feat(capture): route analytics through v1 submitter (capture v1, 4/6)

[eli-r-ph]

💡 Motivation and Context

Fourth PR in the stacked Capture V1 series (stacked on #703). This is the one that makes capture_mode actually do something: it wires send_v1_batch (from #703) into both send paths, so the previously-inert v1 transport is now selectable end to end. Default is still v0, so existing callers are unaffected.

• Async path (Consumer.request) — refactored to route via _send_analytics / _send_ai. _send_analytics picks the submitter by capture_mode: v1 -> the partial-retry send_v1_batch, v0 -> the legacy batch_post loop. _send_ai always uses the legacy submitter.
• Sync path (Client._enqueue, sync_mode=True) — same branch: an analytics event in v1 goes through send_v1_batch([msg]); everything else stays on batch_post.
• The dedicated AI endpoint has no v1 form, so $ai_* events routed to it always use the legacy submitter regardless of capture_mode. When the dedicated AI endpoint is not enabled, all events (including $ai_*) go to the single analytics destination and therefore follow capture_mode — exactly mirroring the v0 single-endpoint behavior.

Supporting changes: Client.max_retries is now stored so the sync path can forward it, and gzip/timeout/retries/historical_migration are forwarded to the v1 submitter so it honors the same config as v0.

💚 How did you test it?

• test_consumer.py — new TestConsumerCaptureModeRouting: v0 -> batch_post, v1 -> send_v1_batch, config-forwarding, dedicated-AI split (analytics -> v1 submitter / $ai_* -> legacy AI endpoint), and AI-only batch skips the v1 submitter.
• test_client.py — new TestClientSyncCaptureMode: v0 vs v1 sync submitter selection, config forwarding, dedicated-AI $ai_* event stays legacy, dedicated-AI analytics event uses v1.

Full test_consumer.py (25) and the new client class green; ruff format/check clean; mypy clean on client.py + consumer.py; regenerated references/public_api_snapshot.txt.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change (v0 remains the default wire protocol).

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Authored with Cursor (Claude Opus 4.8) per the agreed plan. The routing split intentionally keeps the dedicated-AI destination on the legacy submitter — there is no v1 AI ingestion endpoint, so capture_mode only swaps the analytics submitter. This mirrors posthog-go, where CaptureMode likewise governs only the analytics path.

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posthog-python Compliance Report

Date: 2026-06-29 18:39:52 UTC
Duration: 530082ms

✅ All Tests Passed!

45/45 tests passed

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Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	516ms
Format Validation.Event Has Uuid	✅	10007ms
Format Validation.Event Has Lib Properties	✅	10007ms
Format Validation.Distinct Id Is String	✅	10007ms
Format Validation.Token Is Present	✅	10007ms
Format Validation.Custom Properties Preserved	✅	10006ms
Format Validation.Event Has Timestamp	✅	10007ms
Retry Behavior.Retries On 503	✅	18019ms
Retry Behavior.Does Not Retry On 400	✅	12004ms
Retry Behavior.Does Not Retry On 401	✅	10007ms
Retry Behavior.Respects Retry After Header	✅	16013ms
Retry Behavior.Implements Backoff	✅	30018ms
Retry Behavior.Retries On 500	✅	13010ms
Retry Behavior.Retries On 502	✅	16011ms
Retry Behavior.Retries On 504	✅	16010ms
Retry Behavior.Max Retries Respected	✅	30017ms
Deduplication.Generates Unique Uuids	✅	7003ms
Deduplication.Preserves Uuid On Retry	✅	16015ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	23019ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	16004ms
Deduplication.No Duplicate Events In Batch	✅	10003ms
Deduplication.Different Events Have Different Uuids	✅	10007ms
Compression.Sends Gzip When Enabled	✅	10007ms
Batch Format.Uses Proper Batch Structure	✅	10007ms
Batch Format.Flush With No Events Sends Nothing	✅	5004ms
Batch Format.Multiple Events Batched Together	✅	10005ms
Error Handling.Does Not Retry On 403	✅	12009ms
Error Handling.Does Not Retry On 413	✅	10007ms
Error Handling.Retries On 408	✅	14013ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	9501ms
Request Payload.Flags Request Uses V2 Query Param	✅	10006ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10007ms
Request Payload.Flags Request Omits Authorization Header	✅	10007ms
Request Payload.Token In Flags Body Matches Init	✅	10006ms
Request Payload.Groups Round Trip	✅	10007ms
Request Payload.Groups Default To Empty Object	✅	10006ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	10007ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	10006ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	10007ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10008ms
Request Lifecycle.No Flags Request On Init Alone	✅	5003ms
Request Lifecycle.No Flags Request On Normal Capture	✅	10507ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	9511ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	10003ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	10509ms

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