CultMeshRudpSnapshotSource gains served_record: the record the source
would serve for a received put's document. Admission sizes that record,
so a source that serves another shape than it receives (dropping
provenance, or adding its own, as Odin's presence records do) keeps
admission exact by overriding it. The default serves the record as
received, so existing sources, closures included, are unchanged. A
source that fails to answer refuses the put as SnapshotSourceFailed.
Tests: a stripping source admits a put that is over the bound only as
received and serves it at exactly the bound; the existing at-bound
fixture stays as the default-method test; a failing served_record
refuses the put.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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