fix(story-mode): read right by a screen reader, and the last of review round 6

Accessibility (review6-c):
- A panel is named "Panel 2 of 7" and its caption is read once, as its
  content (it was the name and the content both).
- Balloons say who speaks, visually hidden ("Claude says: ", "You say: ",
  "Claude asks: ", "Notice: "); Save image leaves those words out.
- The overlay is named "Story Mode: <session>", the drawer by its kind and
  title ("Diff 2 files"), the final panel's chips by what they open, and
  the wire's panel labels are headings.
- While a file preview opened from a panel is up, the overlay is not
  aria-modal (the preview sits beside it), and is again once focus returns.
- The focus ring on a click region gets a light band under its dashes; on
  the loop's magenta halftone it vanished.

From review6-b:
- "Mission complete!" no longer shows while a helper or a background
  command is still out ("To be continued…").
- A background command's drawer says "Started in the background…", then
  "Finished in the background, exit code 0…", instead of the launch note
  meant for Claude ("do not poll that file").
- `sed -n '5,25p' README.md` is a printed file, offered in the drawer.
- A report turn no longer counts the helper it answers as one it started.
- A helper's `cd /work/x && ls` keeps its folder as ".".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/fixtures/story-corpus/bash-script-background-helper.expected.json

@@ -104,7 +104,7 @@
     "filesChanged": 0,
     "added": 0,
     "removed": 0,
-    "helpers": 1,
+    "helpers": 0,
     "helpersRunning": 0,
     "panels": [
       {
@@ -141,7 +141,7 @@
         "kind": "complete",
         "ok": null,
         "story": "Done in 21 seconds.",
-        "director": "turn_duration · 21 s · 2 tool calls · 1 helper",
+        "director": "turn_duration · 21 s · 2 tool calls",
         "balloon": "I built rename_by_date.sh, the helper agent wrote README.md, and the script passed every test I ran on sample files in samples/. Nothing is committed because this folder isn't a git repository, even though the session context said it was.",
         "tests": null,
         "roundsOk": null,

test/fixtures/story-corpus/text-plan-dry-run-helper.expected.json

@@ -117,7 +117,7 @@
     "filesChanged": 0,
     "added": 0,
     "removed": 0,
-    "helpers": 1,
+    "helpers": 0,
     "helpersRunning": 0,
     "panels": [
       {
@@ -144,7 +144,7 @@
         "kind": "complete",
         "ok": null,
         "story": "Done in 9 seconds.",
-        "director": "turn_duration · 9 s · 1 tool call · 1 helper",
+        "director": "turn_duration · 9 s · 1 tool call",
         "balloon": "The background helper has finished README.md, and I've checked its work.",
         "tests": null,
         "roundsOk": null,

test/story-mode-ui.test.ts

@@ -151,9 +151,12 @@ describe('story-mode.js overlay', () => {
       'save',
       'complete',
     ]);
-    expect($('.story-panel[data-kind="mission"] .story-balloon')!.textContent).toBe(
+    expect($('.story-panel[data-kind="mission"] .story-balloon-text')!.textContent).toBe(
       'The checkout button does nothing on phones. Can you fix it?'
     );
+    // Who speaks, for a screen reader (visually hidden; the art shows it).
+    expect($('.story-panel[data-kind="mission"] .story-balloon .story-vh')!.textContent).toBe('You say: ');
+    expect($('.story-panel[data-kind="mission"]')!.getAttribute('aria-label')).toBe('Panel 1 of 7');
     expect($('.story-panel[data-kind="mission"] .story-balloon')!.className).toContain('story-balloon--you');
     expect($('.story-panel[data-kind="investigate"] .story-cap-story')!.textContent).toBe(
       'Claude reads 2 files to find its way around.'
@@ -535,7 +538,8 @@ describe('story-mode.js overlay', () => {
     await settle();
     const balloon = $('.story-panel[data-kind="mission"] .story-balloon')!;
     expect(balloon.className).toContain('story-balloon--note');
-    expect(balloon.textContent).toBe('Agent "Docs" finished');
+    expect(balloon.querySelector('.story-balloon-text')!.textContent).toBe('Agent "Docs" finished');
+    expect(balloon.querySelector('.story-vh')!.textContent).toBe('Notice: ');
   });
 
   it("the helper drawer fetches and lists the helper's own steps", async () => {
@@ -680,6 +684,8 @@ describe('story-mode.js overlay', () => {
     await settle();
     sizeAndDraw();
     expect($('.story-panel[data-kind="complete"] .story-chips')!.textContent).toContain('1 helper, 1 still working');
+    // Work still out is not a finished mission.
+    expect($('.story-panel[data-kind="complete"] .story-splash-title')!.textContent).toBe('To be continued…');
     $('.story-panel[data-kind="backup"] .story-hit')!.click();
     await settle();
     expect($('.story-drawer-sub')!.textContent).toContain('in the background');

test/story-mode.test.ts

@@ -735,6 +735,10 @@ describe('buildStoryTurns', () => {
     const first = buildStoryPage(turns[0]);
     expect(first.events[1]).toMatchObject({ intent: 'test', ok: true });
     expect(first.events[1].running).toBeUndefined();
+    // Its drawer says what happened, not the launch note meant for Claude.
+    expect(first.events[1].output).toBe(
+      'Finished in the background, exit code 0. Its report is the turn it came back in.'
+    );
     const second = buildStoryPage(turns[1]);
     expect(second.panels.find((p) => p.kind === 'check')).toMatchObject({
       caption: { story: 'The tests pass.' },
@@ -751,6 +755,7 @@ describe('buildStoryTurns', () => {
     const page = buildStoryPage(alone);
     expect(page.events[1]).toMatchObject({ running: true });
     expect(page.events[1].ok).toBeUndefined();
+    expect(page.events[1].output).toBe('Started in the background. Its result comes back as a report of its own.');
     expect(page.panels.find((p) => p.kind === 'check')!.caption.story).toBe(
       'Claude starts the tests in the background.'
     );
@@ -1033,6 +1038,12 @@ describe('buildStoryPage', () => {
     expect(whole.hunks[0].atEnd).toBeUndefined();
   });
 
+  it('sed -n prints part of a file, like head', () => {
+    expect(printedFiles("sed -n '5,25p' README.md")).toEqual(['README.md']);
+    expect(printedFiles('sed -n 10p src/a.py && ls')).toEqual(['src/a.py']);
+    expect(printedFiles("sed -i 's/a/b/' a.py")).toEqual([]);
+  });
+
   it('files a command prints are on its event, resolved against its cwd, whatever it does', () => {
     const lines = [
       prompt('rewrite and test'),