Handle relative system temporary directories

docs/roadmap/remediation.md

@@ -255,7 +255,9 @@ candidate output still leaves the worktree clean.
 **Resolution:** Candidate and CLI delivery builds use shared system temporary
 storage allocated by `internal/tempdir`, with worktree containment checks and
 caller-owned cleanup. Regressions execute both operations with read-only
-repository parents and confirm clean worktrees. Affected suites pass.
+repository parents and confirm clean worktrees. Additional helper regressions
+cover relative system temporary paths and cleanup after rejecting in-worktree
+storage. Affected suites pass.
 
 ### R7 — Medium: Attachment origin restrictions exceed credential isolation
 

internal/tempdir/tempdir.go

@@ -14,6 +14,12 @@ func Outside(repositoryDir, pattern string) (string, error) {
 	if err != nil {
 		return "", err
 	}
+	absolute, err := filepath.Abs(directory)
+	if err != nil {
+		os.RemoveAll(directory)
+		return "", err
+	}
+	directory = absolute
 	repository, err := filepath.Abs(repositoryDir)
 	if err == nil && !strings.EqualFold(filepath.VolumeName(repository), filepath.VolumeName(directory)) {
 		return directory, nil

internal/tempdir/tempdir_test.go

@@ -0,0 +1,52 @@
+package tempdir
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+func TestOutsideHonorsRelativeTemporaryDirectory(t *testing.T) {
+	parent := t.TempDir()
+	repository := t.TempDir()
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	relative, err := filepath.Rel(cwd, parent)
+	if err != nil {
+		t.Skip("temporary directory is on another volume")
+	}
+	setTemporaryDirectory(t, relative)
+	directory, err := Outside(repository, "fixture-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(directory)
+	if !filepath.IsAbs(directory) || filepath.Dir(directory) != parent {
+		t.Fatalf("temporary storage=%q want parent %q", directory, parent)
+	}
+}
+
+func TestOutsideRejectsAndCleansStorageInsideWorktree(t *testing.T) {
+	repository := t.TempDir()
+	setTemporaryDirectory(t, repository)
+	if directory, err := Outside(repository, "fixture-"); err == nil {
+		os.RemoveAll(directory)
+		t.Fatal("storage created inside worktree")
+	}
+	remaining, err := os.ReadDir(repository)
+	if err != nil || len(remaining) != 0 {
+		t.Fatalf("temporary storage left behind: %v %v", remaining, err)
+	}
+}
+
+func setTemporaryDirectory(t *testing.T, directory string) {
+	t.Helper()
+	variable := "TMPDIR"
+	if runtime.GOOS == "windows" {
+		variable = "TMP"
+	}
+	t.Setenv(variable, directory)
+}