feat(messages): word diff of the last edit on "(edited)" hover (#144)

Hovering or focusing "(edited)" shows a tooltip with only the most recent
edit as a word diff — removed words struck, added words bold — plus a
+N/−N summary. Clicking still opens the full history viewer. On touch, a
long-press on the label shows the same diff as a popout (a plain tap opens
the viewer; the message's own long-press action sheet is not triggered).

utils/wordDiff.ts is a unit-tested LCS over words that ignores whitespace-
only changes and gives up past 400 words. Only plain-text bodies are
diffed; formatted edits fall back to the viewer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/RenderMessageContent.tsx

@@ -26,6 +26,8 @@ import {
   VerificationRequestContent,
   VideoContent,
 } from './message';
+import { DiffToken } from '../utils/wordDiff';
+import { EditDiffContext } from './message/content/EditDiffContext';
 import { UrlPreviewCard, UrlPreviewHolder } from './url-preview';
 import { Image, MediaControl, Video } from './media';
 import { ImageViewer } from './image-viewer';
@@ -74,8 +76,17 @@ type RenderMessageContentProps = {
   onOpenImageViewer?: () => void;
   /** [Gitea #159] The event, for the undecryptable placeholder's reason + retry. */
   mEvent?: MatrixEvent;
+  /** [Gitea #144] Word diff of the last edit, shown on "(edited)" hover. */
+  editDiff?: DiffToken[];
 };
-export function RenderMessageContent({
+export function RenderMessageContent({ editDiff, ...props }: RenderMessageContentProps) {
+  return (
+    <EditDiffContext.Provider value={editDiff}>
+      <RenderMessageContentBody {...props} />
+    </EditDiffContext.Provider>
+  );
+}
+function RenderMessageContentBody({
   displayName,
   msgType,
   ts,
@@ -91,7 +102,7 @@ export function RenderMessageContent({
   eventId,
   onOpenImageViewer,
   mEvent,
-}: RenderMessageContentProps) {
+}: Omit<RenderMessageContentProps, 'editDiff'>) {
   const renderUrlsPreview = (urls: string[]) => {
     // Cap previews per message so a link-dump doesn't spawn dozens of preview
     // fetches + iframes at once. De-dupe first: a message linking the same URL