Prevent page deletion on save

assets/style.css

@@ -141,7 +141,7 @@ header {
     padding: var(--space-3) var(--space-4);
     border-bottom: var(--border-dashed);
     display: grid;
-    grid-template-columns: 1fr minmax(0, 60rem) 1fr;
+    grid-template-columns: 1fr minmax(0, 50rem) 1fr;
     grid-template-areas: "crumbs search actions";
     align-items: center;
     gap: var(--space-2);

main.go

@@ -426,9 +426,14 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 		}
 		rawMD, _ := os.ReadFile(indexPath)
 		sections := splitSections(rawMD)
-		if sectionIndex < len(sections) {
-			sections[sectionIndex] = []byte(content)
+		// Out of range means the file changed under the editor (or the index
+		// never matched it). Writing back the untouched file would swallow the
+		// edit silently, so refuse and keep the editor's content in the browser.
+		if sectionIndex >= len(sections) {
+			http.Error(w, "section no longer exists — the page changed since you opened the editor", http.StatusConflict)
+			return
 		}
+		sections[sectionIndex] = []byte(content)
 		content = string(joinSections(sections))
 		// Section index ≥ 1 is a heading-anchored section. Redirect to its
 		// anchor so the user lands on the section they just saved, even if
@@ -441,28 +446,30 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 		}
 	}
 
+	// A save must never remove a page. An empty POST — a truncated mobile
+	// request, a lost `section` field, an editor that came up blank — is
+	// indistinguishable from "clear this page", and deleting index.md on that
+	// signal loses the whole file even though the user only edited one section.
+	// Removing a page is the explicit ?delete action's job (moves.go).
 	if strings.TrimSpace(content) == "" {
-		if err := os.Remove(indexPath); err != nil && !os.IsNotExist(err) {
-			http.Error(w, "delete failed: "+err.Error(), http.StatusInternalServerError)
-			return
-		}
-	} else {
-		// Stat first so we know whether MkdirAll actually created the folder
-		// — if it did, the search index needs a new entry.
-		_, statErr := os.Stat(fsPath)
-		newlyCreated := os.IsNotExist(statErr)
-		if err := os.MkdirAll(fsPath, 0755); err != nil {
-			http.Error(w, "mkdir failed: "+err.Error(), http.StatusInternalServerError)
-			return
-		}
-		if err := os.WriteFile(indexPath, []byte(content), 0644); err != nil {
-			http.Error(w, "write failed: "+err.Error(), http.StatusInternalServerError)
-			return
-		}
-		if newlyCreated {
-			if rel, err := filepath.Rel(h.root, fsPath); err == nil {
-				folderIndexAdd(filepath.ToSlash(rel))
-			}
+		http.Error(w, "refusing to save empty content — use DELETE to remove this page", http.StatusBadRequest)
+		return
+	}
+	// Stat first so we know whether MkdirAll actually created the folder
+	// — if it did, the search index needs a new entry.
+	_, statErr := os.Stat(fsPath)
+	newlyCreated := os.IsNotExist(statErr)
+	if err := os.MkdirAll(fsPath, 0755); err != nil {
+		http.Error(w, "mkdir failed: "+err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if err := os.WriteFile(indexPath, []byte(content), 0644); err != nil {
+		http.Error(w, "write failed: "+err.Error(), http.StatusInternalServerError)
+		return
+	}
+	if newlyCreated {
+		if rel, err := filepath.Rel(h.root, fsPath); err == nil {
+			folderIndexAdd(filepath.ToSlash(rel))
 		}
 	}
 	// The editor saves via fetch so the save and its result share one history