Frontend: Build Granular Error Boundary with Soroban RPC Retry Handler

[ONEONUORA]

📌 Target Component

frontend/components/ui/ErrorBoundary.tsx

📝 Description

Uncaught RPC network glitches crash component subtrees without graceful fallback or retry buttons.

📋 Implementation Requirements

1. Upgrade ErrorBoundary.tsx with detailed technical error drawer and 1-click RPC node switcher fallback.
2. Automatically suppress transient 504 Gateway errors with backoff retry.

🎯 Testnet Goal

Resilience against testnet RPC node instability.

[bilhokista]

I have opened #1207 for this issue.

The core problem turned out to be that the boundary's only recovery action was window.location.reload(), and hasError was never cleared — so for a testnet node returning 504 for a moment, the subtree stayed dead until the reader threw away all client state with a reload. It can now recover in place, and transient failures retry automatically with backoff (500ms, 1s, 2s, capped at 8s, ±25% jitter so every open tab does not hit a recovering node at the same instant).

The part I would most like reviewed is the classification. Terminal contract failures are checked before the transient patterns, because a revert message can mention a timeout in its own text — "simulation failed: timeout in host function" must not be retried, since the node answered correctly and the answer was "no"; retrying burns time and fees on an outcome that cannot change. There is a test for that exact string. The default is also conservative: an error matching nothing is treated as not retryable, since auto-retrying anything unrecognised risks looping on a real bug.

On the RPC node switcher, I want to flag a real limitation rather than let it look finished. network.ts has a single SOROBAN_RPC_URL, so there was no list to switch between. I added NEXT_PUBLIC_SOROBAN_RPC_URLS (comma-separated), defaulting to empty, and deliberately did not seed it with public third-party nodes — which providers this app sends user traffic to is an operator's decision about trust and rate limits, not a default that should arrive inside a UI component. The consequence is that the button is hidden until someone configures endpoints and passes an onEndpointChange handler, so the switcher is inert as shipped. If you would rather I pick default fallback nodes, tell me which and I will add them.

The technical details drawer is collapsed by default and shows the stack, React's component stack (now stored rather than only logged) and the active endpoint.

On tests: this frontend has Vitest configured, so the new tests/lib/stellar/rpcHealth.test.ts will run in CI as a normal test file — 25 cases. I could not execute it locally, so I also ran the module standalone against 39 assertions covering the same ground, all passing. I did not add a component test for the boundary itself: that needs a throwing child plus fake timers for the backoff, which is worth doing but larger, and I preferred landing the policy with the pure module fully covered over a shallow component test. Glad to add it here if you want it.