fix: pre-v0.1 review feedback (#14)

* fix(sdk-android): add @JvmOverloads to Uatu.start

Java callers can now invoke start(application) without supplying a
Configuration, matching the Kotlin default-arg ergonomics.

* feat(agent): add protocol_version to HELLO handshake

ProtocolVersion=1 lives on Message and is set by Hello(). Server.Accept
rejects mismatches with a clear error. SDK upgrades that don't change
the wire format keep the same protocol_version; bump on breaking changes.

* test(agent): assert protocol_version in Hello round-trip

* feat(sdk-android): send protocol_version=1 in HELLO

Mirrors agent.ProtocolVersion on the Go side. Bump in lockstep with
the Go constant when the wire format breaks.

* chore(sample-app): pull @uatu/spec from npm next tag

Replaces the file: dep. Copy-paste users can now npm install against
the registry. The release workflow publishes pre-release tags to
npm dist-tag 'next', so the sample tracks the latest rc without
manual version bumps. Lockfile currently resolves to 0.0.1-rc3.

sdk/android/src/main/kotlin/dev/uatu/sdk/Protocol.kt

@@ -26,6 +26,7 @@ enum class MessageType(val wire: String) {
 data class Message(
     val type: MessageType,
     val id: Long = 0L,
+    val protocolVersion: Int = 0,
     val version: String? = null,
     val platform: String? = null,
     val appPackage: String? = null,
@@ -37,7 +38,13 @@ data class Message(
 ) {
     companion object {
         fun hello(version: String, platform: String, appPackage: String): Message =
-            Message(MessageType.HELLO, version = version, platform = platform, appPackage = appPackage)
+            Message(
+                MessageType.HELLO,
+                protocolVersion = Protocol.PROTOCOL_VERSION,
+                version = version,
+                platform = platform,
+                appPackage = appPackage,
+            )
 
         fun pause(id: Long): Message = Message(MessageType.PAUSE, id = id)
 
@@ -56,6 +63,9 @@ data class Message(
 object Protocol {
     const val MAX_FRAME_SIZE: Int = 16 * 1024 * 1024
 
+    // Wire-format version. Must match agent.ProtocolVersion on the Go side.
+    const val PROTOCOL_VERSION: Int = 1
+
     @Throws(IOException::class)
     fun write(output: OutputStream, message: Message) {
         val bytes = toJson(message).toString().toByteArray(Charsets.UTF_8)
@@ -85,6 +95,7 @@ object Protocol {
         val json = JSONObject()
         json.put("type", message.type.wire)
         if (message.id != 0L) json.put("id", message.id)
+        if (message.protocolVersion != 0) json.put("protocol_version", message.protocolVersion)
         message.version?.let { json.put("version", it) }
         message.platform?.let { json.put("platform", it) }
         message.appPackage?.let { json.put("app_package", it) }
@@ -108,6 +119,7 @@ object Protocol {
         return Message(
             type = MessageType.fromWire(typeString),
             id = json.optLong("id", 0L),
+            protocolVersion = json.optInt("protocol_version", 0),
             version = json.optStringOrNull("version"),
             platform = json.optStringOrNull("platform"),
             appPackage = json.optStringOrNull("app_package"),

sdk/android/src/main/kotlin/dev/uatu/sdk/Uatu.kt

@@ -14,6 +14,7 @@ object Uatu {
 
     @Volatile private var runtime: UatuRuntime? = null
 
+    @JvmOverloads
     @Synchronized
     fun start(application: Application, configuration: Configuration = Configuration()) {
         if (runtime != null) return

sdk/android/src/test/kotlin/dev/uatu/sdk/ProtocolTest.kt

@@ -24,6 +24,7 @@ class ProtocolTest {
     @Test fun roundTripHello() {
         val got = roundTrip(Message.hello("0.0.1", "android", "in.okcredit.merchant"))
         assertEquals(MessageType.HELLO, got.type)
+        assertEquals(Protocol.PROTOCOL_VERSION, got.protocolVersion)
         assertEquals("0.0.1", got.version)
         assertEquals("android", got.platform)
         assertEquals("in.okcredit.merchant", got.appPackage)
@@ -140,6 +141,7 @@ class ProtocolTest {
         Protocol.write(output, Message.hello("0.0.1", "android", "com.x"))
         val payload = String(output.toByteArray().copyOfRange(4, output.size()), Charsets.UTF_8)
         assertTrue(payload.contains("\"type\":\"HELLO\""))
+        assertTrue(payload.contains("\"protocol_version\":1"))
         assertTrue(payload.contains("\"version\":\"0.0.1\""))
         assertTrue(payload.contains("\"platform\":\"android\""))
         assertTrue(payload.contains("\"app_package\":\"com.x\""))