Support Responses API in Azure BYOK

[vijayupadya]

Fixes #318114

When using an Azure BYOK model with Entra auth and a Responses API URL (e.g. behind APIM), VS Code was sending
Chat Completions request bodies (messages) instead of Responses bodies (input), which Azure rejects with:

Unsupported parameter: 'messages'. In the Responses API, this parameter has moved to 'input'.

Cause

The Entra auth path in azureProvider.ts builds its modelInfo manually and never set supported_endpoints, so the endpoint defaulted to Chat
Completions. The API-key path already marked Responses URLs correctly.

Fix

Extracted a small testable helper azureSupportedEndpointsForUrl(url) that returns [ChatCompletions, Responses] for /responses URLs (including APIM vanity domains) and undefined otherwise. The Entra path now applies it to modelInfo.supported_endpoints, mirroring the existing API-key behavior.

[Copilot]

Pull request overview

This PR fixes Azure BYOK (Bring Your Own Key) Entra-authenticated request shaping when users configure an explicit Responses API URL (including APIM vanity domains). It adds a small helper to detect Responses URLs and ensures the Entra auth path sets modelInfo.supported_endpoints so the request body uses input (Responses) instead of messages (Chat Completions).

Changes:

• Add azureSupportedEndpointsForUrl(url) to detect /responses URLs and advertise Responses support via supported_endpoints.
• Apply the helper in the Azure Entra auth path so request bodies are shaped for the Responses API when appropriate.
• Add unit tests covering APIM /responses URL preservation and supported-endpoints detection.

Show a summary per file

File	Description
extensions/copilot/src/extension/byok/vscode-node/azureProvider.ts	Adds azureSupportedEndpointsForUrl and uses it in the Entra auth flow to set modelInfo.supported_endpoints for Responses API URLs.
extensions/copilot/src/extension/byok/vscode-node/test/azureProvider.spec.ts	Adds tests for APIM /responses URL preservation and for supported-endpoints detection behavior.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 2