fix: enable tool_search for BYOK custom Responses endpoints

[PenguinDOOM]

Fixes #313098

Summary

Enable tool_search for BYOK custom OpenAI-compatible endpoints on the Responses API path.

This change fixes cases where tool_search was advertised in prompts but was not included in the actual Responses request for BYOK custom endpoints.

What changed

• update Responses API tool gating so BYOK custom endpoints can send client-executed tool_search
• allow the actual BYOK request locations used by the custom endpoint flow
• keep existing guards for unsupported models, first-party endpoints, and subagents
• add focused regression coverage for BYOK Responses endpoint behavior

Testing

• npm exec vitest run src/platform/endpoint/node/test/responsesApiToolSearch.spec.ts --pool=forks

Notes

This PR is intentionally scoped to the BYOK custom endpoint request path.
It does not address the broader prompt/request condition sync for tool_search.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds first-class tool-search capability support for extension-contributed and BYOK endpoints, and expands Responses request construction to enable client-side tool_search under BYOK scenarios where the tool may be filtered from the request tool list.

Changes:

• Expose supportsToolSearch on ExtensionContributedChatEndpoint based on model capability matching.
• Update Responses request body logic to implicitly enable client tool_search for BYOK (auth-owned) endpoints in more locations.
• Extend and add tests covering tool search enablement/forwarding and tool filtering behavior across endpoints and locations.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
extensions/copilot/src/platform/endpoint/vscode-node/extChatEndpoint.ts	Adds supportsToolSearch getter for extension-contributed endpoints.
extensions/copilot/src/platform/endpoint/node/responsesApi.ts	Adjusts tool-search enablement rules for BYOK Responses endpoints and locations.
extensions/copilot/src/platform/endpoint/node/test/responsesApiToolSearch.spec.ts	Adds coverage for BYOK implicit client tool_search behavior when request tools omit it.
extensions/copilot/src/extension/tools/node/test/testToolsService.ts	Includes model-specific tools in enabled-tools computation for tests.
extensions/copilot/src/extension/test/vscode-node/endpoints.test.ts	Tests supportsToolSearch exposure for vendor-overridden extension-contributed endpoints.
extensions/copilot/src/extension/prompt/node/test/defaultIntentRequestHandler.spec.ts	Tests forwarding of tool-search support into request model capabilities.
extensions/copilot/src/extension/intents/node/test/backgroundTodoEnablement.spec.ts	Tests tool_search enabled-tools presence for supported extension-contributed endpoints.
extensions/copilot/src/extension/byok/vscode-node/test/customEndpointProvider.spec.ts	Tests BYOK endpoint supportsToolSearch inheritance from supported metadata.
extensions/copilot/src/extension/byok/common/test/byokProvider.spec.ts	Tests preserving model ids/family for tool-search capability matching.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

[PenguinDOOM]

This call is intentional. modelSupportsToolSearch accepts LanguageModelChat | IChatEndpoint | string in chatModelCapabilities.ts, and internally normalizes object inputs via getModelId(model) plus model.family. So passing this.languageModel here is supported and does not evaluate incorrectly.

[PenguinDOOM]

I have confirmed that tool_search is called and the found tools are used in local builds.
I found an issue where the prompts in tool_search and the branching conditions in the actual tool did not match, but I haven't fixed it yet because it would be too broad to include in this pull request.

[PenguinDOOM]

chatmock-log-4.txt
Customized ChatMock logs
ChatMock is connected via the BYOK custom endpoint, responses.
You can see that tool_search is included in the tool.