fix(flags): local eval dependency fail to match

[matheus-vb]

💡 Motivation and Context

Under local evaluation a release condition of the form "flag X evaluates to false" never matched, so the dependent flag returned false for every locally evaluated user. The chain walk in evaluate_flag_dependency rejected any falsy flag in the chain before the value comparison ran, and since the referenced flag is always last in the chain the users whose flag X was false (exactly the ones the condition should match) were dropped.

This reworks the chain walk to only evaluate and cache each member and to decide the outcome solely from the referenced flag's cached value, matching the Go and C# SDKs and the Rust /flags service. A malformed value: null condition now falls back to the server instead of silently returning true.

💚 How did you test it?

Added end to end tests in posthog/test/test_feature_flags.py covering value: false with variant and true controls, the multi level A/B/D chain, an inactive base flag, an inconclusive base that falls back to /flags, and value: null. Reran the bug report reproduction and the full suite passes.

📝 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

[github-actions]

posthog-python Compliance Report

Date: 2026-07-10 02:53:56 UTC
Duration: 338856ms

✅ 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	✅	516ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	1009ms
Required Headers.Has Authorization Bearer Header	✅	1009ms
Required Headers.Has Content Type Json	✅	1008ms
Required Headers.Has Posthog Sdk Info Format	✅	1009ms
Required Headers.Has Posthog Attempt Header	✅	1008ms
Required Headers.Has Posthog Request Id	✅	1009ms
Required Headers.Has Posthog Request Timestamp	✅	1007ms
Required Headers.Has User Agent	✅	1009ms
Body Format.Body Has Created At And Batch	✅	1010ms
Body Format.No Api Key In Body	✅	1009ms
Body Format.No Sent At In Body	✅	1008ms
Event Format.Event Has Required Root Fields	✅	1009ms
Event Format.Event Uuid Is Valid	✅	1009ms
Event Format.Event Timestamp Is Rfc3339	✅	1008ms
Event Format.Distinct Id Is String	✅	1009ms
Event Format.Distinct Id At Root Not Properties	✅	1009ms
Event Format.Custom Properties Preserved	✅	1008ms
Event Format.Set Properties Preserved	✅	1008ms
Event Format.Set Once Properties Preserved	✅	1009ms
Event Format.Groups Properties Preserved	✅	1009ms
Event Format.Sdk Generates Uuid If Not Provided	✅	1008ms
Event Format.Event Has Required Root Fields Batch	✅	1012ms
Event Format.Event Uuid Is Valid Batch	✅	1012ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	1012ms
Event Format.Distinct Id Is String Batch	✅	1012ms
Event Format.Distinct Id At Root Not Properties Batch	✅	1013ms
Event Format.Custom Properties Preserved Batch	✅	1011ms
Event Format.Set Properties Preserved Batch	✅	1012ms
Event Format.Set Once Properties Preserved Batch	✅	1012ms
Event Format.Groups Properties Preserved Batch	✅	1012ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	1012ms
Batch Behavior.Multiple Events In Single Batch	✅	1506ms
Batch Behavior.Batch Envelope Smoke	✅	1014ms
Batch Behavior.Flush With No Events Sends Nothing	✅	1005ms
Batch Behavior.Flush At Triggers Batch	✅	1508ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	1010ms
Deduplication.Generates Unique Uuids	✅	1506ms
Deduplication.Different Events Same Content Different Uuids	✅	1507ms
Deduplication.Preserves Uuid On Retry	✅	7512ms
Deduplication.Preserves Timestamp On Retry	✅	7513ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7522ms
Deduplication.No Duplicate Events In Batch	✅	1504ms
Header Behavior On Retry.Attempt Header Starts At One	✅	1009ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	14523ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	7508ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3515ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	7514ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	1006ms
Response Format Validation.Success Response Has Ok For Each Event	✅	1506ms
Response Format Validation.Success No Retry After When All Ok	✅	1507ms
Response Format Validation.Success Retry After Present When Retry Events	✅	2510ms
Response Format Validation.Success No Retry After When Drop Only	✅	1507ms
Response Format Validation.Response Echoes Request Id	✅	1009ms
Retry Behavior.Retries On 408	✅	7513ms
Retry Behavior.Retries On 500	✅	7511ms
Retry Behavior.Retries On 503	✅	9519ms
Retry Behavior.Retries On 504	✅	7510ms
Retry Behavior.Retryable Errors Have Retry After	✅	4512ms
Retry Behavior.Respects Retry After On Retryable Error	✅	12516ms
Retry Behavior.Does Not Retry On 400	✅	3504ms
Retry Behavior.Does Not Retry On 401	✅	3506ms
Retry Behavior.Does Not Retry On 402	✅	3508ms
Retry Behavior.Does Not Retry On 413	✅	3508ms
Retry Behavior.Does Not Retry On 415	✅	3507ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	3506ms
Retry Behavior.Implements Backoff	✅	23522ms
Retry Behavior.Max Retries Respected	✅	23533ms
Partial Batch Handling.Handles 200 Full Success	✅	2999ms
Partial Batch Handling.Handles 200 With All Ok	✅	4509ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	4505ms
Partial Batch Handling.Does Not Retry Limited Events	✅	4511ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	7512ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	7513ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	7510ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	7507ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	7516ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	7512ms
Partial Batch Handling.Respects Retry After On Partial	✅	9507ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	4511ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	4507ms
Compression.Sends Gzip Content Encoding	✅	1007ms
Compression.No Content Encoding When Disabled	✅	1009ms
Compression.Compressed Body Is Decompressible	✅	1008ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	3509ms
Event Options.Cookieless Mode Override	✅	1008ms
Event Options.Disable Skew Correction Override	✅	1008ms
Event Options.Process Person Profile Override	✅	1009ms
Event Options.Product Tour Id Override	✅	1008ms
Event Options.Unset Options Omitted	✅	1009ms
Event Options.Options Override In Batch	✅	1012ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	1009ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	1009ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	1008ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	1006ms
Request Payload.Flags Request Uses V2 Query Param	✅	1007ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	1006ms
Request Payload.Flags Request Omits Authorization Header	✅	1007ms
Request Payload.Token In Flags Body Matches Init	✅	1006ms
Request Payload.Groups Round Trip	✅	1007ms
Request Payload.Groups Default To Empty Object	✅	1007ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	1006ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	1006ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	1007ms
Request Lifecycle.No Flags Request On Init Alone	✅	502ms
Request Lifecycle.No Flags Request On Normal Capture	✅	1508ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	1010ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	1003ms
Retry Behavior.Retries Flags On 502	✅	1006ms
Retry Behavior.Retries Flags On 504	✅	1007ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	1509ms

[ioannisj]

LG