fix(replay): split uploads at session and identity boundaries

[dustinbyrne]

💡 Motivation and Context

Replay ingestion attributes an entire /s/ request to its first snapshot's session and distinct ID. Android's persisted replay queue could batch snapshots across those boundaries, filing a new session's opening frames under the preceding session after an app restart.

This ports the batching fix released in posthog-ios 3.88.2:

• Split replay requests when either the session ID or distinct ID changes.
• Send contiguous groups sequentially within the original count-limited flush window, preserving FIFO.
• Delete only completed or terminally rejected groups; retain a retryable failed group and all unsent groups.
• Keep analytics/log batching, public APIs, and configuration defaults unchanged.

This preserves the existing event-batcher specification and implements the replay-attribution contract proposed in sdk-specs #92, which is still open. Patch changesets cover posthog and posthog-android.

💚 How did you test it?

Local validation with JDK 17:

• Added 10 wire-level queue tests using MockWebServer, including session/identity boundaries, persisted restart, count limits, threshold flushes, retry retention, terminal errors, HTTP 413, corrupt records, and unchanged analytics batching. Eight boundary tests fail on the unchanged base; all ten pass with the fix.
• make testJava: all 1,022 core tests passed.
• make checkFormat: passed.
• ./gradlew :posthog:apiCheck :posthog-android:apiCheck :posthog-android:compileReleaseKotlin: passed.
• Fresh read-only independent review: no findings.

Validation is at the queue/HTTP layer. Android device kill/relaunch and Cloud ingestion/playback have not been tested.

📝 Checklist

• Reviewed the submitted code.
• Added regression tests.
• No public API or configuration-default changes.
• Added patch changesets for the core and Android packages.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Pi implemented the Android port, with a fresh read-only reviewer agent checking the diff, callers, retry/lifecycle behavior, and tests. Tools used: read, edit, write, bash, and subagent. The implementation keeps replay attribution policy in the existing endpoint specification and reuses the shared durable queue and retry handling.

[greptile-apps]

[Medium risk] Changes how session replay batches are split and sent.

The PR appears safe to merge; no actionable issues were found.

_{Reviews (1) · Last reviewed commit: "fix(replay): split uploads at session an..."}

[github-actions]

posthog-android Compliance Report

Date: 2026-10-03 02:12:49 UTC
Duration: 117774ms

✅ All Tests Passed!

46/46 tests passed

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Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	245ms
Format Validation.Event Has Uuid	✅	19ms
Format Validation.Event Has Lib Properties	✅	21ms
Format Validation.Distinct Id Is String	✅	17ms
Format Validation.Token Is Present	✅	17ms
Format Validation.Custom Properties Preserved	✅	16ms
Format Validation.Event Has Timestamp	✅	19ms
Retry Behavior.Retries On 503	✅	7022ms
Retry Behavior.Does Not Retry On 400	✅	4017ms
Retry Behavior.Does Not Retry On 401	✅	4018ms
Retry Behavior.Respects Retry After Header	✅	7022ms
Retry Behavior.Implements Backoff	✅	17030ms
Retry Behavior.Retries On 500	✅	7017ms
Retry Behavior.Retries On 502	✅	7016ms
Retry Behavior.Retries On 504	✅	7017ms
Retry Behavior.Max Retries Respected	✅	17019ms
Deduplication.Generates Unique Uuids	✅	40ms
Deduplication.Preserves Uuid On Retry	✅	7012ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	12017ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7017ms
Deduplication.No Duplicate Events In Batch	✅	25ms
Deduplication.Different Events Have Different Uuids	✅	16ms
Compression.Sends Gzip When Enabled	✅	11ms
Batch Format.Uses Proper Batch Structure	✅	11ms
Batch Format.Flush With No Events Sends Nothing	✅	8ms
Batch Format.Multiple Events Batched Together	✅	23ms
Error Handling.Does Not Retry On 403	✅	4016ms
Error Handling.Does Not Retry On 413	✅	4013ms
Error Handling.Retries On 408	✅	5020ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	22ms
Request Payload.Flags Request Uses V2 Query Param	✅	15ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	17ms
Request Payload.Flags Request Omits Authorization Header	✅	15ms
Request Payload.Token In Flags Body Matches Init	✅	14ms
Request Payload.Groups Round Trip	✅	16ms
Request Payload.Groups Default To Empty Object	✅	18ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	25ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	15ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	15ms
Request Lifecycle.No Flags Request On Init Alone	✅	5ms
Request Lifecycle.No Flags Request On Normal Capture	✅	12ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	26ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	12ms
Retry Behavior.Retries Flags On 502	✅	313ms
Retry Behavior.Retries Flags On 504	✅	315ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	14ms