diff --git a/internal/storage/legacy_test.go b/internal/storage/legacy_test.go
index 6fe7898..efb7309 100644
--- a/internal/storage/legacy_test.go
+++ b/internal/storage/legacy_test.go
@@ -7,6 +7,205 @@ import (
 	"github.com/webinstall/webi-installers/internal/storage"
 )
 
+// TestExportLegacyDrops verifies that ExportLegacy correctly drops and counts
+// assets that can't be represented in the Node.js legacy cache format.
+func TestExportLegacyDrops(t *testing.T) {
+	t.Run("variant_builds_dropped", func(t *testing.T) {
+		// Assets with variant tags (rocm, installer, fxdependent, etc.) are
+		// dropped because Node.js has no variant-selection logic.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "ollama-linux-amd64-rocm.tgz", OS: "linux", Arch: "x86_64", Format: ".tar.gz", Variants: []string{"rocm"}},
+				{Filename: "ollama-linux-amd64.tgz", OS: "linux", Arch: "x86_64", Format: ".tar.gz"},
+			},
+		}
+		lc, stats := storage.ExportLegacy("ollama", pd)
+		if stats.Variants != 1 {
+			t.Errorf("Variants dropped = %d, want 1", stats.Variants)
+		}
+		if len(lc.Releases) != 1 {
+			t.Errorf("releases = %d, want 1 (baseline only)", len(lc.Releases))
+		}
+		if lc.Releases[0].Name != "ollama-linux-amd64.tgz" {
+			t.Errorf("kept wrong release: %q", lc.Releases[0].Name)
+		}
+	})
+
+	t.Run("unknown_formats_dropped", func(t *testing.T) {
+		// .apk, .AppImage, .deb, .rpm are not in the Node.js format set.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "tool.apk", OS: "android", Format: ".apk"},
+				{Filename: "tool.AppImage", OS: "linux", Format: ".AppImage"},
+				{Filename: "tool.deb", OS: "linux", Format: ".deb"},
+				{Filename: "tool.rpm", OS: "linux", Format: ".rpm"},
+				{Filename: "tool-linux-amd64.tar.gz", OS: "linux", Arch: "x86_64", Format: ".tar.gz"},
+			},
+		}
+		lc, stats := storage.ExportLegacy("tool", pd)
+		if stats.Formats != 4 {
+			t.Errorf("Formats dropped = %d, want 4", stats.Formats)
+		}
+		if len(lc.Releases) != 1 {
+			t.Errorf("releases = %d, want 1 (tar.gz only)", len(lc.Releases))
+		}
+	})
+
+	t.Run("empty_format_passes_through", func(t *testing.T) {
+		// Assets with empty format (e.g. bare binaries, git sources) pass through.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "jq-linux-amd64", OS: "linux", Arch: "x86_64", Format: ""},
+			},
+		}
+		lc, stats := storage.ExportLegacy("jq", pd)
+		if stats.Formats != 0 {
+			t.Errorf("Formats dropped = %d, want 0", stats.Formats)
+		}
+		if len(lc.Releases) != 1 {
+			t.Errorf("releases = %d, want 1", len(lc.Releases))
+		}
+	})
+}
+
+// TestExportLegacyTranslations verifies that legacyFieldBackport applies the
+// correct field translations for Node.js compatibility. Translations are lossy
+// in canonical terms but necessary for the legacy resolver.
+func TestExportLegacyTranslations(t *testing.T) {
+	t.Run("solaris_translated_to_sunos", func(t *testing.T) {
+		// Node.js only knows "sunos" for Sun/Oracle platforms.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "go1.20.1.solaris-amd64.tar.gz", OS: "solaris", Arch: "x86_64", Format: ".tar.gz"},
+			},
+		}
+		lc, _ := storage.ExportLegacy("go", pd)
+		if len(lc.Releases) != 1 {
+			t.Fatalf("releases = %d, want 1", len(lc.Releases))
+		}
+		if lc.Releases[0].OS != "sunos" {
+			t.Errorf("OS = %q, want %q", lc.Releases[0].OS, "sunos")
+		}
+	})
+
+	t.Run("illumos_translated_to_sunos", func(t *testing.T) {
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "caddy_2.9.0_illumos_amd64.tar.gz", OS: "illumos", Arch: "x86_64", Format: ".tar.gz"},
+			},
+		}
+		lc, _ := storage.ExportLegacy("caddy", pd)
+		if len(lc.Releases) != 1 {
+			t.Fatalf("releases = %d, want 1", len(lc.Releases))
+		}
+		if lc.Releases[0].OS != "sunos" {
+			t.Errorf("OS = %q, want %q", lc.Releases[0].OS, "sunos")
+		}
+	})
+
+	t.Run("ffmpeg_windows_gz_to_exe", func(t *testing.T) {
+		// ffmpeg Windows releases are .gz archives containing a bare .exe.
