CodexAcpServer.ts

import * as acp from "@agentclientprotocol/sdk";
import {RequestError, type SessionId, type SessionModeState} from "@agentclientprotocol/sdk";
import {CodexEventHandler} from "./CodexEventHandler";
import {CodexApprovalHandler} from "./CodexApprovalHandler";
import {CodexElicitationHandler} from "./CodexElicitationHandler";
import {type CodexAuthRequest, getCodexAuthMethods, isCodexAuthRequest} from "./CodexAuthMethod";
import {CodexAcpClient, type SessionMetadata, type SessionMetadataWithThread} from "./CodexAcpClient";
import type {McpStartupResult} from "./CodexAppServerClient";
import {ACPSessionConnection, type AcpClientConnection, type UpdateSessionEvent} from "./ACPSessionConnection";
import type {InputModality, ReasoningEffort} from "./app-server";
import type {
    Account,
    Model,
    ReasoningEffortOption,
    Thread,
    ThreadItem,
    TurnCompletedNotification,
    UserInput
} from "./app-server/v2";
import type {RateLimitsMap} from "./RateLimitsMap";
import {ModelId} from "./ModelId";
import {AgentMode, MODE_CONFIG_ID} from "./AgentMode";
import {
    createModelConfigOption,
    createReasoningEffortConfigOption,
    findSupportedEffort,
    MODEL_CONFIG_ID,
    REASONING_EFFORT_CONFIG_ID,
} from "./ModelConfigOption";
import type {TokenCount} from "./TokenCount";
import {toPromptUsage} from "./TokenCount";
import {CodexCommands} from "./CodexCommands";
import type {QuotaMeta} from "./QuotaMeta";
import {logger} from "./Logger";
import {sanitizeMcpServerName} from "./McpServerName";
import {createResponseItemHistoryFallbackUpdates} from "./ResponseItemHistoryFallback";
import {
    type LegacyLoadSessionResponse,
    type LegacyNewSessionResponse,
    type LegacyResumeSessionResponse,
    type LegacySessionModelState,
    type LegacySetSessionModelRequest,
    type LegacySetSessionModelResponse,
    isExtMethodRequest,
    LEGACY_SET_SESSION_MODEL_METHOD,
} from "./AcpExtensions";
import {
    createCollabAgentToolCallUpdate,
    createCommandExecutionCompleteUpdate,
    createCommandExecutionUpdate,
    createDynamicToolCallUpdate,
    createFileChangeUpdate,
    createImageGenerationUpdate,
    createImageViewUpdate,
    createMcpToolCallUpdate,
    formatWebSearchTitle,
} from "./CodexToolCallMapper";
import {
    createFastModeConfigOption,
    FAST_MODE_CONFIG_ID,
    FAST_MODE_OFF,
    FAST_MODE_ON,
    modelSupportsFast,
    resolveFastServiceTier,
} from "./FastModeConfig";
import packageJson from "../package.json";
import {isJetBrains2026_1Client} from "./JBUtils";
import {resolveTerminalOutputMode, type TerminalOutputMode} from "./TerminalOutputMode";

export interface ThreadGoalSnapshot {
    objective: string;
    status: string;
    tokenBudget: number | null;
}

export interface SessionState {
    sessionId: string,
    currentModelId: string,
    availableModels: Array<Model>,
    supportedReasoningEfforts: Array<ReasoningEffortOption>,
    supportedInputModalities: Array<InputModality>,
    agentMode: AgentMode,
    currentTurnId: string | null;
    lastTokenUsage: TokenCount | null;
    totalTokenUsage: TokenCount | null;
    modelContextWindow: number | null;
    rateLimits: RateLimitsMap | null;
    account: Account | null;
    authConfigured: boolean;
    authProvider: string | null;
    cwd: string;
    additionalDirectories: string[];
    fastModeEnabled: boolean;
    currentModelSupportsFast: boolean;
    sessionMcpServers?: Array<string>;
    terminalOutputMode: TerminalOutputMode;
    currentGoal?: ThreadGoalSnapshot | null;
}

interface ActiveAuthState {
    account: Account | null;
    authConfigured: boolean;
}

interface PendingMcpStartupSession {
    requestedServers: Set<string>;
    afterVersion: number;
}

interface PendingTurnStart {
    promise: Promise<string | null>;
    resolve: (turnId: string | null) => void;
}

interface ActivePrompt {
    completion: Promise<void>;
    closeSignal: Promise<null>;
    cancelSignal: Promise<null>;
    signal: AbortSignal;
    currentTurn: { threadId: string, turnId: string } | null;
    requestCancel: () => void;
    requestClose: () => void;
    complete: () => void;
}

export class CodexAcpServer {
    private static readonly MODEL_NAME_TOKEN_OVERRIDES: Record<string, string> = {
        gpt: "GPT",
        mini: "Mini",
        codex: "Codex",
    };

    private readonly codexAcpClient: CodexAcpClient;
    private readonly connection: AcpClientConnection;
    private readonly defaultAuthRequest: CodexAuthRequest | null;
    private readonly getExitCode: () => number | null;
    private readonly getRecentStderr: () => string;
    private readonly availableCommands: CodexCommands;
    private clientInfo: acp.Implementation | null;
    private terminalOutputMode: TerminalOutputMode;

    private readonly sessions: Map<string, SessionState>;
    private readonly pendingMcpStartupSessions: Map<string, PendingMcpStartupSession>;
    private readonly pendingTurnStarts: Map<string, PendingTurnStart>;
    private readonly activePrompts: Map<string, ActivePrompt>;
    private readonly closingSessions: Map<string, number>;
    private readonly sessionGenerations: Map<string, number>;
    private readonly sessionOpenGenerations: Map<string, number>;

    constructor(
        connection: AcpClientConnection,
        codexAcpClient: CodexAcpClient,
        defaultAuthRequest?: CodexAuthRequest,
        getExitCode?: () => number | null,
        getRecentStderr?: () => string,
    ) {
        this.sessions = new Map();
        this.pendingMcpStartupSessions = new Map();
        this.pendingTurnStarts = new Map();
        this.activePrompts = new Map();
        this.closingSessions = new Map();
        this.sessionGenerations = new Map();
        this.sessionOpenGenerations = new Map();
        this.connection = connection;
        this.codexAcpClient = codexAcpClient;
        this.defaultAuthRequest = defaultAuthRequest ?? null;
        this.getExitCode = getExitCode ?? (() => null);
        this.getRecentStderr = getRecentStderr ?? (() => "");
        this.clientInfo = null;
        this.terminalOutputMode = "terminal_output_delta";
        this.availableCommands = new CodexCommands(
            connection,
            codexAcpClient,
            (operation) => this.runWithProcessCheck(operation),
            () => this.refreshSessionsAuthState(null)
        );
    }

    async initialize(
        _params: acp.InitializeRequest,
    ): Promise<acp.InitializeResponse> {
        logger.log("Initialize request received");
        this.clientInfo = _params.clientInfo ?? null;
        this.terminalOutputMode = resolveTerminalOutputMode(_params.clientCapabilities);
        await this.runWithProcessCheck(() => this.codexAcpClient.initialize(_params));
        return {
            protocolVersion: acp.PROTOCOL_VERSION,
            agentInfo: {
                name: packageJson.name,
                title: "Codex",
                version: packageJson.version,
            },
            agentCapabilities: {
                auth: {
                    logout: {},
                },
                loadSession: true,
                promptCapabilities: {
                    embeddedContext: true,
                    image: true
                },
                sessionCapabilities: {
                    resume: { },
                    list: { },
                    close: { },
                    delete: { },
                    additionalDirectories: {},
                },
                mcpCapabilities: {
                    acp: false,
                    http: true,
                    sse: false
                }
            },
            authMethods: getCodexAuthMethods(_params.clientCapabilities),
        };
    }

