Chronicle: Cut-Point Replay for Regression Testing of LLM Agents

Tisha Chawla, Susheem Koul


Abstract
Large language model responses are non-deterministic, so failures in LLM agents are hard to reproduce: a failure depends on inference that is not bitwise reproducible, on tools that read changing state, and on a multi-step trajectory that a re-run rarely repeats. Record-and-replay makes a run reproducible, but existing agent tooling records runs only to trace or score them, not to test a code change against them. We present Chronicle, which records an agent run at its non-deterministic boundaries as immutable envelopes and replays it from the record. Its central operation, cut-point replay, serves a chosen subset of boundaries from the record and executes the complementary subset live with new code, turning a recorded incident into a regression test that runs in continuous integration. On a benchmark of 6 recorded failures with simulated model boundaries, recording adds 23 μs per crossing (0.008% of an assumed 300 ms model call), full replay issues zero model calls and is bit-stable across 20 repetitions, and cut-point tests fail on faulty code and pass on guarded and benign changes for all 6 incidents. In a mutation study of the guarded tools, cut-point tests catch every mutant that lets the recorded unsafe action through, while a baseline that stubs every boundary, using the same assertion, catches none. Chronicle and the benchmark are publicly available at https://github.com/theagentplane/chronicle.
Anthology ID:
2026.realm-1.71
Volume:
Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Ehsan Kamalloo, Nicolas Gontier, Nikolai Rozanov, Maryam Hashemzadeh, Akhil Arora
Venues:
REALM | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
1026–1031
Language:
URL:
https://aclanthology.org/2026.realm-1.71/
DOI:
Bibkey:
Cite (ACL):
Tisha Chawla and Susheem Koul. 2026. Chronicle: Cut-Point Replay for Regression Testing of LLM Agents. In Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026), pages 1026–1031, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Chronicle: Cut-Point Replay for Regression Testing of LLM Agents (Chawla & Koul, REALM 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.realm-1.71.pdf