fix(streamable-http): fail request when resumable SSE stream can't complete

[Epochex]

Fixes #1577.

When a POST responds with ext/event-stream and the stream disconnects before a terminal JSON-RPC response/error arrives, the client transport tries to resume via GET + Last-Event-ID. If the server is gone (session 404s) or resumption otherwise can't succeed, the current code returns silently after exhausting retries.

Because ClientSession defaults to
ead_timeout_seconds=None, the original send_request() waits forever on the missing response.

Changes:

• If an SSE response stream ends without completion and we have no resumable event id, send a CONNECTION_CLOSED JSON-RPC error for the original request id.
• If resumption retries are exhausted, send the same request-scoped error (includes the last event id in data).

Tests:

• Adds an interaction regression test that closes a call's SSE stream and deletes the server-side session on the first reconnect GET, asserting the call fails (no hang).

[cubic-dev-ai]

2 issues found across 3 files

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[maxisbey]

Thanks for the PR, and sorry it sat here without a proper review.

We're closing most of the open PR backlog. v2 is out and changed a lot of the SDK, so many older PRs no longer apply as written, and we're a small team that realistically doesn't have the capacity to work through the rest.

If this still matters to you on v2, the most useful thing you can do is open an issue (or comment on the existing one) with your use case and a repro. Hearing why it matters to you is what we use to decide what to prioritise.

_{AI Disclaimer}