Implement idempotency key support

[Chigala]

I noticed idempotency keys are on the roadmap. Looking at the codebase, the infrastructure is already in place, the DB schema has the column, the backend interface accepts it, but the client always passes null.

What I'm proposing

Wire up idempotency keys at the trigger level, similar to how Trigger.dev does it:

await orderWorkflow.run(
  { orderId: "123" },
  { 
    idempotencyKey: "order-123-process",
    idempotencyTTL: "24h"  // optional
  }
);

If the same key is used within the TTL window, return the existing run instead of creating a duplicate. We could even drop the TTL option for now.

Most of the plumbing already seems to exist, this would mainly be connecting the dots.

Future enhancement

Later we could maybe add workflow-level idempotency with CEL expressions. Starting with trigger-time keys covers most use cases.

What do you think @jamescmartinez ? 


Happy to pick this up if it sounds reasonable.

[jamescmartinez]

I agree. Very open to a PR for this. As you mentioned, the plumbing is already there (for this and a few othe upcoming-but-still-unimplemented features).

In your proposal, you break out impotency into a separate object. Why do you think this should be separate from the WorkflowSpec where { name: "" } is defined?