feat(capture): v1 transport + partial-retry send loop (capture v1, 3/6)

[eli-r-ph]

💡 Motivation and Context

Third PR in the stacked Capture V1 series (stacked on #702). Adds the HTTP transport and partial-retry send loop for POST /i/v1/analytics/events, on top of the pure transforms from #702. Still inert — send_v1_batch has no caller until the consumer-wiring PR.

New in posthog/capture_v1.py:

• post_v1(...) — a single attempt. Bearer auth (no api_key in the body), the required v1 headers (PostHog-Sdk-Info, PostHog-Attempt, PostHog-Request-Id, PostHog-Request-Timestamp), and optional gzip. Returns the raw response; this is also the monkeypatch seam the test harness adapter will drive.
• parse_v1_response(...) — classifies one response without raising: 2xx parses the per-uuid results map (an unparseable 2xx body is flagged malformed), non-2xx best-effort extracts an error message, and Retry-After (delta-seconds or HTTP-date) is parsed in both cases.
• send_v1_batch(...) — the v1 sibling of Consumer._send. Loops up to max_retries + 1 attempts, but shrinks the batch to only the events the server tagged retry after each 2xx. ok/warning/absent events succeed silently; drop events are logged (a request the server accepted-but-dropped is not a delivery failure, so it is not raised). Raises CaptureV1Error (an APIError subclass, so the consumer's existing on_error(exc, batch) keeps working) on a batch-level terminal/transport failure or once retries are exhausted.
• CaptureV1Error / V1ParsedResponse / V1EventResult types.

Behavior choices, verified against the Rust contract and posthog-go's capture_v1_send.go:

• 429 is terminal in v1 (v0 retries it) — the backend signals overload via retryable 5xx + Retry-After.
• A stable PostHog-Request-Id and created_at span all attempts; PostHog-Attempt increments — so the backend can correlate/dedupe a retried batch.
• A 2xx with an unparseable body is terminal — re-sending against a broken success would loop forever.
• Backoff reuses the v0 policy (Retry-After wins, else capped exponential) so both wire protocols back off identically.

Also factors a shared gzip_compress helper out of request.post — pure refactor, no v0 behavior change (covered by the existing test_request.py).

💚 How did you test it?

posthog/test/test_capture_v1.py now has 74 cases (47 transform + 27 transport). New transport coverage: post_v1 header/url/no-key-in-body/gzip-magic; parse_v1_response success/malformed/missing-results/error-body-variants/text-fallback/Retry-After; and send_v1_batch driven by a stubbed post_v1 with mocked sleeps — all-ok, absent-uuid-accepted, partial-retry-shrinks-to-retry-uuids, stable-request-id + incrementing-attempt, drop-logged-not-raised, retry-exhausted-raises, malformed-2xx-terminal, 400/429-terminal-not-retried, 503-then-success (honors Retry-After), 503-exhausted-raises, transport-error-then-success, transport-error-exhausted-reraises.

ruff format/check clean; mypy clean on capture_v1.py + request.py; test_request.py (61) still green after the gzip refactor; 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 (additive; send_v1_batch has no caller yet).

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Authored with Cursor (Claude Opus 4.8) per the agreed plan. posthog-go's sendV1 is woven into its client lifecycle (channels, notifyFailure/notifySuccess, maxAttempts); this port instead fits posthog-python's Consumer._send shape — a synchronous loop that raises on failure so the existing upload() -> on_error(exc, batch) path fires unchanged — while preserving go's partial-retry algorithm, status matrix, stable-request-id semantics, and per-event drop/retry handling.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "feat(capture): add v1 transport and part..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-06-28 00:55:20 UTC
Duration: 530116ms

✅ All Tests Passed!

45/45 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	518ms
Format Validation.Event Has Uuid	✅	10008ms
Format Validation.Event Has Lib Properties	✅	10006ms
Format Validation.Distinct Id Is String	✅	10007ms
Format Validation.Token Is Present	✅	10007ms
Format Validation.Custom Properties Preserved	✅	10007ms
Format Validation.Event Has Timestamp	✅	10007ms
Retry Behavior.Retries On 503	✅	18017ms
Retry Behavior.Does Not Retry On 400	✅	12006ms
Retry Behavior.Does Not Retry On 401	✅	10007ms
Retry Behavior.Respects Retry After Header	✅	16013ms
Retry Behavior.Implements Backoff	✅	30009ms
Retry Behavior.Retries On 500	✅	13018ms
Retry Behavior.Retries On 502	✅	16011ms
Retry Behavior.Retries On 504	✅	16010ms
Retry Behavior.Max Retries Respected	✅	30017ms
Deduplication.Generates Unique Uuids	✅	7002ms
Deduplication.Preserves Uuid On Retry	✅	16015ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	23015ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	16009ms
Deduplication.No Duplicate Events In Batch	✅	10002ms
Deduplication.Different Events Have Different Uuids	✅	10006ms
Compression.Sends Gzip When Enabled	✅	10007ms
Batch Format.Uses Proper Batch Structure	✅	10007ms
Batch Format.Flush With No Events Sends Nothing	✅	5005ms
Batch Format.Multiple Events Batched Together	✅	10005ms
Error Handling.Does Not Retry On 403	✅	12007ms
Error Handling.Does Not Retry On 413	✅	10007ms
Error Handling.Retries On 408	✅	14014ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	9502ms
Request Payload.Flags Request Uses V2 Query Param	✅	10007ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10006ms
Request Payload.Flags Request Omits Authorization Header	✅	10007ms
Request Payload.Token In Flags Body Matches Init	✅	10007ms
Request Payload.Groups Round Trip	✅	10006ms
Request Payload.Groups Default To Empty Object	✅	10007ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	10007ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	10007ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	10008ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10006ms
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	✅	10002ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	10510ms