Handle deeplinks fallback mode

[Fabcien]

When a deeplink is not handled by an app on the user device, the browser opens the /app page and attempts to open the cashtab web wallet.

The cashtab extension is managed on the client-side and doesn't need to happen on the server side: if the user has no app nor extension installed, redirecting to cashtab is the expected behavior.

This has been tested on a dev server by manually calling the URL like so: http://localhost:3000/app?address=ecash:qplv39yx80kdqejh4ag6c3t30aatj9mausupeyjzr7&amount=100.00

Summary by CodeRabbit

• New Features
  • Added a new endpoint for handling cryptocurrency payment links
  • Payment links automatically redirect to Cashtab with properly formatted transaction data
  • Implemented error handling that displays user-friendly messages for invalid payment links

[Fabcien]

This might actually not be needed as it seems impossible to install the cashtab extension on mobile anyway, so we could jump to cashtab web directly and only handle cashtab-connect on the client to save a redirect. Waiting for confirmation.

[coderabbitai]

Note

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Caution

Review failed

Failed to post review comments

📝 Walkthrough

Walkthrough

Two files are modified to implement a new BIP21 redirect handler. The auth configuration adds "/app" to authorized unlogged URLs, and a new Next.js page handles server-side BIP21 validation and client-side redirect logic to Cashtab with appropriate error handling.

Changes

Cohort / File(s)	Summary
Authentication Configuration pages/_app.tsx	Added "/app" to AUTHORIZED_UNLOGGED_URLS to allow unauthenticated access to the new app redirect page.
BIP21 Redirect Handler pages/app/index.tsx	New page implementing server-side BIP21 string construction via getServerSideProps with address validation and query parameter filtering. Client component redirects to Cashtab or displays error/redirect message accordingly.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰✨ A path to BIP21 so fine,
Server-side logic in perfect line,
Validate and redirect with care,
To Cashtab's wallet, swift through air! 🪙

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	❓ Inconclusive	The description explains the feature context and testing approach, but omits the required 'Related to #' issue reference and 'Test plan' section from the template.	Add the GitHub issue reference (Related to #) and provide a more detailed test plan section beyond the single manual test example.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Handle deeplinks fallback mode' accurately and concisely describes the main change: implementing a fallback flow for deeplinks when apps are unavailable.

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Warning

Review ran into problems

🔥 Problems

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[Fabcien]

Simplified by not handling cashtab-connect which is not needed, see PayButton/paybutton#611