Module journal 

Record-once, replay-forever — the durability half of effectful execution.

A run that calls a model is not reproducible by re-running it. The answer differs, so a crash halfway through means starting over, and an experiment record of “what this agent did” cannot be checked against anything.

Durable-execution engines solve this by journaling: perform each effect once, write the result down, and on replay serve the recorded result instead of performing it again. The orchestration is deterministic; only the recorded edges are not.

Soma already has the storage for that — the same two-table action store the filter cache uses ([ActionCache] for small records, [BlobStore] for payloads). What this module adds is the keying, and the distinction the filter cache cannot express:

Effect kind	Key includes	Reused
Pure (a graph run)	the effect’s content	across every run, like a filter
Impure (a model call, a tool)	run, node, turn, effect	only when replaying that run

That second row is the point. Asking a model the same question twice is genuinely two events, so memoizing by content would freeze the first answer forever — the _deterministic = false foot-gun wearing a hat. Scoping the key to (run, node, turn) means a resumed run sees exactly what the original saw, while a fresh run asks afresh.

Structs

EffectJournal

Reads and writes effect results.

EffectSite

Where an effect happened, for keying its record.