multica-ai/multica · error

mklink /J %s %s: %s: %w

Error message

mklink /J %s %s: %s: %w

What it means

Windows-only createDirLink: os.Symlink failed (no Developer Mode / admin), and the cmd mklink /J junction fallback also failed. The error includes mklink's combined output, so the reason (existing destination, invalid path, privilege issue) is in the message text.

Source

Thrown at server/internal/daemon/execenv/codex_home_link_windows.go:20

package execenv

import (
	"fmt"
	"os"
	"os/exec"
)

// createDirLink tries os.Symlink first (requires Developer Mode or admin on
// Windows). If that fails, it falls back to a directory junction (mklink /J)
// which works without elevated privileges.
func createDirLink(src, dst string) error {
	if err := os.Symlink(src, dst); err == nil {
		return nil
	}
	out, err := exec.Command("cmd", "/c", "mklink", "/J", dst, src).CombinedOutput()
	if err != nil {
		return fmt.Errorf("mklink /J %s %s: %s: %w", dst, src, out, err)
	}
	return nil
}

// createFileLink tries os.Symlink first. If that fails, it falls back to
// copying the file so the content is still available.
func createFileLink(src, dst string) error {
	if err := os.Symlink(src, dst); err == nil {
		return nil
	}
	return copyFile(src, dst)
}

View on GitHub (pinned to 2c0912b6ec)

Solutions

1. Read the embedded mklink output — 'Cannot create a file when that file already exists' means the dst must be removed first
2. Delete the stale junction/directory at dst and retry
3. Enable Windows Developer Mode so os.Symlink succeeds directly

if _, err := os.Lstat(dst); err == nil {
	return fmt.Errorf("link destination already exists: %s", dst)
}

if err := createDirLink(src, dst); err != nil {
	if strings.Contains(err.Error(), "Already exists") || strings.Contains(err.Error(), "already exists") {
		_ = os.Remove(dst)
		err = createDirLink(src, dst)
	}
}

When it happens

Trigger: Exposing the shared plugin cache into a task home where the junction destination already exists; path with characters cmd misparses; mklink unavailable on the Windows edition.

Common situations: Reused task home already containing plugins\cache; leftover junction from a crashed run; Windows Server Core without standard cmd tooling.

Related errors

• replace binary: %w
• open codex home %s: %w
• stat opened codex home %s: %w
• stat codex home %s: %w
• create %s directory %s: %w

AI-assisted analysis of multica-ai/multica@2c0912b6ec (2026-08-15). Data as JSON: /api/errors/e7ae920617cc4937. Report an issue: GitHub.