fix(replay): Preserve segment ID after buffer-to-session conversion

After a buffer-to-session conversion, the replay type stays BUFFER
but the segment counter reflects the real sequence. If the app
crashes and finalizePreviousReplay recovers the last segment,
fromDisk() was normalizing the segment ID to 0 for all BUFFER
replays, creating a duplicate segment 0 that overwrites the original.

Add a persisted isFlushed flag set when the buffer is successfully
flushed. fromDisk() now only normalizes to 0 when the buffer was
never flushed (no segments were ever sent to the server).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: romtsn

sentry-android-replay/src/main/java/io/sentry/android/replay/ReplayCache.kt

@@ -317,6 +317,7 @@ public class ReplayCache(private val options: SentryOptions, private val replayI
     internal const val SEGMENT_KEY_REPLAY_SCREEN_AT_START = "replay.screen-at-start"
     internal const val SEGMENT_KEY_REPLAY_RECORDING = "replay.recording"
     internal const val SEGMENT_KEY_ID = "segment.id"
+    internal const val SEGMENT_KEY_FLUSHED = "replay.flushed"
 
     fun makeReplayCacheDir(options: SentryOptions, replayId: SentryId): File? =
       if (options.cacheDirPath.isNullOrEmpty()) {
@@ -415,8 +416,11 @@ public class ReplayCache(private val options: SentryOptions, private val replayI
       }
 
       cache.frames.sortBy { it.timestamp }
-      // TODO: this should be removed when we start sending buffered segments on next launch
-      val normalizedSegmentId = if (replayType == SESSION) segmentId else 0
+      val wasFlushed = lastSegment[SEGMENT_KEY_FLUSHED]?.toBooleanStrictOrNull() == true
+      // In buffer mode, if the buffer was never flushed (no error triggered captureReplay),
+      // no segments were ever sent, so we normalize to 0. After a flush + conversion to
+      // session mode, the persisted segmentId is the real sequence number.
+      val normalizedSegmentId = if (replayType == SESSION || wasFlushed) segmentId else 0
       val normalizedTimestamp =
         if (replayType == SESSION) {
           segmentTimestamp

sentry-android-replay/src/main/java/io/sentry/android/replay/ReplayIntegration.kt

@@ -261,6 +261,7 @@ public class ReplayIntegration(
       onSegmentSent = { newTimestamp ->
         captureStrategy?.currentSegment = captureStrategy?.currentSegment!! + 1
         captureStrategy?.segmentTimestamp = newTimestamp
+        captureStrategy?.isFlushed = true
       },
     )
     captureStrategy = captureStrategy?.convert()

sentry-android-replay/src/main/java/io/sentry/android/replay/capture/BaseCaptureStrategy.kt

@@ -13,6 +13,7 @@ import io.sentry.SentryReplayEvent.ReplayType.BUFFER
 import io.sentry.SentryReplayEvent.ReplayType.SESSION
 import io.sentry.android.replay.ReplayCache
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_BIT_RATE
+import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_FLUSHED
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_FRAME_RATE
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_HEIGHT
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_ID
@@ -89,6 +90,8 @@ internal abstract class BaseCaptureStrategy(
     get() = cache?.replayCacheDir
 
   override var replayType by persistableAtomic<ReplayType>(propertyName = SEGMENT_KEY_REPLAY_TYPE)
+  override var isFlushed: Boolean by
+    persistableAtomic(initialValue = false, propertyName = SEGMENT_KEY_FLUSHED)
 
   protected val currentEvents: Deque<RRWebEvent> = ConcurrentLinkedDeque()
   private val traceIdsLock = Any()

sentry-android-replay/src/main/java/io/sentry/android/replay/capture/BufferCaptureStrategy.kt

@@ -105,7 +105,6 @@ internal class BufferCaptureStrategy(
 
       if (segment is ReplaySegment.Created) {
         segment.capture(scopes)
-
         // we only want to increment segment_id in the case of success, but currentSegment
         // might be irrelevant since we changed strategies, so in the callback we increment
         // it on the new strategy already

sentry-android-replay/src/main/java/io/sentry/android/replay/capture/CaptureStrategy.kt

@@ -29,6 +29,7 @@ internal interface CaptureStrategy {
   val replayCacheDir: File?
   var replayType: ReplayType
   var segmentTimestamp: Date?
+  var isFlushed: Boolean
 
   fun start(segmentId: Int = 0, replayId: SentryId = SentryId(), replayType: ReplayType? = null)
 

sentry-android-replay/src/test/java/io/sentry/android/replay/ReplayCacheTest.kt

@@ -9,6 +9,7 @@ import io.sentry.SentryOptions
 import io.sentry.SentryReplayEvent.ReplayType
 import io.sentry.android.replay.ReplayCache.Companion.ONGOING_SEGMENT
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_BIT_RATE
+import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_FLUSHED
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_FRAME_RATE
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_HEIGHT
 import io.sentry.android.replay.ReplayCache.Companion.SEGMENT_KEY_ID
@@ -443,7 +444,7 @@ class ReplayCacheTest {
   }
 
   @Test
-  fun `sets segmentId to 0 for buffer mode`() {
+  fun `sets segmentId to 0 for buffer mode when not flushed`() {
     fixture.options.run { cacheDirPath = tmpDir.newFolder()?.absolutePath }
     val replayId = SentryId()
     val replayCacheFolder =
@@ -474,6 +475,39 @@ class ReplayCacheTest {
     assertEquals(0, lastSegment.id)
   }
 
+  @Test
+  fun `preserves segmentId for buffer mode when already flushed`() {
+    fixture.options.run { cacheDirPath = tmpDir.newFolder()?.absolutePath }
+    val replayId = SentryId()
+    val replayCacheFolder =
+      File(fixture.options.cacheDirPath!!, "replay_$replayId").also { it.mkdirs() }
+    File(replayCacheFolder, ONGOING_SEGMENT).also {
+      it.writeText(
+        """
+                $SEGMENT_KEY_HEIGHT=912
+                $SEGMENT_KEY_WIDTH=416
+                $SEGMENT_KEY_FRAME_RATE=1
+                $SEGMENT_KEY_BIT_RATE=75000
+                $SEGMENT_KEY_ID=5
+                $SEGMENT_KEY_TIMESTAMP=2024-07-11T10:25:21.454Z
+                $SEGMENT_KEY_REPLAY_TYPE=BUFFER
+                $SEGMENT_KEY_FLUSHED=true
+                """
+          .trimIndent()
+      )
+    }
+
+    val screenshot = File(replayCacheFolder, "1720693523997.jpg").also { it.createNewFile() }
+    screenshot.outputStream().use {
+      Bitmap.createBitmap(1, 1, ARGB_8888).compress(JPEG, 80, it)
+      it.flush()
+    }
+
+    val lastSegment = ReplayCache.fromDisk(fixture.options, replayId)!!
+
+    assertEquals(5, lastSegment.id)
+  }
+
   @Test
   fun `when screenshot is corrupted, deletes it immediately`() {
     ShadowBitmapFactory.setAllowInvalidImageData(false)