Ruby SDK 1.4.0 repairs the subscriptions/listen stream and lets buffering hosts decline it

The official Ruby SDK released v1.4.0 on 2026-08-28, a release aimed entirely at subscriptions/listen, the 2026-07-28 method that streams change notifications to a client over one long-lived response.

Two of the three changes enforce the stream's ordering guarantees: a notification can no longer reach a client before the acknowledgement that opens the stream (#532), and writes are serialized so the graceful closing result is always the final message a client sees (#535). Out of order, either failure mode leaves a client unable to tell a healthy close from a dropped stream.

The third change is an escape hatch. Not every Ruby host can hold an SSE stream open; the SDK's own documented Rails controller pattern buffers its responses. serve_subscriptions_listen: false lets such a host decline the method outright rather than answer a modern client with a streaming body it cannot actually deliver (#533).

The SDK's promotion from Tier 2 to Tier 1 remained pending as of 2026-09-02: PR #3248, which proposes the promotion on conformance evidence, was still open with no activity since 2026-08-23.