[Feature] Introduce widgets.ErrorBoundary for Component-Level Crash Isolation

[HaHiepThanh]

📋 Context & Problem Description

In WebAssembly Go runtimes, if a widget panics during its Build() cycle, lifecycle callbacks, or event execution (due to a nil pointer dereference, slice index out of bounds, etc.), the entire WASM main-thread panic crashes. This freezes the client-side execution, forcing the user to reload the page to make the site responsive again.

💡 Proposed Solution & Implementation Plan

Introduce a component-level error boundary widget to contain panics:

1. widgets.ErrorBoundary Definition:
   Create a new wrapper widget:

   type ErrorBoundary struct {
       Fallback func(err error) gutter.Widget
       Child    gutter.Widget
   }

2. Panic Recovery in Reconciler:
   • Inside the element tree reconciliation and build cycles (element_wasm.go), wrap the Build() and reconcile invocations with a defer recover() check.
   • If a panic is caught:
     • Halt rendering for the affected subtree.
     • Propagate the error up to the nearest ErrorBoundary element.
     • Render the fallback widget returned by Fallback(err) in place of the crashed component, preserving the rest of the application tree.

🎯 Impact & Benefits

• App Stability: Prevent a minor crash in a non-critical sidebar widget from crashing the entire SPA dashboard.
• Graceful Degradation: Display clean error states and retry buttons rather than a blank frozen screen.

🏷️ Suggested Labels

feature, wasm, widgets