Long uninterrupted URLs can otherwise force user message bubbles beyond the chat column. The fix keeps the bubble constrained to its parent and allows safe breaks inside continuous URL text, with the same guard applied to markdown paragraphs and links.
Constraint: Issue #378 reports desktop chat overflow when a conversation contains a long URL
Rejected: Add horizontal scrolling to user messages | this preserves the overflow instead of fixing normal chat readability
Confidence: high
Scope-risk: narrow
Tested: cd desktop && bunx vitest run src/components/chat/UserMessage.test.tsx src/components/chat/MessageList.test.tsx
Tested: cd desktop && bun run lint
Tested: cd desktop && bun run build
Tested: bun run check:desktop
Tested: browser layout fixture PASS shell=619 bubbleClient=619 bubbleScroll=619
Not-tested: full root quality gate
Related: https://github.com/NanmiCoder/cc-haha/issues/378
