Fix CSV path joining and relative exclusions; add scan benchmark script

internal/scan/scan.go

@@ -138,6 +138,17 @@ type inodeKey struct{ dev, ino uint64 }
 // Start stats root, creates the tree and begins scanning in the background.
 func Start(ctx context.Context, root string, opts Options) (*Scanner, error) {
 	opts.defaults()
+	// Path-style exclusions are matched against absolute paths.
+	excl := make([]string, len(opts.Excludes))
+	for i, p := range opts.Excludes {
+		excl[i] = p
+		if strings.ContainsAny(p, `/\`) {
+			if a, err := filepath.Abs(p); err == nil {
+				excl[i] = a
+			}
+		}
+	}
+	opts.Excludes = excl
 	abs, err := filepath.Abs(root)
 	if err != nil {
 		return nil, err

internal/scan/scan_test.go

@@ -237,6 +237,12 @@ func TestExcludes(t *testing.T) {
 	if tr.Stats.Excluded != 2 || tr.Node(0).Files != 1 {
 		t.Fatalf("excluded=%d files=%d", tr.Stats.Excluded, tr.Node(0).Files)
 	}
+	// Relative path patterns resolve against the working directory.
+	t.Chdir(root)
+	tr = runScan(t, root, Options{Workers: 2, Excludes: []string{"./skip"}})
+	if tr.Stats.Excluded != 1 {
+		t.Fatalf("relative exclude: excluded=%d", tr.Stats.Excluded)
+	}
 }
 
 func TestUnicodeAndHostileNames(t *testing.T) {