feat(CopilotCLI): support reasoning effort (#308951)

* feat(CopilotCLI): support reasoning effort

* Enable reasoning effort for Copilot CLI

Author: DonJayamanne

extensions/copilot/package.json

@@ -4582,7 +4582,7 @@
 					},
 					"github.copilot.chat.cli.thinkingEffort.enabled": {
 						"type": "boolean",
-						"default": false,
+						"default": true,
 						"markdownDescription": "%github.copilot.config.cli.thinkingEffort.enabled%",
 						"tags": [
 							"advanced"

extensions/copilot/src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts

@@ -44,7 +44,7 @@ import { emptyWorkspaceInfo, getWorkingDirectory, isIsolationEnabled, IWorkspace
 import { ICustomSessionTitleService } from '../copilotcli/common/customSessionTitleService';
 import { IChatDelegationSummaryService } from '../copilotcli/common/delegationSummaryService';
 import { getCopilotCLISessionDir } from '../copilotcli/node/cliHelpers';
-import { ICopilotCLIAgents, ICopilotCLIModels, ICopilotCLISDK, isWelcomeView } from '../copilotcli/node/copilotCli';
+import { COPILOT_CLI_REASONING_EFFORT_PROPERTY, ICopilotCLIAgents, ICopilotCLIModels, ICopilotCLISDK, isWelcomeView } from '../copilotcli/node/copilotCli';
 import { CopilotCLIPromptResolver } from '../copilotcli/node/copilotcliPromptResolver';
 import { builtinSlashSCommands, CopilotCLICommand, copilotCLICommands, ICopilotCLISession } from '../copilotcli/node/copilotcliSession';
 import { ICopilotCLISessionItem, ICopilotCLISessionService } from '../copilotcli/node/copilotcliSessionService';
@@ -447,6 +447,10 @@ function isIsolationOptionFeatureEnabled(configurationService: IConfigurationSer
 	return configurationService.getConfig(ConfigKey.Advanced.CLIIsolationOption);
 }
 
+function isReasoningEffortFeatureEnabled(configurationService: IConfigurationService): boolean {
+	return configurationService.getConfig(ConfigKey.Advanced.CLIThinkingEffortEnabled);
+}
+
 export class CopilotCLIChatSessionContentProvider extends Disposable implements vscode.ChatSessionContentProvider {
 	private readonly _onDidChangeChatSessionOptions = this._register(new Emitter<vscode.ChatSessionOptionChangeEvent>());
 	readonly onDidChangeChatSessionOptions = this._onDidChangeChatSessionOptions.event;
@@ -1349,23 +1353,23 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 				// This is a request that was created in createCLISessionAndSubmitRequest with attachments already resolved.
 				const { prompt, attachments } = contextForRequest;
 				this.contextForRequest.delete(session.object.sessionId);
-				await session.object.handleRequest(request, { prompt }, attachments, model ? { model } : undefined, authInfo, token);
+				await session.object.handleRequest(request, { prompt }, attachments, model, authInfo, token);
 				await this.commitWorktreeChangesIfNeeded(request, session.object, token);
 			} else if (request.command && !request.prompt && !isUntitled) {
 				const input = (copilotCLICommands as readonly string[]).includes(request.command)
 					? { command: request.command as CopilotCLICommand, prompt: '' }
 					: { prompt: `/${request.command}` };
-				await session.object.handleRequest(request, input, [], model ? { model } : undefined, authInfo, token);
+				await session.object.handleRequest(request, input, [], model, authInfo, token);
 				await this.commitWorktreeChangesIfNeeded(request, session.object, token);
 			} else if (request.prompt && Object.values(builtinSlashSCommands).some(command => request.prompt.startsWith(command))) {
 				// Sessions app built-in slash commands
 				const { prompt, attachments } = await this.promptResolver.resolvePrompt(request, undefined, [], session.object.workspace, [], token);
-				await session.object.handleRequest(request, { prompt }, attachments, model ? { model } : undefined, authInfo, token);
+				await session.object.handleRequest(request, { prompt }, attachments, model, authInfo, token);
 				await this.commitWorktreeChangesIfNeeded(request, session.object, token);
 			} else {
 				// Construct the full prompt with references to be sent to CLI.
 				const { prompt, attachments } = await this.promptResolver.resolvePrompt(request, undefined, [], session.object.workspace, [], token);
-				await session.object.handleRequest(request, { prompt }, attachments, model ? { model } : undefined, authInfo, token);
+				await session.object.handleRequest(request, { prompt }, attachments, model, authInfo, token);
 				await this.commitWorktreeChangesIfNeeded(request, session.object, token);
 			}
 
