fix(ui): contain Mermaid diagrams in Lighthouse chat

ui/app/(prowler)/lighthouse/_components/chat/message-bubble.test.tsx

@@ -26,6 +26,21 @@ vi.mock("streamdown", () => ({
       );
     }
 
+    if (text.includes("graph TD")) {
+      // Mirrors streamdown's real mermaid DOM: pan/zoom wrapper + inline max-width on the svg
+      return (
+        <div data-streamdown="mermaid-block">
+          <div className="my-4 overflow-hidden">
+            <div role="application">
+              <div aria-label="Mermaid chart" role="img">
+                <svg aria-hidden="true" style={{ maxWidth: "1024px" }} />
+              </div>
+            </div>
+          </div>
+        </div>
+      );
+    }
+
     return <>{children}</>;
   },
   defaultRehypePlugins: { katex: undefined, harden: undefined },
@@ -87,6 +102,30 @@ describe("MessageBubble", () => {
       "min-w-0",
     );
   });
+
+  it("keeps Mermaid diagrams inside the constrained markdown wrapper", () => {
+    // Given
+    const mermaidMessage = buildAssistantMessage([
+      textPart("part-1", "```mermaid\ngraph TD\n  A --> B\n```"),
+    ]);
+
+    // When
+    render(<MessageBubble message={mermaidMessage} />);
+
+    // Then
+    const mermaid = screen.getByRole("img", { name: "Mermaid chart" });
+    const markdown = mermaid.closest(".lighthouse-markdown");
+    if (!(markdown instanceof HTMLElement)) {
+      throw new Error("Expected markdown wrapper around Mermaid diagram");
+    }
+
+    expect(markdown).toHaveClass("min-w-0", "max-w-full", "overflow-x-auto");
+    expect(markdown.parentElement).toHaveClass("min-w-0");
+    expect(markdown.parentElement?.parentElement).toHaveClass(
+      "min-w-0",
+      "max-w-full",
+    );
+  });
 });
 
 function isBefore(first: HTMLElement, second: HTMLElement): boolean {

ui/styles/globals.css

@@ -317,6 +317,17 @@
     min-width: 100%;
     width: max-content;
   }
+
+  .lighthouse-markdown [data-streamdown="mermaid-block"] {
+    max-width: 100%;
+    min-width: 0;
+  }
+
+  /* !important beats the inline max-width px that mermaid sets on the svg */
+  .lighthouse-markdown [data-streamdown="mermaid-block"] svg {
+    max-width: 100% !important;
+    height: auto;
+  }
 }
 
 /* ===== UTILITY LAYER ===== */