feat(surveys): add optional intro screen before the first question

[jakesciotto]

💡 Motivation and Context

Surveys can show a confirmation ("thank you") screen after the last question, but there is no equivalent screen before the first one — the built-in survey sheet drops respondents straight into question 1 with no framing.

This is the posthog-ios part of the cross-SDK intro screen rollout tracked in PostHog/posthog#74064. The web/RN renderer shipped in PostHog/posthog-js#4436; this PR brings the native SwiftUI rendering to parity.

What it does:

• New SurveyAppearance fields decoded from the API and exposed on PostHogDisplaySurveyAppearance (for custom delegates too): displayIntroScreen, introScreenHeader, introScreenDescription, introScreenDescriptionContentType, introScreenButtonText.
• New IntroMessage SwiftUI view, the leading mirror of ConfirmationMessage, rendered by SurveySheet before the first question when displayIntroScreen is on.
• Advancing past the intro (dismissIntroScreen) is a pure UI transition: no response recorded, no survey event sent, no effect on $survey_partially_completed. The X button on the intro still dismisses the survey with the normal survey dismissed event, and the confirmation branch still wins for completed surveys.
• Intro copy is translatable (introScreenHeader / introScreenDescription / introScreenButtonText in survey translations), wired through PostHogSurveyTranslation, the resolver's change gate, and the display-appearance overlay.
• Drive-by fix: getAppearanceWithDefaults never passed thankYouMessageDescription through to the sheet appearance, so the thank-you description never rendered in the built-in UI. Fixed while mirroring the field for the intro screen.

💚 How did you test it?

Unit tests added:

• Raw → display appearance mapping for the 5 new fields, plus default-off behavior when absent (PostHogSurveysTest.swift).
• Display controller intro state machine: starts on the intro only when enabled, and advancing keeps the survey open without invoking the close callback (PostHogSurveyTranslationsTest.swift).
• Translation fixture extended: translated intro header/button apply, untranslated description falls back.

Written on Linux, so the suite was not executed locally — please rely on CI (make test / iOS simulator tests). The public API snapshot (api/posthog-ios.public-api.txt) was updated by hand following the snapshot format; the Build workflow's apiCheck verifies it, and make apiUpdate on macOS produces the canonical version if it disagrees.

📝 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 (.changeset/survey-intro-screen.md, minor)

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

• Authored with PostHog Code (Claude) as part of the cross-SDK rollout requested in review of feat(surveys): add optional intro screen shown before the first question posthog-js#4436; design per Feature request: Survey intro/start screen (shown before the first question) posthog#74064.
• Key decision: the intro is a @Published showingIntroScreen flag on SurveyDisplayController, initialized in showSurvey and flipped by a dedicated dismissIntroScreen() that deliberately does not touch dismissSurvey()/onSurveyClosed, so no event can leak from the advance path. The confirmation branch stays first in surveyContent so a completed survey never shows the intro.
• The thank-you-description drive-by fix was included because the intro fields would otherwise have mirrored the same dropped-parameter bug.

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Created with PostHog Code

[greptile-apps]

Prompt To Fix All With AI

### Issue 1
PostHog/Surveys/IntroMessage.swift:26
**HTML intro descriptions disappear**

When an intro description uses the supported `html` content type, this guard renders nothing, causing respondents to see the intro header and button without the configured description.

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

_{Reviews (1): Last reviewed commit: "chore(surveys): add intro screen fields ..." | Re-trigger Greptile}

[marandaneto]

moving to draft until we hear from @PostHog/team-surveys

[github-actions]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week.

[github-actions]

posthog-ios Compliance Report

Date: 2026-08-19 21:53:25 UTC
Duration: 218944ms

✅ All Tests Passed!

45/45 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	2818ms
Format Validation.Event Has Uuid	✅	2765ms
Format Validation.Event Has Lib Properties	✅	2788ms
Format Validation.Distinct Id Is String	✅	2728ms
Format Validation.Token Is Present	✅	2722ms
Format Validation.Custom Properties Preserved	✅	2772ms
Format Validation.Event Has Timestamp	✅	2827ms
Retry Behavior.Retries On 503	✅	11255ms
Retry Behavior.Does Not Retry On 400	✅	4794ms
Retry Behavior.Does Not Retry On 401	✅	4858ms
Retry Behavior.Respects Retry After Header	✅	7812ms
Retry Behavior.Implements Backoff	✅	15363ms
Retry Behavior.Retries On 500	✅	9196ms
Retry Behavior.Retries On 502	✅	8752ms
Retry Behavior.Retries On 504	✅	9218ms
Retry Behavior.Max Retries Respected	✅	15349ms
Deduplication.Generates Unique Uuids	✅	2925ms
Deduplication.Preserves Uuid On Retry	✅	9163ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	16602ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7805ms
Deduplication.No Duplicate Events In Batch	✅	2864ms
Deduplication.Different Events Have Different Uuids	✅	394ms
Compression.Sends Gzip When Enabled	✅	2850ms
Batch Format.Uses Proper Batch Structure	✅	2697ms
Batch Format.Flush With No Events Sends Nothing	✅	304ms
Batch Format.Multiple Events Batched Together	✅	2810ms
Error Handling.Does Not Retry On 403	✅	4719ms
Error Handling.Does Not Retry On 413	✅	4783ms
Error Handling.Retries On 408	✅	9240ms

Feature_Flags Tests

✅ 16/16 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	2721ms
Request Payload.Flags Request Uses V2 Query Param	✅	2771ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	2752ms
Request Payload.Flags Request Omits Authorization Header	✅	2679ms
Request Payload.Token In Flags Body Matches Init	✅	2944ms
Request Payload.Groups Round Trip	✅	2717ms
Request Payload.Groups Default To Empty Object	✅	2656ms
Request Payload.Person Properties Distinct Id Auto Populated When Caller Omits It	✅	2790ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	2836ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	2850ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	2830ms
Request Lifecycle.No Flags Request On Init Alone	✅	138ms
Request Lifecycle.No Flags Request On Normal Capture	✅	3055ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	5473ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	2778ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	2944ms

[greptile-apps]

_{Reviews (2): Last reviewed commit: "fix(surveys): repair intro screen build ..." | Re-trigger Greptile}