From 1a174548cca921a6136bfe7b1c3a4190ec1f5eda Mon Sep 17 00:00:00 2001
From: Kenneth Yeh <kenneth.yeh@amplitude.com>
Date: Thu, 7 May 2026 22:50:41 -0700
Subject: [PATCH] fix: include experiment key on local-eval exposure events
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Set [Experiment] Experiment Key on exposure event properties when
variant.metadata["experimentKey"] is present, so proxy-emitted
exposures are run-aware when a flag is reused across experiment runs.

Mirrors the same change in experiment-jvm-server#53 and
experiment-node-server#83. Additive only — metadata blob, flag key,
variant, user properties, and insertId are unchanged.
---
 .../main/kotlin/exposure/ExposureTracker.kt   |  4 +++
 .../kotlin/exposure/ExposureTrackerTest.kt    | 31 +++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/core/src/main/kotlin/exposure/ExposureTracker.kt b/core/src/main/kotlin/exposure/ExposureTracker.kt
index a2fdc63..071b450 100644
--- a/core/src/main/kotlin/exposure/ExposureTracker.kt
+++ b/core/src/main/kotlin/exposure/ExposureTracker.kt
@@ -108,6 +108,10 @@ internal fun Exposure.toAmplitudeEvents(): List<Event> {
                 if (variant.key != null) {
                     put("[Experiment] Variant", variant.key)
                 }
+                val experimentKey = variant.metadata?.get("experimentKey") as? String
+                if (experimentKey != null) {
+                    put("[Experiment] Experiment Key", experimentKey)
+                }
                 if (variant.metadata != null) {
                     put("metadata", JSONObject(variant.metadata))
                 }
diff --git a/core/src/test/kotlin/exposure/ExposureTrackerTest.kt b/core/src/test/kotlin/exposure/ExposureTrackerTest.kt
index 22a234f..6c15752 100644
--- a/core/src/test/kotlin/exposure/ExposureTrackerTest.kt
+++ b/core/src/test/kotlin/exposure/ExposureTrackerTest.kt
@@ -55,6 +55,37 @@ class ExposureTrackerTest {
             }
         }
 
+    @Test
+    fun `test exposure includes experiment key when present in metadata`() =
+        runBlocking {
+            val context = user(userId = "user", deviceId = "device").toEvaluationContext()
+            val results =
+                mapOf(
+                    "with-exp-key" to
+                        EvaluationVariant(
+                            key = "treatment",
+                            metadata = mapOf("deployed" to true, "experimentKey" to "exp-1"),
+                        ),
+                    "without-exp-key" to
+                        EvaluationVariant(
+                            key = "on",
+                            metadata = mapOf("deployed" to true),
+                        ),
+                )
+            val exposure = Exposure(context, results)
+            val events = exposure.toAmplitudeEvents()
+
+            Assert.assertEquals(2, events.size)
+            for (event in events) {
+                val flagKey = event.eventProperties.getString("[Experiment] Flag Key")
+                if (flagKey == "with-exp-key") {
+                    Assert.assertEquals("exp-1", event.eventProperties.getString("[Experiment] Experiment Key"))
+                } else {
+                    Assert.assertFalse(event.eventProperties.has("[Experiment] Experiment Key"))
+                }
+            }
+        }
+
     @Test
     fun `test exposure skips default variants`() =
         runBlocking {