Add checkout-only mode for web2app flows

[KanishkKundu05]

Summary

• Adds openWebCheckout(forPlacement:) public convenience method for web2app flows that skip the intermediate paywall UI and go directly to the Stripe checkout sheet
• Adds checkoutOnly option to PaywallOverrides (defaults to false, fully backward compatible)
• The paywall webview still loads invisibly to generate the checkout URL, while a native loading spinner is shown to the user

File Changes

File	Change	Reason
PaywallOverrides.swift	Added checkoutOnly: Bool property (default false)	Opt-in flag for checkout-only mode
PublicPresentation.swift	Added openWebCheckout() methods; threaded paywallOverrides through internallyRegister()	Public API + plumbing overrides to presentation pipeline
PaywallViewController.swift	Added checkout-only UI logic (hidden webview, spinner, auto-dismiss)	Implements the invisible-webview + spinner UX
PaywallOverridesTests.swift	5 new unit tests	Verifies checkoutOnly defaults and initialization
CHANGELOG.md	Added entry	Documents the new feature
docs/checkout-only-mode.md	New documentation file	Usage guide with code examples and architecture explanation

How It Works

1. User calls Superwall.shared.openWebCheckout(forPlacement: "placement")
2. The paywall loads invisibly (webview hidden, native spinner shown)
3. Paywall JS fires openPaymentSheet → spinner removed, Stripe checkout sheet presented
4. On checkout dismiss: if cancelled, invisible paywall auto-dismissed; if purchased, normal flow continues

Dashboard Requirement

The paywall must be configured to auto-trigger the purchase action on page load via custom JS in the paywall editor.

Test plan

• Build passes (xcodebuild build)
• Lint passes (scripts/lint.sh)
• All 5 new unit tests pass
• Manual test: Call openWebCheckout(forPlacement:) with an auto-trigger paywall and verify no intermediate paywall is shown

🤖 Generated with Claude Code

Greptile Summary

This PR introduces checkout-only mode for web2app flows, allowing users to skip the intermediate paywall UI and go directly to the Stripe checkout sheet.

• Added openWebCheckout(forPlacement:) public convenience methods (with and without feature gates)
• Added checkoutOnly: Bool property to PaywallOverrides (defaults to false for full backward compatibility)
• Implemented invisible webview loading with native spinner UI in PaywallViewController
• Auto-dismisses paywall when checkout is cancelled in checkout-only mode
• Properly handles webview failures by cleaning up spinner and dismissing
• Includes 5 unit tests verifying default behavior and initialization
• Well-documented in CHANGELOG and comprehensive docs file

The implementation is clean and follows the existing architectural patterns. All initializers properly default checkoutOnly to false, ensuring no breaking changes.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation is well-designed with proper backward compatibility (all defaults set correctly), comprehensive test coverage for the new property, clear documentation, and follows existing architectural patterns. The checkout-only mode is properly isolated with early returns to prevent interference with normal flows. Edge cases like webview failures and checkout cancellations are handled correctly.
• No files require special attention

Important Files Changed

Filename	Overview
Sources/SuperwallKit/Paywall/Presentation/Internal/Presentation Request/PaywallOverrides.swift	Added checkoutOnly boolean property with proper defaults across all initializers
Sources/SuperwallKit/Paywall/Presentation/PublicPresentation.swift	Added two openWebCheckout() convenience methods and threaded paywallOverrides parameter through
Sources/SuperwallKit/Paywall/View Controller/PaywallViewController.swift	Implemented checkout-only mode with invisible webview, native spinner, and auto-dismiss logic

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[User calls openWebCheckout] --> B[Create PaywallOverrides with checkoutOnly=true]
    B --> C[Paywall presents]
    C --> D{isCheckoutOnly?}
    D -->|Yes| E[setupCheckoutOnlyMode]
    D -->|No| F[Normal paywall flow]
    E --> G[webView.alpha = 0]
    E --> H[Show native spinner]
    E --> I[Hide exit/refresh buttons]
    G --> J[Webview loads invisibly]
    H --> J
    I --> J
    J --> K{Webview success?}
    K -->|No| L[handleWebViewFailure]
    L --> M[removeCheckoutOnlySpinner]
    M --> N[Dismiss paywall]
    K -->|Yes| O[JS fires openPaymentSheet]
    O --> P[removeCheckoutOnlySpinner]
    P --> Q[Show Stripe checkout sheet]
    Q --> R{User action?}
    R -->|Purchase| S[Normal purchase flow]
    R -->|Cancel| T[Auto-dismiss paywall]
    S --> U[didRedeemSucceedDuringCheckout=true]
    U --> V[Keep paywall for completion]

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_{Last reviewed commit: 16a344e}

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[yusuftor]

Closing as this is resolved on Slack