Follow-up to the salvaged #47450 fix:
- Extract expandProviderDefaults() so the curated-default expansion rule
lives in one place (was duplicated between defaultVisibleKeys and
resolveVisibleKeys).
- Drop the redundant new Set() wrap in toggleModelVisibility (resolveVisibleKeys
already returns a fresh Set; effectiveVisibleKeys already relied on this).
- Document the intentional re-enable behavior (re-enabling one model of a
hidden-all provider restores only that model, not the curated defaults) and
tighten the toggleModelVisibility JSDoc.
- Add 7 hardening tests: re-enable-restores-only-that-model, full hide/re-enable
round-trip, empty-non-null stored, single toggle-off from null defaults,
zero-model provider, and direct resolveVisibleKeys null/empty assertions.
461fcc0964