feat(editor): eslint/tsconfig migration + type fixes

@robonen/editor: migrate to eslint flat config + composite tsconfig; fix
convergence test type annotations.

vue/editor/src/model/marks.ts

@@ -0,0 +1,57 @@
+import type { Attrs } from './attrs';
+import { attrsEq } from './attrs';
+
+/**
+ * An inline formatting mark applied to a run of text (bold, italic, link, ...).
+ * `type` is the registry key; `attrs` holds mark-specific data (e.g. link href).
+ */
+export interface Mark {
+  readonly type: string;
+  readonly attrs?: Attrs;
+}
+
+/** A normalized set of marks: at most one per type, sorted by `type`. */
+export type Marks = readonly Mark[];
+
+/** Structural equality for two marks (type + attrs). */
+export function markEq(a: Mark, b: Mark): boolean {
+  return a.type === b.type && attrsEq(a.attrs, b.attrs);
+}
+
+/** Ordered structural equality for two normalized mark sets. */
+export function marksEq(a: Marks, b: Marks): boolean {
+  if (a === b)
+    return true;
+
+  if (a.length !== b.length)
+    return false;
+
+  return a.every((mark, i) => markEq(mark, b[i]!));
+}
+
+/**
+ * Canonicalize a mark set: keep the last occurrence per `type` (so a re-applied
+ * mark with new attrs wins) and sort by `type`. The deterministic order is what
+ * makes {@link marksEq} an O(n) comparison and keeps the model diff-stable.
+ */
+export function normalizeMarks(marks: Marks): Marks {
+  if (marks.length <= 1)
+    return marks;
+
+  const byType = new Map<string, Mark>();
+
+  for (const mark of marks)
+    byType.set(mark.type, mark);
+
+  return [...byType.values()].sort((a, b) => (a.type < b.type ? -1 : a.type > b.type ? 1 : 0));
+}
+
+/** Whether `marks` contains a mark structurally equal to `mark`. */
+export function hasMark(marks: Marks, mark: Mark): boolean {
+  return marks.some(m => markEq(m, mark));
+}
+
+/** Whether `marks` contains any mark of the given `type`. */
+export function hasMarkType(marks: Marks, type: string): boolean {
+  return marks.some(m => m.type === type);
+}