No atomic CAS existed, so concurrent writers to the same KV key raced. Add
set_if(key, expected, new): writes only when the current value equals expected,
or (expected absent) only when the key is missing — the primitive for lock-free
counters / optimistic concurrency.
- KvService + GroupKvService traits gain set_if with a defaulted "unsupported"
impl (Noop + other impls untouched); the real services override it.
- kv_repo/group_kv_repo: atomic set_if — a single UPDATE ... WHERE value =
$expected (JSONB semantic equality) or INSERT ... ON CONFLICT DO NOTHING.
Atomic without a transaction; returns whether the write happened.
- Services enforce the same value-size cap + (group) writes-authed + row/byte
quotas as set; the event fires only on a successful swap.
- Executor Rhai SDK: kv::collection(c).set_if(key, expected, new) and the
shared_collection variant; Rhai () for expected means "only if absent".
Pinned by kv_service/group_kv_service set_if unit tests (CAS + fail-closed) +
sdk_kv::kv_set_if_compare_and_swap (through a real script). No migration.
docs/sdk-shape.md documents the primitive.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
0f05c270d1