Add per-model configuration support for language models

[sandy081]

Summary

Adds per-model configuration support, allowing extensions to declare configurable properties per model (e.g., thinking effort for Anthropic models) via a configurationSchema, and users can customize values through the model management editor and chatLanguageModels.json.

What's included

Extension API (vscode.proposed.chatProvider.d.ts)

• configurationSchema on LanguageModelChatInformation — extensions declare per-model config properties
• modelConfiguration on ProvideLanguageModelChatResponseOptions — resolved config passed to providers at request time
• modelConfiguration on ChatRequest — resolved config available to chat participants

Core service (languageModels.ts)

• getModelConfiguration(modelId) — returns resolved config (schema defaults + user overrides)
• setModelConfiguration(modelId, values) — persists per-model config, auto-removes default values
• getModelConfigurationActions(modelId) — returns SubmenuAction[] for enum-based config properties
• configureModel(modelId) — opens chatLanguageModels.json with snippet for the model
• Config stored under settings property in chatLanguageModels.json groups

Model management editor (chatModelsWidget.ts)

• Gear menu and context menu with per-model config actions

Config delivery

• sendChatRequest merges stored config into options (caller overrides take precedence)
• IChatAgentRequest.modelConfiguration carries config to chat participants
• Subagent tool forwards model configuration

JSON schema (languageModelsConfigurationService.ts)

• IntelliSense support for per-model settings in chatLanguageModels.json via if/then conditional schemas

Tests

• Unit tests for getModelConfiguration, default merging, unknown models
• Mock service updates for test compatibility

[Copilot]

Pull request overview

Adds per-model configuration support for language models, allowing model providers to declare configurable per-model settings (via a schema) and having resolved configuration flow through core, UI, and the extension host into providers/participants.

Changes:

• Extend proposed API to allow models to declare a configurationSchema and to expose resolved modelConfiguration on requests.
• Implement per-model configuration resolution/storage in LanguageModelsService and surface enum-based config actions in the model management UI.
• Propagate resolved configuration through chat requests (including subagent invocations) and add unit tests for config merging/defaults.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/vscode-dts/vscode.proposed.chatProvider.d.ts	Adds proposed API surface for per-model config schema + resolved config on requests.
src/vs/workbench/contrib/chat/common/languageModels.ts	Core implementation: config caching, merging defaults, persistence, and UI actions.
src/vs/workbench/contrib/chat/common/languageModelsConfiguration.ts	Extends provider group model to include settings for per-model config.
src/vs/workbench/contrib/chat/browser/languageModelsConfigurationService.ts	Adds JSON schema/intellisense support for settings in chatLanguageModels.json.
src/vs/workbench/contrib/chat/browser/chatManagement/chatModelsWidget.ts	Adds model gear/context menu entries for per-model configuration actions.
src/vs/workbench/contrib/chat/common/chatService/chatServiceImpl.ts	Carries model configuration into chat agent request construction.
src/vs/workbench/contrib/chat/common/participants/chatAgents.ts	Extends IChatAgentRequest to include modelConfiguration.
src/vs/workbench/contrib/chat/common/tools/builtinTools/runSubagentTool.ts	Forwards model configuration into subagent invocations.
src/vs/workbench/api/common/extHostTypeConverters.ts	Exposes model configuration on vscode.ChatRequest objects.
src/vs/workbench/api/common/extHostLanguageModels.ts	Passes resolved per-model config into provider options (modelConfiguration).
src/vs/workbench/api/common/extHostChatSessions.ts	Threads modelConfiguration through session request handling.
src/vs/workbench/api/common/extHostChatAgents2.ts	Threads modelConfiguration through agent/detector request conversion.
src/vs/workbench/api/common/extHost.protocol.ts	Updates protocol types for request options plumbing.
src/vs/workbench/contrib/chat/test/common/languageModels.ts	Updates mock service surface to match new ILanguageModelsService API.
src/vs/workbench/contrib/chat/test/common/languageModels.test.ts	Adds unit tests for resolved per-model config and default merging.
src/vs/workbench/contrib/chat/test/browser/chatManagement/chatModelsViewModel.test.ts	Updates mock service to satisfy new interface requirements.

Comments suppressed due to low confidence (2)

src/vs/workbench/contrib/chat/common/languageModels.ts:1098

• Default-value pruning uses propSchema.default === value, which will fail for non-primitive defaults (objects/arrays) and can leave default values persisted. Consider using the existing equals(...) helper (already imported) for JSON-schema defaults, or otherwise ensuring deep equality when comparing defaults.

		if (schema?.properties) {
			for (const [key, value] of Object.entries(updatedConfig)) {
				const propSchema = schema.properties[key];
				if (propSchema?.default !== undefined && propSchema.default === value) {
					delete updatedConfig[key];
				}
			}

src/vs/workbench/contrib/chat/common/languageModels.ts:1074

• New behavior in setModelConfiguration (merging values, pruning defaults, and updating/removing groups) isn’t covered by tests. Adding unit tests for default-pruning and group removal/creation would help prevent regressions as the per-model settings format evolves.

	async setModelConfiguration(modelId: string, values: IStringDictionary<unknown>): Promise<void> {
		const metadata = this._modelCache.get(modelId);
		if (!metadata) {
			return;
		}

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