Fix LayerBuilder crash on Windows: absolute root path in tar headers

[alongubkin]

Summary

• On Windows, Path::is_absolute() requires a drive letter, so Unix-style paths like /app/foo pass through normalize_archive_path unchanged. ensure_parent_dirs_exist then walks ancestors up to /, which the tar crate rejects as non-relative.
• normalize_archive_path now strips leading / via string check as a fallback for Windows.
• ensure_parent_dirs_exist skips the root "/" path as a safety net.

Closes ALIEN-13

Test plan

• All 13 existing layer tests pass
• Verify OCI image build on Windows with x86_64-pc-windows-gnu target

🤖 Generated with Claude Code

[linear]

ALIEN-13 Fix LayerBuilder crash on Windows: absolute root path in tar directory headers

Bug

When building an OCI image on Windows using BuildStrategy::FromScratch, dockdash's LayerBuilder creates a tar layer with a directory entry for / (the root). The tar crate rejects this because tar archive paths must be relative.

Error

CONTAINER_OPERATION_FAILED: Container operation failed
├─▶ GENERIC_ERROR: I/O error: Failed to set path for directory header: /: paths in archives must be relative

Root cause

normalize_archive_path uses Path::is_absolute() to detect absolute paths and strip the leading /. On Windows, is_absolute() requires a drive letter (e.g. C:\), so Unix-style paths like /app/alien-test-server are not detected as absolute. The path passes through unchanged, and ensure_parent_dirs_exist walks ancestors up to /, which the tar crate rejects.

Fix

Two changes in src/layer.rs:

1. normalize_archive_path: Add a fallback that checks for a leading / in the string representation and strips it, handling Unix-style absolute paths on Windows.
2. ensure_parent_dirs_exist: Skip paths equal to "/" as a safety net, in addition to the existing empty-string check.

Repro

Build any Rust function on Windows via alien-build with the local platform target (x86_64-pc-windows-gnu). The binary builds successfully but OCI image creation fails when LayerBuilder tries to add a directory header for the root path /.

[greptile-apps]

Your free trial has ended. If you'd like to continue receiving code reviews, you can add a payment method here.