feat(capability): 转码能力包（vendor 纯 Go AMR-NB 解码器 + 黄金向量逐样本对照 + 8 哨兵 + 注册面）

internal/capability/transcode/format_test.go

@@ -0,0 +1,73 @@
+package transcode
+
+import "testing"
+
+// TestFormatOfNormalizes 断言「字符串 → Format」只有一处转换，且归一化口径稳定：
+// 去空白、转小写、去前导点（design/25 §6.2：与 mediafetch.AudioFormatOf 同源）。
+func TestFormatOfNormalizes(t *testing.T) {
+	cases := map[string]Format{
+		"amr":    FormatAMR,
+		".amr":   FormatAMR,
+		"AMR":    FormatAMR,
+		"  .AmR": FormatAMR,
+		"wav":    FormatWAV,
+		".WAV":   FormatWAV,
+		"":       Format(""),
+	}
+	for in, want := range cases {
+		if got := FormatOf(in); got != want {
+			t.Errorf("FormatOf(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+// TestFormatName 断言 FormatName 是 FormatOf 的逆（对已归一的格式名）。
+func TestFormatName(t *testing.T) {
+	for _, f := range []Format{FormatAMR, FormatAMRWB, FormatWAV} {
+		if got := FormatOf(FormatName(f)); got != f {
+			t.Errorf("FormatOf(FormatName(%q)) = %q, want %q", f, got, f)
+		}
+	}
+}
+
+// TestSniff 断言魔数嗅探：认得出（AMR-NB / AMR-WB / WAV）、嗅不出即 false
+// （deny-by-default）。
+func TestSniff(t *testing.T) {
+	riffWAV := append([]byte("RIFF\x24\x00\x00\x00WAVE"), make([]byte, 8)...)
+	cases := []struct {
+		name string
+		data []byte
+		want Format
+		ok   bool
+	}{
+		{"amr-nb magic", []byte(amrNBMagic), FormatAMR, true},
+		{"amr-nb stream", amrStubBytes(0x3c, 1, 2, 3), FormatAMR, true},
+		{"amr-wb magic", []byte(amrWBMagic), FormatAMRWB, true},
+		{"wav", riffWAV, FormatWAV, true},
+		{"empty", nil, "", false},
+		{"short", []byte("#!AM"), "", false},
+		{"text", []byte("hello world"), "", false},
+		{"riff without wave", []byte("RIFF\x24\x00\x00\x00AVI "), "", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, ok := Sniff(tc.data)
+			if ok != tc.ok || got != tc.want {
+				t.Fatalf("Sniff = (%q, %v), want (%q, %v)", got, ok, tc.want, tc.ok)
+			}
+		})
+	}
+}
+
+// TestAMRWBMagicIsRecognizedButUnsupported 断言「认得出但没这条路」：
+// AMR-WB 的魔数能被嗅出（报错因此能说清问题），但注册表里没有它 →
+// ErrUnsupportedFormat（design/25 §3.3 后置）。
+func TestAMRWBMagicIsRecognizedButUnsupported(t *testing.T) {
+	eng := NewEngine(DefaultLimits(), WithCodecs(DefaultCodecs()...))
+	if got, ok := Sniff([]byte(amrWBMagic)); !ok || got != FormatAMRWB {
+		t.Fatalf("Sniff(amr-wb) = (%q, %v)", got, ok)
+	}
+	if eng.Supports(FormatAMRWB, FormatWAV) {
+		t.Fatalf("amr-wb -> wav must stay unsupported this round")
+	}
+}