chore(logs): internal plumbing for upcoming logs feature

[turnipdabeets]

💡 Motivation and Context

Sets up the internal plumbing for the upcoming logs feature so that the
public-facing PR (next) is purely additive on top of a proven wire path.

Adds:

• PostHogLogRecord and PostHogLogSeverity (both internal)
• OTLP/JSON payload builder (PostHogLogsOTLP)
• PostHogApi.sendLogs(...) — POSTs to /i/v1/logs?token=<apiKey>
• EndpointSpec.logs(...) factory — wires a third PostHogQueue into
  PostHog.setup alongside events and replay

No public log() API in this PR — that lands in the follow-up,
along with PostHogLogsConfig (service.name / environment / beforeSend
hook), capture-time context snapshot (distinctId / sessionId / screen
name), and screen-name tracking via Application.ActivityLifecycleCallbacks.
That follow-up will carry the changeset and the version bump; this PR
ships zero runtime behavior change.

The logs queue is constructed but not started in setup() — nothing
can enqueue records yet, so spinning up the periodic flush timer would
waste a daemon thread. A one-line // logsQueue.start() marker sits in
PostHog.setup where it'll be uncommented when the public capture API
ships.

Worth noting for review:

• Retry policy for /i/v1/logs is narrower than /batch /
  /snapshot: 408, 429, and 5xx only. 3xx redirects aren't retried
  (would loop on a misconfigured host). Regression-guarded so events
  don't accidentally inherit the broader set.
• Wire format follows OTLP LogsService JSON
  (resourceLogs[].scopeLogs[].logRecords[]). Multi-record batches
  share a single resource + scope envelope, locked in by test.
• ABI delta: one synthetic constructor parameter on private PostHog(...)
  (unreachable from outside the class) plus two @PostHogInternal
  accessors for logsStoragePrefix. No public surface change.

💚 How did you test it?

• ./gradlew :posthog:test — OTLP shape, storage round-trip (both
  direct and through config.serializer), retry policy, multi-record
  batching, sendLogs 408 / 500, per-key collision rules,
  parameterized severity coverage
• ./gradlew :posthog-android:testDebugUnitTest
• ./gradlew :posthog:apiCheck — confirms ABI is additive
• ./gradlew spotlessCheck detekt

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file

[github-actions]

⚠️ 2 packages modified but this PR has no changeset

This is informational — the PR is not blocked. Click the triangle above to collapse, or push a fix and this comment will auto-delete.

Modified in this PR but no changeset added:

• posthog
• posthog-android

If this change should ship, run pnpm changeset and select a bump level.
If it isn't user-facing (refactor with no behavior change, internal tooling, generated files), no action needed.

[github-actions]

posthog-android Compliance Report

Date: 2026-05-20 13:54:30 UTC
Duration: 2822ms

⚠️ Some Tests Failed

0/16 tests passed, 16 failed

---

Feature_Flags Tests

⚠️ 0/16 tests passed, 16 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	286ms
Request Payload.Flags Request Uses V2 Query Param	❌	21ms
Request Payload.Flags Request Hits Flags Path Not Decide	❌	25ms
Request Payload.Flags Request Omits Authorization Header	❌	28ms
Request Payload.Token In Flags Body Matches Init	❌	16ms
Request Payload.Groups Round Trip	❌	16ms
Request Payload.Groups Default To Empty Object	❌	14ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	❌	14ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	❌	16ms
Request Payload.Disable Geoip Omitted Defaults To False	❌	15ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	❌	14ms
Request Lifecycle.No Flags Request On Init Alone	❌	12ms
Request Lifecycle.No Flags Request On Normal Capture	❌	2045ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	❌	15ms
Request Lifecycle.Mock Response Value Is Returned To Caller	❌	13ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	❌	13ms

Failures

request_payload.request_with_person_properties_device_id

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_uses_v2_query_param

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_hits_flags_path_not_decide

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flags_request_omits_authorization_header

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.token_in_flags_body_matches_init

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.groups_round_trip

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.groups_default_to_empty_object

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.person_properties_distinct_id_auto_populated_when_caller_omits_it

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.disable_geoip_false_propagates_as_geoip_disable_false

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.disable_geoip_omitted_defaults_to_false

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_payload.flag_keys_to_evaluate_contains_only_requested_key

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_lifecycle.no_flags_request_on_init_alone

Expected 0 /flags requests, got 1

request_lifecycle.no_flags_request_on_normal_capture

Expected 0 /flags requests, got 1

request_lifecycle.two_flag_calls_produce_two_remote_requests

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

request_lifecycle.mock_response_value_is_returned_to_caller

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

side_effect_events.get_feature_flag_captures_feature_flag_called_event

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'

[ioannisj]

LG, left one last comment but I'll leave that up to you.