feat!: report capture v1 results through CaptureError and on_error

[eli-r-ph]

💡 Motivation and Context

Capture v1 returns a per-event verdict for every event in a 2xx results map, keyed by the canonical lowercase hyphenated uuid. This PR makes the SDK report those verdicts, and every other capture failure, through one error type and one reporting path, aligned with posthog-go's v1 branch.

Error model

• CaptureError now carries endpoint, request_id, attempts, retry_exhausted, drops and event_results (a new public CaptureEventResult(result, details) per uuid). verdict_summary() renders counts such as drop/billing=1, retry/not_persisted=1.
• A transport failure on the last attempt raises CaptureError(status=0) with the original exception as __cause__, like go's CaptureRequestError.

UUIDs

• Caller-supplied event uuids are sent and returned in canonical form, and results are matched by canonical uuid. Before this, an uppercase or unhyphenated uuid missed its result entry and was treated as accepted. Same fix for go: fix: correlate capture results for non-canonical event uuids posthog-go#358.
• Generated event uuids and request ids are UUIDv7, matching what capture generates server-side.
• A uuid missing from a 2xx results map still counts as accepted, matching go and rs. With canonical keys, the server answers every event, so this only matters if the server breaks its contract.

Reporting

• With on_error, every failure goes to it, and the SDK logs nothing extra.
• Without on_error, each failed batch logs one aggregate line: N event(s) not persisted by <endpoint>: .... The line has counts, verdicts, the error type and the status. It never includes payloads, uuids or server error text.
• sync_mode failures now go to on_error too, called on the calling thread after the send slot is released, so shutdown() from the callback works. capture() returns None on failure. This reverses the contract asserted by #832's test_sync_send_failure_does_not_invoke_async_on_error.
• A capture that fails inside on_error logs the aggregate line instead of calling on_error again. This applies to sync mode, AsyncPosthog.capture_immediate and the async consumer, and stops a callback that captures from recursing while the endpoint is down.

Retries

• Backoff is 100ms × 2^attempt, capped at 30s, matching go. It was 1s.
• The Consumer default retries is 3 (4 attempts), matching the client default. It was 10.

💚 How did you test it?

• New tests cover:
  • non-canonical uuid result matching
  • the loss-message format
  • CaptureError endpoint, event_results and verdict_summary
  • transport-error wrapping
  • v7 event uuids and request ids
  • canonical returned uuids
  • sync-mode on_error with shutdown() from inside the callback
  • recursion guards (sync, async immediate, async background)
  • the aggregate line without on_error
• The recursion guards, the canonical result matching, uuid canonicalization and v7 generation were each checked by removing the code and confirming the matching test fails.
• I ran ruff, mypy (baseline), the full pytest suite, the adapter tests, python -W error -c "import posthog", the public API snapshot and uv lock --check.

📝 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 sampo add to generate a changeset file

Covered by the existing capture-v1-major changeset; the migration guide lands later in this stack.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Written with Cursor (Claude Opus) under the direction of the assignee.

Agreed before implementation:

• missing uuid = accepted, plus the canonical fix
• sync_mode calls on_error, with a reentrancy guard

Agent calls worth review:

• wrapping transport errors in CaptureError(status=0)
• the 100ms backoff base
• the Consumer retries default
• keeping server error text out of the aggregate log line, which extends the async client's existing rule to the sync consumer

[github-actions]

posthog-python Compliance Report

Date: 2026-10-08T16:31:23.117692+00:00
Duration: 247318ms

✅ All Tests Passed!

