fix(llm-obs): route experiment create/update through the raw client - #682

Problem

experiments create and experiments update both report failure on requests that already succeeded, because the generated typed client rejects the API's actual responses.

experiments update — a successful PATCH /api/v2/llm-obs/v1/experiments/{id} answers HTTP 200 with a zero-byte body. Verified against the live API:

PATCH .../experiments/{id}  ->  HTTP 200, body bytes=0

The generated client deserializes any non-error response unconditionally:

if !local_status.is_client_error() && !local_status.is_server_error() {
    match serde_json::from_str::<LLMObsExperimentResponse>(&local_content) {
        Ok(e)  => ...,
        Err(e) => return Err(datadog::Error::Serde(e)),   // empty body lands here
    }
}

from_str::<T>("") fails with EOF while parsing a value, line 1 column 0, so the command exits 1 after the write has landed. Anything scripting pup reads that exit code as failure and retries — double-writing. I hit this four times in one session; every write had applied.

experiments create — the API's 200 response omits config, which the generated model requires:

response attribute keys: [author, created_at, experiment, is_auto_experiment, name, project_id, updated_at]
has config key? False

So it fails with missing field 'config', again after the experiment exists.

Fix

Both now use the raw client, which is what every other llm-obs command in this file already does — the typed client was the outlier here. Route, request body and required fields are unchanged, so the API contract is untouched; only the handling of a valid response changes. update prints {"experiment_id": ..., "status": "updated"} when the body is empty rather than a bare null.

Also fixes the underlying cause in raw_client::parse_response_json, which had the same intolerance: an empty body is valid on a successful response (204, or 200 with no payload) and now yields JSON null instead of an EOF error. That helper is shared by every raw_* function, so a 204 from any endpoint no longer surfaces as a parse failure.

Verification

End to end against the live API:

Tests added: empty-200 body, normal JSON body, a 500, and a create response missing config. Full suites pass — llm_obs 97, raw_client 23 (the latter covering the shared-parser change for regressions).

cargo fmt --check clean, cargo clippy --bin pup -- -D warnings clean. No Cargo.toml change, so the dependency set is untouched.

Note on the alternative

The stricter fix is upstream in datadog-api-client-rust — treat an empty 2xx as entity: None, or mark these responses optional in the OpenAPI spec it's generated from. That's the more correct layer but it's generated code in another repo; this change makes pup behave today without waiting on it, and stays consistent with how the rest of the file already calls these endpoints.

🤖 Generated with Claude Code