session.ts

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *--------------------------------------------------------------------------------------------*/

/**
 * Copilot Session - represents a single conversation session with the Copilot CLI.
 * @module session
 */

import type { MessageConnection } from "vscode-jsonrpc/node.js";
import { ConnectionError, ErrorCodes, ResponseError } from "vscode-jsonrpc/node.js";
import { createSessionRpc } from "./generated/rpc.js";
import type {
    ClientSessionApiHandlers,
    CanvasActionInvokeResult,
    CurrentToolMetadata,
    McpOauthPendingRequestResponse,
    FactoryLogLine,
    FactoryRunRequest,
    FactoryExecuteResult,
    FactoryJournalPutRequest,
    FactoryRunResult as WireFactoryRunResult,
} from "./generated/rpc.js";
import { type Canvas, CanvasError } from "./canvas.js";
import type { OpenCanvasInstance } from "./generated/rpc.js";
import { getTraceContext } from "./telemetry.js";
import type {
    CommandHandler,
    AutoModeSwitchHandler,
    AutoModeSwitchRequest,
    AutoModeSwitchResponse,
    ElicitationHandler,
    ElicitationParams,
    ElicitationResult,
    ElicitationContext,
    ExitPlanModeHandler,
    ExitPlanModeRequest,
    ExitPlanModeResult,
    BearerTokenProvider,
    UiInputOptions,
    MessageOptions,
    McpAuthHandler,
    McpAuthRequest,
    PermissionHandler,
    PermissionRequest,
    ContextTier,
    ReasoningEffort,
    ReasoningSummary,
    ModelCapabilitiesOverride,
    SectionTransformFn,
    SessionCapabilities,
    SessionEvent,
    SessionEventHandler,
    SessionEventPayload,
    SessionEventType,
    SessionHooks,
    SessionUiApi,
    Tool,
    ToolHandler,
    ToolResult,
    ToolResultObject,
    TraceContextProvider,
    TypedSessionEventHandler,
    UserInputHandler,
    UserInputRequest,
    UserInputResponse,
} from "./types.js";
import {
    getFactoryDefinition,
    FactoryResumeError,
    isFactoryRunTerminal,
    type FactoryResumeErrorCode,
    type FactoryRunResult,
    type RunOptions,
    type SessionFactoryApi,
    type FactoryContext,
    type FactoryHandle,
    type JsonValue,
    type FactoryStepOptions,
} from "./factory.js";

function isFactoryResumeErrorCode(value: unknown): value is FactoryResumeErrorCode {
    return (
        value === "not_found" ||
        value === "non_resumable" ||
        value === "already_active" ||
        value === "reapproval_declined" ||
        value === "no_approval_provider"
    );
}

/**
 * Convert a raw hook input received over the wire into its public-facing shape.
 * This deserializes the numeric Unix-ms `timestamp` field on BaseHookInput
 * into a Date and maps the wire `cwd` field to `workingDirectory`.
 */
function deserializeHookInput(raw: unknown): unknown {
    if (
        !raw ||
        typeof raw !== "object" ||
        typeof (raw as { timestamp?: unknown }).timestamp !== "number"
    ) {
        return raw;
    }
    const obj = raw as Record<string, unknown> & {
        timestamp: number;
        cwd?: string;
        stop_hook_active?: boolean;
    };
    const { cwd, stop_hook_active, ...rest } = obj;
    return {
        ...rest,
        timestamp: new Date(obj.timestamp),
        workingDirectory: cwd,
        ...(stop_hook_active === undefined ? {} : { stopHookActive: stop_hook_active }),
    };
}

function isOpenCanvasInstance(value: unknown): value is OpenCanvasInstance {
    if (!value || typeof value !== "object") {
        return false;
    }
    const instance = value as Partial<OpenCanvasInstance>;
    return (
        typeof instance.instanceId === "string" &&
        instance.instanceId.length > 0 &&
        typeof instance.extensionId === "string" &&
        instance.extensionId.length > 0 &&
        typeof instance.canvasId === "string" &&
        instance.canvasId.length > 0
    );
}

const FACTORY_LOG_FLUSH_DELAY_MS = 10;
const MAX_FACTORY_FANOUT_ITEMS = 4096;

function assertFactoryFanoutSize(kind: "parallel" | "pipeline", size: number): void {
    if (size > MAX_FACTORY_FANOUT_ITEMS) {
        throw new Error(
            `${kind}() accepts at most ${MAX_FACTORY_FANOUT_ITEMS} items; got ${size}.`
        );
    }
}

