feat: write our own filesystem tools

[shadowfax92]

No description provided.

[greptile-apps]

Greptile Summary

Replaced external @mariozechner/pi-agent-core and @mariozechner/pi-coding-agent dependencies with custom filesystem tools implementation.

Major Changes:

• Implemented 7 filesystem tools: read, write, edit, bash, find, grep, ls
• Added path validation utilities with symlink resolution
• Comprehensive test coverage for all tools
• Cross-platform support (Unix and Windows)
• Features include: image support, line ending preservation, BOM handling, output truncation

Critical Issue Found:

• Path traversal vulnerability in path-utils.ts allowing sibling directory access (lines 27, 40, 46)

Confidence Score: 2/5

• This PR contains a critical path traversal vulnerability that must be fixed before merging
• Score reflects one critical security issue in path-utils.ts where startsWith checks don't validate path separators, allowing sibling directory access. While the implementation is otherwise well-architected with comprehensive tests, this vulnerability could allow unauthorized filesystem access outside the sandbox.
• apps/server/src/tools/filesystem/path-utils.ts requires immediate attention for the path traversal fix at lines 27, 40, and 46

Important Files Changed

Filename	Overview
apps/server/src/tools/filesystem/path-utils.ts	Path traversal vulnerability in startsWith checks (lines 27, 40, 46) - allows sibling directory access
apps/server/src/tools/filesystem/build-toolset.ts	Clean toolset builder with proper error handling and metrics logging
apps/server/src/tools/filesystem/read.ts	Robust file reading with image support, pagination, and truncation
apps/server/src/tools/filesystem/write.ts	Simple write implementation with automatic directory creation
apps/server/src/tools/filesystem/edit.ts	Sophisticated edit tool with line ending detection, BOM preservation, and exact matching
apps/server/tests/tools/filesystem/path-utils.test.ts	Path validation tests - missing sibling directory test case for the vulnerability

_{Last reviewed commit: f8ecc87}

[greptile-apps]

_{22 files reviewed, 1 comment}

_{Edit Code Review Agent Settings | Greptile}

[greptile-apps]

Path traversal vulnerability: startsWith check doesn't validate path separator, allowing access to sibling directories with matching prefixes.

Example attack:

• cwd: /tmp/safe
• path: ../safe-evil/malicious.txt
• Result: /tmp/safe-evil/malicious.txt.startsWith(/tmp/safe) → true ✗

Fix: import sep from node:path and check for separator after prefix:

Suggested change

	if (!realParent.startsWith(realCwd) && realParent !== realCwd) {
	if (!realParent.startsWith(realCwd + sep) && realParent !== realCwd) {

Also apply same fix to lines 40 and 46.

Prompt To Fix With AI

This is a comment left during a code review.
Path: apps/server/src/tools/filesystem/path-utils.ts
Line: 27

Comment:
Path traversal vulnerability: `startsWith` check doesn't validate path separator, allowing access to sibling directories with matching prefixes.

Example attack:
- cwd: `/tmp/safe`
- path: `../safe-evil/malicious.txt`
- Result: `/tmp/safe-evil/malicious.txt`.startsWith(`/tmp/safe`) → `true` ✗

Fix: import `sep` from `node:path` and check for separator after prefix:
```suggestion
        if (!realParent.startsWith(realCwd + sep) && realParent !== realCwd) {
```

Also apply same fix to lines 40 and 46.

How can I resolve this? If you propose a fix, please make it concise.