cortexkit-usage-steps

The wire contract of the live usage step feed, contract version 1: the usage.steps.subscribe notice stream and the paged usage.steps.read. Apps on every platform decode the same shapes, so the Rust types here, the normative text in CONTRACT.md and the vectors in test-vectors/usage-steps-v1/ are one definition for all of them.

The crate is pure serde plus one helper, LatestRows, which applies rows in the order reads return them and keeps the last row per harness plus step_ref. It has no transport and no runtime.

Use

[dependencies]
cortexkit-usage-steps = { path = "../commons/crates/cortexkit-usage-steps" }

The crate is not on crates.io yet; depend on it by path or git until it is.

use cortexkit_usage_steps::{LatestRows, ReadReply, ReadRequest};

let mut latest = LatestRows::new();
let request = ReadRequest::new(); // then .after(cursor) for later reads
// send `request`, decode the result as a ReadReply, then:
// latest.apply_reply(reply);
// the next read starts at latest.resume_after()

Readers ignore unknown members on rows, replies and notices, and keep an unknown verdict, source or request size as Other. Requests are strict.

Both requests take an optional session filter: for_session(harness, session) on ReadRequest and SubscribeRequest narrows the feed to one session's rows or notices. The pair comes together or not at all, and check_pairing on either request reports a request naming one alone; the provider refuses one invalid_request. An unfiltered request encodes exactly as before the filter existed.

A row's output includes reasoning: reasoning is a breakdown of output, never an addition to it, so reasoning <= output whenever both are present. Charge output once and never add reasoning on top. The provider's tests can check this with StepRow::check_counts; readers still decode a row that breaks it.