Add persitent URLs for year/month/day in the diary

main.go

@@ -37,8 +37,19 @@ type specialPage struct {
 
 // pageTypeHandler is implemented by each special folder type (diary, gallery, …).
 // handle returns nil when the handler does not apply to the given path.
+// redirect returns ok=true with an absolute URL when the request should be
+// short-circuited with a 302 redirect (e.g. persistent date links in a diary).
+// defaultHeading returns ok=true with custom pre-fill heading text for the
+// editor when no index.md exists yet (e.g. German long-form date for a diary
+// day). Handlers that don't need a hook should return the zero value.
+//
+// When adding a new hook, prefer a sibling method here over folding logic
+// into main.go or render.go. If this list grows much beyond three, consider
+// collapsing into a single overrides struct returned per request.
 type pageTypeHandler interface {
 	handle(root, fsPath, urlPath string) *specialPage
+	redirect(root, fsPath, urlPath string) (target string, ok bool)
+	defaultHeading(root, fsPath, urlPath string) (heading string, ok bool)
 }
 
 // pageTypeHandlers is the registry. Each type registers itself via init().
@@ -204,6 +215,13 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 		return
 	}
 
+	for _, ph := range pageTypeHandlers {
+		if target, ok := ph.redirect(h.root, fsPath, urlPath); ok {
+			http.Redirect(w, r, target, http.StatusFound)
+			return
+		}
+	}
+
 	indexPath := filepath.Join(fsPath, "index.md")
 	rawMD, _ := os.ReadFile(indexPath)
 
@@ -255,7 +273,14 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 			rawContent = string(sections[sectionIndex])
 		}
 	} else if editMode && rawContent == "" && urlPath != "/" {
-		rawContent = "# " + pageTitle(urlPath) + "\n\n"
+		heading := pageTitle(urlPath)
+		for _, ph := range pageTypeHandlers {
+			if custom, ok := ph.defaultHeading(h.root, fsPath, urlPath); ok {
+				heading = custom
+				break
+			}
+		}
+		rawContent = "# " + heading + "\n\n"
 	}
 
 	data := pageData{