feat(traces): span handles

[turnipdabeets]

💡 Motivation and Context

Adds the Span interface (posthog.tracing.span, the only public module in the package) and its three handles:

• Recording span: timing on a monotonic clock, children of a local parent on the root's clock basis so they stay inside it. end() is idempotent and hands the pipeline one record.
• No-op handle: returned when tracing cannot run.
• Pass-through handle: echoes an inbound traceparent / tracestate so a service with tracing off still forwards the trace, including from spans nested inside it.

Entering a handle makes it the active span for the block and records an exception raised out of it. Not reachable from the client yet.

Stack (PR 3 of 9, based on traces/02-otlp-encoding):

1. feat(traces): W3C trace context ids and traceparent parsing #949 traces/01-ids-traceparent
2. feat(traces): OTLP span encoding and client-side validity #950 traces/02-otlp-encoding
3. feat(traces): span handles #951 traces/03-span-handles ← this PR
4. feat(traces): span batch transport #952 traces/04-transport
5. feat(traces): span pipeline #953 traces/05-pipeline
6. feat(traces): span export queue with retries #954 traces/06-export
7. feat(traces): per-span limits and exception stacktraces #955 traces/07-span-limits
8. feat(traces): before_span_send hook #956 traces/08-before-span-send
9. feat(traces): wire tracing into the client #957 traces/09-client-wiring

💚 How did you test it?

Unit tests in posthog/test/tracing/test_span.py cover timing, idempotent end(), active-span scoping, exception recording and pass-through propagation.

📝 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

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented with Claude Code (Claude Opus 5) against the traces spec, one commit per slice so each PR reviews on its own. Rebased onto main and opened as a stacked draft in a later Claude Code session (Claude Fable 5.1).

🤖 Generated with Claude Code

https://claude.ai/code/session_012o7CtHLfcypjmXL7g9ZGRC

[github-actions]

posthog-python Compliance Report

Date: 2026-09-17 03:43:06 UTC
Duration: 256023ms

✅ All Tests Passed!

111/111 tests passed

---

Capture_V1 Tests

✅ 94/94 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	513ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	510ms
Required Headers.Has Authorization Bearer Header	✅	508ms
Required Headers.Has Content Type Json	✅	508ms
Required Headers.Has Posthog Sdk Info Format	✅	508ms
Required Headers.Has Posthog Attempt Header	✅	508ms
Required Headers.Has Posthog Request Id	✅	508ms
Required Headers.Has Posthog Request Timestamp	✅	508ms
Required Headers.Has User Agent	✅	509ms
Body Format.Body Has Created At And Batch	✅	508ms
Body Format.No Api Key In Body	✅	509ms
Body Format.No Sent At In Body	✅	508ms
Event Format.Event Has Required Root Fields	✅	508ms
Event Format.Event Uuid Is Valid	✅	509ms
Event Format.Event Timestamp Is Rfc3339	✅	508ms
Event Format.Distinct Id Is String	✅	508ms
Event Format.Distinct Id At Root Not Properties	✅	508ms
Event Format.Custom Properties Preserved	✅	508ms
Event Format.Set Properties Preserved	✅	510ms
Event Format.Set Once Properties Preserved	✅	509ms
Event Format.Groups Properties Preserved	✅	508ms
Event Format.Sdk Generates Uuid If Not Provided	✅	508ms
Event Format.Event Has Required Root Fields Batch	✅	511ms
Event Format.Event Uuid Is Valid Batch	✅	511ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	510ms
Event Format.Distinct Id Is String Batch	✅	511ms
Event Format.Distinct Id At Root Not Properties Batch	✅	511ms
Event Format.Custom Properties Preserved Batch	✅	511ms
Event Format.Set Properties Preserved Batch	✅	511ms
Event Format.Set Once Properties Preserved Batch	✅	510ms
Event Format.Groups Properties Preserved Batch	✅	511ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	511ms
Batch Behavior.Multiple Events In Single Batch	✅	514ms
Batch Behavior.Batch Envelope Smoke	✅	512ms
Batch Behavior.Flush With No Events Sends Nothing	✅	505ms
Batch Behavior.Flush At Triggers Batch	✅	1008ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	509ms
Deduplication.Generates Unique Uuids	✅	514ms
Deduplication.Different Events Same Content Different Uuids	✅	510ms
Deduplication.Preserves Uuid On Retry	✅	6516ms
Deduplication.Preserves Timestamp On Retry	✅	6518ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6519ms
Deduplication.No Duplicate Events In Batch	✅	514ms
Header Behavior On Retry.Attempt Header Starts At One	✅	508ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	13524ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6517ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3017ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6517ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	509ms
Response Format Validation.Success Response Has Ok For Each Event	✅	511ms
Response Format Validation.Success No Retry After When All Ok	✅	510ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1513ms
Response Format Validation.Success No Retry After When Drop Only	✅	510ms
Response Format Validation.Response Echoes Request Id	✅	508ms
Retry Behavior.Retries On 408	✅	6513ms
Retry Behavior.Retries On 500	✅	6512ms
Retry Behavior.Retries On 503	✅	8520ms
Retry Behavior.Retries On 504	✅	6517ms
Retry Behavior.Retryable Errors Have Retry After	✅	3512ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11514ms
Retry Behavior.Does Not Retry On 400	✅	2512ms
Retry Behavior.Does Not Retry On 401	✅	2511ms
Retry Behavior.Does Not Retry On 402	✅	2511ms
Retry Behavior.Does Not Retry On 413	✅	2511ms
Retry Behavior.Does Not Retry On 415	✅	2512ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2510ms
Retry Behavior.Implements Backoff	✅	22522ms
Retry Behavior.Max Retries Respected	✅	22518ms
Partial Batch Handling.Handles 200 Full Success	✅	2511ms
Partial Batch Handling.Handles 200 With All Ok	✅	3515ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3514ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3510ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6519ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6518ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6517ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6518ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6514ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6516ms
Partial Batch Handling.Respects Retry After On Partial	✅	8519ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3513ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3514ms
Compression.Sends Gzip Content Encoding	✅	508ms
Compression.No Content Encoding When Disabled	✅	508ms
Compression.Compressed Body Is Decompressible	✅	508ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2511ms
Event Options.Cookieless Mode Override	✅	509ms
Event Options.Disable Skew Correction Override	✅	508ms
Event Options.Process Person Profile Override	✅	508ms
Event Options.Product Tour Id Override	✅	508ms
Event Options.Unset Options Omitted	✅	508ms
Event Options.Options Override In Batch	✅	511ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	508ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	508ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	508ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	8ms
Request Payload.Flags Request Uses V2 Query Param	✅	8ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	7ms
Request Payload.Flags Request Omits Authorization Header	✅	7ms
Request Payload.Token In Flags Body Matches Init	✅	7ms
Request Payload.Groups Round Trip	✅	7ms
Request Payload.Groups Default To Empty Object	✅	7ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	7ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	7ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	7ms
Request Lifecycle.No Flags Request On Init Alone	✅	2ms
Request Lifecycle.No Flags Request On Normal Capture	✅	508ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	11ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	7ms
Retry Behavior.Retries Flags On 502	✅	310ms
Retry Behavior.Retries Flags On 504	✅	310ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	509ms

