Make UrlElicitationRequiredErrorData.Elicitations consistent with other Protocol DTOs

[Copilot]

UrlElicitationRequiredErrorData.Elicitations was the sole outlier among Protocol DTOs, using IReadOnlyList<T> with init instead of IList<T> with set.

Changes

• UrlElicitationRequiredErrorData.cs: IReadOnlyList<ElicitRequestParams> + init → IList<ElicitRequestParams> + set
• UrlElicitationRequiredException.cs:
  • Internal _elicitations field narrowed from IReadOnlyList<T> to List<T> (matching what Validate() already returns), eliminating the need for a cast when assigning to Elicitations
  • Validate() return type updated to List<T> accordingly
  • TryParseElicitations(): out parameter changed from IReadOnlyList<T> to IList<T>, allowing the deserialized value to be assigned directly without any conversion

The public Elicitations property on the exception remains IReadOnlyList<T>—that's the exception type's API, not a Protocol DTO, so read-only exposure is appropriate there.

Original prompt

Problem

The Protocol DTOs in src/ModelContextProtocol.Core/Protocol/ consistently use IList<T> for collection properties on their public API surface. However, UrlElicitationRequiredErrorData.Elicitations is the sole outlier — it uses IReadOnlyList<ElicitRequestParams> instead of IList<ElicitRequestParams>.

Inconsistency

Every other Protocol DTO uses IList<T>:

File	Property	Type
Prompt.cs	Arguments	IList<PromptArgument>?
Prompt.cs	Icons	IList<Icon>?
Tool.cs	Icons	IList<Icon>?
ResourceTemplate.cs	Icons	IList<Icon>?
ListResourcesResult.cs	Resources	IList<Resource>
ListPromptsResult.cs	Prompts	IList<Prompt>
ListRootsResult.cs	Roots	IList<Root>
Completion.cs	Values	IList<string>
Annotations.cs	Audience	IList<Role>?
Icon.cs	Sizes	IList<string>?
ElicitRequestParams.RequestSchema	Required	IList<string>?
UrlElicitationRequiredErrorData.cs	Elicitations	IReadOnlyList<ElicitRequestParams> ⬅️ outlier

I also checked for IDictionary vs IReadOnlyDictionary inconsistencies in the Protocol folder. All Protocol DTOs consistently use IDictionary<TKey, TValue> (e.g., CompleteContext.Arguments, CallToolRequestParams.Arguments, GetPromptRequestParams.Arguments, ElicitResult.Content, ElicitRequestParams.RequestSchema.Properties, ClientCapabilities.Experimental, ServerCapabilities.Experimental), so there is no inconsistency there.

Fix

Change UrlElicitationRequiredErrorData.Elicitations from IReadOnlyList<ElicitRequestParams> to IList<ElicitRequestParams> to be consistent with all other Protocol DTOs. Also change the init accessor to set to match the pattern used by the other DTOs.

The file is at: src/ModelContextProtocol.Core/Protocol/UrlElicitationRequiredErrorData.cs

Current code:

public required IReadOnlyList<ElicitRequestParams> Elicitations { get; init; }

Should be changed to:

public required IList<ElicitRequestParams> Elicitations { get; set; }

Note: UrlElicitationRequiredException in src/ModelContextProtocol.Core/UrlElicitationRequiredException.cs stores this data internally as IReadOnlyList<ElicitRequestParams> and exposes it via its Elicitations property as IReadOnlyList<ElicitRequestParams>. That's fine — that class is an exception type, not a Protocol DTO, and using IReadOnlyList on the exception's public API is appropriate. However, any code that creates a UrlElicitationRequiredErrorData and assigns to its Elicitations property will need to be compatible with the change from IReadOnlyList to IList. Since List<T> implements both IList<T> and IReadOnlyList<T>, typical usages should continue to work. Verify that the code in UrlElicitationRequiredException.CreateErrorDataNode() and TryParseElicitations still compiles and works correctly after this change, making any necessary adjustments.

This pull request was created from Copilot chat.

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