fix: preserve multi-line paste in code blocks (#203)

[zacharias-ona]

Closes #203

What

Pasting multi-line text into a code block only preserved the first line. Lexical's default rich-text paste handler ($insertDataTransferForRichText) splits pasted text on newlines and calls selection.insertParagraph() for each \n. Inside a CodeNode, this breaks out of the code block and creates new paragraph nodes, discarding all lines after the first from the code block.

How

Added a PASTE_COMMAND handler at COMMAND_PRIORITY_HIGH in CodeHighlightPlugin that intercepts paste events when the selection is inside a CodeNode. Instead of delegating to the default handler, it splits the pasted plain text on newlines and inserts CodeHighlightNode + LineBreakNode pairs — keeping all lines inside the code block. The existing syntax-highlighting transform from registerCodeHighlighting re-tokenizes the pasted code automatically.

Testing

• Added Playwright E2E test e2e/editor-code-paste.spec.ts with two cases:
  • Multi-line paste: verifies all 3 lines are present in the code block and separated by line breaks
  • Single-line paste: verifies basic paste still works inside code blocks
• All 222 unit tests pass, all 49 E2E tests pass

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Project	Deployment	Actions	Updated (UTC)
memo	Ready	Preview, Comment	Apr 17, 2026 10:34pm

[zacharias-ona]

✅ UI verification passed — design spec compliance confirmed.

Summary: The changed file (src/components/editor/code-highlight-plugin.tsx) is a headless Lexical plugin that returns null — no visual output. The PR modifies paste behavior inside code blocks, not rendering. Static analysis found no color tokens, typography, spacing, or component violations. Visual screenshots of the editor page (desktop dark + mobile) confirm code blocks render correctly with bg-muted rounded-sm per spec, and no layout regressions are present.

[zacharias-ona]

✅ Post-merge verification passed.

E2E suite: 47/52 passed, 2 failed, 3 skipped (dependent on failures).

The 2 failures are pre-existing and unrelated to this PR's code-block paste changes:

• members.spec.ts — "owner can re-invite and invited user can accept" (strict mode violation: duplicate E2E Member elements)
• search.spec.ts — "search with no matches shows empty state" (empty state text not found)

This PR's new tests (editor-code-paste.spec.ts — multi-line paste and single-line paste) both passed.

Ad-hoc smoke tests (production):

• ✅ Landing page — loads, has title
• ✅ Sign-in page — renders with email input
• ✅ Health endpoint — returns OK
• ✅ Authenticated flow — login, workspace load
• ✅ No console errors (unauthenticated or authenticated)
• ⏭️ Skipped: /dashboard (not yet built), editor page navigation (no page buttons in test workspace)