> ## Documentation Index
> Fetch the complete documentation index at: https://docs.reconifyhq.com/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Reconify's API reference is read-only for customer data. Do not invent endpoints or authentication behavior beyond the OpenAPI contract.
> The public OpenAPI document contains only the documented external /v2 contract.

# Causation IDs

> Preserve the event a producer says led to this event.

`causation_id` is an optional opaque value that points to the single earlier event
that led to the event carrying it. Correlation is shared context; causation points.

Use the earlier event's `id`, whether it came from your service or an upstream
service. The value may name an event Reconify has not received, and it is not
resolved at ingest.

## Value rules

The value must be 1 to 200 visible ASCII characters. `null`, empty, whitespace-
padded, control-character, or overlong values are rejected. It need not have an
`evt_` shape; it is opaque evidence.

## Idempotency

`causation_id` is part of the canonical event payload. Retrying a stored `id` with
a changed, added, or removed causation ID returns `idempotency_conflict`; retrying
the unchanged event returns `duplicate`.

Reconify preserves the claim and returns it on event reads. It does not infer
causation from ordering or timing, and sharing a causation value does not merge
operations. See [Trace a flow across services](/guides/trace-across-services).