Fade the multipage paywall header during page transitions

[vegaro]

Multipage paywall headers used to pop. When one page has a header and the next doesn't, the header vanished the instant the slide finished (or snapped in at the start). Now the header rides the slide.

The header fades with the page transition:

• present → absent: the outgoing header fades out
• absent → present: the incoming header fades in
• both present, or neither: unchanged (no fade)

It rides the same animatable.value progress as the slide, read inside graphicsLayer { alpha }, so it stays in lock-step and adds no recompositions per frame. The old !toHasHeroImage special-case is dropped: the header now fades even when the incoming page has a hero image, instead of dropping abruptly.

Screen_recording_20260604_075517.mp4

---

Note

Low Risk
Paywall UI and transition animation only; layout workaround for leaving headers is localized but worth a quick visual pass on header↔no-header and header↔hero flows.

Overview
Multipage workflow paywalls now fade the header in sync with the slide when a step gains or loses a header, instead of popping at the end of the transition.

Header selection returns a WorkflowHeaderPresentation (step id + ENTERING / LEAVING / STABLE). Present→absent uses the outgoing header with LEAVING; absent→present uses the incoming with ENTERING; when both steps have headers, behavior stays STABLE with the existing outgoing/incoming pick rules. The old case that dropped the header immediately when navigating to a hero page without a header is replaced by a LEAVING fade.

Alpha follows the same transition progress as the slide via graphicsLayer (no per-frame recomposition). LEAVING headers are drawn as a Box overlay in main content—not in the scaffold header slot—so headerHeightPx on the incoming step is not set from the fading header (hero top inset stays correct).

Tests cover presentation selection (including the hero behavior change) and headerAlpha mapping.

^{Reviewed by Cursor Bugbot for commit f632931. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.96%. Comparing base (c3e9a45) to head (f632931).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

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[facumenzella]

Haven't manually tested it but looks legit. A video in the PR description would be amazing 👍

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit b5fb3c4. Configure here.}