    async extMethod(method: string, params: Record<string, unknown>): Promise<Record<string, unknown>> {
        const methodRequest = { method: method, params: params };
        if (!isExtMethodRequest(methodRequest)) {
            return {};
        }
        switch (methodRequest.method) {
            case "authentication/status":
                return await this.runWithProcessCheck(() => this.codexAcpClient.getAuthenticationStatus());
            case "authentication/logout": {
                await this.logout({});
                return {};
            }
            case LEGACY_SET_SESSION_MODEL_METHOD:
                return await this.unstable_setSessionModel(this.parseLegacySetSessionModelParams(methodRequest.params));
        }
    }

    async checkAuthorization(){
        const authNeeded = await this.runWithProcessCheck(() => this.codexAcpClient.authRequired());
        logger.log("Auth requirement checked", {authRequired: authNeeded});
        if (authNeeded) {
            if (this.defaultAuthRequest) {
                logger.log("Authenticating with default auth request...", {
                    authRequest: this.defaultAuthRequest
                });
                await this.authenticate(this.defaultAuthRequest)
                logger.log("Authentication completed");
            } else {
                logger.log("Authentication required but no default auth request provided, return to IDE");
                throw RequestError.authRequired();
            }
        }
    }

    async getOrCreateSession(request: acp.NewSessionRequest | acp.ResumeSessionRequest): Promise<[SessionId, LegacySessionModelState, SessionModeState]> {
        try {
            return await this.tryCreateSession(request);
        } catch (e) {
            const error = e instanceof Error ? e : new Error(String(e));
            await this.handleError(error);
            throw e;
        }
    }

    async handleError(e: Error){
        if (e.message.includes("log out") || e.message.includes("cloud requirements")) {
            await this.runWithProcessCheck(() => this.codexAcpClient.logout());
            await this.refreshSessionsAuthState(null);
            throw RequestError.internalError(`${(e.message)}\n\nYou have been logged out. Please try again.`);
        }
    }

    private beginSessionOpen(sessionId: string): number {
        const generation = this.getSessionGeneration(sessionId);
        if (this.sessionIsClosing(sessionId)) {
            throw RequestError.invalidRequest(`Session ${sessionId} is closing`);
        }
        this.sessionOpenGenerations.set(sessionId, generation);
        return generation;
    }

    private sessionOpenCanInstall(sessionId: string, generation: number): boolean {
        return !this.sessionIsClosing(sessionId) && this.getSessionGeneration(sessionId) === generation;
    }

    private async cleanupStaleSessionOpen(sessionId: string, generation: number): Promise<boolean> {
        if (this.sessionOpenGenerations.get(sessionId) === generation) {
            if (!this.sessionIsClosing(sessionId)) {
                this.bumpSessionGeneration(sessionId);
            }
            this.beginSessionCloseFence(sessionId);
            try {
                await this.runWithProcessCheck(() => this.codexAcpClient.closeSession(sessionId));
            } catch (err) {
                logger.error(`Failed to close stale session open for ${sessionId}`, err);
            } finally {
                this.endSessionCloseFence(sessionId);
            }
            return true;
        }
        return false;
    }

    private async closeStaleSessionOpen(sessionId: string, generation: number): Promise<void> {
        await this.cleanupStaleSessionOpen(sessionId, generation);
        throw RequestError.invalidRequest(`Session ${sessionId} is closing`);
    }

    private sessionIsClosing(sessionId: string): boolean {
        return (this.closingSessions.get(sessionId) ?? 0) > 0;
    }

    private beginSessionCloseFence(sessionId: string): void {
        this.closingSessions.set(sessionId, (this.closingSessions.get(sessionId) ?? 0) + 1);
    }

    private endSessionCloseFence(sessionId: string): void {
        const count = this.closingSessions.get(sessionId) ?? 0;
        if (count <= 1) {
            this.closingSessions.delete(sessionId);
            return;
        }
        this.closingSessions.set(sessionId, count - 1);
    }

    private getSessionGeneration(sessionId: string): number {
        return this.sessionGenerations.get(sessionId) ?? 0;
    }

    private bumpSessionGeneration(sessionId: string): number {
        const generation = this.getSessionGeneration(sessionId) + 1;
        this.sessionGenerations.set(sessionId, generation);
        return generation;
    }

    async tryCreateSession(request: acp.NewSessionRequest | acp.ResumeSessionRequest): Promise<[SessionId, LegacySessionModelState, SessionModeState]> {
        const requestedSessionGeneration = "sessionId" in request
            ? this.beginSessionOpen(request.sessionId)
            : null;
        await this.checkAuthorization();
        const requestedMcpServers = request.mcpServers ?? [];
        const mcpServerStartupVersion = requestedMcpServers.length > 0
            ? this.codexAcpClient.getMcpServerStartupVersion()
            : null;

        let sessionMetadata: SessionMetadata;
        let resumeSubscribed = false;
        if ("sessionId" in request) {
            logger.log(`Resume existing session: ${request.sessionId}...`);
            try {
                sessionMetadata = await this.runWithProcessCheck(() =>
                    this.codexAcpClient.resumeSession(request, () => {
                        resumeSubscribed = true;
                    })
                );
            } catch (err) {
                if (resumeSubscribed && requestedSessionGeneration !== null) {
                    await this.cleanupStaleSessionOpen(request.sessionId, requestedSessionGeneration);
                }
                throw err;
            }
        } else {
            logger.log(`Create new session...`);
            sessionMetadata = await this.runWithProcessCheck(() => this.codexAcpClient.newSession(request));
        }

        const {sessionId, currentModelId, models} = sessionMetadata;
        const authProvider = sessionMetadata.modelProvider ?? this.codexAcpClient.getModelProvider();
        let authState: ActiveAuthState;
        try {
            authState = await this.getAuthStateForProvider(authProvider);
        } catch (err) {
            if (resumeSubscribed && requestedSessionGeneration !== null) {
                await this.cleanupStaleSessionOpen(sessionId, requestedSessionGeneration);
            }
            throw err;
        }
        const sessionGeneration = requestedSessionGeneration ?? this.beginSessionOpen(sessionId);
        if (!this.sessionOpenCanInstall(sessionId, sessionGeneration)) {
            resumeSubscribed = false;
            await this.closeStaleSessionOpen(sessionId, sessionGeneration);
        }
        const sessionMcpServers = this.resolveSessionMcpServers(requestedMcpServers, "sessionId" in request);
        const currentModel = this.findCurrentModel(models, currentModelId);
        const currentModelSupportsFast = modelSupportsFast(currentModel);
        const sessionState: SessionState = {
            sessionId: sessionId,
            currentModelId: currentModelId,
            availableModels: models,
            supportedReasoningEfforts: currentModel?.supportedReasoningEfforts ?? [],
            supportedInputModalities: currentModel?.inputModalities ?? ["text", "image"],
            agentMode: AgentMode.getInitialAgentMode(),
            currentTurnId: null,
            lastTokenUsage: null,
            totalTokenUsage: null,
            modelContextWindow: null,
            rateLimits: null,
            account: authState.account,
            authConfigured: authState.authConfigured,
            authProvider: authProvider,
            cwd: request.cwd,
            additionalDirectories: sessionMetadata.additionalDirectories,
            fastModeEnabled: sessionMetadata.currentServiceTier === "fast",
            currentModelSupportsFast: currentModelSupportsFast,
            sessionMcpServers: sessionMcpServers,
            terminalOutputMode: this.terminalOutputMode,
        };
        this.sessions.set(sessionId, sessionState);
        resumeSubscribed = false;

