feat(02-05): wire compost beat toast (Plan 02-04 deferral)

- src/ui/settings/compost-toast.tsx: thin transient toast (D-07,
  GARD-04). Reads a rotating line from uiStrings[1].post_harvest_beat
  on each compost dispatch; fades out after 3.5s. Co-located with
  PersistenceToast as the plan specified ('folded into the persistence-
  toast UI surface').
- src/store/session-slice.ts: compostBeatTick monotonic counter +
  bumpCompostBeat action. Counter (vs boolean) ensures consecutive
  composts re-fire the toast without dedup.
- src/game/scenes/Garden.ts: handleTilePointerDown's compost branch
  calls bumpCompostBeat after enqueueCommand.
- src/App.tsx: mounts <CompostToast />.
- 4 new compost-toast tests; 312/312 vitest green; e2e still 1.6s
  green; npm run ci exits 0.

Implementation choice (per plan 'surfaced in SUMMARY'): minimum-viable
toast surface chosen over the Ink runtime path. The Ink-authored
compost-acknowledgements.ink content remains compiled + runtime-
loadable via loadInkStory + InkRenderer, so a future plan can swap
this component for the richer voice without touching sim or store.

src/App.tsx

@@ -5,7 +5,7 @@ import { SeedPicker } from './ui/garden';
 import { FragmentRevealModal, JournalIcon } from './ui/journal';
 import { LuraDialogue } from './ui/dialogue';
 import { Letter } from './ui/letter';
-import { Settings, PersistenceToast } from './ui/settings';
+import { Settings, PersistenceToast, CompostToast } from './ui/settings';
 import { useAppStore } from './store';
 
 function App() {
@@ -59,6 +59,7 @@ function App() {
       <Letter />
       <Settings open={settingsOpen} onClose={() => setSettingsOpen(false)} />
       <PersistenceToast show={showPersistenceToast} />
+      <CompostToast />
       <button
         data-testid="settings-icon"
         aria-label="Open settings"

src/game/scenes/Garden.ts

@@ -234,12 +234,13 @@ export class Garden extends Phaser.Scene {
       appStore.getState().enqueueCommand({ kind: 'harvest', tileIdx: idx });
     } else {
       // GARD-04 + D-07: compost an immature plant (sprout / mature).
-      // TODO Plan 02-04: replace with the Ink-authored compost beat
-      //   rendered through the dialogue overlay (compost-acknowledgements.ink).
-      //   Plan 02-03 ships the authored content under
-      //   /content/dialogue/season1/ so Plan 02-04 can wire the runtime
-      //   without re-authoring.
+      // Plan 02-05 — bump the compost-beat tick so CompostToast fires
+      // a transient one-line acknowledgement from uiStrings.post_harvest_beat.
+      // The Ink-authored richer voice in compost-acknowledgements.ink
+      // remains compiled + runtime-loadable (loadInkStory + InkRenderer)
+      // for Phase 4+ to swap in if richer branching is needed.
       appStore.getState().enqueueCommand({ kind: 'compost', tileIdx: idx });
+      appStore.getState().bumpCompostBeat();
     }
   }
 

src/store/session-slice.ts

@@ -19,11 +19,23 @@ export interface SessionSlice {
   letterOverlayOpen: boolean;
   /** OfflineEventBlock; populated by the boot path's silent catchup loop. */
   pendingLetterEventBlock: unknown | null;
+  /**
+   * Plan 02-05 — compost-acknowledgement transient marker (D-07 + GARD-04).
+   * Garden.ts sets this to a monotonic counter on each compost dispatch so
+   * the CompostToast component can re-fire on every compost (vs. boolean,
+   * which would deduplicate consecutive composts as the same notification).
+   * The runtime line shown is chosen from `uiStrings[seasonId].post_harvest_beat`
+   * by the CompostToast component (a minimum-viable surface; the Ink-authored
+   * /content/dialogue/season1/compost-acknowledgements.ink is fully compiled
+   * and runtime-loadable for Phase 4+ to swap in if richer voice is needed).
+   */
+  compostBeatTick: number;
   dismissBeginGate: () => void;
   setPersistenceToastShown: (v: boolean) => void;
   setShowPersistenceToast: (v: boolean) => void;
   openLetter: (block: unknown) => void;
   dismissLetter: () => void;
+  bumpCompostBeat: () => void;
 }
 
 export const createSessionSlice: StateCreator<SessionSlice, [], [], SessionSlice> = (set) => ({
@@ -32,9 +44,11 @@ export const createSessionSlice: StateCreator<SessionSlice, [], [], SessionSlice
   showPersistenceToast: false,
   letterOverlayOpen: false,
   pendingLetterEventBlock: null,
+  compostBeatTick: 0,
   dismissBeginGate: () => set({ beginGateDismissed: true }),
   setPersistenceToastShown: (v) => set({ persistenceToastShown: v }),
   setShowPersistenceToast: (v) => set({ showPersistenceToast: v }),
   openLetter: (block) => set({ letterOverlayOpen: true, pendingLetterEventBlock: block }),
   dismissLetter: () => set({ letterOverlayOpen: false, pendingLetterEventBlock: null }),
+  bumpCompostBeat: () => set((s) => ({ compostBeatTick: s.compostBeatTick + 1 })),
 });

