Three distinct data-loss paths fixed:
§A — Reasoning text was accumulated in a thread-local _reasoning_text
inside _run_agent_streaming. cancel_stream() never saw it because it
went out of scope when the thread was interrupted. Now mirrored to a
new shared dict STREAM_REASONING_TEXT keyed by stream_id, populated
in on_reasoning() and the reasoning branch of on_tool(), read in
cancel_stream().
§B — Live tool calls in thread-local _live_tool_calls were similarly
invisible to cancel_stream(). Now mirrored to STREAM_LIVE_TOOL_CALLS
on tool.started + tool.completed.
§C — Reasoning-only streams produced no partial message because the
thinking-block regex strip returned empty string and the `if _stripped:`
guard skipped the append. Now appends the partial message when EITHER
content text, reasoning trace, OR tool calls exist.
Mirrors the existing STREAM_PARTIAL_TEXT pattern from #893 exactly:
same dict creation in _run_agent_streaming, same _live_config fallback
in cancel_stream, same cleanup in _periodic_checkpoint.
8 regression tests in tests/test_issue1361_cancel_data_loss.py
covering all three sections plus tools+text combinations.
Co-authored-by: bergeouss <bergeouss@users.noreply.github.com>
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