fix(core): preserve ordering in RunnableRetry batch/abatch results

[VMinB12]

Description: Fixes a bug in RunnableRetry where .batch / .abatch could return misordered outputs (e.g. inputs [0,1,2] yielding [1,1,2]) when some items succeeded on an earlier attempt and others were retried. Root cause: successful results were stored keyed by the index within the shrinking “pending” subset rather than the original input index, causing collisions and reordered/duplicated outputs after retries. Fix updates _batch and _abatch to:

• Track remaining original indices explicitly.
• Call underlying batch/abatch only on remaining inputs.
• Map results back to original indices.
• Preserve final ordering by reconstructing outputs in original positional order.

Issue: Fixes #21326

Tests:

• Added regression tests: test_retry_batch_preserves_order and test_async_retry_batch_preserves_order asserting correct ordering after a single controlled failure + retry.
• Existing retry tests still pass.

Dependencies:

• None added or changed.

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ignored	Preview		Sep 11, 2025 7:55pm

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32526 will not alter performance

_{Comparing vincentmin:vmin/fix-retry-batch (ababe7b) with master (5795ec3)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32526 will not alter performance

_{Comparing vincentmin:vmin/fix-retry-batch (ababe7b) with master (bd76575)¹}

Summary

✅ 14 untouched

Footnotes

1. No successful run was found on master (5795ec3) during the generation of this report, so bd76575 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[VMinB12]

@eyurtsev Did you have a chance to look at this PR by any chance? I feel it is of quite high priority to get this bug fixed. Let me know if you have questions.

[eyurtsev]

Thank you @VMinB12