Why is my Blazor EditForm not calling OnValidSubmit on /auth/register route?

by 
# Why is my Blazor EditForm not calling OnValidSubmit on /auth/register route?

**Summary**
The `EditForm`'s `OnValidSubmit` handler fails to execute due to the **Blazor component lacking interactivity**. Instead of leveraging Blazor's event handling, the browser performs a classic HTML form submission via POST, bypassing client-side logic.

**Root Cause**
- The `/auth/register` route component (**Register.razor**) **wasn't assigned an interactive render mode**.  
- Without explicit interactivity directives:
  1. Blazor treats the form as a static HTML element.
  2. JavaScript event handlers for `OnValidSubmit` aren't injected.
  3. Submissions default to traditional browser form behavior (`application/x-www-form-urlencoded`).

**Why This Happens in Real Systems**
- **New rendering model in .NET 8**: Components default to **static rendering**. Blazor requires explicit opt-in for interactivity.
- **Component isolation**: Developers often assume parent layout settings cascade to child components (they don’t for render modes).
- **Route mismatches**: Legacy MVC/Razor Pages endpoints might intercept `/auth/register` if dual-framework projects exist.
- **Template confusion**: Starting from an MVC template but adding Blazor components creates routing conflicts.

**Real-World Impact**
- Critical user flows (like registration) fail silently.
- Server receives raw form data without client-side validation.
- Unclear debugging signals (page renders normally, no errors).
- Broken user experience requiring full-page reloads.

**Example** or Code
**Incorrect Register.razor** (static rendering):  
```razor
@page "/auth/register"

Corrected Register.razor (interactive rendering): 

@page "/auth/register"
@rendermode InteractiveServer

Router Configuration Check (App.razor):

How Senior Engineers Fix It

  1. Explicitly declare interactivity in Register.razor using @rendermode InteractiveServer.
  2. Verify endpoint conflicts:
    • Check for duplicate /auth/register routes in MVC controllers or Razor Pages.
    • Use app.UseExceptionHandler("/Error") and app.MapControllers() before MapRazorComponents().
  3. Debug interactivity:
    • Inspect browser dev tools for Blazor script errors (_framework/blazor.web.js).
    • Check element classes—interactive forms include blazor-server-rendered.
  4. Enable global rendering via App.razor/RouteView if interactivity is broadly needed.
  5. Validate CSP: Ensure connect-src allows websockets (wss://*) for SignalR connections.

Why Juniors Miss It

  • Assumption of defaults: Expecting Blazor forms to “just work” without render mode configuration.
  • Debugging blind spots:
    • Focusing on server logs instead of browser console/web socket activity.
    • Overlooking HTML source inspection (<form> tags vs component structure).
  • Overgeneralization: Assuming layout-level settings enable interactivity for child routes.
  • Legacy knowledge gaps: Mistaking .NET 6/7 behaviors (stateful by default) for .NET 8’s static-by-design.
  • Symptom misinterpretation: Confusing this issue with validation errors or API failures.