From f9d76b23412a42937ac7ca28113556c16015d315 Mon Sep 17 00:00:00 2001
From: Taylor Lanclos <lanclos@google.com>
Date: Wed, 4 Mar 2026 19:12:16 +0000
Subject: [PATCH] Extract timestamp as double for InMemorySessionService events

InMemorySessionService sets a Session's last modified time based on when
the last appended event's timestamp. The timestamp in an event is
recorded in millis while the Session's timestamp is an Instant. During
the transformation, Events perform this converstion using division.
Before this change, the timestamp was truncated to the second, yet the
code was trying to extract nanos which were always 0. This fixes that
bug with a simple type change. I've also added a test to prevent
regressions.
---
 .../adk/sessions/InMemorySessionService.java  |  4 ++--
 .../sessions/InMemorySessionServiceTest.java  | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/com/google/adk/sessions/InMemorySessionService.java b/core/src/main/java/com/google/adk/sessions/InMemorySessionService.java
index b2a584b11..da338ed57 100644
--- a/core/src/main/java/com/google/adk/sessions/InMemorySessionService.java
+++ b/core/src/main/java/com/google/adk/sessions/InMemorySessionService.java
@@ -163,8 +163,8 @@ public Maybe<Session> getSession(
   }
 
   // Helper to get event timestamp as epoch seconds
-  private long getEventTimestampEpochSeconds(Event event) {
-    return event.timestamp() / 1000L;
+  private double getEventTimestampEpochSeconds(Event event) {
+    return event.timestamp() / 1000.0;
   }
 
   @Override
diff --git a/core/src/test/java/com/google/adk/sessions/InMemorySessionServiceTest.java b/core/src/test/java/com/google/adk/sessions/InMemorySessionServiceTest.java
index 41e156ffd..0d9235b1b 100644
--- a/core/src/test/java/com/google/adk/sessions/InMemorySessionServiceTest.java
+++ b/core/src/test/java/com/google/adk/sessions/InMemorySessionServiceTest.java
@@ -20,6 +20,7 @@
 import com.google.adk.events.Event;
 import com.google.adk.events.EventActions;
 import io.reactivex.rxjava3.core.Single;
+import java.time.Instant;
 import java.util.HashMap;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
@@ -214,6 +215,24 @@ public void appendEvent_removesState() {
     assertThat(retrievedSessionRemove.state()).doesNotContainKey("temp:tempKey");
   }
 
+  @Test
+  public void appendEvent_updatesSessionTimestampWithFractionalSeconds() {
+    InMemorySessionService sessionService = new InMemorySessionService();
+    Session session =
+        sessionService.createSession("app", "user", new HashMap<>(), "session1").blockingGet();
+
+    // Add an event with a timestamp that contains a fractional second
+    Event eventAdd = Event.builder().timestamp(5500).build();
+    var unused = sessionService.appendEvent(session, eventAdd).blockingGet();
+
+    // Verify the last modified timestamp contains a fractional second
+    Session retrievedSession =
+        sessionService
+            .getSession(session.appName(), session.userId(), session.id(), Optional.empty())
+            .blockingGet();
+    assertThat(retrievedSession.lastUpdateTime()).isEqualTo(Instant.ofEpochSecond(5, 500000000L));
+  }
+
   @Test
   public void sequentialAgents_shareTempState() {
     InMemorySessionService sessionService = new InMemorySessionService();