@@ -1671,7 +1675,7 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 		}
 	}
 
-	private async getOrCreateSession(request: vscode.ChatRequest, chatSessionContext: vscode.ChatSessionContext, stream: vscode.ChatResponseStream, options: { model: string | undefined; agent: SweCustomAgent | undefined }, disposables: DisposableStore, token: vscode.CancellationToken): Promise<{ session: IReference<ICopilotCLISession> | undefined; trusted: boolean }> {
+	private async getOrCreateSession(request: vscode.ChatRequest, chatSessionContext: vscode.ChatSessionContext, stream: vscode.ChatResponseStream, options: { model: { model: string; reasoningEffort?: string } | undefined; agent: SweCustomAgent | undefined }, disposables: DisposableStore, token: vscode.CancellationToken): Promise<{ session: IReference<ICopilotCLISession> | undefined; trusted: boolean }> {
 		const { resource } = chatSessionContext.chatSessionItem;
 		const existingSessionId = this.sessionItemProvider.untitledSessionIdMapping.get(SessionIdForCLI.parse(resource));
 		const id = existingSessionId ?? SessionIdForCLI.parse(resource);
@@ -1689,8 +1693,8 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 		const debugTargetSessionIds = extractDebugTargetSessionIds(request.references);
 		const mcpServerMappings = buildMcpServerMappings(request.tools);
 		const session = isNewSession ?
-			await this.sessionService.createSession({ model, workspace: workspaceInfo, agent, debugTargetSessionIds, mcpServerMappings }, token) :
-			await this.sessionService.getSession({ sessionId: id, model, workspace: workspaceInfo, agent, debugTargetSessionIds, mcpServerMappings }, token);
+			await this.sessionService.createSession({ model: model?.model, reasoningEffort: model?.reasoningEffort, workspace: workspaceInfo, agent, debugTargetSessionIds, mcpServerMappings }, token) :
+			await this.sessionService.getSession({ sessionId: id, model: model?.model, reasoningEffort: model?.reasoningEffort, workspace: workspaceInfo, agent, debugTargetSessionIds, mcpServerMappings }, token);
 		this.sessionItemProvider.notifySessionsChange();
 		// TODO @DonJayamanne We need to refresh to add this new session, but we need a label.
 		// So when creating a session we need a dummy label (or an initial prompt).
@@ -1718,15 +1722,29 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 		return { session, trusted };
 	}
 
-	private async getModelId(request: vscode.ChatRequest | undefined, token: vscode.CancellationToken): Promise<string | undefined> {
+	private async getModelId(request: vscode.ChatRequest | undefined, token: vscode.CancellationToken): Promise<{ model: string; reasoningEffort?: string } | undefined> {
 		const promptFile = request ? await this.getPromptInfoFromRequest(request, token) : undefined;
 		const model = promptFile?.header?.model ? await getModelFromPromptFile(promptFile.header.model, this.copilotCLIModels) : undefined;
-		if (model || token.isCancellationRequested) {
-			return model;
+		if (token.isCancellationRequested) {
+			return undefined;
+		}
+		if (model) {
+			return { model };
 		}
 		// Get model from request.
 		const preferredModelInRequest = request?.model?.id ? await this.copilotCLIModels.resolveModel(request.model.id) : undefined;
-		return preferredModelInRequest ?? await this.copilotCLIModels.getDefaultModel();
+		if (preferredModelInRequest) {
+			const reasoningEffort = isReasoningEffortFeatureEnabled(this.configurationService) ? request?.modelConfiguration?.[COPILOT_CLI_REASONING_EFFORT_PROPERTY] : undefined;
+			return {
+				model: preferredModelInRequest,
+				reasoningEffort: typeof reasoningEffort === 'string' && reasoningEffort ? reasoningEffort : undefined
+			};
+		}
+		const defaultModel = await this.copilotCLIModels.getDefaultModel();
+		if (!defaultModel) {
+			return undefined;
+		}
+		return { model: defaultModel };
 	}
 
