diff --git a/frontend/src/v2/__tests__/V2InactiveFold.test.tsx b/frontend/src/v2/__tests__/V2InactiveFold.test.tsx
index 76bc621aff..806f4a71ca 100644
--- a/frontend/src/v2/__tests__/V2InactiveFold.test.tsx
+++ b/frontend/src/v2/__tests__/V2InactiveFold.test.tsx
@@ -20,6 +20,13 @@ test('inactive rows are hidden until the shared count fold opens', async () => {
   expect(screen.getByText('Expired grant')).toBeInTheDocument();
 
   fireEvent.click(toggle);
+  expect(toggle).toHaveAttribute('aria-expanded', 'false');
+  // The rows stay mounted, inert, until the close animation ends.
+  const body = screen.getByText('Revoked grant').closest('.v2-connectors__inactive-fold-body');
+  expect(body).toHaveClass('v2-connectors__inactive-fold-body--closing');
+  expect(body).toHaveAttribute('inert');
+
+  fireEvent.animationEnd(body as Element);
   expect(screen.queryByText('Revoked grant')).not.toBeInTheDocument();
 });
 
diff --git a/frontend/src/v2/components/V2InactiveFold.tsx b/frontend/src/v2/components/V2InactiveFold.tsx
index 589ce2ca8e..d5ca11386f 100644
--- a/frontend/src/v2/components/V2InactiveFold.tsx
+++ b/frontend/src/v2/components/V2InactiveFold.tsx
@@ -10,7 +10,10 @@ type V2InactiveFoldProps = {
 const V2InactiveFold: React.FC<V2InactiveFoldProps> = ({ count, children }) => {
   const { t } = useTranslation();
   const [open, setOpen] = useState(false);
+  // A closing fold stays mounted until its close animation ends, then unmounts. It is inert while it closes.
+  const [closing, setClosing] = useState(false);
   if (count === 0) return null;
+  const showBody = open || closing;
 
   return (
     <div className="v2-connectors__inactive-fold">
@@ -18,12 +21,30 @@ const V2InactiveFold: React.FC<V2InactiveFoldProps> = ({ count, children }) => {
         type="button"
         className="v2-connectors__inactive-toggle"
         aria-expanded={open}
-        onClick={() => setOpen((wasOpen) => !wasOpen)}
+        onClick={() => {
+          if (open) {
+            setOpen(false);
+            setClosing(true);
+          } else {
+            setClosing(false);
+            setOpen(true);
+          }
+        }}
       >
         <span className="v2-connectors__inactive-caret" aria-hidden="true" />
         {t('connectors.inactiveFold', { defaultValue: 'inactive · {{n}}', n: count })}
       </button>
-      {open && <div className="v2-connectors__inactive-rows">{children}</div>}
+      {showBody && (
+        <div
+          className={`v2-connectors__inactive-fold-body${closing ? ' v2-connectors__inactive-fold-body--closing' : ''}`}
+          {...(closing ? { inert: '' } : {})}
+          onAnimationEnd={(event) => {
+            if (event.target === event.currentTarget && closing) setClosing(false);
+          }}
+        >
+          <div className="v2-connectors__inactive-rows">{children}</div>
+        </div>
+      )}
     </div>
   );
 };
diff --git a/frontend/src/v2/utils/__tests__/theme.test.ts b/frontend/src/v2/utils/__tests__/theme.test.ts
index 6fafb97b1c..252bd8fa21 100644
--- a/frontend/src/v2/utils/__tests__/theme.test.ts
+++ b/frontend/src/v2/utils/__tests__/theme.test.ts
@@ -49,6 +49,44 @@ describe('v2 appearance preference (D216)', () => {
     expect(decls(explicit![1])).toContain('--v2-focus-ring: 0 0 0 2px var(--v2-bg), 0 0 0 4px #8aa2ff');
   });
 
+  test('setV2Theme crossfades inside a view transition when the browser supports it (TASK-700)', () => {
+    const doc = document as Document & { startViewTransition?: (cb: () => void) => unknown };
+    const startViewTransition = jest.fn((cb: () => void) => cb());
+    doc.startViewTransition = startViewTransition as unknown as Document['startViewTransition'];
+    try {
+      setV2Theme('dark');
+      expect(startViewTransition).toHaveBeenCalledTimes(1);
+      expect(document.documentElement.getAttribute('data-v2-theme')).toBe('dark');
+    } finally {
+      delete doc.startViewTransition;
+    }
+  });
+
+  test('setV2Theme skips the crossfade under reduced motion and without the API', () => {
+    const doc = document as Document & { startViewTransition?: (cb: () => void) => unknown };
+    const startViewTransition = jest.fn((cb: () => void) => cb());
+    doc.startViewTransition = startViewTransition as unknown as Document['startViewTransition'];
+    const original = window.matchMedia;
+    window.matchMedia = jest.fn().mockImplementation((q: string) => ({ matches: q.includes('reduce'), media: q })) as unknown as typeof window.matchMedia;
+    try {
+      setV2Theme('light');
+      expect(startViewTransition).not.toHaveBeenCalled();
+      expect(document.documentElement.getAttribute('data-v2-theme')).toBe('light');
+    } finally {
+      window.matchMedia = original;
+      delete doc.startViewTransition;
+    }
+    setV2Theme('dark');
+    expect(document.documentElement.getAttribute('data-v2-theme')).toBe('dark');
+  });
+
+  test('v2.css declares the motion tokens and one global reduced-motion switch (TASK-700)', () => {
+    expect(v2css).toContain('--v2-dur-fast: 120ms;');
+    expect(v2css).toContain('--v2-dur: 200ms;');
+    expect(v2css).toContain('--v2-dur-slow: 320ms;');
+    expect(v2css).toMatch(/@media \(prefers-reduced-motion: reduce\) \{\n  \*,[\s\S]*?animation-duration: 0\.01ms !important;/);
+  });
+
   test('index.html applies a stored Light or Dark choice before first paint (code-gate HOLD, rhea)', () => {
     const html = fs.readFileSync(path.join(__dirname, '../../../../index.html'), 'utf8');
     const head = html.slice(0, html.indexOf('</head>'));
diff --git a/frontend/src/v2/utils/theme.ts b/frontend/src/v2/utils/theme.ts
index 667dfd9c4b..e8d4af289e 100644
--- a/frontend/src/v2/utils/theme.ts
+++ b/frontend/src/v2/utils/theme.ts
@@ -19,11 +19,21 @@ export function applyV2Theme(pref: V2ThemePref): void {
   document.documentElement.setAttribute('data-v2-theme', pref);
 }
 