        if (requestedMcpServers.length > 0 && mcpServerStartupVersion !== null) {
            this.pendingMcpStartupSessions.set(sessionId, {
                requestedServers: new Set(getRequestedMcpServerNames(requestedMcpServers)),
                afterVersion: mcpServerStartupVersion,
            });
            this.publishMcpStartupStatusAsync(sessionId);
        }

        this.publishAvailableCommandsAsync(sessionState);
        const sessionModelState: LegacySessionModelState = this.createModelState(models, currentModelId);
        const sessionModeState: SessionModeState = sessionState.agentMode.toSessionModeState();

        return [sessionId, sessionModelState, sessionModeState];
    }

    private async getAuthStateForProvider(authProvider: string | null): Promise<ActiveAuthState> {
        if (!this.authProviderUsesOpenAiAccount(authProvider)) {
            return {
                account: null,
                authConfigured: true,
            };
        }
        const accountResponse = await this.runWithProcessCheck(() => this.codexAcpClient.getAccount());
        return {
            account: accountResponse.account,
            authConfigured: accountResponse.account !== null || !accountResponse.requiresOpenaiAuth,
        };
    }

    private authProviderUsesOpenAiAccount(authProvider: string | null): boolean {
        return authProvider === null || authProvider === "openai";
    }

    private authProvidersMatch(a: string | null, b: string | null): boolean {
        if (this.authProviderUsesOpenAiAccount(a) && this.authProviderUsesOpenAiAccount(b)) {
            return true;
        }
        return a === b;
    }

    private getAuthProviderForAuthenticateRequest(request: acp.AuthenticateRequest): string | null {
        if (isCodexAuthRequest(request) && request.methodId === "gateway") {
            return "custom-gateway";
        }
        return null;
    }

    async loadSession(params: acp.LoadSessionRequest): Promise<LegacyLoadSessionResponse> {
        logger.log("Loading session...", {sessionId: params.sessionId});
        const {
            sessionId,
            modelState,
            modeState,
            thread,
        } = await this.getOrCreateSessionWithHistory(params);

        await this.streamThreadHistory(sessionId, thread);

        logger.log("Session loaded", {
            sessionId: sessionId,
            modelId: modelState.currentModelId,
            availableModelCount: modelState.availableModels.length
        });
        return {
            models: modelState,
            modes: modeState,
            ...this.createSessionConfigOptionsResponse(this.getSessionState(sessionId)),
        };
    }

    async resumeSession(params: acp.ResumeSessionRequest): Promise<LegacyResumeSessionResponse> {
        logger.log("Resuming session...", {sessionId: params.sessionId});
        const [sessionId, modelState, modeState] = await this.getOrCreateSession(params);

        logger.log("Session resumed", {
            sessionId: sessionId,
            modelId: modelState.currentModelId,
            availableModelCount: modelState.availableModels.length
        });
        return {
            models: modelState,
            modes: modeState,
            ...this.createSessionConfigOptionsResponse(this.getSessionState(sessionId)),
        };
    }

    async listSessions(params: acp.ListSessionsRequest): Promise<acp.ListSessionsResponse> {
        logger.log("Listing sessions...", {cwd: params.cwd, cursor: params.cursor});
        await this.checkAuthorization();
        const response = await this.runWithProcessCheck(() => this.codexAcpClient.listSessions(params));
        return {
            ...response,
            sessions: response.sessions.map((session) => {
                const activeSession = this.sessions.get(session.sessionId);
                if (!activeSession || activeSession.additionalDirectories.length === 0) {
                    return session;
                }
                return {
                    ...session,
                    additionalDirectories: activeSession.additionalDirectories,
                };
            }),
        };
    }

    async closeSession(params: acp.CloseSessionRequest): Promise<acp.CloseSessionResponse> {
        logger.log("Closing session...", {sessionId: params.sessionId});
        const closeGeneration = this.bumpSessionGeneration(params.sessionId);
        const sessionState = this.sessions.get(params.sessionId);
        this.beginSessionCloseFence(params.sessionId);

        try {
            if (sessionState) {
                await this.interruptSessionTurn(sessionState, "Close", true);
            } else {
                logger.log("Close request received for unknown local session", {sessionId: params.sessionId});
            }

            const activePrompt = this.activePrompts.get(params.sessionId);
            if (activePrompt) {
                activePrompt.requestClose();
                await activePrompt.completion;
            }

            await this.runWithProcessCheck(() => this.codexAcpClient.closeSession(params.sessionId));
            logger.log("Session closed", {sessionId: params.sessionId});
        } finally {
            if (this.getSessionGeneration(params.sessionId) === closeGeneration) {
                this.sessions.delete(params.sessionId);
                this.pendingMcpStartupSessions.delete(params.sessionId);
                this.pendingTurnStarts.delete(params.sessionId);
                this.activePrompts.delete(params.sessionId);
            }
            this.endSessionCloseFence(params.sessionId);
        }

        return {};
    }

    async deleteSession(params: acp.DeleteSessionRequest): Promise<acp.DeleteSessionResponse> {
        logger.log("Deleting session...", {sessionId: params.sessionId});
        const sessionId = params.sessionId;
        const shouldCloseLocalSession = this.hasLocalSession(sessionId);

        this.beginSessionCloseFence(sessionId);
        try {
            if (shouldCloseLocalSession) {
                await this.closeSession({sessionId});
            } else {
                this.bumpSessionGeneration(sessionId);
            }

            await this.runWithProcessCheck(() => this.codexAcpClient.deleteSession(sessionId));
            logger.log("Session deleted", {sessionId});
        } finally {
            this.endSessionCloseFence(sessionId);
        }

        return {};
    }

    private hasLocalSession(sessionId: string): boolean {
        return this.sessions.has(sessionId)
            || this.pendingMcpStartupSessions.has(sessionId)
            || this.pendingTurnStarts.has(sessionId)
            || this.activePrompts.has(sessionId)
            || this.hasPendingSessionOpen(sessionId)
            || this.sessionIsClosing(sessionId);
    }

    private hasPendingSessionOpen(sessionId: string): boolean {
        return this.sessionOpenGenerations.get(sessionId) === this.getSessionGeneration(sessionId);
    }

    async newSession(
        params: acp.NewSessionRequest,
    ): Promise<LegacyNewSessionResponse> {
        logger.log("Starting new session...");
        const [sessionId, modelState, modeState] = await this.getOrCreateSession(params);

        logger.log("New session created", {
            sessionId: sessionId,
            modelId: modelState.currentModelId,
            availableModelCount: modelState.availableModels.length
        });

        return {
            sessionId: sessionId,
            models: modelState,
            modes: modeState,
            ...this.createSessionConfigOptionsResponse(this.getSessionState(sessionId)),
        };
    }

    async authenticate(
        _params: acp.AuthenticateRequest,
    ): Promise<acp.AuthenticateResponse> {
        logger.log("Authenticate request received");
        const isAuthenticated = await this.runWithProcessCheck(() => this.codexAcpClient.authenticate(_params));
        if (!isAuthenticated) {
            logger.log("Authenticate request failed");
            throw RequestError.invalidParams();
        }
        await this.refreshSessionsAuthState(this.getAuthProviderForAuthenticateRequest(_params));
        logger.log("Authenticate request completed");
        return { };
    }

