TxPipelineIdentityStrategy

Embedder-owned strategy for deriving durable pipeline identity.

Implementations are invoked exactly once for each successfully normalized submission. The returned identity is then reused for the initial replay lookup, record creation, collision convergence, and idempotency alias binding. canonicalPayloadHash must be deterministic and collision-resistant over the normalized request and identity scope: admission treats equal hashes as proof that two submissions carry the same canonical request. The pipeline id must be deterministic and the returned hash/id pair must remain stable across every writer and reader that shares durable pipeline state.