[greptile-apps]

Prompt To Fix All With AI

### Issue 1
posthog/tracing/_span.py:333-339
**Shared spans end early**

The implementation supports entering one span from several threads or tasks, but each `__exit__` ends that shared span. If one block exits while another is still active, later events and exceptions from the remaining block are ignored, producing an incomplete trace. Track active scope ownership and end only after the final scope exits, or explicitly reject concurrent entry.

### Issue 2
posthog/tracing/_span.py:302-305
**Concurrent end exports duplicates**

`end()` checks and sets `_ended` without synchronization. Concurrent callers can both pass the check and invoke `_on_end`, violating the documented idempotency contract and exporting duplicate span records. Protect the check-and-set transition with a lock.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "feat(traces): span handles" | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "feat(traces): span handles" | Re-trigger Greptile}

[dustinbyrne]

Reviewed cf74b0b17bcf0e496fd4f35b9a63837f4e6a7cf2 via source inspection and existing CI. No issues found in this staged span-handle slice. Approval covers this slice; #950 precedes it in the stack.

[jzhu13]

Reviewed against traces/02-otlp-encoding. Tests pass at the head, ruff and mypy are clean, and the ContextVar token handling held up under nested, threaded, async, and copied-context probes. Two items I would fix before merge.

Blocking

1. posthog/tracing/_span.py:335 __exit__ records every BaseException as an error span with an exception event: GeneratorExit, asyncio.CancelledError, KeyboardInterrupt, SystemExit. Reproduced: a generator holding with span: that is closed early yields SpanStatus('error') and exception.type='GeneratorExit'. A streaming endpoint whose consumer breaks out of the loop, or any request cancelled on client disconnect, ships as a failure. OTel's use_span catches Exception only for this reason. Suggest isinstance(exc, Exception) for the record-and-error path while still calling end() unconditionally, tighten the span.py docstrings from "an exception" to "an Exception", and add a parametrized case for GeneratorExit and CancelledError.
2. posthog/tracing/_span.py:333 end() runs before _deactivate(), so on_end (and, from #956, the before_span_send hook) sees the ending span as still active. Reproduced at the stack tip: a hook that calls start_span during scoped exit gets parent_span_id == outer.span_id, a child that starts after its parent ended. OTel detaches first, then ends. Swap the order.

Non-blocking

3. posthog/tracing/_span.py:302 end() idempotence is a non-atomic check-then-set on _ended. Two threads ending one handle can call on_end twice, contradicting the public "Idempotent" docstring. Wrapping the flag flip in the existing _tokens_lock makes the guarantee the handle's own rather than #953's.
4. posthog/tracing/_span.py:76 _deactivate is a silent no-op when no token matches the current context (exit in a copy_context() child, or a thread that entered and died). The span stays active and a stale token stays in the list. A debug log would make "why is my span still active" diagnosable.
5. posthog/tracing/span.py:24 says None removes the key, but at this PR the record stores None and only the encoder drops it. #955 makes the sentence true. Either pop here or move the sentence.
6. Nits: Span is never rendered by bin/docs_scripts/generate_json_schemas.py, which only visits Client and module functions, so #957's start_span documents a return type with no page; no __slots__ on handles that carry ~19 attributes with a default cap of 10000 live spans; the PR body cites a spec but links no issue, which CONTRIBUTING asks for on public API changes.

Reviewed with Claude Code (Claude Fable 5.1). Behaviors above were reproduced by probe against this branch head or the stack tip where noted.

[turnipdabeets]

Thanks. Fixed in ceddd18:

• 1: scoped exit records Exception only, still ends on every exit. Tests for GeneratorExit, CancelledError, KeyboardInterrupt and a closed generator.
• 2: the span is detached before end().
• 3: end() flips its flag under the handle's lock.
• 4: a deactivate with no token logs at debug.
• 5: true since feat(traces): per-span limits and exception stacktraces #955. Docs rendering for Span and the issue link we'll handle separately.

[turnipdabeets]

Follow-up: nothing further changed here since ceddd18; the stack below it was rebased. Ready for another look.