Fix markdown editor escaped list markers

ui/src/lib/markdown.ts

@@ -0,0 +1,47 @@
+const FENCE_RE = /^\s*(`{3,}|~{3,})/;
+const SPACE_ENTITY_RE = / /gi;
+const ESCAPED_UNORDERED_LIST_RE = /^(\s{0,3})\\([*+-])([ \t]+)/;
+
+/**
+ * Normalize markdown artifacts emitted by rich-text serialization so
+ * plain markdown list syntax remains usable in Paperclip editors.
+ */
+export function normalizeMarkdownArtifacts(markdown: string): string {
+  if (!markdown) return markdown;
+
+  const lines = markdown.split(/\r?\n/);
+  let inFence = false;
+  let fenceMarker: "`" | "~" | null = null;
+  let fenceLength = 0;
+  let changed = false;
+
+  const normalized = lines.map((line) => {
+    const fenceMatch = FENCE_RE.exec(line);
+    if (fenceMatch) {
+      const marker = fenceMatch[1];
+      if (!inFence) {
+        inFence = true;
+        fenceMarker = marker[0] as "`" | "~";
+        fenceLength = marker.length;
+      } else if (marker[0] === fenceMarker && marker.length >= fenceLength) {
+        inFence = false;
+        fenceMarker = null;
+        fenceLength = 0;
+      }
+      return line;
+    }
+
+    if (inFence) return line;
+
+    let next = line;
+    if (next.includes(" ")) {
+      next = next.replace(SPACE_ENTITY_RE, " ");
+    }
+    const unescaped = next.replace(ESCAPED_UNORDERED_LIST_RE, "$1$2$3");
+    if (unescaped !== line) changed = true;
+    return unescaped;
+  });
+
+  if (!changed) return markdown;
+  return normalized.join("\n");
+}