[release/11.0] Allow unconstrained relationships to break SaveChanges command cycles

[Copilot]

Fixes #38978

Description
Relationships configured with IsConstrained(false) were treated as mandatory SaveChanges command dependencies, causing false circular-dependency errors despite having no database constraint. The change makes an unconstrained foreign-key edge breakable only when it does not require a store-generated-value batching boundary.

Customer impact
Affected applications cannot persist otherwise valid graphs containing an unconstrained reverse relationship in one SaveChanges call; EF Core throws a circular-dependency exception. A workaround is to persist the entities in separate operations or avoid the cyclic relationship configuration.

How found
Customer reported in #38978. The number of affected customers is unknown.

Regression
No, unconstrained relationships are a new feature in EF 11

Testing
Tests added.

Risk
Low. The behavior is limited to unconstrained relationships.

[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]

🟡 Changes recommended

The generated-key boundary guard lacks direct regression coverage.

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Pull request overview

Allows unconstrained foreign-key dependencies to break SaveChanges command cycles while preserving generated-key batching boundaries.

Changes:

• Marks eligible unconstrained FK graph edges as breakable.
• Adds regression coverage for cyclic insert ordering.

File summaries

File	Description
CommandBatchPreparer.cs	Updates dependency-edge breakability.
CommandBatchPreparerTest.cs	Tests unconstrained cycle resolution.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

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

...

Updated the PR summary using the requested template, including #38978 and the implementation, impact, testing, and risk details.

[Copilot]

🟢 Approval recommended

The focused implementation matches the required semantics and covers both key paths.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Balanced