## Summary
Hot-loop writers — `streams.writer` / `streams.pipe` on the run-scoped
side, `chat.response.write` / `chat.stream.*` on the session side — were
issuing a fresh `PUT` to mint S2 credentials for every chunk. On run
streams, each PUT also pushed the streamId onto
`TaskRun.realtimeStreams`,
so a chat-agent turn writing N chunks produced N PUTs and N duplicate
array pushes against the same row.
The SDK now caches the initialize response per cache slot: `(runId,
key)`
for run streams, the session id for session streams. First call PUTs as
before; subsequent calls reuse the cached promise. Hot-loop writers do
one PUT per slot for the lifetime of the cache.
S2 access tokens have a 1-day TTL. If a writer's `wait()` rejects (auth
error, expired token, network blip), the cache evicts the matching slot
so the next call re-PUTs and mints fresh credentials, identity-checked
so a concurrent caller's fresh promise isn't accidentally cleared.
## chat.agent guardrail
`streams.pipe / writer / append / read` called inside a `chat.agent` run
now logs a one-time warning pointing at `chat.response.write` /
`chat.stream.*` — `streams.*` is run-scoped and isn't visible on the
chat session. The ai-chat docs are updated to drop the old guidance
toward run-scoped streams.
Eric Allam
8b98e21b4b