fix(client-web): reject unknown web kind, lock fixture to contract, observe web card in boot smoke

- webCardModel returns null for an unknown web `kind` (wire from a newer host)
  instead of drawing it as a malformed fetch, matching the unknown-`card` and
  terminal-model wire-boundary default.
- Fixture WEB_SEARCH_RESULT/WEB_FETCH_RESULT and the source type derive from the
  contract's ToolResultView via Extract, so a new contract field fails at the
  type level rather than drifting silently.
- built-boot smoke asserts the web_search/web_fetch turns render their keyed
  WebRow cards, giving the registration and wire projection an assembled check.
- DetailsPanel comment no longer claims the card omits content for search.
- ui-primitives README inline-Chinese limitation now lists WebBlock's controls.

packages/client/ui-conversation/src/client/contract/web-card-model.ts

@@ -40,6 +40,9 @@ export const CHAT_WEB_MAX_SOURCES = 8
  *   cannot be trusted to be one of the compiled variants, and a generic result
  *   view (a web tool's error path returns the generic card, whose text the
  *   generic path preserves).
+ * - A web card whose `kind` this UI version does not know (a newer host's
+ *   value): the wire cannot be trusted to be `search` or `fetch`, so it takes
+ *   the generic path rather than rendering as a malformed fetch.
  * @param block - RunningToolCall or ToolResultNode off the snapshot caches.
  * @returns the web-card props, or null for the generic path.
  */
@@ -61,10 +64,21 @@ export function webCardModel(block: ToolCallBlock): WebBlockProps | null {
       truncated: result.truncated,
     }
   }
-  return {
-    kind: 'fetch',
-    url: result.url,
-    statusCode: result.statusCode,
-    truncated: result.truncated,
+  // Discriminate `fetch` explicitly rather than treating it as the else of
+  // `search`: a `kind` this UI version does not know arrives over the wire from
+  // a newer host, and reading it as a fetch would draw an empty URL and
+  // `HTTP undefined`. It takes the generic path, the same wire-boundary default
+  // an unknown `card` tag takes above. The static union narrows `kind` to
+  // `'fetch'` here, but the runtime value is off the wire, so the guard and its
+  // null fallthrough are load-bearing despite the type.
+  // oxlint-disable-next-line typescript/no-unnecessary-condition
+  if (result.kind === 'fetch') {
+    return {
+      kind: 'fetch',
+      url: result.url,
+      statusCode: result.statusCode,
+      truncated: result.truncated,
+    }
   }
+  return null
 }

packages/client/ui-conversation/src/client/skeleton/DetailsPanel.tsx

@@ -152,10 +152,12 @@ function OutputBody({ material, cwd }: { material: CallMaterial; cwd: string | u
   }
   const web = webCardModel(material.block)
   // Full source-list allowance here (the panel is the single-call reading
-  // surface); the chat rows cap it at CHAT_WEB_MAX_SOURCES. The card is a
-  // summary — a web_fetch card shows only the URL and status — so the details
-  // panel also renders the flattened result content below it (the fetched body,
-  // the search answer + source markdown), which the card does not carry.
+  // surface); the chat rows cap it at CHAT_WEB_MAX_SOURCES. Below the card the
+  // panel also renders the flattened result content — the model-visible text
+  // the card does not carry verbatim (a web_fetch card shows only the URL and
+  // status, so its fetched body lives only here; a search card's answer and
+  // sources are structured, so the flattened form repeats them as the raw text
+  // the model saw).
   if (web !== null) {
     const settled = 'kind' in material.block ? material.block : null
     const body = settled === null ? '' : renderResult(settled)