fix(windows): path handling fixes for Windows

[pschiel]

Summary

This fix solves a whole series of bugs, resulting from filepath issues with backslashes occuring on Windows.

→ Solution: normalize all internal paths to forward slashes using centralized Filesystem wrappers

Why this works: all win32 shells work with forward slash paths, this is de-facto industry standard (git, vscode, cmake, ... all use this pattern)

Observed issues

❌ git rev-parse --show-toplevel returns E:/x/y forward slash format → worktree/directory mismatch ❌ path.resolve(), path.relative(), realpathSync.native(), realpath (bash) break with git bash paths (various issues) ❌ /d/x within C drive (/c/) results in things like C:\d\x ❌ relative paths not working like expected using cross-drive ❌ contains logic not working → issues with permission system and external_directory ❌ /tmp inside git bash is something else outside of it ❌ tools break using backslash paths (some backslashes get "eaten") ❌ escaping hell for agents → requires double/quadruple escaping ❌ observed in all win32 native shells (git bash, cmd, powershell/pwsh) ❌ few issues in app/desktop (wrong filepath splits/usage)

Tested with fix

✅ local test suite succeeds now with 100% (bun test in packages/opencode) ✅ all possible path variants (C:\a\b, C:/a/b, /c/a/b, /cygdrive/c/a/b) are normalized into C:/a/b format ✅ full functionality of all tools (ENOENT errors gone, permissions, relative paths, external directory, LSP) ✅ worktree/sandbox handling correct ✅ tested TUI and desktop

How to reproduce/test

• test suite
• running prompts with various problematic/mixed filepaths (see attached md example)

Notes

A few more places would require normalization - but they're unused/dead code (should be removed):

• packages/ui/src/context/sync.tsx line 16 absolute()
• packages/ui/src/context/local.tsx line 392, 420, 455, 546 - file tree operations (no file tree used)

[github-actions[bot]]

Hey! Your PR title (feat) support MSYS forward slashes with experimental flag doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions[bot]]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[Hona]

This sounds perfect @pschiel

If you can get it ready and finish the cleanup you said I can test and approve.

Btw don't put it behind an experimental flag. We'll ship once it's working.