    async logout(_params: acp.LogoutRequest): Promise<void> {
        logger.log("Logout request received");
        await this.runWithProcessCheck(() => this.codexAcpClient.logout());
        await this.refreshSessionsAuthState(null);
        logger.log("Logout request completed");
    }

    private async refreshSessionsAuthState(authProvider: string | null): Promise<void> {
        if (this.sessions.size === 0) return;

        const sessionsToRefresh = [...this.sessions.values()]
            .filter(sessionState => this.authProvidersMatch(sessionState.authProvider, authProvider));
        if (sessionsToRefresh.length === 0) return;

        const authState = await this.getAuthStateForProvider(authProvider);
        for (const sessionState of sessionsToRefresh) {
            sessionState.account = authState.account;
            sessionState.authConfigured = authState.authConfigured;
        }
    }

    async setSessionMode(
        _params: acp.SetSessionModeRequest,
    ): Promise<acp.SetSessionModeResponse> {
        logger.log("Set session mode requested", {
            sessionId: _params.sessionId,
            modeId: _params.modeId
        });
        const sessionState = this.sessions.get(_params.sessionId);
        if (!sessionState) throw new Error(`Session ${_params.sessionId} not found`);

        this.applyModeChange(sessionState, _params.modeId);
        return {};
    }

    async setSessionConfigOption(params: acp.SetSessionConfigOptionRequest): Promise<acp.SetSessionConfigOptionResponse> {
        logger.log("Set session config option requested", {
            sessionId: params.sessionId,
            configId: params.configId,
        });
        const sessionState = this.sessions.get(params.sessionId);
        if (!sessionState) throw new Error(`Session ${params.sessionId} not found`);

        if (typeof params.value !== "string") {
            throw RequestError.invalidParams();
        }
        const value = params.value;

        switch (params.configId) {
            case FAST_MODE_CONFIG_ID:
                this.applyFastModeChange(sessionState, value);
                break;
            case MODE_CONFIG_ID:
                this.applyModeChange(sessionState, value);
                break;
            case MODEL_CONFIG_ID:
                this.applyModelChange(sessionState, value);
                break;
            case REASONING_EFFORT_CONFIG_ID:
                this.applyReasoningEffortChange(sessionState, value);
                break;
            default:
                throw RequestError.invalidParams();
        }

        return {
            configOptions: this.createSessionConfigOptions(sessionState),
        };
    }

    private applyFastModeChange(sessionState: SessionState, value: string): void {
        if (value !== FAST_MODE_ON && value !== FAST_MODE_OFF) {
            throw RequestError.invalidParams();
        }
        sessionState.fastModeEnabled = value === FAST_MODE_ON;
    }

    private applyModeChange(sessionState: SessionState, value: string): void {
        const newMode = AgentMode.find(value);
        if (!newMode) {
            throw RequestError.invalidParams();
        }
        sessionState.agentMode = newMode;
    }

    private applyModelChange(sessionState: SessionState, value: string): void {
        const model = sessionState.availableModels.find(m => m.id === value);
        if (!model) {
            const currentModel = ModelId.fromString(sessionState.currentModelId).model;
            if (value === currentModel) {
                return;
            }
            throw RequestError.invalidParams();
        }
        const currentEffort = ModelId.fromString(sessionState.currentModelId).effort;
        const effort = findSupportedEffort(model.supportedReasoningEfforts, currentEffort)
            ?? model.defaultReasoningEffort;
        this.applyModelAndEffort(sessionState, model, effort);
    }

    private applyReasoningEffortChange(sessionState: SessionState, value: string): void {
        const effort = findSupportedEffort(sessionState.supportedReasoningEfforts, value);
        if (!effort) {
            throw RequestError.invalidParams();
        }
        const {model} = ModelId.fromString(sessionState.currentModelId);
        sessionState.currentModelId = ModelId.create(model, effort).toString();
    }

    private applyModelAndEffort(sessionState: SessionState, model: Model, effort: ReasoningEffort): void {
        sessionState.currentModelId = ModelId.fromComponents(model, effort).toString();
        sessionState.supportedReasoningEfforts = model.supportedReasoningEfforts;
        sessionState.supportedInputModalities = model.inputModalities;
        sessionState.currentModelSupportsFast = modelSupportsFast(model);
    }

    async unstable_setSessionModel(params: LegacySetSessionModelRequest): Promise<LegacySetSessionModelResponse> {
        logger.log("Set session model requested", {
            sessionId: params.sessionId,
            modelId: params.modelId
        });
        const sessionState = this.sessions.get(params.sessionId);
        if (!sessionState) throw new Error(`Session ${params.sessionId} not found`);

        const {model: requestedModelName, effort: requestedEffort} = ModelId.fromString(params.modelId);

        const models = await this.codexAcpClient.fetchAvailableModels();
        const model = models.find(m => m.id === requestedModelName);
        if (!model) throw new Error(`Unknown model ${params.modelId}`);

        let reasoningEffort: ReasoningEffort;
        if (requestedEffort) {
            const matchedEffort = findSupportedEffort(model.supportedReasoningEfforts, requestedEffort);
            if (!matchedEffort) {
                throw new Error(`Unsupported reasoning effort ${requestedEffort} for model ${requestedModelName}`);
            }
            reasoningEffort = matchedEffort;
        } else {
            reasoningEffort = model.defaultReasoningEffort;
        }

        sessionState.availableModels = models;
        this.applyModelAndEffort(sessionState, model, reasoningEffort);

        return {};
    }

    private parseLegacySetSessionModelParams(params: Record<string, unknown>): LegacySetSessionModelRequest {
        const sessionId = params["sessionId"];
        const modelId = params["modelId"];
        if (typeof sessionId !== "string" || typeof modelId !== "string") {
            throw RequestError.invalidParams();
        }
        return {
            sessionId: sessionId,
            modelId: modelId,
        };
    }

    private createSessionConfigOptions(sessionState: SessionState): Array<acp.SessionConfigOption> {
        const currentModelId = ModelId.fromString(sessionState.currentModelId);
        const configOptions = [
            sessionState.agentMode.toConfigOption(),
            createModelConfigOption(sessionState.availableModels, currentModelId.model),
        ];
        if (sessionState.supportedReasoningEfforts.length > 0) {
            configOptions.push(
                createReasoningEffortConfigOption(sessionState.supportedReasoningEfforts, currentModelId.effort),
            );
        }
        if (sessionState.currentModelSupportsFast) {
            configOptions.push(createFastModeConfigOption(sessionState.fastModeEnabled));
        }
        return configOptions;
    }

    private createSessionConfigOptionsResponse(sessionState: SessionState): {
        configOptions?: Array<acp.SessionConfigOption>;
    } {
        if (!this.isSessionConfigEnabled()) {
            return {};
        }
        return {
            configOptions: this.createSessionConfigOptions(sessionState),
        };
    }

    private isSessionConfigEnabled(): boolean {
        // Temporarily disabled for JB IDEs 2026.1 due to issues in session_config (LLM-28118)
        return !isJetBrains2026_1Client(this.clientInfo);
    }

    private publishAvailableCommandsAsync(sessionState: SessionState) {
        void this.availableCommands.publish(sessionState);
    }

    private findCurrentModel(models: Model[], currentModelId: string): Model | undefined {
        const modelId = ModelId.fromString(currentModelId);
        return models.find(m => m.id === modelId.model);
    }

    private normalizeModelDisplayName(displayName: string): string {
        return displayName
            .split("-")
            .map((token) => CodexAcpServer.MODEL_NAME_TOKEN_OVERRIDES[token.toLowerCase()] ?? token)
            .join("-");
    }

