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Slate browser nested selection proofs must pass handle keys and build the v2 dist the site actually runs

docs/solutions/logic-errors/2026-04-04-slate-browser-nested-selection-proofs-must-pass-handle-keys-and-build-the-v2-dist-the-site-actually-runs.md

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Slate browser nested selection proofs must pass handle keys and build the v2 dist the site actually runs

What happened

The mixed-inline browser proof exposed two separate lies in the test layer:

  1. the nested selection helper could succeed in the page and still report null in the assertion helper
  2. the browser copy proof could stay red even after core and DOM clipboard tests were green

Those were not the same bug.

What fixed it

Two fixes made the browser proof honest:

  1. slate-browser/playwright page-eval selection snapshots now pass the browser-handle key explicitly into the page context, and the helper waits a beat for handle hydration before falling back
  2. build:slate-browser:playwright now rebuilds slate-v2 alongside the other v2 packages, because the site examples consume built package dist files

Without the first fix, nested-path selection assertions could return null even while the real page selection was correct.

Without the second, the browser lane could run stale slate-v2 fragment logic and make clipboard proofs look broken after the core contract was already green.

Why this works

Playwright page-eval functions do not get free access to module locals.

If a helper depends on a key like __slateBrowserHandle, that key has to be serialized into the browser function explicitly.

Likewise, if the site runs built package outputs, browser proofs are only as fresh as the dist artifacts they load.

That means browser truth depends on both:

  • correct browser-context serialization
  • rebuilding every package dist the site actually imports

Reusable rule

For slate-browser and site-example browser proofs:

  • never rely on module-scope values inside page-eval without passing them in
  • if the site imports package dist files, rebuild every touched package before trusting browser results

If core tests are green but the browser proof still looks red, check for stale dist output before rewriting working logic.