ADR-0004: Returned streams are detached from the client lifetime (use<>)

Status: Accepted (M1) · Date: 2026-07

Context

In edition 2024, return-position impl Trait captures all in-scope lifetimes by default. Every SDK method returning impl Stream from &self therefore borrowed the client for the stream’s whole life — even though the bodies only clone cheap handles. tokio::spawn-ing a stream (the dominant consumer pattern) failed to compile (E0505) without pre-cloning the client.

Decision

Every stream-returning method declares precise capturing — impl Stream + Send + use<> — and bodies clone what they need up front. A permanent compile-test (canton-ledger/tests/stream_capture_probe.rs) drops the client and spawns each stream; any signature regression breaks the build.

Consequences

• let s = client.updates(...).await?; drop(client); tokio::spawn(s) works.
• Method bodies must not actually borrow from self past the first await — enforced by the compiler through the use<> bound itself.