Fix Blazor persistent component state restoration for components without keys and add E2E test coverage

[Copilot]

The _ignoreComponentPropertyValue flag in PersistentValueProviderComponentSubscription was only being set conditionally within if (!skipNotifications) blocks, causing restored values to be ignored when components are destroyed and re-added during navigation or when components don't use @key.

Problem

When a component is added, removed, then added again (for example, during page navigation or when a component doesn't use @key), the restored value from persistent state storage was being ignored. This happened because:

1. During initial component setup, skipNotifications is often true
2. The _ignoreComponentPropertyValue = true assignment was inside the if (!skipNotifications) block
3. Without this flag set, GetOrComputeLastValue() would return the component's current property value instead of the restored value

Solution

Moved _ignoreComponentPropertyValue = true; outside the conditional blocks so it's set unconditionally whenever we successfully restore from persistent state. This ensures that the restored value always takes precedence over the component's initial property value, regardless of notification settings.

Before:

if (!skipNotifications)
{
    _ignoreComponentPropertyValue = true;
    _subscriber.NotifyCascadingValueChanged(ParameterViewLifetime.Unbound);
}

After:

_ignoreComponentPropertyValue = true;
if (!skipNotifications)
{
    _subscriber.NotifyCascadingValueChanged(ParameterViewLifetime.Unbound);
}

Test Coverage

Added comprehensive test coverage including:

Unit Tests

• Enhanced existing unit tests to properly simulate cascading parameter behavior
• Added debug test to verify the _ignoreComponentPropertyValue flag behavior
• Fixed test timing issues by ensuring proper state consumption patterns

E2E Tests

Following feedback from @javiercn, added E2E test infrastructure for two critical scenarios:

1. PageWithConditionalPersistentComponents.razor - New test page supporting:

   • Component without @key that always renders (tests navigation scenarios)
   • Component conditionally rendered based on query parameters (tests add/remove scenarios)

2. StatePersistenceTest.cs - New E2E tests covering:

   • CanRestoreStateForComponentsWithoutKeysAndConditionalRendering - Validates both components restore state correctly
   • CanRestoreStateAfterConditionalComponentToggling - Tests state restoration after component toggling

The E2E tests use query string parameters to control component rendering and validate that persistent state works correctly in all scenarios where components are dynamically added/removed, particularly during enhanced navigation in Blazor applications.

Fixes #63193.

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[javiercn]

@copilot

We should look at the E2E test cases in #62824 to add also support for these other two scenarios.

Specifically src/Components/test/E2ETest/Tests/StatePersistenceTest.cs and src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/PersistentState/PageWithDeclarativeEnhancedNavigationPersistentComponents.razor

Our test could be designed to use a query string to choose to render or not render the components. There would be one component without a key that renders always and a component that gets added/removed depending on the value of the query string.

In both cases the state should be restored successfully

[Copilot]

@copilot

We should look at the E2E test cases in #62824 to add also support for these other two scenarios.
...

I've added E2E test support for the two scenarios you mentioned:

1. PageWithConditionalPersistentComponents.razor - A new test page that uses query parameters to control component rendering:

   • Always-rendered component without @key (tests navigation scenarios)
   • Conditionally-rendered component based on show-conditional query parameter (tests add/remove scenarios)

2. StatePersistenceTest.cs - New E2E tests:

   • CanRestoreStateForComponentsWithoutKeysAndConditionalRendering - Tests both components restore state correctly
   • CanRestoreStateAfterConditionalComponentToggling - Tests state restoration after toggling components on/off

The page follows the same pattern as the existing declarative enhanced navigation page, with links in PageWithoutComponents.razor for navigation. Both scenarios should validate that persistent state restoration works correctly regardless of when components are destroyed and recreated.

Implemented in 6b82560.

[Copilot]

Pull Request Overview

This PR fixes a bug in Blazor's persistent component state restoration where restored values were being ignored for components without @key attributes or during navigation scenarios. The core issue was that the _ignoreComponentPropertyValue flag was only being set conditionally within notification blocks, causing restored values to be overridden by component property values when notifications were skipped.

Key changes:

• Moved the _ignoreComponentPropertyValue = true assignment outside conditional notification blocks to ensure it's always set when state is restored
• Added comprehensive E2E test infrastructure with a new test page for conditional component rendering scenarios
• Enhanced existing unit tests to better validate the flag behavior

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
PersistentValueProviderComponentSubscription.cs	Core fix - moves the _ignoreComponentPropertyValue = true assignment outside conditional blocks
PageWithConditionalPersistentComponents.razor	New test page supporting conditional component rendering scenarios
PageWithoutComponents.razor	Updated navigation links and added support for new test scenarios
PageWithDeclarativeEnhancedNavigationPersistentComponents.razor	Enhanced to support components with and without @key attributes
StatePersistenceTest.cs	Updated existing E2E tests to support new test parameters
PersistentValueProviderComponentSubscriptionTests.cs	Enhanced unit tests with better validation of state restoration behavior

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