Fix per-request SSE reconnection budget on clean EOF

[ump45nose]

Summary

Fix per-request SSE reconnection budget on clean EOF

A per-request reconnect that opens successfully, emits an id-bearing priming event, and then reaches EOF without a JSON-RPC response used to recurse with attempt=0, resetting the reconnection budget. A no-timeout request (subscriptions/listen) could therefore reconnect forever instead of resolving its waiter with CONNECTION_CLOSED after MAX_RECONNECTION_ATTEMPTS.

The clean EOF path now consumes the same per-request budget as the failed-reconnect path.

Fixes #3307

Verification

• uv run --frozen pytest tests/client/test_streamable_http.py -q — 29 passed
• Red-green: the new regression test fails on unpatched main (unbounded reconnects) and passes with the fix
• ruff check / ruff format --check clean; pyright 0 errors; strict-no-cover passed

AI assistance disclosure: AI was used to discover this opportunity and draft the change or text. The submission was checked against the prepared artifact and recorded verification evidence.

[github-actions]

This PR has been closed automatically. This repo only keeps pull requests open when they come from a maintainer, or from a contributor a maintainer has assigned to the linked issue, and you aren't currently assigned to #3307.

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Maintainers: reopen, remove missing-issue-link, or add bypass-issue-check to override.