uiMeta returned undefined for both "this bag declares no ui" and "its ui
is unusable", so a content item declaring `ui: null` fell through and was
granted whatever a BROADER carrier asked for — wrong precedence, wrong
direction to fail in. It now distinguishes the two: no `ui` key means
keep looking, a declared-but-malformed one decides for "no hints".
Also pin the full three-way precedence with a case carrying all three
carriers at once (no prior case would have caught the first two operands
being swapped), and state why a permission's object value need not be
empty: `{}` is the spec's extension point, so rejecting a populated one
would drop grants from servers written against a newer spec.
Signed-off-by: cliffhall <cliff@futurescale.com>
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