put_prepared_batch refuses an empty key or stored_at before any store is
touched. Its one-home check covers the staged records only, and the home store
receives only its own records (those this cache holds for it plus the staged
ones), so a single-home batch is no longer refused because other homes hold
records.
load_soa builds the next view in a local map, refusing an unregistered type or,
once a store is attached, a type with no home store; the view is replaced in one
step, so a refused load leaves the prior view intact.
load_envelope is deleted: it had no callers and admitted records into the view
without a store.
Tests: refuse-at-load and pull start from a non-empty cache and assert prior
state intact; atomic load_soa; single-home batch beside other homes' records;
batch with empty key or stored_at.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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