    private createModelState(availableModels: Model[], selectedModelId: string): LegacySessionModelState {
        const allowedModels = availableModels
            .flatMap((model) =>
                model.supportedReasoningEfforts.map((effort) => ({
                    modelId: ModelId.fromComponents(model, effort.reasoningEffort).toString(),
                    name: `${this.normalizeModelDisplayName(model.displayName)} (${effort.reasoningEffort})`,
                    description: `${model.description} ${effort.description}`,
                }))
            );
        return {
            availableModels: allowedModels,
            currentModelId: selectedModelId,
        }
    }

    private async getOrCreateSessionWithHistory(
        request: acp.LoadSessionRequest
    ): Promise<{
        sessionId: SessionId;
        modelState: LegacySessionModelState;
        modeState: SessionModeState;
        thread: Thread;
    }> {
        const requestedSessionGeneration = this.beginSessionOpen(request.sessionId);
        await this.checkAuthorization();
        const requestedMcpServers = request.mcpServers ?? [];
        const mcpServerStartupVersion = requestedMcpServers.length > 0
            ? this.codexAcpClient.getMcpServerStartupVersion()
            : null;

        logger.log(`Load existing session: ${request.sessionId}...`);
        let subscribed = false;
        let sessionMetadata: SessionMetadataWithThread;
        try {
            sessionMetadata = await this.runWithProcessCheck(() =>
                this.codexAcpClient.loadSession(request, () => {
                    subscribed = true;
                })
            );
        } catch (err) {
            if (subscribed) {
                await this.cleanupStaleSessionOpen(request.sessionId, requestedSessionGeneration);
            }
            throw err;
        }

        const {sessionId, currentModelId, models, thread} = sessionMetadata;
        const authProvider = sessionMetadata.modelProvider ?? this.codexAcpClient.getModelProvider();
        let authState: ActiveAuthState;
        try {
            authState = await this.getAuthStateForProvider(authProvider);
        } catch (err) {
            if (subscribed) {
                await this.cleanupStaleSessionOpen(request.sessionId, requestedSessionGeneration);
            }
            throw err;
        }
        if (!this.sessionOpenCanInstall(sessionId, requestedSessionGeneration)) {
            subscribed = false;
            await this.closeStaleSessionOpen(sessionId, requestedSessionGeneration);
        }
        const sessionMcpServers = this.resolveSessionMcpServers(requestedMcpServers, true);
        const currentModel = this.findCurrentModel(models, currentModelId);
        const currentModelSupportsFast = modelSupportsFast(currentModel);
        const sessionState: SessionState = {
            sessionId: sessionId,
            currentModelId: currentModelId,
            availableModels: models,
            supportedReasoningEfforts: currentModel?.supportedReasoningEfforts ?? [],
            supportedInputModalities: currentModel?.inputModalities ?? ["text", "image"],
            agentMode: AgentMode.getInitialAgentMode(),
            currentTurnId: null,
            lastTokenUsage: null,
            totalTokenUsage: null,
            modelContextWindow: null,
            rateLimits: null,
            account: authState.account,
            authConfigured: authState.authConfigured,
            authProvider: authProvider,
            cwd: request.cwd,
            additionalDirectories: sessionMetadata.additionalDirectories,
            fastModeEnabled: sessionMetadata.currentServiceTier === "fast",
            currentModelSupportsFast: currentModelSupportsFast,
            sessionMcpServers: sessionMcpServers,
            terminalOutputMode: this.terminalOutputMode,
        };
        this.sessions.set(sessionId, sessionState);
        subscribed = false;

        if (requestedMcpServers.length > 0 && mcpServerStartupVersion !== null) {
            this.pendingMcpStartupSessions.set(sessionId, {
                requestedServers: new Set(getRequestedMcpServerNames(requestedMcpServers)),
                afterVersion: mcpServerStartupVersion,
            });
            this.publishMcpStartupStatusAsync(sessionId);
        }

        await this.availableCommands.publish(sessionState);
        const sessionModelState: LegacySessionModelState = this.createModelState(models, currentModelId);
        const sessionModeState: SessionModeState = sessionState.agentMode.toSessionModeState();

        return {
            sessionId: sessionId,
            modelState: sessionModelState,
            modeState: sessionModeState,
            thread: thread,
        };
    }

    private async streamThreadHistory(sessionId: string, thread: Thread): Promise<void> {
        const session = new ACPSessionConnection(this.connection, sessionId);
        const sessionState = this.getSessionState(sessionId);
        const responseItemFallbackUpdates = await createResponseItemHistoryFallbackUpdates(
            thread,
            sessionState.terminalOutputMode,
        );

        const threadUpdates: UpdateSessionEvent[] = [];
        for (const turn of thread.turns) {
            for (const item of turn.items) {
                const updates = await this.createHistoryUpdates(item, sessionState);
                threadUpdates.push(...updates);
            }
        }

        const updates = responseItemFallbackUpdates
            ? mergeHistoryUpdates(responseItemFallbackUpdates, threadUpdates)
            : threadUpdates;
        for (const update of updates) {
            await session.update(update);
        }
    }

    private async createHistoryUpdates(item: ThreadItem, sessionState: SessionState): Promise<UpdateSessionEvent[]> {
        switch (item.type) {
            case "userMessage":
                return this.createUserMessageUpdates(item);
            case "hookPrompt":
            case "subAgentActivity":
            case "sleep":
                return [];
            case "agentMessage":
                return [{
                    sessionUpdate: "agent_message_chunk",
                    content: { type: "text", text: item.text },
                }];
            case "reasoning":
                return this.createReasoningUpdates(item);
            case "fileChange":
                return [await createFileChangeUpdate(item)];
            case "commandExecution": {
                const updates = [await createCommandExecutionUpdate(item)];
                const completeUpdate = createCommandExecutionCompleteUpdate(item, sessionState.terminalOutputMode);
                if (completeUpdate) {
                    updates.push(completeUpdate);
                }
                return updates;
            }
            case "mcpToolCall":
                return [await createMcpToolCallUpdate(item)];
            case "dynamicToolCall":
                return [await createDynamicToolCallUpdate(item)];
            case "collabAgentToolCall":
                return [createCollabAgentToolCallUpdate(item)];
            case "webSearch":
                return [this.createWebSearchUpdate(item)];
            case "imageView":
                return [createImageViewUpdate(item)];
            case "imageGeneration":
                return [createImageGenerationUpdate(item)];
            case "enteredReviewMode":
                return [this.createReviewModeUpdate(item, true)];
            case "exitedReviewMode":
                return [this.createReviewModeUpdate(item, false)];
            case "contextCompaction":
                return [this.createContextCompactionUpdate()];
            case "plan":
                return [this.createPlanUpdate(item)];
        }
    }

    private createUserMessageUpdates(item: ThreadItem & { type: "userMessage" }): UpdateSessionEvent[] {
        const updates: UpdateSessionEvent[] = [];
        for (const input of item.content) {
            const blocks = this.userInputToContentBlocks(input);
            for (const block of blocks) {
                updates.push({
                    sessionUpdate: "user_message_chunk",
                    content: block,
                });
            }
        }
        return updates;
    }

    private createReasoningUpdates(item: ThreadItem & { type: "reasoning" }): UpdateSessionEvent[] {
        const parts = item.summary.length > 0 ? item.summary : item.content;
        return parts.map((text) => ({
            sessionUpdate: "agent_thought_chunk",
            content: { type: "text", text: text },
        }));
    }