+		// Production releases.js overrides ext to 'exe' for install compatibility.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "ffmpeg-7.0-windows-amd64.gz", OS: "windows", Arch: "x86_64", Format: ".gz"},
+				{Filename: "ffmpeg-7.0-linux-amd64.tar.gz", OS: "linux", Arch: "x86_64", Format: ".tar.gz"},
+			},
+		}
+		lc, _ := storage.ExportLegacy("ffmpeg", pd)
+		if len(lc.Releases) != 2 {
+			t.Fatalf("releases = %d, want 2", len(lc.Releases))
+		}
+		var windowsExt string
+		for _, r := range lc.Releases {
+			if r.OS == "windows" {
+				windowsExt = r.Ext
+			}
+		}
+		if windowsExt != ".exe" {
+			t.Errorf("ffmpeg windows ext = %q, want %q", windowsExt, ".exe")
+		}
+	})
+
+	t.Run("ffmpeg_translation_not_applied_to_other_packages", func(t *testing.T) {
+		// The ffmpeg .gz→.exe translation is package-specific.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "othertool-windows-amd64.gz", OS: "windows", Arch: "x86_64", Format: ".gz"},
+			},
+		}
+		lc, _ := storage.ExportLegacy("othertool", pd)
+		if len(lc.Releases) != 1 {
+			t.Fatalf("releases = %d, want 1", len(lc.Releases))
+		}
+		if lc.Releases[0].Ext != ".gz" {
+			t.Errorf("ext = %q, want %q (no translation outside ffmpeg)", lc.Releases[0].Ext, ".gz")
+		}
+	})
+
+	t.Run("universal2_passes_through", func(t *testing.T) {
+		// universal2 (x86_64 + ARM64 fat binary) is kept as-is in the legacy
+		// cache. The Node.js side handles resolution via its WATERFALL/CompatArches.
+		pd := storage.PackageData{
+			Assets: []storage.Asset{
+				{Filename: "hugo_0.145.0_darwin-universal.tar.gz", OS: "darwin", Arch: "universal2", Format: ".tar.gz"},
+			},
+		}
+		lc, stats := storage.ExportLegacy("hugo", pd)
+		if stats.Variants != 0 || stats.Formats != 0 {
+			t.Errorf("unexpected drops: variants=%d formats=%d", stats.Variants, stats.Formats)
+		}
+		if len(lc.Releases) != 1 {
+			t.Fatalf("releases = %d, want 1", len(lc.Releases))
+		}
+		if lc.Releases[0].Arch != "universal2" {
+			t.Errorf("arch = %q, want %q", lc.Releases[0].Arch, "universal2")
+		}
+	})
+}
+
+// TestExportLegacyMixed verifies correct counting when multiple drop/translate
+// categories appear together in a single export call.
+func TestExportLegacyMixed(t *testing.T) {
+	pd := storage.PackageData{
+		Assets: []storage.Asset{
+			// kept: baseline linux build
+			{Filename: "tool-linux-amd64.tar.gz", OS: "linux", Arch: "x86_64", Format: ".tar.gz"},
+			// dropped: variant build
+			{Filename: "tool-linux-amd64-rocm.tar.gz", OS: "linux", Arch: "x86_64", Format: ".tar.gz", Variants: []string{"rocm"}},
+			// dropped: .apk format
+			{Filename: "tool.apk", OS: "android", Format: ".apk"},
+			// kept: illumos (translated to sunos)
+			{Filename: "tool-illumos-amd64.tar.gz", OS: "illumos", Arch: "x86_64", Format: ".tar.gz"},
+		},
+	}
+	lc, stats := storage.ExportLegacy("tool", pd)
+
+	if stats.Variants != 1 {
+		t.Errorf("Variants = %d, want 1", stats.Variants)
+	}
+	if stats.Formats != 1 {
+		t.Errorf("Formats = %d, want 1", stats.Formats)
+	}
+	if len(lc.Releases) != 2 {
+		t.Errorf("releases = %d, want 2 (linux + sunos)", len(lc.Releases))
+	}
+
+	// Verify the illumos → sunos translation was applied.
+	var foundSunos bool
+	for _, r := range lc.Releases {
+		if r.OS == "sunos" {
+			foundSunos = true
+		}
+		if r.OS == "illumos" {
+			t.Error("illumos should have been translated to sunos")
+		}
+	}
+	if !foundSunos {
+		t.Error("expected a sunos release (translated from illumos)")
+	}
+}
+
 // TestDecodeLegacyJSON verifies we can parse the exact JSON format
 // the Node.js server writes to _cache/.
 func TestDecodeLegacyJSON(t *testing.T) {