Admission wrapped every prepare error in Unavailable, so a key the leaf
could not compose reached the client as an unavailable organ. One private
prepare(document, cache) now keys through the leaf first, mapped to
MindRefusal::Document, then encodes; Mind::admit and the derived-write loop
both use it. Unavailable stays for store, cache-encode and decode faults.
Tests: an_unkeyable_document_is_refused_as_a_document (store and receipts
unchanged), prepare_classifies_a_key_refusal_as_a_document_and_encodes_the_rest
(the derived path cannot reach an unkeyable resolution after the per-kind
bound, so the helper is pinned directly), and the #[ignore]
snapshot_admits_and_reads_back, which opens a scratch copy of the live mind
named by HUGINN_MIND_SNAPSHOT, views every stored document back unchanged,
resolves the six stuck findings and withdraws one long-keyed resolution.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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