* fix: cancel compaction instead of truncating history when summarization fails
When the compaction safeguard cannot generate a summary (no model, no API
key, or LLM error), it previously returned a "Summary unavailable" fallback
string and still truncated history. This caused irreversible data loss -
older messages were discarded even though no meaningful summary was produced.
Now returns `{ cancel: true }` in all three failure paths so the framework
aborts compaction entirely and preserves the full conversation history.
Fixes#10332
Co-authored-by: Cursor <cursoragent@cursor.com>
* fix: use deterministic timestamps in compaction safeguard tests
Replace Date.now() with fixed timestamp (0) in test data to prevent
nondeterministic behavior in snapshot-based or order-dependent tests.
Co-authored-by: Cursor <cursoragent@cursor.com>
* Changelog: note compaction cancellation safeguard fix
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Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>
ea47ab29bd