feat(web-shell): render streaming charts with markdown-chart

docs/design/markdown-chart-skill-integration.md

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+# Markdown Chart Skill Integration
+
+Status: accepted
+
+## Integration contract
+
+Qwen Code WebShell owns the rendering side of the contract:
+
+- `@qwen-code/web-shell` includes the `markdown-chart` renderer and ECharts
+  runtime.
+- Hosts install the canonical
+  [`markdown-chart` skill](https://github.com/datafe/markdown-chart/tree/main/skills/markdown-chart)
+  so the model emits renderable chart blocks.
+- Qwen Code core does not bundle or inject the skill. A project can install it
+  at `.qwen/skills/markdown-chart/SKILL.md`; user-level skill installation is
+  also supported.
+
+For the normal `data.kind="inline"` output produced by the skill, the WebShell
+host needs no chart-specific code:
+
+```tsx
+import { WebShellWithProviders } from '@qwen-code/web-shell';
+
+<WebShellWithProviders
+  baseUrl="http://127.0.0.1:4170"
+  token={token}
+  sessionId={sessionId}
+/>;
+```
+
+## Referenced data
+
+If the host exposes real controlled datasets to the skill and allows
+`data.kind="ref"`, it provides `resolveDataRef` through a custom registry:
+
+```tsx
+import {
+  createMarkdownChartRegistry,
+  WebShellWithProviders,
+} from '@qwen-code/web-shell';
+
+const chartRegistry = createMarkdownChartRegistry({
+  resolveDataRef: async (ref, context) =>
+    loadControlledChartDataset(ref, context),
+});
+const markdown = { chart: { registry: chartRegistry } };
+
+<WebShellWithProviders
+  baseUrl="http://127.0.0.1:4170"
+  token={token}
+  sessionId={sessionId}
+  markdown={markdown}
+/>;
+```
+
+The renderer never fetches a ref or reads a local path by itself.
+`resolveDataRef` is the host-owned boundary from a model-visible reference to a
+trusted dataset. The default registry accepts normalized `artifact://` and
+`session-file://` refs, parses the block as JSON, validates the option, and then
+passes the normalized ref plus declared format and dimensions to the resolver.
+Resolver waits are bounded to 30 seconds. Keep `markdown`, `chart`, and
+`labels` overrides referentially stable while charts are mounted.
+
+## Streaming behavior
+
+The shared React adapter distinguishes a closed chart fence from the active
+unterminated tail fence:
+
+- A closed `markdown-chart` block renders immediately and remains mounted while
+  later answer text streams, including when the fence is inside a blockquote.
+- Only the active unterminated chart fence displays the loading state.
+
+## Scope
+
+- The skill defines the model output contract; it does not load the renderer.
+- WebShell defines the rendering contract; it does not automatically install
+  the skill.
+- No daemon, ACP, or client-capability negotiation change is required.
+- No automatic network or filesystem access is introduced.