116/116 tests passed

---

Capture_V1 Tests

✅ 95/95 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	517ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	511ms
Required Headers.Has Authorization Bearer Header	✅	510ms
Required Headers.Has Content Type Json	✅	511ms
Required Headers.Has Posthog Sdk Info Format	✅	510ms
Required Headers.Has Posthog Attempt Header	✅	510ms
Required Headers.Has Posthog Request Id	✅	510ms
Required Headers.Has Posthog Request Timestamp	✅	510ms
Required Headers.Has User Agent	✅	510ms
Body Format.Body Has Created At And Batch	✅	512ms
Body Format.No Api Key In Body	✅	510ms
Body Format.No Sent At In Body	✅	511ms
Event Format.Event Has Required Root Fields	✅	510ms
Event Format.Event Uuid Is Valid	✅	511ms
Event Format.Event Timestamp Is Rfc3339	✅	510ms
Event Format.Non Utc Event Timestamp Is Converted To Utc	✅	517ms
Event Format.Distinct Id Is String	✅	510ms
Event Format.Distinct Id At Root Not Properties	✅	510ms
Event Format.Custom Properties Preserved	✅	510ms
Event Format.Set Properties Preserved	✅	511ms
Event Format.Set Once Properties Preserved	✅	510ms
Event Format.Groups Properties Preserved	✅	510ms
Event Format.Sdk Generates Uuid If Not Provided	✅	511ms
Event Format.Event Has Required Root Fields Batch	✅	514ms
Event Format.Event Uuid Is Valid Batch	✅	513ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	514ms
Event Format.Distinct Id Is String Batch	✅	513ms
Event Format.Distinct Id At Root Not Properties Batch	✅	514ms
Event Format.Custom Properties Preserved Batch	✅	514ms
Event Format.Set Properties Preserved Batch	✅	513ms
Event Format.Set Once Properties Preserved Batch	✅	514ms
Event Format.Groups Properties Preserved Batch	✅	513ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	514ms
Batch Behavior.Multiple Events In Single Batch	✅	517ms
Batch Behavior.Batch Envelope Smoke	✅	515ms
Batch Behavior.Flush With No Events Sends Nothing	✅	507ms
Batch Behavior.Flush At Triggers Batch	✅	1011ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	510ms
Deduplication.Generates Unique Uuids	✅	517ms
Deduplication.Different Events Same Content Different Uuids	✅	513ms
Deduplication.Preserves Uuid On Retry	✅	6515ms
Deduplication.Preserves Timestamp On Retry	✅	6520ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6524ms
Deduplication.No Duplicate Events In Batch	✅	518ms
Header Behavior On Retry.Attempt Header Starts At One	✅	510ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	12528ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6519ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3021ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6515ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	511ms
Response Format Validation.Success Response Has Ok For Each Event	✅	515ms
Response Format Validation.Success No Retry After When All Ok	✅	512ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1516ms
Response Format Validation.Success No Retry After When Drop Only	✅	513ms
Response Format Validation.Response Echoes Request Id	✅	510ms
Retry Behavior.Retries On 408	✅	6516ms
Retry Behavior.Retries On 500	✅	6520ms
Retry Behavior.Retries On 503	✅	7524ms
Retry Behavior.Retries On 504	✅	6516ms
Retry Behavior.Retryable Errors Have Retry After	✅	3517ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11525ms
Retry Behavior.Does Not Retry On 400	✅	2513ms
Retry Behavior.Does Not Retry On 401	✅	2513ms
Retry Behavior.Does Not Retry On 402	✅	2513ms
Retry Behavior.Does Not Retry On 413	✅	2513ms
Retry Behavior.Does Not Retry On 415	✅	2512ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2514ms
Retry Behavior.Implements Backoff	✅	18530ms
Retry Behavior.Max Retries Respected	✅	18526ms
Partial Batch Handling.Handles 200 Full Success	✅	2514ms
Partial Batch Handling.Handles 200 With All Ok	✅	3519ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3516ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3515ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6521ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6518ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6524ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6521ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6517ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6522ms
Partial Batch Handling.Respects Retry After On Partial	✅	8519ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3514ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3519ms
Compression.Sends Gzip Content Encoding	✅	511ms
Compression.No Content Encoding When Disabled	✅	510ms
Compression.Compressed Body Is Decompressible	✅	511ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2513ms
Event Options.Cookieless Mode Override	✅	511ms
Event Options.Disable Skew Correction Override	✅	510ms
Event Options.Process Person Profile Override	✅	511ms
Event Options.Product Tour Id Override	✅	510ms
Event Options.Unset Options Omitted	✅	510ms
Event Options.Options Override In Batch	✅	514ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	510ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	510ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	510ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	11ms
Request Payload.Flags Request Uses V2 Query Param	✅	9ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	9ms
Request Payload.Flags Request Omits Authorization Header	✅	10ms
Request Payload.Token In Flags Body Matches Init	✅	9ms
Request Payload.Groups Round Trip	✅	9ms
Request Payload.Groups Default To Empty Object	✅	10ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	9ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	9ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	9ms
Request Lifecycle.No Flags Request On Init Alone	✅	4ms
Request Lifecycle.No Flags Request On Normal Capture	✅	509ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	15ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	9ms
Retry Behavior.Retries Flags On 502	✅	313ms
Retry Behavior.Retries Flags On 504	✅	313ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	511ms

Feature_Flags_Local_Evaluation Tests

✅ 4/4 tests passed

View Details

Test	Status	Duration
Versioned Boolean Matching.Matching Version Missing	✅	70ms
Versioned Boolean Matching.Matching Version 1	✅	68ms
Versioned Boolean Matching.Matching Version 2	✅	70ms
Versioned Boolean Matching.Version Only Reload 1 2 1 2 Missing	✅	35ms

[eli-r-ph]

@greptileai review

[dustinbyrne]

Looks good to me. Two optional documentation clarifications below; neither requires changing the runtime behavior.

AI-assisted review.