fix(windows): better support MSYS/Git Bash path handling

[nielpattin]

Fix MSYS/Git Bash path handling on Windows

Summary

• Add toNativePath() to convert MSYS/Git Bash/Cygwin paths (/c/Users/...) to Windows paths (C:\Users\...)
• Add safeRelative() to handle cross-drive paths and deep parent traversals
• Fix TUI path display with Locale.truncateMiddle for long paths

Details

When running opencode in Git Bash on Windows, the shell uses POSIX-style paths (/f/test/file.txt) but Node.js/Bun APIs expect Windows paths (F:\test\file.txt). This caused:

1. File operations failing - ENOENT: no such file or directory because Node can't resolve /f/... paths
2. Garbage display - path.relative() across different drives produced ..\..\..\..\..\..\f\test
3. Long paths unreadable - No truncation for deeply nested paths

Before

→ Read ..\..\..\..\..\..\..\f\test\file.txt
Error: ENOENT: no such file or directory

After

→ Read F:\test\file.txt

Files Changed

• packages/opencode/src/util/filesystem.ts - Added toNativePath() and safeRelative()
• packages/opencode/src/tool/*.ts - Applied path conversion at entry points (read, write, edit, glob, grep, ls, patch)
• packages/opencode/src/cli/cmd/tui/routes/session/index.tsx - Fixed TUI display with path abbreviation

Test Cases

Setup (run once in Git Bash)

# Cross-drive test files (F: drive)
mkdir -p /f/test
echo "hello world foo bar" > /f/test/test.txt
echo "another hello" > /f/test/test2.txt

# Long nested path on different drive
mkdir -p /f/test/very/deeply/nested/folder/structure/that/is/really/long
echo "deeply nested content" > /f/test/very/deeply/nested/folder/structure/that/is/really/long/file.txt

# Parent traversal test files (same drive, different depths)
mkdir -p /c/Users/<user_name>/repo/sst/testdir
echo "2 levels up" > /c/Users/<user_name>/repo/sst/testdir/two-up.txt

mkdir -p /c/Users/<user_name>/repo/testdir
echo "3 levels up" > /c/Users/<user_name>/repo/testdir/three-up.txt

# Long nested path inside worktree
mkdir -p /c/Users/<user_name>/repo/sst/opencode/very/deeply/nested/folder/structure/that/is/really/long
echo "deep test" > /c/Users/<user_name>/repo/sst/opencode/very/deeply/nested/folder/structure/that/is/really/long/file.txt

---

I don't touch LSP or MultipleEdit tools because unsure about those. (But it's working by default)

Feature 1: MSYS/Git Bash Path Conversion

Tests that /c/... and /f/... paths are converted to C:\... and F:\....

LIST Tool

Use the LIST tool to show all files in /f/test/

Expected: → List F:\test (not ..\..\..\..\f\test)

READ Tool

Use the READ tool to read /f/test/test.txt

Expected: → Read F:\test\test.txt

WRITE Tool

Use the WRITE tool to create /f/test/write-test.txt with content "written by opencode"

Expected: → Wrote F:\test\write-test.txt

EDIT Tool

Use the EDIT tool to replace "hello" with "goodbye" in /f/test/test.txt

Expected: → Edit F:\test\test.txt

GLOB Tool

Use the GLOB tool to find all *.txt files in /f/test/

Expected: → ✱ Glob "*.txt" in F:\test\ (4 matches)

GREP Tool

Use the GREP tool to search for "hello" in /f/test/

Expected: → ✱ Grep "hello" in F:\test\ (1 matches)

---

Feature 2: Parent Traversal Threshold (3+)

Paths with 3+ parent traversals (../../..) show absolute path. Paths with 0-2 show relative.

2 levels up - shows RELATIVE

Use the READ tool to read /c/Users/<user_name>/repo/sst/opencode/PR.md

Expected: → Read ..\..\.PR.md (relative path)

3+ levels up - shows ABSOLUTE

Use the READ tool to read /c/Users/<user_name>/repo/testdir/three-up.txt

Expected: → Read C:\Users\<user_name>\repo\testdir\three-up.txt (absolute path)

Use the READ tool to read /c/Users/<user_name>/.config/opencode/opencode.jsonc

Expected: → Read C:\Users\<user_name>\.config\opencode\opencode.jsonc (absolute path)

---

Feature 3: Long Path Truncation

Long paths are truncated with ... in the middle, using Locale.truncateMiddle.

Long path on different drive

Use the READ tool to read /f/test/very/deeply/nested/folder/structure/that/is/really/long/file.txt

Expected: → Read F:\test\very\deeply\…\that\is\really\long\file.txt (truncated)

Long path inside worktree

Use the READ tool to read /c/Users/<user_name>/repo/sst/opencode/very/deeply/nested/folder/structure/that/is/really/long/file.txt

Expected: → Read ..\..\very\deeply\ne…\that\is\really\long\file.txt (truncated relative path)

---

Checklist

• No-op on non-Windows platforms for toNativePath() (gated by process.platform === "win32")
• Parent traversal check (3+) applies to ALL platforms
• Uses existing Locale.truncateMiddle for path abbreviation (consistent with sidebar)
• No breaking changes for normal Windows or Unix paths

[rekram1-node]

/review

[nielpattin]

@rekram1-node lgtm after refactor