Harden private media migration compatibility

bitchatTests/Services/BLENoisePayloadFactoryTests.swift

@@ -1,5 +1,6 @@
 import Foundation
 import Testing
+import BitFoundation
 @testable import bitchat
 
 struct BLENoisePayloadFactoryTests {
@@ -44,10 +45,38 @@ struct BLENoisePayloadFactoryTests {
 
         let payload = try #require(BLENoisePayloadFactory.privateFile(file))
 
-        #expect(payload.first == NoisePayloadType.privateFile.rawValue)
+        #expect(payload.first == 0x20, "Encrypted files must use Android's deployed wire value")
         let decoded = try #require(BitchatFilePacket.decode(Data(payload.dropFirst())))
         #expect(decoded.fileName == "secret.pdf")
         #expect(decoded.mimeType == "application/pdf")
         #expect(decoded.content == content)
     }
+
+    @Test
+    func androidB7f0b33PrivateFilePlaintextFixtureIsByteCompatible() throws {
+        // Runtime-emitted by Android commit b7f0b33d from
+        // BitchatFilePacket("a.txt", 3, "text/plain", [01, 02, 03]) and
+        // NoisePayload(type = FILE_TRANSFER, data = file.encode()).encode().
+        let fixtureHex = "20010005612e7478740200040000000303000a746578742f706c61696e0400000003010203"
+        let fixture = try #require(Data(hexString: fixtureHex))
+
+        let typed = try #require(NoisePayload.decode(fixture))
+        #expect(typed.type == .privateFile)
+        let file = try #require(BitchatFilePacket.decode(typed.data))
+        #expect(file.fileName == "a.txt")
+        #expect(file.fileSize == 3)
+        #expect(file.mimeType == "text/plain")
+        #expect(file.content == Data([0x01, 0x02, 0x03]))
+        #expect(BLENoisePayloadFactory.privateFile(file) == fixture)
+    }
+
+    @Test
+    func prereleasePrivateFileTypeCanonicalizesOnDecode() throws {
+        let encoded = Data([NoisePayloadType.prereleasePrivateFileRawValue, 0xCA, 0xFE])
+        let decoded = try #require(NoisePayload.decode(encoded))
+
+        #expect(decoded.type == .privateFile)
+        #expect(decoded.data == Data([0xCA, 0xFE]))
+        #expect(decoded.encode().first == 0x20)
+    }
 }