[http-client-csharp] Allow @@override options bag to apply to protocol methods (currently only convenience)

[m-nash]

Summary

When an operation is customized with an options-bag parameter model via @@override, only the convenience method adopts the options bag. The protocol method still lists every parameter individually, so operations with many parameters keep a large protocol signature. It would be useful for the options-bag grouping to apply to the protocol method as well.

Reproduction

main.tsp:

import "@typespec/http";
using Http;

@service(#{ title: "Widget Service" })
@server("https://example.com", "endpoint")
namespace WidgetService;

model Widget { id: string; }

@route("/widgets/{id}") @get
op getWidget(@path id: string, @query filter?: string, @query top?: int32, @query skip?: int32): Widget;

client.tsp:

import "./main.tsp";
import "@typespec/http";
import "@azure-tools/typespec-client-generator-core";
using Http;
using Azure.ClientGenerator.Core;

model GetWidgetOptions {
  @path id: string;
  @query filter?: string;
  @query top?: int32;
  @query skip?: int32;
}

op getWidgetCustomized(options: GetWidgetOptions): void;

@@override(WidgetService.getWidget, getWidgetCustomized);

tspconfig.yaml:

emit: ["@typespec/http-client-csharp"]
options:
  "@typespec/http-client-csharp":
    package-name: "WidgetService"

Actual

// protocol method - still fully flattened, ignores the override's options bag
public virtual ClientResult GetWidget(string id, string filter = default, int? top = default, int? skip = default, RequestOptions options = null)

// convenience method - correctly uses the options bag
public virtual ClientResult<Widget> GetWidget(GetWidgetOptions options, CancellationToken cancellationToken = default)

Expected / request

The @@override options-bag shape should also apply to the protocol method, so the modeled parameters (path/query/body) are grouped into the options model rather than listed individually, keeping only the trailing RequestOptions/RequestContext. Operations with many parameters (e.g. tiler/imaging APIs with 20-40+ query params) would then get a compact protocol signature instead of a very long one.

Versions

• @typespec/compiler: 1.13.0
• @typespec/http-client-csharp: 1.0.0-alpha.20260703.2

[github-actions]

🎯 Issue Triage

Feature request for the @typespec/http-client-csharp emitter: when @@override`` is used to replace an operation with an options-bag model, the protocol method should also group parameters using the options model rather than listing them individually. This especially impacts APIs with many parameters (20–40+ query params) where the protocol method signature becomes unwieldy.

Category: Feature Request

Area: emitter:client:csharp

🔍 Analysis

• The @@override`` decorator's options-bag grouping currently applies only to the convenience method; the protocol method remains fully flattened regardless of the override
• This creates an asymmetry: the convenience method correctly exposes GetWidgetOptions options, while the protocol method exposes all parameters individually (string id, string filter, int? top, int? skip, RequestOptions options)
• Related closed issue: Add support for Override decorator #8898 "Add support for Override decorator" — initial override decorator support landed, but protocol method handling was not included; that issue even noted this gap: "the one piece we need to handle in the C# generator is the conversion from the convenience method model to the protocol parameters"
• Implementation would require flowing correspondingMethodParams from TCGC through the input types to the C# generator's protocol method signature builder

📝 Suggested next steps

• Confirm this is an intentional gap vs. an incomplete implementation from Add support for Override decorator #8898
• Add correspondingMethodParams mapping to the protocol parameter input types in the emitter
• Update the C# generator to use that mapping when constructing protocol method signatures
• Add a Spector test covering the options-bag-on-protocol-method scenario

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