fix(ui): prevent layerchart circular dependency in thumbs submissions

AGENTS.md

@@ -431,6 +431,37 @@ When cleanup or reset must follow a specific lifecycle moment, use the matching
 
 Use `.server.ts` files for server-side code to isolate API keys.
 
+### Chart Imports and SSR
+
+`layerchart` has internal circular dependencies that Vite cannot reliably evaluate during SSR. Never statically import `layerchart` or the `@cio/ui/base/chart` runtime barrel from a component that can enter the server module graph.
+
+- Import chart types from the dependency-free types module: `import type { ChartConfig } from '@cio/ui/base/chart/types'` (or the equivalent relative path inside `packages/ui`).
+- Load chart runtime components with a browser-only dynamic import and render them inside an `{#await}` block guarded by `browser` or `typeof window !== 'undefined'`.
+- In exercise submission renderers, reuse `submission-response-bar-chart.svelte` or `submission-response-pie-chart.svelte`; do not import the chart barrel directly.
+
+```svelte
+<script module lang="ts">
+  function loadChart() {
+    if (typeof window === 'undefined') return Promise.reject(new Error('browser-only'));
+
+    return import('@cio/ui/base/chart');
+  }
+</script>
+
+<script lang="ts">
+  import { browser } from '$app/environment';
+  import type { ChartConfig } from '@cio/ui/base/chart/types';
+</script>
+
+{#if browser}
+  {#await loadChart() then Chart}
+    <Chart.ChartContainer {config}>
+      <Chart.BarChart data={chartData} x="label" y="value" />
+    </Chart.ChartContainer>
+  {/await}
+{/if}
+```
+
 ### UI Components
 
 - Add new UI components under `packages/ui/src` following existing folder patterns.

packages/ui/src/custom/exercise-question/renderers/thumbs/submission.svelte

@@ -1,7 +1,8 @@
 <script lang="ts">
-  import * as Chart from '../../../../base/chart';
   import type { ExerciseQuestionRendererProps } from '@cio/question-types';
+  import type { ChartConfig } from '../../../../base/chart/types';
 
+  import SubmissionResponsePieChart from '../shared/submission-response-pie-chart.svelte';
   import { getAnswerForQuestion, getSubmissionLabel, normalizeLabel, withChartColors } from '../submission-utils';
 
   let {
@@ -30,7 +31,7 @@
       label: getSubmissionLabel(labels, 'submission.chart.responses', 'Responses'),
       color: 'var(--chart-1)'
     }
-  } satisfies Chart.ChartConfig);
+  } satisfies ChartConfig);
 
   const chartData = $derived.by(() => {
     let yesCount = 0;
@@ -81,13 +82,8 @@
   });
 </script>
 
-{#if chartData.length > 0}
-  <Chart.Container config={chartConfig} class="ui:h-[280px] ui:w-full ui:flex-col ui:items-center">
-    <Chart.PieChart data={chartData} key="key" label="label" value="responses" c="color" />
-    <Chart.ChartLegend items={chartData.map((d) => ({ label: d.label, color: d.color, value: d.responses }))} />
-  </Chart.Container>
-{:else}
-  <p class="ui:text-muted-foreground ui:text-sm">
-    {getSubmissionLabel(labels, 'submission.chart.no_data', 'No responses yet')}
-  </p>
-{/if}
+<SubmissionResponsePieChart
+  {chartData}
+  {chartConfig}
+  emptyLabel={getSubmissionLabel(labels, 'submission.chart.no_data', 'No responses yet')}
+/>