es-optimistic-concurrency-via-expected-version

Status: IN

`append(..., expected_version=V)` succeeds only if the current stream version equals V; a stale version raises `ConcurrencyConflict`.

Source: entries/2026/05/29/event-sourcing-store-test_event_store.md

Example

if expected_version is not None:
    current = self.stream_version(stream_id)
    if current != expected_version:
        raise ConcurrencyConflict(...)

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