DC-STORE-07

DC derived enforced

Snapshot cadence determinism: the decision to take a snapshot at slot S is a pure function of (slot, block_no, cadence_params, last_snapshot). Same canonical input chain history produces the same set of snapshot slot keys. Cadence is BLUE-structural; not operator-tunable in this cluster (operator-tunable cadence is out of scope until represented as anchored, replay-derivable runtime data).

Source: docs/planning/ledger-snapshot-rollback-invariants.md §1 (I-8)
Cluster: PHASE4-N-I
Authority surface: snapshot cadence decision + in-memory cache

Enforcement trace

Code

Tests 7

should_snapshot_after_block_every_n_returns_true_at_cadence
should_snapshot_after_block_returns_false_off_cadence
should_snapshot_after_block_returns_false_when_already_at_or_after_slot
should_snapshot_after_block_is_pure
snapshot_cadence_default_is_100_blocks
in_memory_snapshot_cache_nearest_le_returns_largest_key
in_memory_snapshot_cache_iteration_is_btreemap_ordered

CI 1

ci_check_snapshot_cadence_purity.sh

Cross-references

Evidence

should_snapshot_after_block_is_pure replays inputs and asserts identical outputs across two runs.
CI gate ci_check_snapshot_cadence_purity.sh enforces that SnapshotCadence has exactly one field (every_n_blocks) — no operator-tunable runtime input.
InMemorySnapshotCache uses BTreeMap iteration only (no HashMap); iteration test pins ordering.