Expose EnsureInitialized on IRefreshableItemSource; add non-cancellable async RefreshableSelector tests

[Copilot]

Overview:

The goal for this PR was to ensure that background tasks during viewmodel initialization can safely perform complex interactions with the RefreshableSelectors.

EnsureInitialized and EnsureInitializedAsync existed on RefreshableSelector but were not part of IRefreshableItemSource, making them inaccessible through the interface.

Changes

IRefreshableItemSource

• Added void EnsureInitialized(TimeSpan? maxWaitTime = null)
• Added Task EnsureInitializedAsync(CancellationToken token)

RefreshableSelectorSequenceTests (new)

Demonstrates a ViewModel-style flow using the Func<Task<TList>> (non-cancellable async) constructor. Constructor parameters are exposed as class-level properties configured in [TestInitialize]:

/* Overview
 *  "ProcessViewModel()" here represents an async call that occurred on the viewmodel after binding was established
 * 
 * Sequence:
 *  - View binds to Selector1, triggering its refresh
 *  - ProcessViewModel() ensures Selector1 is initialized, then selects an item from the collection
 *  - Selector1's selection change triggers a refresh on Selector2 (Cancelling the previous refresh if it hasn't completed yet)
 *      - Since the first refresh is cancelled, Selector3 should not refresh yet
 *   - ProcessViewModel() then ensures Selector2 is initialized (which should be against the second collection) and selects an item from that collection
 *      - Selector3 should have now had 2 refreshes triggered, the first of which is cancelled due to selector 2's selection change
 *  - ProcessViewModel() exits after ensuring Selector3 is initialized against the second refresh
 */

[RFBomb]

Copilot completely missed the mark on this request. Reworking the test class to demonstrate the following:

• ViewModel has 2 selectors
• Selector 1 becomes populated
• Method ensures selector 1 is populated
• Method picks selector 1 item
• Selector 2 refresh triggered
• Method waits for selector 2 refresh completion via EnsureInitializedAsync, then selected selector 2 value.

[RFBomb]

@copilot : After the review, update the initial PR comment to reflect changes and the overview.

[Copilot]

Pull request overview

This PR exposes EnsureInitialized / EnsureInitializedAsync on IRefreshableItemSource and refines RefreshableSelector async refresh/initialization behavior, alongside new/updated tests covering refresh sequencing and “don’t cancel in-flight refresh on repeated calls” semantics.

Changes:

• Add EnsureInitialized(TimeSpan?) and EnsureInitializedAsync(CancellationToken) to IRefreshableItemSource.
• Update RefreshableSelector async refresh/initialization waiting logic to track the latest execution task and avoid canceling an in-flight refresh due to repeated RefreshAsync calls.
• Adjust selector/ItemSource change-notification ordering and add a new test suite for refresh sequencing.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/MvvmControlsTests/Mvvm.Tests/RefreshableSelectorTests.cs	Updates async refresh test to verify repeated calls do not cancel the running refresh.
tests/MvvmControlsTests/Mvvm.Tests/RefreshableSelectorSequenceTests.cs	Adds multi-selector sequence tests validating chained refresh behavior and initialization waiting.
tests/MvvmControlsTests/CSharp9_MissingComponents.cs	Removes a NETFRAMEWORK NotNullAttribute shim from the test project.
tests/.Playlists/RefreshableSelectorTests.playlist	Adds a playlist including the new sequence tests.
src/Mvvm.Controls/Mvvm/RefreshableSelector.cs	Introduces helpers to await the latest async command execution task; adjusts command options and refresh flow.
src/Mvvm.Controls/Mvvm/Primitives/SelectorDefinition.cs	Adds a collection-change flag to avoid resetting selection when selecting during collection change.
src/Mvvm.Controls/Mvvm/Primitives/ItemSource.cs	Reorders _onCollectionChanged callback vs. OnItemsChanged() invocation.
src/Mvvm.Controls/Mvvm/IRefreshableItemSource.cs	Exposes EnsureInitialized / EnsureInitializedAsync on the interface.
src/Mvvm.Controls/Mvvm/ExtensionMethods.cs	Adds [NotNull]/[DoesNotReturn] annotations and a new null-check helper.
src/Mvvm.Controls/CSharp9_MissingComponents.cs	Adds NETFRAMEWORK shims for NotNullAttribute and DoesNotReturnAttribute.
RFBCodeWorks.Mvvm.sln	Adds AGENTS.md to solution items.
AGENTS.md	Updates solution/component documentation and Roslyn 5.x wording.