src/ui/settings/compost-toast.test.tsx

@@ -0,0 +1,72 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { render, screen, cleanup, act } from '@testing-library/react';
+import { appStore } from '../../store';
+
+vi.mock('../../game/event-bus', () => ({
+  eventBus: {
+    on: vi.fn(),
+    off: vi.fn(),
+    emit: vi.fn(),
+    removeAllListeners: vi.fn(),
+  },
+}));
+
+import { CompostToast } from './compost-toast';
+
+describe('CompostToast (D-07 + GARD-04 — transient compost beat toast)', () => {
+  beforeEach(() => {
+    appStore.setState({ compostBeatTick: 0 });
+    vi.useFakeTimers();
+  });
+  afterEach(() => {
+    cleanup();
+    vi.useRealTimers();
+    vi.clearAllMocks();
+  });
+
+  it('returns null at initial state (compostBeatTick=0)', () => {
+    const { container } = render(<CompostToast />);
+    expect(container.firstChild).toBeNull();
+  });
+
+  it('appears after bumpCompostBeat is called', async () => {
+    render(<CompostToast />);
+    await act(async () => {
+      appStore.getState().bumpCompostBeat();
+    });
+    expect(screen.getByTestId('compost-toast')).toBeTruthy();
+    // The line shown comes from uiStrings.post_harvest_beat[1] (cycle of 3).
+    // We don't pin the exact line — that's a content concern — only that
+    // it has non-empty text content.
+    expect(screen.getByTestId('compost-toast').textContent?.length).toBeGreaterThan(0);
+  });
+
+  it('fades out after the timeout duration', async () => {
+    render(<CompostToast />);
+    await act(async () => {
+      appStore.getState().bumpCompostBeat();
+    });
+    expect(screen.queryByTestId('compost-toast')).toBeTruthy();
+    await act(async () => {
+      vi.advanceTimersByTime(4000);
+    });
+    expect(screen.queryByTestId('compost-toast')).toBeNull();
+  });
+
+  it('re-fires when bumpCompostBeat is called again', async () => {
+    render(<CompostToast />);
+    await act(async () => {
+      appStore.getState().bumpCompostBeat();
+    });
+    expect(screen.queryByTestId('compost-toast')).toBeTruthy();
+    await act(async () => {
+      vi.advanceTimersByTime(4000);
+    });
+    expect(screen.queryByTestId('compost-toast')).toBeNull();
+    // Second compost re-fires.
+    await act(async () => {
+      appStore.getState().bumpCompostBeat();
+    });
+    expect(screen.queryByTestId('compost-toast')).toBeTruthy();
+  });
+});

src/ui/settings/compost-toast.tsx

@@ -0,0 +1,69 @@
+import { useEffect, useState, type JSX } from 'react';
+import { useAppStore } from '../../store';
+import { uiStrings } from '../../content';
+
+/**
+ * CompostToast (CONTEXT D-07 + GARD-04 — Plan 02-04 deferred wiring).
+ *
+ * A small transient toast that fires when the player composts a plant.
+ * Surfaces a single line from `uiStrings[1].post_harvest_beat` (which
+ * was authored as a quiet acknowledgement set in Plan 02-02; see
+ * content/seasons/01-soil/ui-strings.yaml).
+ *
+ * Implementation choice (surfaced in Plan 02-05 SUMMARY): Phase 2 ships
+ * the minimum-viable thin-toast variant rather than the Ink runtime
+ * surface. The compost-acknowledgements.ink content authored in Plan
+ * 02-03 + rewritten by Plan 02-04 IS fully compiled (see
+ * src/content/compiled-ink/season1/compost-acknowledgements.ink.json)
+ * and the runtime path is loadInkStory('compost-acknowledgements'); a
+ * future plan that wants richer voice or branching can swap this
+ * component for the Ink runtime without touching the sim or store.
+ *
+ * Triggered by Garden.ts's compost dispatch via session.bumpCompostBeat,
+ * which increments compostBeatTick. We watch the tick value via
+ * useEffect and fire the toast for ~3.5s before fading out.
+ */
+const COMPOST_TOAST_DURATION_MS = 3500;
+
+export function CompostToast(): JSX.Element | null {
+  const tick = useAppStore((s) => s.compostBeatTick);
+  const strings = uiStrings[1];
+  const [visible, setVisible] = useState(false);
+  const [lineIdx, setLineIdx] = useState(0);
+
+  useEffect(() => {
+    if (tick === 0) return; // initial state, no toast
+    setVisible(true);
+    // Cycle through the post_harvest_beat array on each compost so the
+    // player rarely hears the same line twice in a row.
+    setLineIdx((i) => (i + 1) % Math.max(1, strings?.post_harvest_beat?.length ?? 1));
+    const t = setTimeout(() => setVisible(false), COMPOST_TOAST_DURATION_MS);
+    return () => clearTimeout(t);
+  }, [tick, strings]);
+
+  if (!visible || !strings?.post_harvest_beat?.length) return null;
+  const line = strings.post_harvest_beat[lineIdx % strings.post_harvest_beat.length];
+  return (
+    <div
+      role="status"
+      data-testid="compost-toast"
+      style={{
+        position: 'fixed',
+        bottom: 84,
+        left: '50%',
+        transform: 'translateX(-50%)',
+        zIndex: 32,
+        maxWidth: 420,
+        padding: '0.7rem 1.4rem',
+        background: '#1f1f23ee',
+        color: '#e8e0d0',
+        border: '1px solid #4d4d52',
+        fontFamily: 'serif',
+        fontStyle: 'italic',
+        fontSize: '0.95rem',
+      }}
+    >
+      {line}
+    </div>
+  );
+}

src/ui/settings/index.ts

@@ -4,6 +4,10 @@
  * Plan 02-05 ships:
  *   - Settings: D-28 save-management modal (Export / Import / Restore)
  *   - PersistenceToast: D-30 one-time soft toast in voice
+ *   - CompostToast: D-07 + GARD-04 thin transient toast (Plan 02-04
+ *     deferral landed here — co-located with PersistenceToast since
+ *     both share the same toast UX shape).
  */
 export { Settings } from './Settings';
 export { PersistenceToast } from './persistence-toast';
+export { CompostToast } from './compost-toast';