diff --git a/frontend/src/app/pages/AgentChat/tool-ui/ShowUiWidgetView.tsx b/frontend/src/app/pages/AgentChat/tool-ui/ShowUiWidgetView.tsx
index 31315853..bebdf390 100644
--- a/frontend/src/app/pages/AgentChat/tool-ui/ShowUiWidgetView.tsx
+++ b/frontend/src/app/pages/AgentChat/tool-ui/ShowUiWidgetView.tsx
@@ -6,10 +6,12 @@ import LinksWidget from './LinksWidget';
 import VendoredToolUi from '@toolui/VendoredToolUi';
 import type { ShowUiPayload } from './showUiPayload';
 import { useOpenUrlInBrowserCard } from './useOpenUrlInBrowserCard';
+import { useClaudeTokens } from '@/shared/styles/ThemeContext';
 
 /** One switch for every surface that renders a ShowUI payload (chat bubble, pill artifact); ambient = low-cost render for resting surfaces. */
 function ShowUiWidgetView({ payload, ambient }: { payload: ShowUiPayload; ambient?: boolean }): React.ReactElement | null {
   const openUrl = useOpenUrlInBrowserCard();
+  const c = useClaudeTokens();
   if (payload.component === 'weather') return <WeatherWidget props={payload.props} ambient={ambient} />;
   if (payload.component === 'plan') return <PlanWidget props={payload.props} />;
   if (payload.component === 'stats') return <StatsWidget props={payload.props} />;
@@ -50,8 +52,13 @@ function ShowUiWidgetView({ payload, ambient }: { payload: ShowUiPayload; ambien
     return (
       <div>
         <div style={{ marginBottom: 6, paddingLeft: 4, paddingRight: 4 }}>
-          {title && <div style={{ fontSize: '0.9375rem', fontWeight: 600, lineHeight: 1.35 }}>{title}</div>}
-          {desc && <div style={{ fontSize: '0.8125rem', opacity: 0.72, marginTop: 2, lineHeight: 1.4 }}>{desc}</div>}
+          {/* Colour explicitly, never inherited. This header sits above a vendored card whose own
+              surface is dark, and with no colour of its own it took whatever the ancestor happened to
+              carry: on a light-mode app that is near-black text on a dark card, i.e. an invisible
+              title (screenshot 2026-08-31). Same class as ENG-419: a surface that fixes its own
+              background owes its text a token in the same place. */}
+          {title && <div style={{ fontSize: '0.9375rem', fontWeight: 600, lineHeight: 1.35, color: c.text.primary }}>{title}</div>}
+          {desc && <div style={{ fontSize: '0.8125rem', color: c.text.secondary, marginTop: 2, lineHeight: 1.4 }}>{desc}</div>}
         </div>
         {widget}
       </div>
diff --git a/frontend/src/app/pages/AgentChat/tool-ui/showUiHeaderContrast.test.ts b/frontend/src/app/pages/AgentChat/tool-ui/showUiHeaderContrast.test.ts
new file mode 100644
index 00000000..f41d2bed
--- /dev/null
+++ b/frontend/src/app/pages/AgentChat/tool-ui/showUiHeaderContrast.test.ts
@@ -0,0 +1,31 @@
+// The ShowUI host header (ENG-227) renders an agent-supplied title/description ABOVE a vendored
+// card. It set size and weight but no COLOUR, so it inherited whatever the ancestor carried: on a
+// light-mode app the inherited text is near-black, and the card underneath is dark, which is a
+// title you can only find by selecting it (Eric's screenshot, 2026-08-31).
+//
+// Same class as ENG-419: a surface that fixes its own background owes its text an explicit token in
+// the same place. Inheriting is the bug, not the styling.
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+
+const SRC = readFileSync('src/app/pages/AgentChat/tool-ui/ShowUiWidgetView.tsx', 'utf8');
+// The header block only; the rest of the file legitimately has uncoloured wrappers.
+const HEADER = SRC.slice(SRC.indexOf('if (!title && !desc) return widget;'), SRC.indexOf('return widget;', SRC.indexOf('if (!title && !desc)') + 40));
+
+test('the host header title sets its own colour from the theme', () => {
+  const title = HEADER.slice(HEADER.indexOf('{title &&'), HEADER.indexOf('{desc &&'));
+  assert.match(title, /color:\s*c\.text\.primary/, 'the title must not inherit its colour');
+});
+
+test('the description does too, and does not fake contrast with opacity', () => {
+  const desc = HEADER.slice(HEADER.indexOf('{desc &&'));
+  assert.match(desc, /color:\s*c\.text\.secondary/, 'the description must not inherit its colour');
+  assert.doesNotMatch(desc, /opacity:/,
+    'opacity over an inherited colour keeps the bug and only dims it; use the secondary token');
+});
+
+test('the tokens actually come from the theme hook, not a literal', () => {
+  assert.match(SRC, /useClaudeTokens/, 'the component must read live theme tokens');
+  assert.doesNotMatch(HEADER, /color:\s*['"#]/, 'no hardcoded colour: it would break the other mode');
+});