fix(files): an HTML file in the Changes panel shows as the page only on Preview

Changes stays the default view and Whole file shows the source, as for any
file. A Preview button — offered on the Changes diff too, where it was
missing — opens the page; Raw, Changes or Whole file go back to the source.

client/src/components/lanes/LaneChangesPanel.tsx

@@ -14,8 +14,9 @@
  *              is unsaved): Changes folds the unchanged lines away, Whole file
  *              shows them; any other file opens on its read-only diff; a
  *              whole markdown file can also be read rendered (Preview), an HTML
- *              file opens as the page itself (`HtmlFrame`, its relative CSS,
- *              scripts and images read like downloads), and an
+ *              file shown as the page on Preview, from Changes too
+ *              (`HtmlFrame`, its relative CSS, scripts and images read like
+ *              downloads), and an
  *              image file is shown as the picture (`GET …/git/raw`)
  *   history  — recent commits; opening one shows that commit's diff
  *   browse   — quick-open by path, or the repo's tracked file tree (the
@@ -891,9 +892,9 @@ export function LaneChangesPanel({
   const [whole, setWhole] = useState(false);
   // A whole markdown or HTML file shown rendered instead of as source; per
   // file, markdown opening as Settings → Appearance says
-  // (`lib/markdownView.ts`), an HTML page always as the page.
+  // (`lib/markdownView.ts`), an HTML page only once Preview is clicked.
   const [mdPreview, setMdPreview] = useState(readMarkdownPreview);
-  useEffect(() => setMdPreview(isHtml(openFile) || readMarkdownPreview()), [openFile]);
+  useEffect(() => setMdPreview(!isHtml(openFile) && readMarkdownPreview()), [openFile]);
   const [data, setData] = useState<LaneChanges | null>(null);
   // A folder that is not a repo (an empty new workspace, a parent of clones)
   // has no changes, review or history — only its files, which Files reads
@@ -2562,6 +2563,9 @@ export function LaneChangesPanel({
                       aria-pressed={whole === w}
                       onClick={() => {
                         if (whole === w) return;
+                        // Changes and Whole file show an HTML page's source;
+                        // only Preview runs it.
+                        if (isHtml(openFile)) setMdPreview(false);
                         // Both views of a working file are the same editor: the
                         // draft goes along, unsaved or not.
                         if (editable && draft !== null) return setWhole(w);
@@ -2993,16 +2997,21 @@ export function LaneChangesPanel({
                       {t("changes.annotate")}
                     </button>
                   )}
-                  {whole && text && !dirty && (isMarkdown(openFile) || isHtml(openFile)) && (
+                  {/* Offered on Changes too: from there it opens the rendered whole file. */}
+                  {(!whole || text) && !dirty && (isMarkdown(openFile) || isHtml(openFile)) && (
                     <button
                       type="button"
                       data-testid="lane-file-preview"
-                      aria-pressed={mdPreview}
-                      onClick={() => setMdPreview((v) => !v)}
+                      aria-pressed={whole && mdPreview}
+                      onClick={() => {
+                        if (whole) return setMdPreview((v) => !v);
+                        setMdPreview(true);
+                        setWhole(true);
+                      }}
                       className="flex shrink-0 items-center gap-1 self-center rounded border border-border-light px-1.5 py-0.5 text-[11px] text-fg-secondary hover:bg-surface-2 hover:text-fg-primary"
                     >
-                      {mdPreview ? <Code2 className="h-3 w-3" /> : <Eye className="h-3 w-3" />}
-                      {mdPreview ? t("changes.raw") : t("changes.preview")}
+                      {whole && mdPreview ? <Code2 className="h-3 w-3" /> : <Eye className="h-3 w-3" />}
+                      {whole && mdPreview ? t("changes.raw") : t("changes.preview")}
                     </button>
                   )}
                   {!local && range !== "commit" && openFile && (

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

@@ -544,7 +544,7 @@ describe("LaneChangesPanel", () => {
     expect(screen.queryByTestId("lane-file-editor")).toBeNull();
   });
 
-  it("opens a whole HTML file as the page, its source after Raw", async () => {
+  it("opens a whole HTML file as its source, the page after Preview, the source after Raw", async () => {
     vi.mocked(api.lanes.gitTree).mockResolvedValue({
       available: true,
       path: "",
@@ -564,14 +564,48 @@ describe("LaneChangesPanel", () => {
     render(<LaneChangesPanel laneId={7} full />);
     const sidebar = await screen.findByTestId("lane-changes-sidebar");
     await user.click(await within(sidebar).findByText("deck.html"));
+    expect(await screen.findByTestId("lane-file-editor")).toHaveValue("<p>deck</p>");
+    expect(screen.queryByTestId("html-frame")).toBeNull();
+    await user.click(screen.getByTestId("lane-file-preview"));
     const frame = await screen.findByTestId("html-frame");
     expect(frame.getAttribute("srcdoc")).toContain("<p>deck</p>");
-    expect(frame.getAttribute("sandbox")).not.toContain("allow-same-origin");
     await user.click(screen.getByTestId("lane-file-preview"));
     expect(await screen.findByTestId("lane-file-editor")).toHaveValue("<p>deck</p>");
     expect(screen.queryByTestId("html-frame")).toBeNull();
   });
 
+  it("opens a changed HTML file on its Changes, the page only after Preview", async () => {
+    vi.mocked(api.lanes.changes).mockResolvedValue(
+      changes({
+        files: [
+          { path: "deck.html", status: "??", untracked: true, added: 1, deleted: 0, binary: false },
+        ],
+      })
+    );
+    vi.mocked(api.lanes.gitFile).mockResolvedValue({
+      available: true,
+      path: "deck.html",
+      rev: "work",
+      binary: false,
+      truncated: false,
+      lines: ["<p>deck</p>"],
+      sha: "c".repeat(40),
+    });
+    const user = userEvent.setup();
+    render(<LaneChangesPanel laneId={7} />);
+    await user.click(await screen.findByTitle("deck.html"));
+    await screen.findByRole("button", { name: "Changes", pressed: true });
+    expect(screen.queryByTestId("html-frame")).toBeNull();
+    await user.click(await screen.findByTestId("lane-file-preview"));
+    const frame = await screen.findByTestId("html-frame");
+    expect(frame.getAttribute("srcdoc")).toContain("<p>deck</p>");
+    expect(frame.getAttribute("sandbox")).not.toContain("allow-same-origin");
+    // Back to Changes, then Whole file: the source again, not the page.
+    await user.click(screen.getByRole("button", { name: "Changes", pressed: false }));
+    await user.click(screen.getByRole("button", { name: "Whole file", pressed: false }));
+    await waitFor(() => expect(screen.queryByTestId("html-frame")).toBeNull());
+  });
+
   it("shows an image file as the picture, with no edit control", async () => {
     vi.mocked(api.lanes.gitTree).mockResolvedValue({
       available: true,