Propagate case-only principal string key updates to dependent FKs

[Copilot]

Fixes#37023

When a principal key changed only by casing (e.g. "test" → "TEST") before SaveChanges, owned dependents could keep the old FK value if key comparison was case-insensitive. This caused inserted dependents to carry stale FK casing even though the principal PK value changed.

• Key propagation behavior

  • Updated NavigationFixer.SetForeignKeyProperties to propagate when string principal/dependent values are ordinally different, even if GetKeyValueComparer() treats them as equal.
  • This keeps value propagation aligned with the principal’s current key representation, not just comparer equality.

• Regression coverage

  • Added a focused NavigationFixerTest for case-insensitive key comparer scenarios:
    • principal key starts as "test",
    • principal key changes to "TEST",
    • dependent FK is expected to become "TEST" after key fixup.

• Test model setup

  • Added a small case-insensitive string key type mapping in test model configuration so the test exercises comparer-equal / ordinal-different key values.

if(!PrincipalValueEqualsDependentValue(principalProperty,dependentValue,principalValue)||(principalProperty.ClrType==typeof(string)&&StringValuesAreNotOrdinallyEqual(dependentValue,principalValue))){dependentEntry.PropagateValue(principalEntry,principalProperty,dependentProperty,fromQuery,setModified);}

[Copilot]

Pull request overview

This PR fixes key propagation during relationship fixup when a principal string key value changes only by casing (ordinally different), but the key comparer treats old/new as equal (e.g., case-insensitive comparer). The update ensures dependents’ FK values are kept aligned with the principal’s current key representation, avoiding stale FK casing on inserts/updates.

Changes:

• Update NavigationFixer.SetForeignKeyProperties to propagate string key values when principal/dependent strings are ordinally different even if the key comparer reports equality.
• Add a regression test for case-insensitive key comparer scenarios where the principal key casing changes and the dependent FK should be updated accordingly.
• Add a small test-only CoreTypeMapping with a case-insensitive key comparer to reproduce the comparer-equal / ordinal-different behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/EFCore/ChangeTracking/Internal/NavigationFixer.cs	Propagates string FK values when ordinal string value differs even if key comparer says equal.
test/EFCore.Tests/ChangeTracking/Internal/NavigationFixerTest.cs	Adds regression test and a case-insensitive string key type mapping used by the test model.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[cincuranet]

Nice little edge case. :)