`edit` tool: "Could not find oldString" failure — model context drift

[anandgupta42]

Problem

The edit tool fails with:

Could not find oldString in the file. It must match exactly, including whitespace, indentation, and line endings.

236 occurrences in a single day. This is the second most common tool failure after webfetch.

Root cause

The model's in-context representation of a file drifts from the actual file content. This happens when:

1. External processes (formatters, linters) modify files after the model reads them — partially addressed by Edit tool enters retry loop on stale file reads, causing hundreds of consecutive failures #450
2. Multiple edits to the same file where the model uses stale oldString from before previous edits
3. Context compaction drops or summarizes file content, leaving the model with an outdated view
4. Model hallucination — generating oldString that was never in the file

Impact

• Each failed edit wastes a tool call
• Model often retries with the same incorrect oldString, creating short failure bursts
• The existing doom loop detector (threshold=3) catches identical inputs but not semantically similar ones

Suggested investigation

1. Analyze whether failures correlate with files that were recently edited (context drift) vs. files never read (hallucination)
2. Consider including a snippet of the actual file content in the error response so the model can self-correct (similar approach to Edit tool enters retry loop on stale file reads, causing hundreds of consecutive failures #450 for stale files)
3. Evaluate whether the fuzzy matchers (LineTrimmedReplacer, WhitespaceNormalizedReplacer, etc.) are catching enough cases or if thresholds need tuning