Fix Go apply/vendor on Windows read-only module cache (#346)

[Mikola Lysenko (mikolalysenko)]

LLM Description written by Claude Code:claude-opus-5-5

Fixes #346

Summary

On Windows, Go apply (agent mode) and vendor failed on every module with Access is denied. (os error 5). Now the copied module is writable and the patch applies.

Root cause

Go extracts module-cache files read-only, which on Windows means the R attribute. copy_tree::fresh_copy copies the module into .socket/go-patches/… or .socket/vendor/golang/<uuid>/… with std::fs::copy, which carries the attribute over. The apply pipeline then commits patched bytes with stage + rename, and Windows' MoveFileEx(REPLACE_EXISTING) refuses to replace a read-only destination. On Unix, rename ignores the target's mode, which is why only Windows failed.

Fix

fresh_copy grants owner-write to each copied file that arrives read-only. On Unix it adds 0o200; on Windows it clears the read-only attribute. It only touches the fresh inode std::fs::copy just wrote, never the source or a link, so the module cache and any shared inode keep their permissions. Both Go backends (agent apply_go_redirect and vendor_go_module) share this copy step.

I fixed the copy rather than the rename. Clearing the attribute in stage_and_rename would change the attribute on the displaced inode, which can be a hardlinked store file.

Tests (red → green)

• copy_tree::tests::fresh_copy_files_are_writable_even_from_readonly_source: on unpatched code it fails on every platform (the copy is 0o444 / read-only). It passes with the fix.
• golang_local::tests::test_apply_redirect_over_a_read_only_module_cache: the fixture cache files are marked read-only (set_readonly(true)), and apply runs for both the go-patches base and a vendor base. It checks that the copy is patched and that the cache stays read-only and pristine. This is the Windows reproduction, so the Windows test legs are where it would have failed before the fix.

Commands run

• cargo test -p socket-patch-core --lib -- copy_tree golang_local: 56 passed
• cargo clippy --workspace --all-features -- -D warnings: clean
• cargo fmt --all -- --check: the changed files are clean (the only diff is pre-existing, in upstream/mod.rs on main)

🤖 Generated with Claude Code

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Note

Low Risk
Localized filesystem permission fix on private copy inodes with regression tests; does not change auth, patching logic, or source cache permissions.

Overview
Fixes #346: Go apply/vendor on Windows failed with access denied because module-cache copies kept the read-only attribute from std::fs::copy, and the patch pipeline’s stage+rename could not replace read-only destinations on Windows.

fresh_copy now calls make_owner_writable after each copied file: on Unix it ORs 0o200; on Windows it clears the read-only attribute. Only the newly created copy inode is touched—the module cache stays read-only.

Docs on fresh_copy are updated to explain Windows vs Unix behavior. Tests cover writable copies from read-only sources and apply_go_redirect over read-only cache files for both go-patches and vendor copy bases.

^{Reviewed by Cursor Bugbot for commit 6830b65. Configure here.}

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Generated by Claude Code

[Mikola Lysenko (mikolalysenko)]

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