Add IAsyncDisposable to CosmosService and fix async disposal pattern

[anuchandy]

What does this PR do?

[Provide a clear, concise description of the changes]

The .NET DI container prefers DisposeAsync() during shutdown, pr Implement IAsyncDisposable in CosmosService. Following https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/implementing-disposeasync

Fixes: #1148

[Any additional context, screenshots, or information that helps reviewers]

GitHub issue number?

[Link to the GitHub issue this PR addresses]

Pre-merge Checklist

• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
  • Commit history is clean with descriptive messages (cleanup guide)
  • Added comprehensive tests for new/modified functionality
  • Updated servers/Azure.Mcp.Server/CHANGELOG.md and/or servers/Fabric.Mcp.Server/CHANGELOG.md for product changes (features, bug fixes, UI/UX, updated dependencies)
• For MCP tool changes:
  • One tool per PR: This PR adds or modifies only one MCP tool for faster review cycles
  • Updated servers/Azure.Mcp.Server/README.md and/or servers/Fabric.Mcp.Server/README.md documentation
  • Validate README.md changes using script at eng/scripts/Process-PackageReadMe.ps1. See Package README
  • Updated command list in /servers/Azure.Mcp.Server/docs/azmcp-commands.md and/or /docs/fabric-commands.md
  • Run .\eng\scripts\Update-AzCommandsMetadata.ps1 to update tool metadata in azmcp-commands.md (required for CI)
  • For new or modified tool descriptions, ran ToolDescriptionEvaluator and obtained a score of 0.4 or more and a top 3 ranking for all related test prompts
  • For tools with new names, including new tools or renamed tools, update consolidated-tools.json
  • For new tools associated with Azure services or publicly available tools/APIs/products, add URL to documentation in the PR description
• Extra steps for Azure MCP Server tool changes:
  • Updated test prompts in /servers/Azure.Mcp.Server/docs/e2eTestPrompts.md
  • 👉 For Community (non-Microsoft team member) PRs:
    • Security review: Reviewed code for security vulnerabilities, malicious code, or suspicious activities before running tests (crypto mining, spam, data exfiltration, etc.)
    • Manual tests run: added comment /azp run mcp - pullrequest - live to run Live Test Pipeline

[Copilot]

Pull request overview

This PR implements IAsyncDisposable in CosmosService to fix an anti-pattern where the Dispose() method was implemented as async void, which prevented callers from awaiting the disposal operation. The implementation follows the Microsoft async disposal pattern guidelines for sealed classes.

Changes:

• Added IAsyncDisposable to the ICosmosService interface and CosmosService class
• Replaced the async void Dispose(bool disposing) method with a proper DisposeAsyncCore() implementation
• Added DisposeAsync() method that properly implements the async disposal pattern
• Modified synchronous Dispose() to call the async core method synchronously

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
tools/Azure.Mcp.Tools.Cosmos/src/Services/ICosmosService.cs	Added IAsyncDisposable interface to ICosmosService
tools/Azure.Mcp.Tools.Cosmos/src/Services/CosmosService.cs	Implemented async disposal pattern with DisposeAsyncCore(), DisposeAsync(), and updated Dispose() methods; marked class as sealed
servers/Azure.Mcp.Server/changelog-entries/1768937539777.yaml	Added changelog entry documenting the bug fix

[g2vinay]

Any unit tests we can add for this ?

[anuchandy]

Hi Vinay - sorry I missed responding to your comment earlier.

This follows Microsoft’s documented DI pattern for IAsyncDisposable: the DI container is responsible for when and how disposal is invoked. Adding a unit test here would mostly end up testing the framework/container behavior rather than our code, which is why I didn’t include a dedicated test for IAsyncDisposable.