chore: update text and names left stale by the 4.0 changes

[turnipdabeets]

💡 Motivation and Context

Part of the 4.0 stack, on top of #873. This updates text and internal names that #873's changes (iOS 15 minimum, Swift tools 6.2, apiKey removal) left stale. No behavior change.

• Surveys: the @available(..., unavailable) messages on PostHogConfig.surveys and surveysConfig now say "Surveys are only available on iOS". The "15+" is redundant now that iOS 15 is the minimum.
• PostHogEvent.apiKey → projectToken: the internal property and init label now use the public name. The wire field stays api_key, which is what the server expects.
• Setup log: "projectToken or apiKey is empty" now says "projectToken is empty".
• sdk_compliance_adapter: the README and run_tests.sh now require Swift 6.2+, to match the SDK's swift-tools-version:6.2.

apiKey / api_key that stays

Where	Why
"api_key" in event, batch, flags and snapshot JSON	It's the field name the server expects.
PostHogConfig.projectToken doc: "formerly named apiKey"	Migration hint.
scripts/downgrade-compatibility-smoke PostHogConfig(apiKey:)	It compiles against 3.48.0 on purpose.
sdk_compliance_adapter api_key	It's the compliance harness's request format.
POSTHOG_PROJECT_API_KEY in release.yml	CI secret name.

Left alone on purpose

• s.swift_versions = "5.3" in the podspec. That's the Swift language mode, which is still 5 (swiftLanguageModes: [.v5]).
• The watchOS 9.0 clause in PostHogContext's $locale check. It only becomes redundant with chore!: raise minimum macOS to 11, tvOS to 15 and watchOS to 10 #906's watchOS 10 minimum.
• sdk_compliance_adapter/Dockerfile still uses swift:5.9 images. That can't resolve a 6.2-tools package, but changing it is a functional change I haven't verified with Docker, so it's left for a follow-up.

💚 How did you test it?

• xcodebuild build for iOS and watchOS succeeds.
• make test (macOS): all 169 XCTest tests pass. Swift Testing has 13 issues in PostHogStorage app-group tests, which fail the same way on the base branch (macOS blocks access to the app-group container on my machine). One run also failed re-registering a different token after delivery sends again, which passed 5 times out of 5 when run on its own.

📝 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.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

• Made with Claude Code, from an audit for leftover code in the 4.0 release work.

🤖 Generated with Claude Code

[github-actions]

posthog-ios Compliance Report

Date: 2026-10-06 13:56:42 UTC
Duration: 218324ms

⚠️ Some Tests Failed

44/45 tests passed, 1 failed

---

Capture Tests

⚠️ 28/29 tests passed, 1 failed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	2884ms
Format Validation.Event Has Uuid	✅	2872ms
Format Validation.Event Has Lib Properties	✅	375ms
Format Validation.Distinct Id Is String	✅	2749ms
Format Validation.Token Is Present	✅	293ms
Format Validation.Custom Properties Preserved	✅	2739ms
Format Validation.Event Has Timestamp	✅	2754ms
Retry Behavior.Retries On 503	✅	5346ms
Retry Behavior.Does Not Retry On 400	✅	4788ms
Retry Behavior.Does Not Retry On 401	✅	4677ms
Retry Behavior.Respects Retry After Header	✅	7713ms
Retry Behavior.Implements Backoff	✅	21723ms
Retry Behavior.Retries On 500	✅	9352ms
Retry Behavior.Retries On 502	✅	5483ms
Retry Behavior.Retries On 504	✅	5798ms
Retry Behavior.Max Retries Respected	❌	22044ms
Deduplication.Generates Unique Uuids	✅	3293ms
Deduplication.Preserves Uuid On Retry	✅	9270ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	16795ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7800ms
Deduplication.No Duplicate Events In Batch	✅	3015ms
Deduplication.Different Events Have Different Uuids	✅	3011ms
Compression.Sends Gzip When Enabled	✅	2714ms
Batch Format.Uses Proper Batch Structure	✅	418ms
Batch Format.Flush With No Events Sends Nothing	✅	331ms
Batch Format.Multiple Events Batched Together	✅	2847ms
Error Handling.Does Not Retry On 403	✅	4785ms
Error Handling.Does Not Retry On 413	✅	4712ms
Error Handling.Retries On 408	✅	9296ms

Failures

retry_behavior.max_retries_respected

Expected 4 requests, got 6

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	2972ms
Request Payload.Flags Request Uses V2 Query Param	✅	2789ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	2919ms
Request Payload.Flags Request Omits Authorization Header	✅	2831ms
Request Payload.Token In Flags Body Matches Init	✅	2983ms
Request Payload.Groups Round Trip	✅	2845ms
Request Payload.Groups Default To Empty Object	✅	2988ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	2884ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	2976ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	2889ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	2881ms
Request Lifecycle.No Flags Request On Init Alone	✅	109ms
Request Lifecycle.No Flags Request On Normal Capture	✅	2926ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	6384ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	3002ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	3089ms