fix: send fingerprint_version on referrer attribution path

The Play Install Referrer (deterministic) attribution request omitted
fingerprint_version, which the attribution API requires on every request.
The request was rejected with a 400 validation error, so referrer-based
re-engagement matches never landed. buildAttributionBody now sends
fingerprint_version "basic" on the referrer branch.

Adds a regression test for the referrer and enriched body shapes, derives
the FingerprintCollector User-Agent assertion from SDK_VERSION, and bumps
SDK_VERSION to 0.1.1.

Author: WarpLink

CHANGELOG.md

@@ -5,7 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [0.1.0] - Unreleased
+## [Unreleased]
+
+### Fixed
+
+- Referrer-based (Play Install Referrer) install attribution now sends the
+  required `fingerprint_version` field. The deterministic referrer path
+  previously omitted it, so the attribution API rejected the request with a
+  400 validation error and re-engagement matches never landed.
+
+## [0.1.0] - 2026-05-16
 
 ### Added
 

sdk/src/main/kotlin/app/warplink/WarpLink.kt

@@ -13,7 +13,7 @@ import app.warplink.internal.performDeferredCheck
 
 object WarpLink {
 
-    const val SDK_VERSION = "0.1.0"
+    const val SDK_VERSION = "0.1.1"
 
     private val lock = Any()
     private var apiKey: String? = null

sdk/src/main/kotlin/app/warplink/internal/ApiClient.kt

@@ -188,7 +188,8 @@ internal class ApiClient(
         )
     }
 
-    private fun buildAttributionBody(
+    // internal (not private) so unit tests can assert the wire-body contract.
+    internal fun buildAttributionBody(
         signals: DeviceSignals?,
         sdkVersion: String,
         deviceId: String?,
@@ -202,6 +203,9 @@ internal class ApiClient(
         }
         if (referrer != null) {
             body.put("referrer", referrer)
+            // Schema requires fingerprint_version on every request; the
+            // deterministic referrer path carries no enriched signals.
+            body.put("fingerprint_version", "basic")
             return body
         }
         if (signals != null) {

sdk/src/test/kotlin/app/warplink/internal/ApiClientAttributionBodyTest.kt

@@ -0,0 +1,36 @@
+package app.warplink.internal
+
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import kotlin.test.assertEquals
+
+/**
+ * The server's attributionMatchSchema requires fingerprint_version on every
+ * POST /attribution/match request, including the deterministic Play Install
+ * Referrer path (it has no enriched signals but must still send the field, or
+ * the API rejects the request with a 400 validation error).
+ */
+@RunWith(RobolectricTestRunner::class)
+class ApiClientAttributionBodyTest {
+
+    private val client = ApiClient(
+        "wl_test_abcdefghijklmnopqrstuvwxyz012345",
+        "http://localhost:1"
+    )
+    private val linkId = "a1b2c3d4-e5f6-4a7b-8c9d-0e1f2a3b4c5d"
+
+    @Test
+    fun `referrer body includes required fingerprint_version`() {
+        val body = client.buildAttributionBody(null, "0.1.0", null, linkId)
+        assertEquals(linkId, body.getString("referrer"))
+        assertEquals("basic", body.getString("fingerprint_version"))
+    }
+
+    @Test
+    fun `enriched signals body includes fingerprint_version`() {
+        val signals = DeviceSignals("en-US", 1080, 1920, -300, "ua")
+        val body = client.buildAttributionBody(signals, "0.1.0", null, null)
+        assertEquals("enriched", body.getString("fingerprint_version"))
+    }
+}

sdk/src/test/kotlin/app/warplink/internal/FingerprintCollectorTest.kt

@@ -1,6 +1,7 @@
 package app.warplink.internal
 
 import androidx.test.core.app.ApplicationProvider
+import app.warplink.WarpLink
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.robolectric.RobolectricTestRunner
@@ -63,6 +64,6 @@ class FingerprintCollectorTest {
         )
         var signals: DeviceSignals? = null
         collector.collectFingerprint { r -> signals = r.getOrNull() }
-        assertEquals("WarpLink-Android/0.1.0", signals!!.userAgent)
+        assertEquals("WarpLink-Android/${WarpLink.SDK_VERSION}", signals!!.userAgent)
     }
 }