fix(desktop): widen transcript code blocks

apps/desktop/src/renderer/maka-tokens.css

@@ -943,6 +943,12 @@
      fallbacks are redundant. */
   --maka-chat-measure: 680px;
 
+  /* Astryx's AI Chat conversation uses an 800px message area while Markdown
+     keeps prose at 680px and lets code/tables fill the wider container. Keep
+     that exception transcript-scoped so the shared Maka surfaces above do not
+     change width as a side effect of making source evidence readable. */
+  --maka-transcript-measure: 800px;
+
   /* === settings ==========================================================
      One right-edge cap for a settings row's end slot — the read-only value
      and the control cluster share it, so the two kinds of row end stop at
@@ -1507,7 +1513,7 @@
        between-turn gap (.maka-chatContent) — one density, no between/within
        split. */
     gap: var(--space-3);
-    max-width: var(--maka-chat-measure);
+    max-width: var(--maka-transcript-measure);
     margin: 0 auto;
     width: 100%;
     box-sizing: border-box;

packages/ui/src/markdown-body.tsx

@@ -221,6 +221,10 @@ function MarkdownCode(props: {
       <CodeBlock
         code={props.code}
         language={props.language}
+        // Markdown fences are block content. Astryx defaults to fit-content
+        // with a 400px floor, which leaves short-code fences visibly narrow
+        // even when the surrounding transcript has room to stay readable.
+        width="100%"
         // Astryx otherwise overlays the copy button on headerless plaintext.
         // An empty title enables its structural header; once that header becomes
         // a collapse button, give plaintext the same localized code label that

packages/ui/stories/markdown.stories.tsx

@@ -101,6 +101,33 @@ export const TranscriptTurn: Story = {
   ),
 };
 
+// Real path: chat → an assistant turn containing source code. The wide frame
+// keeps the desktop chat measure, rather than the Storybook viewport, as the
+// visible limit so code-line regressions are easy to compare.
+export const TranscriptCodeBlock: Story = {
+  render: () => (
+    <ProseFrame width={1040}>
+      <div className="maka-turn">
+        <ChatMessageBubble variant="ghost" className="maka-chat-message-bubble maka-chat-message-bubble-assistant">
+          <Markdown
+            density="compact"
+            text={[
+              '## Runtime connection',
+              '',
+              'The desktop keeps the full request readable without wrapping source code into short visual fragments.',
+              '',
+              '```ts',
+              'const connection = await runtimeHost.connect({ workspaceRoot, expectedRootId, initialConnectionTimeoutMs: 45_000 });',
+              'await connection.send({ type: \'session.message\', sessionId, content, attachments });',
+              '```',
+            ].join('\n')}
+          />
+        </ChatMessageBubble>
+      </div>
+    </ProseFrame>
+  ),
+};
+
 // Real path: 每日回顾 → a generated report that mixes headings, emphasis, a list,
 // a quote and a table. This is the document density — the Daily Review panel is
 // the caller that leaves `density` unset. (It was annotated as a chat answer,