    private createWebSearchUpdate(
        item: ThreadItem & { type: "webSearch" }
    ): UpdateSessionEvent {
        return {
            sessionUpdate: "tool_call",
            toolCallId: item.id,
            kind: "search",
            title: formatWebSearchTitle(item),
            status: "completed",
            rawInput: {
                query: item.query,
                action: item.action,
            },
        };
    }

    private createReviewModeUpdate(
        item: ThreadItem & { type: "enteredReviewMode" | "exitedReviewMode" },
        entered: boolean
    ): UpdateSessionEvent {
        return {
            sessionUpdate: "agent_message_chunk",
            content: {
                type: "text",
                text: `${entered ? "Entered" : "Exited"} review mode: ${item.review}`,
            },
        };
    }

    private createContextCompactionUpdate(): UpdateSessionEvent {
        return {
            sessionUpdate: "agent_message_chunk",
            content: {
                type: "text",
                text: "Context compacted.",
            },
        };
    }

    private createPlanUpdate(
        item: ThreadItem & { type: "plan" }
    ): UpdateSessionEvent {
        return {
            sessionUpdate: "agent_message_chunk",
            content: {
                type: "text",
                text: `Plan:\n${item.text}`,
            },
        };
    }

    private userInputToContentBlocks(input: UserInput): acp.ContentBlock[] {
        switch (input.type) {
            case "text":
                return input.text.length > 0 ? [{ type: "text", text: input.text }] : [];
            case "image":
                return [{ type: "text", text: this.formatUriAsLink("image", input.url) }];
            case "localImage": {
                const uri = input.path.startsWith("file://") ? input.path : `file://${input.path}`;
                return [{ type: "text", text: this.formatUriAsLink(null, uri) }];
            }
            case "skill":
                return [{ type: "text", text: `skill:${input.name} (${input.path})` }];
        }
        return [];
    }

    private formatUriAsLink(name: string | null, uri: string): string {
        if (name && name.length > 0) {
            return `[@${name}](${uri})`;
        }
        if (uri.startsWith("file://")) {
            const path = uri.replace("file://", "");
            const fileName = path.split("/").pop() ?? path;
            return `[@${fileName}](${uri})`;
        }
        return uri;
    }

    getSessionState(sessionId: string): SessionState {
        const sessionState = this.sessions.get(sessionId);
        if (!sessionState) {
            throw new Error(`Session ${sessionId} not found`);
        }
        return sessionState;
    }

    private resolveSessionMcpServers(
        mcpServers: Array<acp.McpServer>,
        recoverFromStartup: boolean,
    ): Array<string> {
        // Explicit MCP servers from the request are the primary source of truth for the session.
        const requestedServerNames = getRequestedMcpServerNames(mcpServers);
        if (requestedServerNames.length > 0) {
            return requestedServerNames;
        }
        // Fresh sessions without MCP config should not inherit any session MCP state.
        if (!recoverFromStartup) {
            return [];
        }
        // Without a thread-scoped startup completion event, loadSession/resumeSession can no longer
        // recover omitted session MCP server names. Treat the session set as unknown unless ACP
        // explicitly provided mcpServers in the request.
        logger.log("Skipping MCP server recovery for load/resume without explicit mcpServers");
        return [];
    }

    private publishMcpStartupStatusAsync(sessionId: string): void {
        void this.doPublishMcpStartupStatus(sessionId);
    }

    private async doPublishMcpStartupStatus(sessionId: string): Promise<void> {
        const pendingStartup = this.pendingMcpStartupSessions.get(sessionId);
        if (!pendingStartup) {
            return;
        }

        try {
            const mcpStartup = await this.runWithProcessCheck(() =>
                this.codexAcpClient.awaitMcpServerStartup(
                    Array.from(pendingStartup.requestedServers),
                    pendingStartup.afterVersion,
                )
            );
            if (!this.sessions.has(sessionId)
                || this.sessionIsClosing(sessionId)
                || this.pendingMcpStartupSessions.get(sessionId) !== pendingStartup) {
                return;
            }
            await this.publishMcpStartupStatus(sessionId, mcpStartup, pendingStartup.requestedServers);
        } catch (err) {
            logger.error(`Failed to publish MCP startup status for session ${sessionId}`, err);
        } finally {
            if (this.pendingMcpStartupSessions.get(sessionId) === pendingStartup) {
                this.pendingMcpStartupSessions.delete(sessionId);
            }
        }
    }

    private async publishMcpStartupStatus(
        sessionId: string,
        mcpStartup: McpStartupResult,
        requestedServers?: Set<string>
    ): Promise<void> {
        const filteredStartup = requestedServers
            ? {
                ready: mcpStartup.ready.filter(server => requestedServers.has(server)),
                failed: mcpStartup.failed.filter(server => requestedServers.has(server.server)),
                cancelled: mcpStartup.cancelled.filter(server => requestedServers.has(server)),
            }
            : mcpStartup;

        for (const update of CodexEventHandler.createMcpStartupUpdates(filteredStartup)) {
            await this.connection.notify(acp.methods.client.session.update, {
                sessionId,
                update,
            });
        }
    }

    private trackActivePrompt(sessionId: string): ActivePrompt {
        let resolveCompletion: () => void = () => {};
        const completion = new Promise<void>((resolve) => {
            resolveCompletion = resolve;
        });
        let resolveCloseSignal: (value: null) => void = () => {};
        const closeSignal = new Promise<null>((resolve) => {
            resolveCloseSignal = resolve;
        });
        let resolveCancelSignal: (value: null) => void = () => {};
        const cancelSignal = new Promise<null>((resolve) => {
            resolveCancelSignal = resolve;
        });
        const abortController = new AbortController();

        let completed = false;
        let closeRequested = false;
        const activePrompt: ActivePrompt = {
            completion,
            closeSignal,
            cancelSignal,
            signal: abortController.signal,
            currentTurn: null,
            requestCancel: () => {
                if (abortController.signal.aborted) {
                    return;
                }
                abortController.abort();
                resolveCancelSignal(null);
            },
            requestClose: () => {
                if (closeRequested) {
                    return;
                }
                closeRequested = true;
                activePrompt.requestCancel();
                resolveCloseSignal(null);
            },
            complete: () => {
                if (completed) {
                    return;
                }
                completed = true;
                if (this.activePrompts.get(sessionId) === activePrompt) {
                    this.activePrompts.delete(sessionId);
                }
                resolveCompletion();
            },
        };

        this.activePrompts.set(sessionId, activePrompt);
        return activePrompt;
    }

    private cancelBeforeTurnStarted(activePrompt: ActivePrompt): Promise<null> {
        return activePrompt.cancelSignal.then(() => {
            if (activePrompt.currentTurn === null) {
                return null;
            }
            return new Promise<null>(() => {});
        });
    }

    private observePromptRequestCancellation(
        signal: AbortSignal | undefined,
        sessionState: SessionState,
        activePrompt: ActivePrompt,
    ): () => void {
        if (!signal) {
            return () => {};
        }

        const onAbort = () => {
            if (this.activePrompts.get(sessionState.sessionId) !== activePrompt) {
                return;
            }
            logger.log("Prompt request cancelled", {sessionId: sessionState.sessionId});
            activePrompt.requestCancel();
            const turn = activePrompt.currentTurn;
            if (!turn) {
                return;
            }
            void this.requestTurnInterrupt(turn, "Cancel");
        };

        if (signal.aborted) {
            onAbort();
            return () => {};
        }

        signal.addEventListener("abort", onAbort, {once: true});
        return () => signal.removeEventListener("abort", onAbort);
    }

