Replaces the metadata/probe stub with a playwright-core driver (no bundled
browser download; uses a probe-discovered Chrome) exposing navigate/click/type/
observe + idempotent dispose. Browser-unavailable and un-exercisable assertions
return inconclusive (never a false pass/fail); a missing selector returns a
distinct 'absent' negative observation. Driver is a direct export scoped to the
verification run, not registered as a coding-agent tool.
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