fix(prompts): prevent models from hallucinating line numbers in apply_diff

[faitno]

Description

Models such as Gemini output line numbers in the read_file tool (e.g. 137: ...). When attempting to use apply_diff, models often copy these line numbers verbatim into the <<<<<<< SEARCH block. Since the actual source files do not contain these line numbers, the apply_diff tool strictly fails with an Edit Unsuccessful error, eventually leading to a consecutiveMistakeLimit failure in the extension.

This PR strictly updates the system prompt and instructions for the apply_diff tool to explicitly instruct models to strip line numbers from the SEARCH block so that it correctly matches the raw file content.

Summary by CodeRabbit

• Bug Fixes
  • Clarified guidance for applying search-and-replace changes so line numbers are not included in exact-match text.
  • Added stronger warnings to prevent mismatches when using file content from read-only previews.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: ff6baa5f-78d9-42c7-b6ad-900715e7ee12

📥 Commits

Reviewing files that changed from the base of the PR and between 9b6bd77 and 9a63336.

📒 Files selected for processing (1)

• src/core/prompts/tools/native-tools/apply_diff.ts

✅ Files skipped from review due to trivial changes (1)

• src/core/prompts/tools/native-tools/apply_diff.ts

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📝 Walkthrough

Walkthrough

The apply_diff tool description strings in apply_diff.ts are updated to add explicit CRITICAL warnings: read_file-provided line numbers do not exist in actual file content and must be stripped before using SEARCH content for exact matching. The DIFF_PARAMETER_DESCRIPTION template now explicitly prohibits line-number prefixes in the [exact content to find] section.

Changes

apply_diff SEARCH Block Line-Number Warnings

Layer / File(s)	Summary
SEARCH block line-number warning text src/core/prompts/tools/native-tools/apply_diff.ts	APPLY_DIFF_DESCRIPTION and DIFF_PARAMETER_DESCRIPTION template strings are rewritten to include CRITICAL warnings that read_file line numbers must be removed and must not appear in SEARCH block content used for exact file matching.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related issues

• Enhance apply_diff tool description to improve success rate for Gemini models #611: Both changes modify apply_diff.ts to tighten exact-match formatting instructions, directly addressing the same prompt-accuracy concern.

Poem

🐇 A rabbit once searched for a line,
But numbers crept in — oh, what a sign!
"CRITICAL!" I cried with a thump,
"Strip those digits, don't let them clump!"
Now SEARCH blocks match perfectly fine. ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the fix, but it omits the required issue link, test procedure, and checklist sections.	Add the approved issue reference, a test procedure, and the required checklist/notes sections from the template.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly names the main change: preventing hallucinated line numbers in apply_diff.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[navedmerchant]

Thanks for this, please clean up the CR to keep changes relevant to issues at hand

[faitno]

Done! Force-pushed the branch with all unrelated changes removed — the PR now only touches src/core/prompts/tools/native-tools/apply_diff.ts.

[edelauna]

The example format looks off — read_file outputs lines as '1 | ' and '2 | ' (space-padded number + pipe), not '1: ' / '2: '. Could a model following this example end up looking for the wrong pattern to strip? (The actual format comes from addLineNumbers() in extract-text.ts:155.)

[edelauna]

Same here — read_file produces '137 | content' not '137: content'. Worth aligning the example with the actual output format, since the server-side auto-strip in multi-search-replace.ts also keys on the N | pattern.

[edelauna]

I opened this issue: #716