    private createPendingTurnStart(): PendingTurnStart {
        let resolve: (turnId: string | null) => void = () => {};
        const promise = new Promise<string | null>((innerResolve) => {
            resolve = innerResolve;
        });
        return {promise, resolve};
    }

    private async interruptPromptTurn(
        turn: { threadId: string, turnId: string },
        requestName: "Cancel" | "Close",
    ): Promise<void> {
        this.codexAcpClient.markTurnStale({
            threadId: turn.threadId,
            turnId: turn.turnId,
        });
        try {
            await this.requestTurnInterrupt(turn, requestName);
        } finally {
            this.codexAcpClient.resolveTurnInterrupted({
                threadId: turn.threadId,
                turnId: turn.turnId,
            });
        }
    }

    private async requestTurnInterrupt(
        turn: { threadId: string, turnId: string },
        requestName: "Cancel" | "Close",
    ): Promise<void> {
        try {
            await this.runWithProcessCheck(() => this.codexAcpClient.turnInterrupt({
                threadId: turn.threadId,
                turnId: turn.turnId,
            }));
            logger.log(`${requestName} - turnInterrupt succeeded`, {
                sessionId: turn.threadId,
                currentTurnId: turn.turnId,
            });
        } catch (err) {
            logger.error(`${requestName} - turnInterrupt failed`, err);
        }
    }

    private interruptLateStartedTurn(turn: { threadId: string, turnId: string }): void {
        void this.interruptPromptTurn(turn, "Close");
    }

    private promptShouldStop(sessionId: string, activePrompt: ActivePrompt): boolean {
        return activePrompt.signal.aborted || this.activePrompts.get(sessionId) !== activePrompt || this.sessionIsClosing(sessionId);
    }

    private async interruptSessionTurn(
        sessionState: SessionState,
        requestName: "Cancel" | "Close",
        resolveInterruptedTurn: boolean,
    ): Promise<void> {
        const turnId = await this.getInterruptibleTurnId(sessionState, requestName);
        if (!turnId) {
            return;
        }

        logger.log(`${requestName} session requested`, {
            sessionId: sessionState.sessionId,
            currentTurnId: turnId,
        });
        if (resolveInterruptedTurn) {
            this.codexAcpClient.markTurnStale({
                threadId: sessionState.sessionId,
                turnId,
            });
        }
        try {
            await this.runWithProcessCheck(() => this.codexAcpClient.turnInterrupt({
                threadId: sessionState.sessionId,
                turnId,
            }));
            logger.log(`${requestName} - turnInterrupt succeeded`, {
                sessionId: sessionState.sessionId,
                currentTurnId: turnId,
            });
        } catch (err) {
            logger.error(`${requestName} - turnInterrupt failed`, err);
        } finally {
            if (resolveInterruptedTurn) {
                this.codexAcpClient.resolveTurnInterrupted({
                    threadId: sessionState.sessionId,
                    turnId,
                });
            }
        }
    }

    private async getInterruptibleTurnId(
        sessionState: SessionState,
        requestName: "Cancel" | "Close",
    ): Promise<string | null> {
        if (sessionState.currentTurnId) {
            return sessionState.currentTurnId;
        }

        const pendingTurnStart = this.pendingTurnStarts.get(sessionState.sessionId);
        if (!pendingTurnStart) {
            logger.log(`${requestName} request rejected: no current turn`, {sessionId: sessionState.sessionId});
            return null;
        }

        if (requestName === "Close") {
            pendingTurnStart.resolve(null);
            return null;
        }

        const turnId = await pendingTurnStart.promise;
        if (!turnId) {
            logger.log(`${requestName} request rejected: no current turn`, {sessionId: sessionState.sessionId});
        }
        return turnId;
    }

    async prompt(params: acp.PromptRequest, signal?: AbortSignal): Promise<acp.PromptResponse> {
        logger.log("Prompt received", {
            sessionId: params.sessionId,
            prompt: params.prompt,
        });
        const sessionState = this.getSessionState(params.sessionId);
        sessionState.currentTurnId = null;
        sessionState.lastTokenUsage = null;
        const activePrompt = this.trackActivePrompt(params.sessionId);
        let pendingTurnStart: PendingTurnStart | null = null;
        const ensurePendingTurnStart = (): PendingTurnStart => {
            if (pendingTurnStart === null) {
                pendingTurnStart = this.createPendingTurnStart();
                this.pendingTurnStarts.set(params.sessionId, pendingTurnStart);
            }
            return pendingTurnStart;
        };
        const disposePromptRequestCancellation = this.observePromptRequestCancellation(signal, sessionState, activePrompt);

        try {
            const eventHandler = new CodexEventHandler(this.connection, sessionState);
            const approvalHandler = new CodexApprovalHandler(this.connection, sessionState, activePrompt.signal);
            const elicitationHandler = new CodexElicitationHandler(this.connection, sessionState, activePrompt.signal);
            await this.codexAcpClient.subscribeToSessionEvents(params.sessionId,
                (event) => {
                    elicitationHandler.handleNotification(event);
                    return eventHandler.handleNotification(event);
                },
                approvalHandler,
                elicitationHandler);

            if (activePrompt.signal.aborted) {
                return this.cancelledPromptResponse(sessionState);
            }

            const commandPromise = this.availableCommands.tryHandleCommand(params.prompt, sessionState, {
                onTurnStartPending: () => {
                    ensurePendingTurnStart();
                },
                onTurnStarted: (turnId, threadId) => {
                    const turn = {threadId, turnId};
                    activePrompt.currentTurn = turn;
                    if (this.promptShouldStop(params.sessionId, activePrompt)) {
                        this.interruptLateStartedTurn(turn);
                        return;
                    }
                    sessionState.currentTurnId = turnId;
                    pendingTurnStart?.resolve(turnId);
                },
            });
            void commandPromise.catch((err) => {
                if (this.activePrompts.get(params.sessionId) !== activePrompt) {
                    logger.error(`Command for cancelled prompt ${params.sessionId} failed after prompt returned`, err);
                }
            });
            const commandResult = await Promise.race([
                commandPromise,
                activePrompt.closeSignal,
                this.cancelBeforeTurnStarted(activePrompt),
            ]);
            if (commandResult === null) {
                return this.cancelledPromptResponse(sessionState);
            }
            if (commandResult.handled) {
                logger.log("Prompt handled by a command");
                await this.codexAcpClient.waitForSessionNotifications(params.sessionId);
                if (commandResult.turnCompleted?.turn.status === "interrupted") {
                    await this.notifyConversationInterrupted(params.sessionId);
                    return this.cancelledPromptResponse(sessionState);
                }
                const error = eventHandler.getFailure();
                if (error) {
                    // noinspection ExceptionCaughtLocallyJS
                    throw error;
                }
                return {
                    stopReason: "end_turn",
                    usage: this.buildPromptUsage(sessionState.lastTokenUsage),
                    _meta: this.buildQuotaMeta(sessionState),
                };
            }

            if (this.sessionIsClosing(params.sessionId)) {
                return this.cancelledPromptResponse(sessionState);
            }

            const modelId = ModelId.fromString(sessionState.currentModelId);
            const modelLacksReasoning = sessionState.supportedReasoningEfforts.length > 0
                && sessionState.supportedReasoningEfforts.every(e => e.reasoningEffort === "none");

            const disableSummary = sessionState.account?.type === "apiKey" || modelLacksReasoning;
            if (disableSummary) {
                logger.log("Disable reasoning.summary", {
                    sessionId: params.sessionId,
                    reason: sessionState.account?.type === "apiKey" ? "API key" : "model lacks reasoning"
                });
            }