async function runFactoryParallel<TResult>(
    thunks: Array<() => Promise<TResult> | TResult>
): Promise<Array<TResult | null>> {
    if (!Array.isArray(thunks)) {
        throw new Error(
            "parallel() expects an array of functions, not promises. Wrap each call: () => agent(...)"
        );
    }
    assertFactoryFanoutSize("parallel", thunks.length);
    if (thunks.some((thunk) => typeof thunk !== "function")) {
        throw new Error(
            "parallel() expects an array of functions, not promises. Wrap each call: () => agent(...)"
        );
    }
    return Promise.all(
        thunks.map((thunk) =>
            Promise.resolve()
                .then(() => thunk())
                .catch((error) => {
                    // Cancellation and hard runtime failures must propagate out
                    // of the combinator rather than be mapped to a successful
                    // `null`; otherwise an aborted run, or one that hit a
                    // resource ceiling or durable-state failure, could be
                    // reported as completed. An ordinary subagent failure never
                    // rejects — it already resolves `null`.
                    if (isFactoryFatalError(error)) {
                        throw error;
                    }
                    return null;
                })
        )
    );
}

async function runFactoryPipeline(
    items: unknown[],
    ...stages: Array<
        (previous: unknown, item: unknown, index: number) => Promise<unknown> | unknown
    >
): Promise<unknown[]> {
    if (!Array.isArray(items)) {
        throw new Error("pipeline(items, ...stages): items must be an array");
    }
    assertFactoryFanoutSize("pipeline", items.length);
    return Promise.all(
        items.map(async (item, index) => {
            let previous = item;
            for (const stage of stages) {
                try {
                    previous = await stage(previous, item, index);
                } catch (error) {
                    // Propagate cancellation and hard runtime failures instead
                    // of mapping them to `null`, so an aborted stage — or one
                    // that hit a resource ceiling or durable-state failure —
                    // does not let the run report success.
                    if (isFactoryFatalError(error)) {
                        throw error;
                    }
                    return null;
                }
            }
            return previous;
        })
    );
}

class FactoryProgressBuffer {
    private nextSeq = 0;
    private pending: FactoryLogLine[] = [];
    private flushTimer?: ReturnType<typeof setTimeout>;
    private flushTail: Promise<void> = Promise.resolve();
    private flushError: unknown;
    private flushFailed = false;
    private closed = false;

    constructor(private readonly send: (lines: FactoryLogLine[]) => Promise<void>) {}

    enqueue(kind: FactoryLogLine["kind"], text: string): void {
        if (this.closed) {
            throw new Error("Cannot log after the factory run has settled");
        }

        this.pending.push({ seq: this.nextSeq++, kind, text });
        this.scheduleFlush();
    }

    async flush(): Promise<void> {
        this.clearFlushTimer();
        const lines = this.pending.splice(0);
        if (lines.length > 0) {
            this.flushTail = this.flushTail.then(async () => {
                try {
                    await this.send(lines);
                } catch (error) {
                    if (!this.flushFailed) {
                        this.flushFailed = true;
                        this.flushError = error;
                    }
                }
            });
        }
        await this.flushTail;
        if (this.flushFailed) {
            throw this.flushError;
        }
    }

    async close(): Promise<void> {
        this.closed = true;
        this.clearFlushTimer();
        const lines = this.pending.splice(0);
        await this.flushTail;
        if (this.flushFailed) {
            throw this.flushError;
        }
        if (lines.length > 0) {
            try {
                await this.send(lines);
            } catch (error) {
                console.warn(
                    "Failed to flush final factory progress after the factory body settled",
                    error
                );
            }
        }
    }

    private scheduleFlush(): void {
        if (this.flushTimer !== undefined) {
            return;
        }
        this.flushTimer = setTimeout(() => {
            this.flushTimer = undefined;
            void this.flush().catch(() => {});
        }, FACTORY_LOG_FLUSH_DELAY_MS);
        this.flushTimer.unref?.();
    }

    private clearFlushTimer(): void {
        if (this.flushTimer !== undefined) {
            clearTimeout(this.flushTimer);
            this.flushTimer = undefined;
        }
    }
}