Comments suppressed due to low confidence (2)

tests/MvvmControlsTests/CSharp9_MissingComponents.cs:10

• NotNullAttribute was removed for .NET Framework builds, but the test project still uses [NotNull] (e.g., in tests/MvvmControlsTests/XAssert.cs). This will fail to compile for net48 unless NotNullAttribute is available via a referenced assembly/package. Consider reintroducing a local System.Diagnostics.CodeAnalysis.NotNullAttribute definition under #if NETFRAMEWORK (or adding the appropriate package reference) so the net48 target continues to build.

using System.ComponentModel;

#if !NET5_0_OR_GREATER
namespace ClassLibrary
{

src/Mvvm.Controls/Mvvm/Primitives/SelectorDefinition.cs:183

• This ArgumentOutOfRangeException call is using the (string paramName, string message) overload, but the arguments are passed in reverse order. As written, the long text becomes paramName and the message becomes "SelectedIndex", which is misleading for callers and debuggers. Swap the arguments (and ideally include value as actualValue).

                {
                    throw new ArgumentOutOfRangeException($"SelectedIndex property was set to a value outside the valid range (expected value between -1 and number of items in the collection ( currently: {Items.Count} )", nameof(SelectedIndex));
                }

---

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[Copilot]

Copilot completely missed the mark on this request. Reworking the test class to demonstrate the following:

• ViewModel has 2 selectors
  ...

Reworked in e143fa4. The test class now has a single method, Test_ViewModel_TwoSelector_NonCancellableAsyncFlow, that walks the exact scenario you described:

1. Selector1 populated — selector1.EnsureInitialized() blocks until the async refresh completes
2. Selector1 item picked — selector1.SelectedItem = selector1.Items[0], which fires onSelectionChanged → selector2.RefreshCommand.Execute(null) (starts Selector2's non-cancellable async refresh without waiting)
3. Selector2 refresh triggered — asserted immediately after the assignment (selector2.IsRefreshing == true)
4. Wait for Selector2 — await selector2.EnsureInitializedAsync(Token) awaits the in-progress refresh
5. Selector2 value selected — selector2.SelectedItem = selector2.Items[0], then selector2.SelectedValue is asserted against the item's Name

@copilot : After the review, update the initial PR comment to reflect changes and the overview.

Updated. See the revised PR description below.

---

Changes

IRefreshableItemSource (interface change)

Added EnsureInitialized and EnsureInitializedAsync so callers can use these methods through the interface type — they were already implemented on RefreshableSelector but were not part of the interface.

RefreshableSelectorNonCancellableAsyncTests (new test file)

Demonstrates a ViewModel-style flow using the non-cancellable async (Func<Task<TList>>) RefreshableSelector constructor. The constructor parameters are exposed as class-level properties configured in [TestInitialize]:

private Func<Task<SelectorTestItem[]>> refreshAsync = null!;
private Func<bool>?  canRefresh;
private Action?      onCollectionChanged;
private Action?      onSelectionChanged;
private bool         refreshOnFirstCollectionRequest;

CreateSelector2() instantiates Selector2 from those properties. The single test method walks a 2-selector ViewModel flow:

1. selector1.EnsureInitialized() — blocks until the async refresh completes
2. selector1.SelectedItem = selector1.Items[0] — fires onSelectionChanged, starting Selector2's non-cancellable async refresh
3. selector2.IsRefreshing is asserted true immediately after
4. await selector2.EnsureInitializedAsync(Token) — waits for the in-progress Selector2 refresh
5. A Selector2 value is selected and verified via SelectedValue

[RFBomb]

• Deleted nuget.exe as its not supposed to be included in the lib.
• Deleted the file Copilot kept adding with unit tests because it misunderstood initial instructions.
• All unit tests are passing as of this review, so I'm merging in.