Allow usage of ObjectSerializer for Cosmos bindings

[jviau]

Issue describing the changes in this PR

resolves #2911

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Addresses an issue with CosmosDB extension where users could not customize JSON serialization when binding directly to a POCO.

Issue:

CosmosDBConverter was not consuming any user-provided JSON serialization customization. This was a regression from #1924.

Fix:

1. Add a new option to CosmosDBExtensionOptions to provide a ObjectSerializer, defaulting to WorkerOptions.Serializer if no serializer is explicitly set.
2. Update CosmosDBConverter to use this new serializer when deserializing POCOs

Concerns / Discussion:

This is a fix for a regression introduced back in December 2023. But it COULD be seen as a new breaking behavior change for some customers. This poses some risk for this change.

[jviau]

Re-opening. I have reverted back to opt-in for this change.

[Copilot]

Pull request overview

This PR addresses a regression in the CosmosDB extension where custom JSON serialization settings from WorkerOptions.Serializer were not being used when deserializing POCOs in CosmosDB bindings. The fix introduces a new Serializer property to CosmosDBExtensionOptions and a helper method UseCosmosDBWorkerSerializer() to explicitly opt-in to using the worker's serializer for CosmosDB POCO deserialization.

Key changes:

• Added ObjectSerializer? Serializer property to CosmosDBExtensionOptions for custom serialization
• Introduced UseCosmosDBWorkerSerializer() extension method to configure the serializer
• Refactored CosmosDBConverter to use the configured serializer instead of hardcoded System.Text.Json
• Fixed a bug in WorkerCosmosSerializer.FromStream() where streams were being disposed prematurely
• Maintained backward compatibility via a DefaultSerializer with PropertyNameCaseInsensitive = true

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
WorkerCosmosSerializer.cs	Fixed stream disposal bug for Stream-type bindings and minor style improvements
FunctionsWorkerApplicationBuilderExtensions.cs	Added UseCosmosDBWorkerSerializer() method and updated serializer configuration logic
CosmosDBConverter.cs	Replaced hardcoded System.Text.Json with configurable ObjectSerializer throughout
CosmosDBExtensionOptions.cs	Added public Serializer property with TODO for future default behavior
CosmosDBBindingOptions.cs	Added DefaultSerializer and Serializer property getter for fallback behavior
CosmosDBBindingOptionsSetup.cs	Removed unused import and formatting cleanup
release_notes.md	Updated version placeholder and release note description

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[Copilot]

The Serializer property lacks XML documentation. Consider adding a summary comment to document its purpose, especially since this is a public API. For example:

/// <summary>
/// Gets or sets the ObjectSerializer used for deserializing CosmosDB POCOs.
/// If not set, defaults to WorkerOptions.Serializer when UseCosmosDBWorkerSerializer is called.
/// </summary>

Suggested change

	public ObjectSerializer? Serializer { get; set; }
	}
	/// <summary>
	/// Gets or sets the ObjectSerializer used for deserializing CosmosDB POCOs.
	/// If not set, defaults to WorkerOptions.Serializer when UseCosmosDBWorkerSerializer is called.
	/// </summary>
	public ObjectSerializer? Serializer { get; set; }

[Copilot]

The XML documentation for UseCosmosDBWorkerSerializer is incomplete and potentially misleading. It currently says "Configures the CosmosDBExtensionOptions for the Functions Worker Cosmos extension" which is too generic and identical to ConfigureCosmosDBExtensionOptions. Consider updating it to clarify its specific purpose:

/// <summary>
/// Configures the CosmosDB extension to use the WorkerOptions.Serializer for deserializing POCOs.
/// Call this method to ensure custom serialization settings from WorkerOptions are used for CosmosDB bindings.
/// </summary>

Suggested change

	/// Configures the CosmosDBExtensionOptions for the Functions Worker Cosmos extension.
	/// </summary>
	/// <param name="builder">The IFunctionsWorkerApplicationBuilder to add the configuration to.</param>
	/// Configures the CosmosDB extension to use the WorkerOptions.Serializer for deserializing POCOs.
	/// Call this method to ensure custom serialization settings from WorkerOptions are used for CosmosDB bindings.
	/// </summary>
	/// <param name="builder">The <see cref="IFunctionsWorkerApplicationBuilder"/> to configure.</param>

[Copilot]

The relationship and execution order between ConfigureCosmosDBExtension (which uses PostConfigure) and UseCosmosDBWorkerSerializer (which uses Configure) may be confusing to users. Consider adding documentation or examples showing:

1. When to use UseCosmosDBWorkerSerializer vs setting the serializer via ConfigureCosmosDBExtensionOptions
2. That UseCosmosDBWorkerSerializer should typically be called before any manual configuration of the serializer
3. How the serializer resolution works: CosmosExtensionOptions.Serializer (if set) → WorkerOptions.Serializer (if UseCosmosDBWorkerSerializer is called) → DefaultSerializer (fallback)

[Copilot]

[nitpick] The TODO comment mentions ensuring this defaults to WorkerOptions.Serializer in the next major version. Consider adding more context about why this can't be done now (likely to avoid breaking changes) and what the current default behavior is (defaults to DefaultSerializer via CosmosDBBindingOptions.Serializer property unless UseCosmosDBWorkerSerializer is called).

Suggested change

	// TODO: in next major version, ensure this is WorkerOptions.Serializer by default.
	// TODO: In the next major version, ensure this defaults to WorkerOptions.Serializer.
	// This cannot be changed now to avoid breaking existing users who rely on the current default.
	// Currently, this defaults to DefaultSerializer via the CosmosDBBindingOptions.Serializer property,
	// unless UseCosmosDBWorkerSerializer is called.