fix: flush the last SSE event when the stream ends without a blank line

[anxkhn]

Description

• Follow the CONTRIBUTING Guide
• Conventional Commits title
• Tests and linter pass
• Docs updated if necessary

Fixes #1213

Summary

parse_sse_stream only yields on a blank line. If the peer closes after data: {...} with no trailing blank line, leftover payload is dropped.

WHATWG SSE requires dispatching a pending event when the connection closes. JsonRpcTransport and RestTransport both use this parser, so a completed Task or Message can vanish and the client waits as if the stream is still open.

After the aiter_lines loop, if payload_chunks is non-empty, the pending event is now yielded the same way a blank line would. Existing tests already send a trailing newline and stay green.

Testing

Added test_parse_sse_stream_flushes_last_event_without_blank_line in tests/client/transports/test_http_helpers.py.

uv run pytest tests/client/transports/test_http_helpers.py -q

4 passed.

[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/transports/http_helpers.py	95.54%	95.69%	🟢 +0.15%
Total	93.12%	93.12%	⚪️ 0.00%

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