 	private async handleDelegationToCloud(session: ICopilotCLISession, request: vscode.ChatRequest, context: vscode.ChatContext, stream: vscode.ChatResponseStream, token: vscode.CancellationToken) {
@@ -1835,7 +1853,7 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 		const { prompt, attachments, references } = await this.promptResolver.resolvePrompt(request, await requestPromptPromise, (otherReferences || []).concat([]), workspaceInfo, [], token);
 
 		const mcpServerMappings = buildMcpServerMappings(request.tools);
-		const session = await this.sessionService.createSession({ workspace: workspaceInfo, agent, model, mcpServerMappings }, token);
+		const session = await this.sessionService.createSession({ workspace: workspaceInfo, agent, model: model?.model, reasoningEffort: model?.reasoningEffort, mcpServerMappings }, token);
 		const modeInstructions = this.createModeInstructions(request);
 		this.chatSessionMetadataStore.updateRequestDetails(session.object.sessionId, [{ vscodeRequestId: request.id, agentId: agent?.name ?? '', modeInstructions }]).catch(ex => this.logService.error(ex, 'Failed to update request details'));
 		if (summary) {
@@ -1869,7 +1887,7 @@ export class CopilotCLIChatSessionParticipant extends Disposable {
 			// The caller is most likely a chat editor or the like.
 			// Now that we've delegated it to a session, we can get out of here.
 			// Else if the request takes say 10 minutes, the caller would be blocked for that long.
-			session.object.handleRequest(request, { prompt }, attachments, model ? { model } : undefined, authInfo, token)
+			session.object.handleRequest(request, { prompt }, attachments, model, authInfo, token)
 				.then(() => this.commitWorktreeChangesIfNeeded(request, session.object, token))
 				.catch(error => {
 					this.logService.error(`Failed to handle CLI session request: ${error}`);

extensions/copilot/src/platform/configuration/common/configurationService.ts

@@ -618,7 +618,7 @@ export namespace ConfigKey {
 		export const CLIIsolationOption = defineSetting<boolean>('chat.cli.isolationOption.enabled', ConfigType.Simple, true);
 		export const CLIAutoCommitEnabled = defineSetting<boolean>('chat.cli.autoCommit.enabled', ConfigType.Simple, true);
 		export const CLISessionController = defineSetting<boolean>('chat.cli.sessionController.enabled', ConfigType.Simple, false);
-		export const CLIThinkingEffortEnabled = defineSetting<boolean>('chat.cli.thinkingEffort.enabled', ConfigType.Simple, false);
+		export const CLIThinkingEffortEnabled = defineSetting<boolean>('chat.cli.thinkingEffort.enabled', ConfigType.Simple, true);
 		export const CLISessionControllerForSessionsApp = defineSetting<boolean>('chat.cli.sessionControllerForSessionsApp.enabled', ConfigType.Simple, false);
 		export const CLITerminalLinks = defineSetting<boolean>('chat.cli.terminalLinks.enabled', ConfigType.Simple, true);
 		export const RequestLoggerMaxEntries = defineAndMigrateSetting<number>('chat.advanced.debug.requestLogger.maxEntries', 'chat.debug.requestLogger.maxEntries', 100);