pager appends ?p=N to base: no trailing slash, which /{page} would not match.
 	v["base"] = "/" + page.Slug
 	if page.IsHome {
-		v["base"] = ""
+		v["base"] = "/"
 	}
 	s.render(w, r, "blog/page.html", v)
 }
 
+// handleBlogTag lists the published posts carrying a tag, from every page of
+// the blog. A tag that is only on hidden posts is as good as absent.
+func (s *Server) handleBlogTag(w http.ResponseWriter, r *http.Request) {
+	tag, err := blogStore(r).TagBySlug(r.Context(), r.PathValue("tag"))
+	if err != nil {
+		s.blogNotFound(w, r)
+		return
+	}
+	n := pageNum(r)
+	posts, total, err := blogStore(r).PublishedPostsByTag(r.Context(), tag.ID, postsPerPage, (n-1)*postsPerPage)
+	if err != nil {
+		s.serverError(w, err)
+		return
+	}
+	if total == 0 {
+		s.blogNotFound(w, r)
+		return
+	}
+	v, err := s.blogView(r)
+	if err != nil {
+		s.serverError(w, err)
+		return
+	}
+	last := (total + postsPerPage - 1) / postsPerPage
+	v["tag"], v["posts"], v["pageNum"], v["lastPage"], v["base"] = tag, posts, n, last, "/tag/"+tag.Slug
+	s.render(w, r, "blog/tag.html", v)
+}
+
 func (s *Server) handleBlogPost(w http.ResponseWriter, r *http.Request) {
 	page, err := blogStore(r).PageBySlug(r.Context(), r.PathValue("page"))
 	if err != nil {