+type ViewTransitionDocument = Document & { startViewTransition?: (update: () => void) => unknown };
+
 export function setV2Theme(pref: V2ThemePref): void {
   try {
     window.localStorage.setItem(V2_THEME_KEY, pref);
   } catch {
     // Storage can be blocked; the choice still applies for this page view.
   }
+  // The switch crossfades when the browser supports view transitions and the user has not asked
+  // for reduced motion. Everywhere else it applies at once.
+  const reduce = window.matchMedia?.('(prefers-reduced-motion: reduce)').matches;
+  const doc = document as ViewTransitionDocument;
+  if (doc.startViewTransition && !reduce) {
+    doc.startViewTransition(() => applyV2Theme(pref));
+    return;
+  }
   applyV2Theme(pref);
 }
diff --git a/frontend/src/v2/v2.css b/frontend/src/v2/v2.css
index 3014026a6d..cfbf5011a1 100644
--- a/frontend/src/v2/v2.css
+++ b/frontend/src/v2/v2.css
@@ -1,3 +1,15 @@
+/*
+ * Motion tokens (TASK-700). One ease curve and three durations, on :root so the
+ * view-transition pseudo-elements can read them. Animate transform and opacity;
+ * the height moments use grid rows, not a measured height.
+ */
+:root {
+  --v2-dur-fast: 120ms;
+  --v2-dur: 200ms;
+  --v2-dur-slow: 320ms;
+  --v2-ease: cubic-bezier(0.2, 0, 0, 1);
+}
+
 /*
  * V2 design tokens + base styles. All v2 styles are scoped under .v2-root
  * so the existing app's global CSS does not bleed in (and vice versa).
@@ -6023,7 +6035,7 @@ body.modern-ui.v2-canvas {
     width: min(86vw, 320px);
     height: 100vh;
     transform: translateX(-100%);
-    transition: transform 0.22s ease;
+    transition: transform var(--v2-dur-slow) var(--v2-ease);
     box-shadow: 2px 0 24px rgba(15, 17, 21, 0.18);
     border-right: 1px solid var(--v2-border-soft);
   }
@@ -13816,3 +13828,51 @@ body.modern-ui.v2-canvas {
 .v2-legal__section { margin-bottom: 28px; }
 .v2-legal__section h2 { font-size: 18px; font-weight: 600; margin: 0 0 8px; }
 .v2-legal__section p { font-size: 15px; line-height: 1.6; color: var(--v2-text-secondary); margin: 0 0 8px; }
+
+/* ---------- Motion (TASK-700) ---------- */
+
+/* Theme switch: utils/theme.ts runs the change inside document.startViewTransition, and the
+   root snapshots crossfade on the motion tokens. Browsers without the API switch at once. */
+::view-transition-old(root),
+::view-transition-new(root) {
+  animation-duration: var(--v2-dur);
+  animation-timing-function: var(--v2-ease);
+}
+
+/* Folds open by growing their grid row from 0fr to 1fr, so the height animates without a measured
+   pixel value. The rows fade in on the same curve. */
+@keyframes v2-fold-open {
+  from { grid-template-rows: 0fr; opacity: 0; }
+  to { grid-template-rows: 1fr; opacity: 1; }
+}
+@keyframes v2-fold-close {
+  from { grid-template-rows: 1fr; opacity: 1; }
+  to { grid-template-rows: 0fr; opacity: 0; }
+}
+.v2-connectors__inactive-fold-body {
+  display: grid;
+  animation: v2-fold-open var(--v2-dur) var(--v2-ease) both;
+}
+.v2-connectors__inactive-fold-body--closing {
+  animation-name: v2-fold-close;
+}
+.v2-connectors__inactive-fold-body > .v2-connectors__inactive-rows {
+  min-height: 0;
+  overflow: hidden;
+}
+
+/* One global switch for reduced motion: every v2 animation and transition ends at once, and the
+   theme change does not crossfade. */
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+  }
+  ::view-transition-old(root),
+  ::view-transition-new(root) {
+    animation: none !important;
+  }
+}