Detect a live LiveTrack session from its last point, not session["end"]

session["end"].nil? was the active signal since this was first built,
on the assumption Garmin leaves it unset until the activity actually
stops. Checked directly against a real still-recording session today
(2026-09-20): end was already non-nil, set to exactly start + 24h — the
share link's own expiry, not an end time — so every currently-active
session was showing as "Ended". A genuinely ended session's end does
hold its real end time (confirmed against the 2026-09-06 session this
was originally, and only, verified against), which is what made the
bug easy to miss.

Recency of the last track point is a directly-observable signal
instead of reverse-engineering what a given `end` value means: Garmin
posts one roughly every postTrackPointFrequency seconds (~15, observed)
while genuinely still recording.

test/test_livetrack_client.rb

@@ -49,13 +49,22 @@ class LiveTrackClientTest < Minitest::Test
     assert_equal "Test Ride", summary["session_name"]
     assert_equal "CYCLING", summary["activity_type"]
     assert_equal 5000, summary["distance_meters"]
-    refute summary["active"], "session has an end timestamp"
+    refute summary["active"], "last track point is long in the past"
   end
 
-  def test_summarize_marks_active_when_session_has_no_end
+  # Not session["end"].nil? (the original signal, before 2026-09-20 — see
+  # LiveTrackClient's own comment): verified live against a real,
+  # still-recording session that day, Garmin had already set `end` to
+  # exactly start + 24h (the share link's own expiry, not an end time),
+  # so that check called an active session "ended".
+  def test_summarize_marks_active_when_last_point_is_recent
     payloads = @client.send(:parse_payloads, FAKE_PAGE)
     points = @client.send(:clean, @client.send(:search, payloads) { |n| n["trackPoints"] if n["trackPoints"].is_a?(Array) })
-    session = @client.send(:clean, @client.send(:search, payloads) { |n| n if n["sessionName"] }).merge("end" => nil)
+    points[-1] = points[-1].merge("dateTime" => Time.now.utc.iso8601)
+    # end present and in the future, same shape Garmin actually sends for a
+    # session that's still live — active must come from the point, not this.
+    session = @client.send(:clean, @client.send(:search, payloads) { |n| n if n["sessionName"] })
+                      .merge("end" => (Time.now.utc + 24 * 60 * 60).iso8601)
     result = Maptool::LiveTrackClient::Result.new(points: points, session: session)
 
     assert Maptool::LiveTrackClient.summarize(result)["active"]