fix(patch): add idempotency guard to prevent duplicate content loops - #18614
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When the agent retries a patch without re-reading the file, fuzzy matching may find the previously-applied replacement and re-apply it, creating duplicate content blocks. Add a guard that checks whether the matched region already equals new_string before writing. Fixes NousResearch#18426
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Cyrene963
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May 3, 2026
Community PRs applied: - NousResearch#18596: Enable secret redaction by default (SECURITY) - NousResearch#18650: Sanitize malformed tool messages + auto-recover on API 400 - NousResearch#18607: Emergency compression before max_iterations exhaustion - NousResearch#18603: Compression fallback to main model on 413 rate limit - NousResearch#18638: Pass threshold_percent on model switch - NousResearch#18663: Strip extra_content from tool_calls for strict APIs - NousResearch#18618: Forward explicit_api_key to OpenRouter - NousResearch#18632: Show cache tokens in /insights breakdown - NousResearch#18614: Add idempotency guard for patch duplicate loops - NousResearch#18600: Raise ValueError when HERMES_HOME unset in profile mode - NousResearch#18616: Allow ZWJ emoji in context files - NousResearch#18582: Reload .env on /restart - NousResearch#18547: Stabilize system prompt prefix for KV cache reuse - NousResearch#18692: Strip FTS5 operators from session search truncation terms Fix: Add order_by_last_active=True to list_sessions_rich call (pre-existing commit 142b4bf code sync)
teknium1
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Jul 12, 2026
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Thanks for tackling the duplicate-content retry path. The bug is still present on current main, but this guard does not cover the reported failure shape.
Problems
tools/fuzzy_match.py:102compares the selected match span with the complete rawnew_string. Currentcontext_awareaccepts an old-string-sized candidate at 50% line similarity (tools/fuzzy_match.py:696-728), then_apply_replacementsreplaces only that span (tools/fuzzy_match.py:407-415). After an edit that adds a line, a retry can match a changed prefix rather than the full replacement, bypass this guard, and retain a duplicated trailing line.- The added tests do not exercise that multi-line, longer-replacement retry path. The linked #18426 discussion and competing #56570 describe this concrete form; #54575 also targets the permissive fallback strategies.
Suggested changes
- Add a regression that applies a longer multi-line replacement, retries it, and asserts the content is unchanged with a clean failure.
- Guard before permissive fallback matching, or reject divergent fallback candidates before replacement while retaining legitimate formatting-tolerant matches.
Automated hermes-sweeper review.
| # duplicate content in a retry loop (issue #18426). | ||
| matches_to_apply = [ | ||
| m for m in matches | ||
| if content[m[0]:m[1]] != new_string |
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This only detects a selected span equal to the full new_string. context_aware can select an old-string-sized prefix of an already-applied longer replacement; this comparison is then false, and _apply_replacements inserts new_string while retaining the old trailing line. Please add that longer multi-line retry regression and guard before this permissive fallback is allowed to write.
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What does this PR do?
Add an idempotency guard to
fuzzy_find_and_replacethat prevents the patch tool from creating duplicate content when the same patch is applied to an already-patched file.Related Issue
N/A
Type of Change
Changes Made
How to Test
pytest tests/ -q— all tests should passChecklist
Code
fix(scope):,feat(scope):, etc.)pytest tests/ -qand all tests passDocumentation & Housekeeping
docs/, docstrings) — or N/Acli-config.yaml.exampleif I added/changed config keys — or N/ACONTRIBUTING.mdorAGENTS.mdif I changed architecture and workflows — or N/A