Native compaction checkpoints and reasoning items persisted before model
stamping existed carry only `_issuer_kind`. Treating a missing `_issuer_model`
as foreign dropped every such item once the current model was known, which
wiped existing sessions' native-compaction context on upgrade (four consumer
tests in test_native_compaction / test_native_preflight_estimate /
test_413_compression went red on the stack).
Trust the endpoint stamp when no model stamp is present, as main does today.
Items minted after this change carry the model stamp and still drop on a
same-endpoint model switch; a wrong guess on a legacy item is caught by the
invalid_encrypted_content 400 classifier and the replay kill switch.
kshitijk4poor
cb49660bb4