fix(changes): a huge line no longer cuts the diff short; preview pages up to 64 MB

A page that inlines a video as base64 has rows of megabytes. Its patch was read
at the 200 KB per-file cap, so the first such row used the whole budget and
every hunk after it was lost ("Diff cut short"). The patch is now read up to
16 M characters, rows over 4,000 characters are cut to 1,000 with an `elided`
count the diff shows, and only then is the cap applied. Hunk actions re-read
git's own diff by header and are unchanged.

The HTML preview refused a page over 10 MB and showed only the file icon; a
self-contained 18 MB slide deck now opens (limit 64 MB).

client/src/components/HtmlFrame.tsx

@@ -15,8 +15,10 @@ import { FileText, Loader2 } from "lucide-react";
 import { artifactDocument, frameSandbox } from "../lib/artifactView";
 import { blobText, inlineHtml, type FetchFile } from "../lib/htmlInline";
 
-/** A page read by `fetchFile` is shown up to this size. */
-const HTML_MAX = 10 * 1024 * 1024;
+/** A page read by `fetchFile` is shown up to this size. A self-contained
+ *  page (a slide deck with its video and images inlined as base64) is easily
+ *  past 10 MB; the iframe renders far larger documents than this. */
+const HTML_MAX = 64 * 1024 * 1024;
 
 export function HtmlFrame({
   path,

client/src/components/lanes/LaneDiffView.tsx

@@ -179,6 +179,18 @@ export function langFor(filePath: string) {
 }
 
 /** Tokenized line text. `emph` marks the span that actually changed. */
+/** The tail of a row the server cut down (`LaneDiffLine.elided`). */
+function Elided({ n }: { n?: number }) {
+  const { t, i18n } = useTranslation("lanes");
+  if (!n) return null;
+  const size = new Intl.NumberFormat(i18n.language, { notation: "compact" }).format(n);
+  return (
+    <span className="ml-1 select-none rounded bg-surface-3 px-1 font-sans text-[10px] text-fg-muted">
+      {t("changes.lineElided", { size })}
+    </span>
+  );
+}
+
 function Code({ text, lang, emph }: { text: string; lang: string; emph?: [number, number] }) {
   if (emph) {
     const [from, to] = emph;
@@ -544,6 +556,7 @@ function UnifiedLine({
           {line.type === "add" ? "+" : line.type === "del" ? "-" : " "}
         </span>
         <Code text={line.text} lang={lang} emph={emph} />
+        <Elided n={line.elided} />
       </span>
       {bar && <HunkBar change={bar} />}
     </Row>
@@ -621,6 +634,7 @@ function SplitLine({
       />
       <span className="whitespace-pre px-1">
         {line ? <Code text={line.text} lang={lang} emph={e} /> : null}
+        {line ? <Elided n={line.elided} /> : null}
       </span>
       {bar && <HunkBar change={bar} />}
     </Row>

client/src/components/lanes/__tests__/LaneDiffView.test.tsx

@@ -609,3 +609,26 @@ describe("LaneDiffView — line comments", () => {
     expect(screen.queryByTestId("diff-comment-line-1")).toBeNull();
   });
 });
+
+describe("LaneDiffView — a row the server cut down", () => {
+  const CUT: LaneChangeFile = {
+    ...FILE,
+    hunks: [
+      {
+        ...FILE.hunks[0]!,
+        lines: [
+          { type: "del", oldLine: 1, newLine: null, text: '<video src="AAAA', elided: 3_000_000 },
+          { type: "add", oldLine: null, newLine: 1, text: '<video src="BBBB', elided: 3_000_000 },
+        ],
+      },
+    ],
+  };
+
+  it("says how much of the row it hides, in both layouts", () => {
+    const { unmount } = render(<LaneDiffView file={CUT} layout="unified" />);
+    expect(screen.getAllByText(/3M more characters on this line/)).toHaveLength(2);
+    unmount();
+    render(<LaneDiffView file={CUT} layout="split" />);
+    expect(screen.getAllByText(/3M more characters on this line/)).toHaveLength(2);
+  });
+});