fix: CLI file duplication bug when writing files (#5318)

[marius-kilocode]

Summary

Fixes #5318 - CLI writes file content twice when creating or editing files.

Problem

When the Kilo Code CLI creates or edits files, the content was being duplicated at the end of the file. This was visible in logs and caused issues where:

• New files had their content written twice
• When the LLM tried to fix the duplication, it added the code again, creating 3+ copies

Root Causes

1. Multi-line Edit Logic in applyEdit (Primary)

In packages/agent-runtime/src/host/VSCode.ts, the line-based edit logic had a bug:

const lastLine = lines[endLine] || ""
const newContent = firstLine.substring(0, startChar) + textEdit.newText + lastLine.substring(endChar)

When endChar = 0, lastLine.substring(0) returns the entire last line, causing duplication.

2. Multiple applyEdit Calls in CLI Mode (Secondary)

In src/integrations/editor/DiffViewProvider.ts, the update() method made up to 3 applyEdit calls when finalizing. In CLI mode, each call writes to disk, causing race conditions and potential duplication.

Solution

VSCode.ts Changes

• Replaced line-based editing with offset-based editing using slice() operations
• Added [...edits] spread to prevent mutation of the original edit array

DiffViewProvider.ts Changes

• Added CLI-specific code path that makes a single applyEdit call to replace the entire document content
• This eliminates the multiple-write issue in CLI mode

Testing

• Added new test file packages/agent-runtime/src/host/__tests__/VSCode.applyEdit.spec.ts
• Added CLI mode test in src/integrations/editor/__tests__/DiffViewProvider.spec.ts

[changeset-bot]

🦋 Changeset detected

Latest commit: d8980fa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@kilocode/agent-runtime	Patch
kilo-code	Patch
@kilocode/cli	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Overview

This PR fixes a CLI file duplication bug where content was written twice when creating or editing files. The changes include:

1. packages/agent-runtime/src/host/VSCode.ts - Refactored applyEdit to use offset-based string manipulation instead of line-based array manipulation. Added [...edits] spread to avoid mutating the original edits array during sorting.

2. src/integrations/editor/DiffViewProvider.ts - Added CLI-specific code path (KILO_CLI_MODE) to avoid multiple applyEdit calls that can duplicate content in the mock workspace.

3. Test coverage - Added comprehensive tests for both the applyEdit fix and the CLI mode optimization.

Code Quality Notes

• ✅ The offset-based approach correctly handles multi-line edits without the duplication issues of the previous line-based approach
• ✅ The [...edits] spread prevents mutation of the original array when sorting
• ✅ Environment variable cleanup is properly handled in test afterEach blocks
• ✅ Tests verify both sequential edits and multi-line replacements work correctly

Files Reviewed (4 files)

• .changeset/fix-cli-file-duplication.md - Changeset for the fix
• packages/agent-runtime/src/host/VSCode.ts - Core fix for applyEdit
• packages/agent-runtime/src/host/__tests__/VSCode.applyEdit.spec.ts - New test file
• src/integrations/editor/DiffViewProvider.ts - CLI mode optimization
• src/integrations/editor/__tests__/DiffViewProvider.spec.ts - Test for CLI mode

[chrarnoldus]

does this hardcoded newline character work as intended on window?