chore!: remove 5.x-deprecated names for v6

[turnipdabeets]

💡 Motivation and Context

Stacked on #637 (v6 base). This removes the APIs that 5.x deprecates:

Removed	Use instead	Deprecated in
Posthog().enable() / disable()	optIn() / optOut()	#636
PostHogConfig.sendFeatureFlagEvents	sendFeatureFlagEvent	#636

Commits:

1. A cherry-pick of feat: add optIn/optOut and sendFeatureFlagEvent, deprecate old names #636, so this branch builds on its own. It drops out on rebase once feat: add optIn/optOut and sendFeatureFlagEvent, deprecate old names #636 merges into main.
2. Remove the deprecated names. The internal setup key sent to native is unchanged, so there are no Kotlin or Swift changes.

Merge order: #636 into main → rebase #637 → this PR.

💚 How did you test it?

• flutter analyze: no issues, for the plugin and for the example app
• flutter test: 781 pass
• dart format --set-exit-if-changed: clean
• scripts/check-api-dart.sh: snapshot updated per commit

📝 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 pnpm changeset to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

• Made with Claude Code.
• PostHogWidgetState and PostHogMaskWidgetState aren't touched here. chore: make PostHogWidgetState and PostHogMaskWidgetState internal #635 already marks them @internal and hides them from the export, so making them private would only be tidying.
• I kept the TRACK_APPLICATION_LIFECYCLE_EVENTS fallback and getFeatureFlagResult(sendEvent:) out on purpose. The fallback was never deprecated, and sendEvent already matches posthog-js / React Native.

🤖 Generated with Claude Code

[greptile-apps]

[High risk] Removes deprecated API names across the SDK.

This PR appears safe to merge as an intentional v6 breaking change.

_{Reviews (1) · Last reviewed commit: "chore!: remove enable/disable and sendFe..."}

[github-actions]

posthog-flutter Compliance Report

Date: 2026-10-07 00:36:09 UTC
Duration: 96817ms

✅ All Tests Passed!

45/45 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	141ms
Format Validation.Event Has Uuid	✅	124ms
Format Validation.Event Has Lib Properties	✅	117ms
Format Validation.Distinct Id Is String	✅	115ms
Format Validation.Token Is Present	✅	114ms
Format Validation.Custom Properties Preserved	✅	117ms
Format Validation.Event Has Timestamp	✅	118ms
Retry Behavior.Retries On 503	✅	5332ms
Retry Behavior.Does Not Retry On 400	✅	2119ms
Retry Behavior.Does Not Retry On 401	✅	2117ms
Retry Behavior.Respects Retry After Header	✅	8123ms
Retry Behavior.Implements Backoff	✅	15435ms
Retry Behavior.Retries On 500	✅	5227ms
Retry Behavior.Retries On 502	✅	5227ms
Retry Behavior.Retries On 504	✅	5225ms
Retry Behavior.Max Retries Respected	✅	15447ms
Deduplication.Generates Unique Uuids	✅	122ms
Deduplication.Preserves Uuid On Retry	✅	5223ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	10336ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	5232ms
Deduplication.No Duplicate Events In Batch	✅	123ms
Deduplication.Different Events Have Different Uuids	✅	117ms
Compression.Sends Gzip When Enabled	✅	117ms
Batch Format.Uses Proper Batch Structure	✅	114ms
Batch Format.Flush With No Events Sends Nothing	✅	109ms
Batch Format.Multiple Events Batched Together	✅	124ms
Error Handling.Does Not Retry On 403	✅	2117ms
Error Handling.Does Not Retry On 413	✅	2118ms
Error Handling.Retries On 408	✅	5224ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	16ms
Request Payload.Flags Request Uses V2 Query Param	✅	11ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	10ms
Request Payload.Flags Request Omits Authorization Header	✅	11ms
Request Payload.Token In Flags Body Matches Init	✅	11ms
Request Payload.Groups Round Trip	✅	9ms
Request Payload.Groups Default To Empty Object	✅	10ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	11ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	11ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	11ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10ms
Request Lifecycle.No Flags Request On Init Alone	✅	6ms
Request Lifecycle.No Flags Request On Normal Capture	✅	112ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	16ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	8ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	114ms

[turnipdabeets]

@ioannisj thoughts on this?

[ioannisj]

@ioannisj thoughts on this?

I think this makes sense. Naming aligns with other SDKs right? My only thought is that #636 should prob go out soon so that people will get a chance to see the deprecations

[dustinbyrne]

seems somewhat confusing to deprecate as minor and remove as major within a single change. depending on where i'm looking at the changelog i'll be getting different information about enable(), disable(), sendFeatureFlagEvents

[turnipdabeets]

Yea, that changeset was from #636, which has now shipped in 5.51.0. Rebasing the v6 stack on main removed changeset.