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HTML clipboard fallback must not inherit selected inline text

docs/solutions/logic-errors/2026-05-09-html-clipboard-fallback-must-not-inherit-selected-inline-text.md

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Original Source

HTML clipboard fallback must not inherit selected inline text

Problem

Lexical regression 5251 exposed a split between Slate's model fragment path and the real browser paste path. Replacing selected text inside an inline link with rich clipboard content passed through insertFragment correctly in package tests, but browser paste still inherited the link because the DataTransfer fallback inserted plain text directly.

Symptoms

  • packages/slate/test/clipboard-contract.ts passed for rich fragment insertion over selected inline-link text.
  • playwright/integration/examples/inlines.test.ts failed with the link text rendered as replacedlink.
  • The failure only appeared through the browser/DOM clipboard path, not through direct transaction fragment insertion.

What Didn't Work

  • Fixing only insertFragment. That made direct model insertion correct, but text/html without a Slate fragment still fell back to single-line insertText.
  • Treating this as an HTML parser problem. The inlines example does not own a generic HTML import pipeline; the bug was the fallback path inheriting inline context for an expanded same-inline selection.
  • Asserting only final plain text. The text can look right while the pasted text is still inside the link.

Solution

Keep the model and browser paths aligned:

  • insertFragment handles selected one-level inline text with a single replacement operation.
  • DOM clipboard fallback detects expanded selections inside one inline text node and routes single-line plain text through fragment insertion.
  • Browser proof asserts the pasted text is outside the surviving link tail.

Verification:

bash
bun test ./packages/slate/test/clipboard-contract.ts -t "selected inline link text"
bun test ./packages/slate-dom/test/clipboard-boundary.ts -t "selected inline text"
PLAYWRIGHT_RETRIES=0 bunx playwright test playwright/integration/examples/inlines.test.ts --project=chromium -g "selected inline link text"
bun test ./packages/slate/test/clipboard-contract.ts
bun test ./packages/slate-dom/test/clipboard-boundary.ts
PLAYWRIGHT_RETRIES=0 bunx playwright test playwright/integration/examples/inlines.test.ts --project=chromium
bun run lint:fix && bun check

Why This Works

The direct fragment path has enough structure to split the selected inline text into before/paste/after children. The plain-text clipboard fallback previously skipped that structure and called insertText, so the inserted text inherited the current inline node.

Routing expanded same-inline fallback through fragment insertion preserves the generic clipboard law without inventing a link-plugin policy: pasted content replaces the selected inline text and lands before the surviving inline tail.

Prevention

  • Pair package fragment proofs with a DOM clipboard fallback proof when the source regression uses real paste.
  • For inline-link paste rows, assert link containment, not just block text.
  • Treat text/html without data-slate-fragment as a separate transport path; green insertFragment tests do not prove browser paste.