            if (!sessionState.supportedInputModalities.includes("image") && params.prompt.some(b => b.type === "image")) {
                throw RequestError.invalidRequest("The current model does not support image input");
            }
            const agentMode = sessionState.agentMode;
            const serviceTier = resolveFastServiceTier(
                sessionState.fastModeEnabled,
                sessionState.currentModelSupportsFast,
            );
            ensurePendingTurnStart();
            const sendPromptPromise = this.runWithProcessCheck(
                () => this.codexAcpClient.sendPrompt(
                    params,
                    agentMode,
                    modelId,
                    serviceTier,
                    disableSummary,
                    sessionState.cwd,
                    sessionState.additionalDirectories,
                    (turnId) => {
                        const turn = {threadId: params.sessionId, turnId};
                        activePrompt.currentTurn = turn;
                        if (this.promptShouldStop(params.sessionId, activePrompt)) {
                            this.interruptLateStartedTurn(turn);
                            return;
                        }
                        sessionState.currentTurnId = turnId;
                        pendingTurnStart?.resolve(turnId);
                    },
                    () => this.promptShouldStop(params.sessionId, activePrompt),
                ));
            void sendPromptPromise.catch((err) => {
                if (this.activePrompts.get(params.sessionId) !== activePrompt) {
                    logger.error(`Prompt for cancelled session ${params.sessionId} failed after prompt returned`, err);
                }
            });
            const turnCompleted = await Promise.race([
                sendPromptPromise,
                activePrompt.closeSignal,
                this.cancelBeforeTurnStarted(activePrompt),
            ]);

            if (turnCompleted === null) {
                return this.cancelledPromptResponse(sessionState);
            }

            await this.codexAcpClient.waitForSessionNotifications(params.sessionId);

            if (turnCompleted.turn.status === "interrupted") {
                await this.notifyConversationInterrupted(params.sessionId);
                return this.cancelledPromptResponse(sessionState);
            }

            const error = eventHandler.getFailure();
            if (error) {
                // noinspection ExceptionCaughtLocallyJS
                throw error;
            }

            return {
                stopReason: "end_turn",
                usage: this.buildPromptUsage(sessionState.lastTokenUsage),
                _meta: this.buildQuotaMeta(sessionState),
            };
        } catch (err) {
            logger.error(`Prompt for session ${params.sessionId} failed`, err);
            throw err;
        } finally {
            logger.log("Prompt completed", {sessionId: params.sessionId});
            disposePromptRequestCancellation();
            sessionState.currentTurnId = null;
            const registeredPendingTurnStart = this.pendingTurnStarts.get(params.sessionId);
            if (registeredPendingTurnStart !== undefined) {
                this.pendingTurnStarts.delete(params.sessionId);
                registeredPendingTurnStart.resolve(null);
            }
            activePrompt.complete();
        }
    }

    private cancelledPromptResponse(sessionState: SessionState): acp.PromptResponse {
        return {
            stopReason: "cancelled",
            usage: this.buildPromptUsage(sessionState.lastTokenUsage),
            _meta: this.buildQuotaMeta(sessionState),
        };
    }

    private async notifyConversationInterrupted(sessionId: string): Promise<void> {
        if (this.sessionIsClosing(sessionId) || !this.sessions.has(sessionId)) {
            return;
        }
        await this.connection.notify(acp.methods.client.session.update, {
            sessionId,
            update: {
                sessionUpdate: "agent_message_chunk",
                content: {
                    type: "text",
                    text: "*Conversation interrupted*"
                }
            }
        });
    }

    private buildQuotaMeta(sessionState: SessionState): { quota: QuotaMeta } {
        const lastTokenUsage = sessionState.lastTokenUsage;

        // Remove the "[reasoning-level]" suffix from currentModelId if present
        const modelName = sessionState.currentModelId.replace(/\[.*?]$/, '');

        // FIXME: currently all tokens are reported for the current model
        const modelUsage = (lastTokenUsage != null)
            ? [{ model: modelName, token_count: lastTokenUsage }]
            : [];

        return {
            quota: {
                token_count: sessionState.lastTokenUsage,
                model_usage: modelUsage
            }
        };
    }

    private buildPromptUsage(lastTokenUsage: TokenCount | null): acp.Usage | null {
        if (lastTokenUsage == null) {
            return null;
        }
        return toPromptUsage(lastTokenUsage);
    }

    private async runWithProcessCheck<T>(operation: () => Promise<T>): Promise<T> {
        try {
            return await operation();
        } catch (err) {
            const exitCode = this.getExitCode();
            const requestErrorCode = 1001 // Just some magic number
            if (exitCode == 3221225781) {
                throw new RequestError(requestErrorCode, `VC++ redistributable should be installed`);
            }
            if (exitCode !== null) {
                const stderr = this.getRecentStderr().trim();
                const detail = stderr ? `:\n${stderr}` : "";
                throw new RequestError(requestErrorCode, `Codex process has exited with code ${exitCode}${detail}`);
            }
            throw err;
        }
    }

    async cancel(params: acp.CancelNotification): Promise<void> {
        const sessionState = this.sessions.get(params.sessionId);
        if (!sessionState) {
            logger.log("Cancel request rejected: session not found", {sessionId: params.sessionId});
            return;
        }

        // After turnInterrupt(), Codex will send turn/completed, which naturally completes awaitTurnCompleted().
        await this.interruptSessionTurn(sessionState, "Cancel", false);
    }
}

function mergeHistoryUpdates(
    responseItemFallbackUpdates: UpdateSessionEvent[],
    threadUpdates: UpdateSessionEvent[],
): UpdateSessionEvent[] {
    const merged: UpdateSessionEvent[] = [];
    const seen = new Set<string>();
    let fallbackIndex = 0;

    const pushUpdate = (update: UpdateSessionEvent) => {
        const key = historyUpdateKey(update);
        if (key && seen.has(key)) {
            return;
        }
        if (key) {
            seen.add(key);
        }
        merged.push(update);
    };

    const flushFallbackThrough = (targetKey: string): boolean => {
        const matchIndex = responseItemFallbackUpdates.findIndex((update, index) => (
            index >= fallbackIndex && historyUpdateKey(update) === targetKey
        ));
        if (matchIndex === -1) {
            return false;
        }

        while (fallbackIndex <= matchIndex) {
            pushUpdate(responseItemFallbackUpdates[fallbackIndex]!);
            fallbackIndex += 1;
        }
        return true;
    };

    for (const update of threadUpdates) {
        const key = historyUpdateKey(update);
        if (key && flushFallbackThrough(key)) {
            continue;
        }
        pushUpdate(update);
    }

    while (fallbackIndex < responseItemFallbackUpdates.length) {
        pushUpdate(responseItemFallbackUpdates[fallbackIndex]!);
        fallbackIndex += 1;
    }

    return merged;
}

function historyUpdateKey(update: UpdateSessionEvent): string | null {
    switch (update.sessionUpdate) {
        case "user_message_chunk":
        case "agent_message_chunk":
        case "agent_thought_chunk":
            return `${update.sessionUpdate}:${JSON.stringify(update.content)}`;
        case "tool_call":
            return `tool_call:${update.toolCallId}:start`;
        case "tool_call_update":
            return `tool_call:${update.toolCallId}:update`;
        default:
            return null;
    }
}

function getRequestedMcpServerNames(mcpServers: Array<acp.McpServer>): Array<string> {
    return Array.from(new Set(mcpServers.map(server => sanitizeMcpServerName(server.name))));
}