Opus flagged that PR #2151's cancel-handler partial-dedup loop used a
substring check that was too broad: any short prior assistant reply
('OK', 'Here is the answer:') would dedup a longer new partial containing
it, silently dropping the partial and resurrecting the #893 data-loss bug.
Tightened to only dedup against actual prior _partial=True markers with
exact (whitespace-stripped) content match. Three new regression tests
added (short-non-partial-prefix-does-not-dedup, exact-partial-match-still-
dedups, same-content-non-partial-does-not-dedup).
10/10 partial-cancel tests pass after the fix. Also updated CHANGELOG with
the conflict-resolution notes for #2151 vs #2136 and the #2178 test-fix.
Hermes Agent
7209e89ef4