feat: add resilience layer with caching and graceful degradation for …

[ThorstenSuckow]

…Supabase outages

see website/#1

[Copilot]

Pull request overview

This PR implements a resilience layer to handle Supabase outages gracefully by adding caching and fallback mechanisms.

Key Changes

• Implements a caching strategy that pre-fetches signatories data during build/start and stores it locally
• Adds graceful degradation with automatic fallback to cached data when Supabase is unavailable
• Includes a testing mode to simulate Supabase outages via environment variable

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/pages/signatories.tsx	Enables error banner display on the signatories page
src/components/SignersList.tsx	Implements core resilience logic with error handling and cache fallback
src/components/SignersList.module.css	Adds styling for error banner showing cache status
src/components/SignManifest.tsx	Adds outage detection and disables signing when Supabase is unavailable
src/components/SignManifest.module.css	Adds styling for warning banner
scripts/cache-signatories.cjs	Creates script to fetch and cache signatories data from Supabase
package.json	Integrates cache script into prebuild and prestart hooks
docusaurus.config.ts	Adds configuration for simulating Supabase outages
.gitignore	Excludes generated cache file from version control
.env	Adds simulation toggle environment variable

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[Copilot]

The script uses the global fetch API which is only available in Node.js 18+. Consider adding a comment documenting the minimum Node.js version requirement, or add a runtime check with a helpful error message if fetch is not available.

[Copilot]

The dependency array is missing shouldUseMockData. Since shouldUseMockData is calculated from USE_MOCK_DATA and simulateDown, and simulateDown is included in the dependency array, consider adding shouldUseMockData to the dependency array or simplifying by using simulateDown directly in the condition on line 45.

[Copilot]

Missing error handling if cachedSignatories.cached_at contains an invalid date string. Consider wrapping the new Date() call in a try-catch or validating the date before rendering to prevent potential runtime errors.

Suggested change

	{cachedSignatories.cached_at && (
	<span className={styles.cacheDate}>
	{' '}
	(as of {new Date(cachedSignatories.cached_at).toLocaleString('en-US')})
	</span>
	)}
	{cachedSignatories.cached_at && (() => {
	const cacheDate = new Date(cachedSignatories.cached_at);
	if (!isNaN(cacheDate.getTime())) {
	return (
	<span className={styles.cacheDate}>
	{' '}
	(as of {cacheDate.toLocaleString('en-US')})
	</span>
	);
	}
	return (
	<span className={styles.cacheDate}>
	{' '}
	(as of unknown date)
	</span>
	);
	})()}

[Copilot]

The error banner only displays when both error AND usingCache are true. This means if there's an error but no cached data is available (lines 89-91), no error message is shown to the user. Consider showing an error message even when cached data is not available, so users are informed of the issue.

Suggested change

	{showErrorBanner && error && usingCache && (
	<div className={styles.errorBanner}>
	{error}. Showing cached signatories
	{cachedSignatories.cached_at && (
	<span className={styles.cacheDate}>
	{' '}
	(as of {new Date(cachedSignatories.cached_at).toLocaleString('en-US')})
	</span>
	{showErrorBanner && error && (
	<div className={styles.errorBanner}>
	{error}.
	{usingCache ? (
	<>
	{' '}Showing cached signatories
	{cachedSignatories.cached_at && (
	<span className={styles.cacheDate}>
	{' '}
	(as of {new Date(cachedSignatories.cached_at).toLocaleString('en-US')})
	</span>
	)}
	</>
	) : (
	<> No cached data available.</>

[Copilot]

The .env file should not be committed to version control as it contains sensitive credentials. Add .env to .gitignore and create a .env.example file with placeholder values to document required environment variables.