Prevent wrong codeflow subscription configurations

[Copilot]

This PR implements validation to prevent misconfigured VMR codeflow subscriptions that could lead to conflicts and operational issues, while also improving the API design by unifying subscription querying methods.

Problem

Currently, it's possible to create conflicting codeflow subscriptions that can cause problems:

1. Backflow conflicts: Multiple VMR→repository subscriptions targeting the same repository branch
2. Forward flow conflicts: Multiple repository→VMR subscriptions flowing into the same VMR branch and target directory

These misconfigurations can lead to race conditions, merge conflicts, and unexpected behavior in the dependency flow system.

Solution

Comprehensive Validation

Added validation with a shared service architecture:

• ICodeflowSubscriptionValidationService: Common interface in Maestro.Common
• CodeflowSubscriptionValidationService: Single implementation containing all validation logic
• Server-side validation: SubscriptionsController validates on Create() and UpdateSubscription()
• Client-side validation: DARC CLI validates in AddSubscriptionOperation and UpdateSubscriptionOperation
• Shared base class: SubscriptionOperationBase eliminates duplication between Add/Update operations

Validation Rules

Backflow subscriptions (VMR → repository, sourceDirectory set):

• Only one backflow subscription allowed per target repository + target branch combination

Forward flow subscriptions (repository → VMR, targetDirectory set):

• Only one forward flow subscription allowed per VMR repository + VMR branch + target directory combination

API Improvement

Replaced the specific GetCodeflowSubscriptionsAsync method with a more generic GetSubscriptionsAsync that accepts additional optional parameters:

Task<IEnumerable<Subscription>> GetSubscriptionsAsync(
    string sourceRepo = null,
    string targetRepo = null,
    int? channelId = null,
    bool? sourceEnabled = null,        // New
    string sourceDirectory = null,     // New
    string targetDirectory = null);    // New

This provides a cleaner, more flexible API that supports both general subscription filtering and specific codeflow validation needs without code duplication.

Error Messages

Clear, actionable error messages help users understand and resolve conflicts:

A backflow subscription 'abc123' already exists for the same target repository and branch. 
Only one backflow subscription is allowed per target repository and branch combination.

Benefits

• Maintainable: Validation logic exists in one place
• Consistent: Same validation behavior across all entry points
• Clean API: Generic subscription querying without method duplication
• No breaking changes: Existing functionality remains unaffected

Fixes #5204.

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[premun]

@copilot deduplicate the newly added logic so that it's re-used across darc and the controllers

[Copilot]

@copilot deduplicate the newly added logic so that it's re-used across darc and the controllers

I've deduplicated the validation logic as requested. Created a shared ICodeflowSubscriptionValidationService in Maestro.Common that both DARC CLI and the API controller now use. This eliminates the duplicate validation methods and ensures consistent behavior across both entry points. The shared service uses a simple SubscriptionInfo data structure to avoid circular dependencies.

Changes in commit 092a101:

• Added shared validation service interface and implementation
• Updated both DARC operations to use the shared service
• Updated SubscriptionsController to use the shared service
• Removed all duplicate validation methods
• Registered service in DI for both DARC CLI and API

[premun]

@copilot Can you create a common abstract parent for AddSubscriptionOperation.cs and UpdateSubscriptionOperation.cs and put the ValidateCodeflowSubscriptionConflicts there to deduplicate it between these two classes?

[Copilot]

@copilot Can you create a common abstract parent for AddSubscriptionOperation.cs and UpdateSubscriptionOperation.cs and put the ValidateCodeflowSubscriptionConflicts there to deduplicate it betw...

Created SubscriptionOperationBase abstract class that both AddSubscriptionOperation and UpdateSubscriptionOperation now extend. Moved the ValidateCodeflowSubscriptionConflicts method to the base class to eliminate the duplication between the two operation classes. This follows the DRY principle and ensures consistent validation behavior.

Changes in commit 03f97b0.

[Copilot]

Pull Request Overview

This PR implements validation to prevent conflicting VMR codeflow subscriptions and improves the API design by unifying subscription querying methods. The solution adds comprehensive validation to detect and prevent two types of conflicts: backflow conflicts (multiple VMR→repository subscriptions targeting the same repository branch) and forward flow conflicts (multiple repository→VMR subscriptions flowing into the same VMR branch and target directory).

• Server-side and client-side validation through a shared service architecture
• Unified API with enhanced GetSubscriptionsAsync method accepting additional filtering parameters
• Clear error messages and consistent validation behavior across all entry points

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/ProductConstructionService/ProductConstructionService.Api/Api/v2020_02_20/Controllers/SubscriptionsController.cs	Adds server-side validation logic for detecting codeflow subscription conflicts in Create and UpdateSubscription endpoints
src/Microsoft.DotNet.Darc/DarcLib/IBasicBarClient.cs	Extends GetSubscriptionsAsync interface with additional filtering parameters for sourceEnabled, sourceDirectory, and targetDirectory
src/Microsoft.DotNet.Darc/DarcLib/BarApiClient.cs	Implements the enhanced GetSubscriptionsAsync method with new filtering parameters
src/Microsoft.DotNet.Darc/Darc/Operations/SubscriptionOperationBase.cs	New base class containing shared validation logic for subscription operations
src/Microsoft.DotNet.Darc/Darc/Operations/AddSubscriptionOperation.cs	Refactored to inherit from SubscriptionOperationBase and includes client-side validation
src/Microsoft.DotNet.Darc/Darc/Operations/UpdateSubscriptionOperation.cs	Refactored to inherit from SubscriptionOperationBase and includes client-side validation
src/Maestro/Maestro.DataProviders/SqlBarClient.cs	Updates data provider to support new filtering parameters in GetSubscriptionsAsync
test/Microsoft.DotNet.Darc.Tests/Operations/GetSubscriptionsOperationTests.cs	Updates test mocks to accommodate the new GetSubscriptionsAsync signature
test/Microsoft.DotNet.Darc.Tests/Operations/GetBuildOperationTests.cs	Updates test mocks to accommodate the new GetSubscriptionsAsync signature