feat: replace pi-based filesystem tools with native implementation

[shadowfax92]

Summary

• Replace the @mariozechner/pi-agent-core + @mariozechner/pi-coding-agent filesystem tool adapter in apps/server with native in-repo tools.
• Preserve existing filesystem_* tool names and chat-mode behavior while adding explicit session-directory boundary checks and bounded output handling.
• Add focused filesystem tool tests (path utils, truncation, edit behavior) and remove obsolete pi dependencies from apps/server/package.json.

Design

This change keeps the existing ToolLoopAgent integration seam intact (AiSdkAgent still composes browser tools, external MCP tools, and filesystem tools), but swaps the filesystem layer to a modular native implementation under apps/server/src/agent/tool-loop/filesystem-tools/. The new structure follows pi-mono’s small-per-tool module style while applying stricter safety constraints inspired by Gemini CLI, including consistent path validation, deterministic limits/truncation, and normalized model output mapping.

Test plan

• bun run --filter @browseros/server typecheck
• bun test apps/server/tests/agent/filesystem-tools
• bun test apps/server/tests (contains existing unrelated failures in this repo; this change does not modify those areas)

[greptile-apps]

Greptile Summary

Successfully replaces pi-based filesystem tools with a native in-repo implementation while preserving existing tool names and behavior.

Key improvements:

• Removed external dependencies (@mariozechner/pi-agent-core and @mariozechner/pi-coding-agent)
• Added comprehensive security with symlink resolution and session directory boundary checks
• Implemented deterministic output limits and truncation (2000 lines, 50KB)
• Added focused test coverage with 35/36 tests passing (1 test fails only due to environment lacking sleep command)
• Follows project conventions: kebab-case file naming, extensionless imports, minimal comments

Implementation quality:

• Clean modular architecture with separation of concerns
• Type-safe with Zod schemas for all tool inputs
• Proper error handling throughout
• Well-defined exported constants for tool limits
• UTF-8 boundary-aware truncation
• Cross-platform shell detection (bash/cmd)

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• This is a well-architected refactor with comprehensive test coverage (35/36 tests passing), strong security (symlink and path boundary checks), proper error handling, and clean code that follows project conventions. The implementation is modular, type-safe, and thoroughly tested.
• No files require special attention

Important Files Changed

Filename	Overview
apps/server/package.json	removed @mariozechner/pi-agent-core and @mariozechner/pi-coding-agent dependencies as they are replaced by native implementation
apps/server/src/tools/filesystem/native-tool-adapter.ts	new adapter that wraps native filesystem tools, handles tool execution, metrics logging, and model output conversion
apps/server/src/tools/filesystem/path-utils.ts	implements path resolution, symlink security checks, glob pattern matching, and session directory boundary enforcement
apps/server/src/tools/filesystem/read.ts	implements file reading with offset/limit support, image detection, truncation, and path boundary validation
apps/server/src/tools/filesystem/edit.ts	implements exact text replacement with BOM preservation, line ending detection, and uniqueness validation
apps/server/src/tools/filesystem/grep.ts	implements content search with regex support, glob filtering, context lines, binary file detection, and result limits
apps/server/src/tools/filesystem/bash.ts	implements shell command execution with timeout support, cross-platform shell detection, and output truncation

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[AiSdkAgent] -->|buildFilesystemToolSet| B[native-tool-adapter]
    B -->|wraps| C[Native Tool Implementations]
    C --> D[read.ts]
    C --> E[write.ts]
    C --> F[edit.ts]
    C --> G[grep.ts]
    C --> H[find.ts]
    C --> I[ls.ts]
    C --> J[bash.ts]
    
    D -->|uses| K[path-utils]
    E -->|uses| K
    F -->|uses| K
    G -->|uses| K
    H -->|uses| K
    I -->|uses| K
    
    D -->|uses| L[truncate]
    G -->|uses| L
    H -->|uses| L
    I -->|uses| L
    J -->|uses| L
    
    K -->|security| M[Path Boundary Checks]
    K -->|security| N[Symlink Resolution]
    
    G -->|uses| O[scan.ts]
    H -->|uses| O
    
    B -->|returns| P[ToolSet]
    P -->|registered as| Q[filesystem_read, filesystem_write, etc]

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_{Last reviewed commit: c9e638f}