Implement the following plan:

Plan: Add Auto-Play to Markov Babbler Generation Phase

Context

The Markov Babbler's generation phase requires clicking "Next Word" for every single word. The user wants a way to watch it continuously generate text — a play/pause toggle so it can "just rip" without repeated clicking.

Approach

Add play/pause and speed controls to the generation phase in markov-babbler.tsx, reusing the same pattern already established in the walkthrough phases (markov-babbler-walkthrough.tsx uses isPlaying, speed, and setTimeout-based auto-advance).

File Modified

apps/web/components/mdx/markov-babbler.tsx (lines 89-109 for handleStep, lines 226-309 for generation UI)

State additions

const [isPlaying, setIsPlaying] = useState(false);
const [speed, setSpeed] = useState<"slow" | "normal" | "fast">("normal");
const playingRef = useRef(false);

const GENERATION_SPEED_MS = { slow: 1200, normal: 800, fast: 400 };

Refactor handleStep

Current handleStep has a 600ms setTimeout for the probability-bar transition animation. At fast auto-play speed (400ms), this creates a race condition. Fix: skip the animation delay when auto-playing — set the next-word probabilities immediately.

const handleStep = useCallback(() => {
  // ... existing generation logic ...
  if (result) {
    setGeneratedWords((prev) => [...prev, result.word]);
    setLastSelectedWord(result.word);

    const nextResult = generateNext(currentModel, result.word, temperature);
    if (nextResult) {
      if (playingRef.current) {
        // Skip animation delay during auto-play for snappy feel
        setCurrentProbabilities(nextResult.probabilities);
        setLastSelectedWord(undefined);
      } else {
        // Manual click: keep the 600ms animation showing which word was picked
        setCurrentProbabilities(result.probabilities);
        setTimeout(() => {
          setCurrentProbabilities(nextResult.probabilities);
          setLastSelectedWord(undefined);
        }, 600);
      }
    }
  }
}, [generatedWords, temperature]);

Auto-play effect

Standard useEffect + setTimeout pattern (same as walkthrough phases). Triggers on generatedWords change so each new word schedules the next step.

useEffect(() => {
  playingRef.current = isPlaying;
  if (!isPlaying) return;
  const timer = setTimeout(handleStep, GENERATION_SPEED_MS[speed]);
  return () => clearTimeout(timer);
}, [isPlaying, speed, generatedWords, handleStep]);

Stop auto-play in Start Over / New Text

Add setIsPlaying(false) to handleStartOver and handleRetrain.

UI controls

Replace the current button row with:

[▶ Play] [Next Word]            [Slow] [Normal] [Fast]
[Start Over] [New Text]

When playing:

[⏸ Pause] [Next Word (disabled)] [Slow] [Normal] [Fast]
[Start Over] [New Text]

• Play/Pause: primary accent style when playing
• Speed buttons: small outline buttons, border-accent bg-accent/10 text-accent when active (same pattern as text sample selector buttons already in the component)
• "Next Word" disabled during auto-play to avoid double-stepping

E2E Test

Add tests to the existing testing/e2e/tests/markov-babbler.spec.ts file, inside the existing "Markov Babbler" describe block. Tests use the same helper pattern: train → skip walkthrough → reach generation phase.

New data-testid attributes needed

• auto-play-button — the Play/Pause toggle button
• speed-selector — container for speed buttons
• speed-slow, speed-normal, speed-fast — individual speed buttons

Tests to add

1. "auto-play button renders in generation mode" — Train, skip walkthrough, verify auto-play-button is visible and says "Play"

2. "auto-play generates words continuously" — Train, skip, click Play, wait ~2.5s, click Pause, verify generated text has 3+ words (more than the initial 1)

3. "pause stops auto-play" — Train, skip, click Play, wait 1s, click Pause (verify it says "Play" again), record word count, wait 1.5s, verify word count hasn't changed

4. "speed selector changes generation speed" — Train, skip, verify speed buttons visible, click "Fast", verify active state applied

5. "start over stops auto-play" — Train, skip, click Play, wait 1s, click Start Over, verify auto-play button says "Play" (not "Pause")

6. "next word button disabled during auto-play" — Train, skip, click Play, verify next-word-button is disabled, click Pause, verify it's enabled again

Verification

1. bun run tsc — type check passes
2. cd testing/e2e && CI=true bunx playwright test --project=markov-babbler — e2e tests pass
3. Manual: Click Play, words generate continuously at selected speed
4. Manual: Click Pause, generation stops
5. Manual: Switch speed while playing, timing changes immediately
6. Manual: Click "Next Word" while paused, single step works as before
7. Manual: Click "Start Over" while playing, stops and resets

If you need specific details from before exiting plan mode (like exact code snippets, error messages, or content you generated), read the full transcript at: ~/.claude/projects/-Users-challen-www-usingandunderstanding-ai/47135cc7-1e33-4624-b591-71edf2f75b9f.jsonl

Your task

First, run git status, git diff, and git log --oneline -10 to understand the current state.

Then add and commit all modified files with a descriptive message. Break the changes into multiple commits if appropriate. If there are untracked files, ask if they should be added or added to the appropriate .gitignore file. The user may also want to take over at this point, so provide an abort option as well. Always check changes for unnecessary debugging statements or logging that might have been accidentally included. Prompt the user if you find any, and offer to remove each one by one. Do not use interactive git staging (git add -p) as it does not work.

Read the output file to retrieve the result: [tmp-path]

Your task

First, run git status, git diff, and git log --oneline -10 to understand the current state.

Then add and commit all modified files with a descriptive message. Break the changes into multiple commits if appropriate. If there are untracked files, ask if they should be added or added to the appropriate .gitignore file. The user may also want to take over at this point, so provide an abort option as well. Always check changes for unnecessary debugging statements or logging that might have been accidentally included. Prompt the user if you find any, and offer to remove each one by one. Do not use interactive git staging (git add -p) as it does not work.

OK. Now I'm at the point where I need a Chrome content plugin for this course. Here's how I want it to work. I'm on a page. I click a button. The page URL and contents (current DOM, not page source) get sent to the backend for processing. We can probably leave it at that for now, but we should record the URL and the contents in the database. I'd suggest that the plugin be configured with a magic URL that, for now, only instructors can find on their profile page. Uploads to that magic URL are tagged with the user's username and role.

Let's also allow users to set their first name on the /profile page. And perhaps add a photo?