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fix(core): preserve index and timestamp fields when merging #34731

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Merged
Mason Daugherty (mdrxy) merged 1 commit into from
Feb 17, 2026
Merged

fix(core): preserve index and timestamp fields when merging #34731

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9 changes: 8 additions & 1 deletion libs/core/langchain_core/utils/_merge.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,14 @@ def merge_dicts(left: dict[str, Any], *others: dict[str, Any]) -> dict[str, Any]
elif merged[right_k] == right_v:
continue
elif isinstance(merged[right_k], int):
merged[right_k] += right_v
# Preserve identification and temporal fields using last-wins strategy
# instead of summing:
# - index: identifies which tool call a chunk belongs to
# - created/timestamp: temporal values that shouldn't be accumulated
if right_k in {"index", "created", "timestamp"}:
merged[right_k] = right_v
else:
merged[right_k] += right_v
else:
msg = (
f"Additional kwargs key {right_k} already exists in left dict and "
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12 changes: 12 additions & 0 deletions libs/core/tests/unit_tests/utils/test_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,18 @@ def test_check_package_version(
{"a": [{"idx": 0, "b": "f"}]},
{"a": [{"idx": 0, "b": "{"}, {"idx": 0, "b": "f"}]},
),
# Integer 'index' should be preserved, not summed (tool call identification)
({"index": 1}, {"index": 1}, {"index": 1}),
({"index": 0}, {"index": 1}, {"index": 1}),
# 'created' timestamp should be preserved, not summed
({"created": 1700000000}, {"created": 1700000000}, {"created": 1700000000}),
({"created": 1700000000}, {"created": 1700000001}, {"created": 1700000001}),
# 'timestamp' should be preserved, not summed
({"timestamp": 100}, {"timestamp": 100}, {"timestamp": 100}),
({"timestamp": 100}, {"timestamp": 200}, {"timestamp": 200}),
# Other integer fields should still be summed (e.g., token counts)
({"tokens": 10}, {"tokens": 5}, {"tokens": 15}),
({"count": 1}, {"count": 2}, {"count": 3}),
],
)
def test_merge_dicts(
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