fix(web): copying an alert callout keeps its alert Markdown #35932

Both review items were correct. When a selection starts and ends inside a callout, its common ancestor is the callout div, and Range.cloneContents() returns the paragraphs without the wrapper or its data-markdown-alert attribute. The alert branch never ran, and because the label was copy-empty the clipboard got only 'Back up first.', which was worse than main. Fix: (1) the label paragraph loses data-markdown-copy="" and gets data-markdown-alert-label instead, so it copies normally as text. A new serializeQuoteBody, used by serializeBlockquote and serializeInsight, skips that label only when the wrapper itself is serialized and the [!KIND] marker or ★ Insight rule replaces it. (2) chatMarkdownClipboardPayload finds the enclosing [data-markdown-alert] callout from the range's common ancestor. When the selected text (trimmed) equals the callout's full text, it wraps the cloned contents in a shallow clone of the callout, so the alert serializer runs and the copy is '> [!WARNING]\n> Back up first.'. A partial selection inside the callout copies as text, like main ('Warning\n\nBack up'). Selections that extend outside the callout already clone the wrapper and are unchanged. No new regex or parser. The added comparison is linear in the callout's text length.

Fixes pingdotgg/t3code#35894

Reproduction on main#

Commit ed2a319814 (origin/main). In a fresh worktree: vp i, then (scratch only, not committed) added > [!WARNING]\n> Back up first. to the final agent message of apps/server/scripts/dev-replay/showcase_transcript.ndjson. Ran T3CODE_DEV_SEED=0 vp run dev, added an empty project with t3 project add, ran a free Replay (dev) turn with t3 thread start --provider devReplay --model showcase --wait, minted a pairing token with t3 pair, and opened the thread in headless Chromium (Playwright, because the T3 preview browser is blocked by AppArmor here). Selected the whole rendered div[role=note] callout, pressed Ctrl+C, and read navigator.clipboard. The DOM was <div role="note"><p data-thread-find-ignore>…svg…Warning</p><p>Back up first.</p></div> and the plain-text clipboard held "Warning\n\nBack up first.": no [!WARNING] marker and no > prefixes. Added a unit test to apps/web/src/markdown-clipboard.test.ts with the same DOM shape. It fails with exactly that string, and the other 11 tests pass.

Evidence#

Select the whole rendered warning callout, press Ctrl+C, and read the browser clipboard. Both sides use fresh synthetic Replay state, Chromium at 1280×800, and dark theme. The labeled panel displays actual clipboard text.

Before	After
ed2a319814	7a73f2aef0
Before recording	After recording
Clipboard: Warning\n\nBack up first.	Clipboard: > [!WARNING]\n> Back up first.

Driver and replay seeding, server launcher, launcher helper.

Base clipboard and DOM, head clipboard and DOM.

Not shown:

• Other alert types and partial callout selections were not exercised; this proof covers the reported whole-warning selection in the web client.

Tests#

vp test run src/components/ChatMarkdown.browser.test.tsx -t "alert copy" (new browser test: real Range from label start to body end expects alert Markdown; a partial range expects 'Warning\n\nBack up'): passes with the change, fails with 540e0ed's markdown-clipboard.ts and ChatMarkdown.tsx (missing '> [!WARNING]'). vp run check:changed: format, lint, knip, typecheck (2 packages), tests (3 files incl. markdown-clipboard.test.ts), react compiler all pass.

Not in this change#

• The HTML clipboard flavor (sanitizedHtmlFrom) still includes the rendered alert label paragraph; only the plain-text Markdown was in scope.
• The HTML clipboard flavor (sanitizedHtmlFrom) still includes the rendered alert label paragraph; only the plain-text Markdown is in scope.

Who did the work#

• Written by Claude Opus 5.5, in Claude Code
• Reviewed by GPT-6.1 Sol, in Codex, and by Claude Opus 5.5, each on its own
• Proof captured by GPT-6.1 Sol and checked by Claude Opus 5.5

Run by the t3code factory in T3 Code.