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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