[release/10.0] Restore ordinals when transitioning complex collection entries from Deleted state

[Copilot]

Fixes #37724

Description

When changing the state of an entity with a complex collection from Deleted to Unchanged, an InvalidOperationException is thrown with the message "Complex entry ordinal '-1' is invalid for the collection" because deleted entries have -1 as the ordinal in the collection, since they are no longer part of the collection.

Customer impact

This prevents customers from implementing soft-delete patterns with entities that have complex collections.

Workaround: Customers can change the state to Modified instead of Unchanged

How found

Customer reported on 10.0.3.

Regression

No. Complex collections are a new feature in EF Core 10.

Testing

Tests added.

Risk

Low. The fix is surgical and minimal. A quirk mode switch is included to revert to old behavior if needed.

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[AndriySvyryd]

@copilot Update progress by rewriting the PR summary using this template:

Fixes #{number}

**Description**
{Issue description}

**Customer impact**
{How does the reported issue affects customer's app? Are there workarounds?}

**How found**
{Was it customer reported or found during verification? How many customers are affected?}

**Regression**
{Is it a regression from a released version? Which one?}

**Testing**
{How the changes were tested}

**Risk**
{Low/Medium/High, argument why}

[Copilot]

Pull request overview

This PR fixes issue #37724 where changing the state of an entity with a complex collection from Deleted to Unchanged throws an InvalidOperationException about invalid ordinal '-1'. The issue prevents customers from implementing soft-delete patterns with entities that have complex collections in EF Core 10.

Changes:

• Restore Ordinal from OriginalOrdinal when transitioning complex collection entries from Deleted state to prevent validation errors
• Include quirk mode switch UseOldBehavior37724 for backwards compatibility
• Remove dead code that attempted to insert entries into original collection when transitioning from Deleted to Unchanged (this is now handled by the ordinal restoration)
• Refactor InsertEntry method to make early-return logic more explicit

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/EFCore/ChangeTracking/Internal/InternalComplexEntry.cs	Adds quirk mode switch and ordinal restoration logic when transitioning from Deleted state
src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs	Removes duplicate InsertEntry call and refactors null check logic for clarity
test/EFCore.Tests/ChangeTracking/Internal/InternalComplexEntryTest.cs	Adds unit test for Deleted→Unchanged state transition with complex collections
test/EFCore.Specification.Tests/ComplexTypesTrackingTestBase.cs	Adds comprehensive specification tests covering various complex type scenarios (collections, structs, records, fields) for state transitions from Deleted

[roji]

LGTM, but @AndriySvyryd am noticing that only one code path has the quirk.

[artl93]

Approved. New feature. Customer reported. Workaround seems non-obvious.