/**
 * Reconcile the generated envelope with the public one.
 *
 * The two are identical at runtime. They differ only in how `result` is typed:
 * the runtime returns any JSON value, but the schema models the field as an
 * opaque node, which the generator renders as an object. {@link FactoryRunResult}
 * corrects that for the factory surface without changing `x-opaque-json`
 * handling for any other consumer, so the boundary needs a cast rather than a
 * conversion.
 *
 * Delete this along with the {@link FactoryRunResult} override once the schema
 * distinguishes opaque JSON values from opaque in-process values —
 * github/copilot-agent-runtime#14122.
 */
function toPublicFactoryRunResult(envelope: WireFactoryRunResult): FactoryRunResult {
    return envelope as FactoryRunResult;
}

async function awaitFactoryOperation<TResult>(
    operation: () => Promise<TResult>,
    signal: AbortSignal
): Promise<TResult> {
    // The operation is a thunk so an already-aborted run never dispatches the
    // RPC at all, rather than sending it and rejecting locally afterwards.
    let rejectAbort: ((reason?: unknown) => void) | undefined;
    const abortPromise = new Promise<never>((_resolve, reject) => {
        rejectAbort = reject;
    });
    const onAbort = () =>
        rejectAbort?.(signal.reason ?? new DOMException("Factory run was aborted", "AbortError"));
    // Register before the abort check and before dispatching, so an abort can
    // neither be missed by a not-yet-attached listener nor start work on an
    // already-cancelled run.
    signal.addEventListener("abort", onAbort, { once: true });
    try {
        throwIfFactoryAborted(signal);
        return await Promise.race([operation(), abortPromise]);
    } finally {
        signal.removeEventListener("abort", onAbort);
    }
}

function throwIfFactoryAborted(signal: AbortSignal): void {
    if (signal.aborted) {
        throw signal.reason ?? new DOMException("Factory run was aborted", "AbortError");
    }
}

/**
 * Whether an error represents factory run cancellation (an `AbortError`-shaped
 * rejection from {@link awaitFactoryOperation}). Cancellation must bubble out of
 * `parallel`/`pipeline` rather than being flattened into a `null` result.
 */
function isFactoryAbortError(error: unknown): boolean {
    return (
        typeof error === "object" &&
        error !== null &&
        "name" in error &&
        (error as { name?: unknown }).name === "AbortError"
    );
}

/**
 * Errors a factory combinator must never swallow into a `null` item.
 *
 * Cooperative cancellation aborts the run, and a rejected RPC is a hard
 * runtime failure — a reached limit, a durable-state failure, or a dropped
 * transport — that must terminate the run rather than be reported as a
 * successfully-`null` item. An ordinary subagent failure does not reject; the
 * runtime already resolves it as `null`.
 */
function isFactoryFatalError(error: unknown): boolean {
    return (
        isFactoryAbortError(error) ||
        error instanceof ResponseError ||
        error instanceof ConnectionError
    );
}

/** Assistant message event - the final response from the assistant. */
export type AssistantMessageEvent = Extract<SessionEvent, { type: "assistant.message" }>;

const TOOL_SEARCH_TOOL_NAME = "tool_search_tool";

/**
 * Represents a single conversation session with the Copilot CLI.
 *
 * A session maintains conversation state, handles events, and manages tool execution.
 * Sessions are created via {@link CopilotClient.createSession} or resumed via
 * {@link CopilotClient.resumeSession}.
 *
 * @example
 * ```typescript
 * const session = await client.createSession({ model: "gpt-4" });
 *
 * // Subscribe to events
 * session.on((event) => {
 *   if (event.type === "assistant.message") {
 *     console.log(event.data.content);
 *   }
 * });
 *
 * // Send a message and wait for completion
 * await session.sendAndWait({ prompt: "Hello, world!" });
 *
 * // Clean up
 * await session.disconnect();
 * ```
 */
/**
 * Fixed name of the runtime's built-in tool-search tool. A client can replace
 * its behavior by registering a {@link Tool} with this exact name and
 * `overridesBuiltInTool: true`.
 */

export class CopilotSession {
    private eventHandlers: Set<SessionEventHandler> = new Set();
    private typedEventHandlers: Map<SessionEventType, Set<(event: SessionEvent) => void>> =
        new Map();
    private toolHandlers: Map<string, ToolHandler> = new Map();
    private canvases: Map<string, Canvas> = new Map();
    private bearerTokenProviders: Map<string, BearerTokenProvider> = new Map();
    private commandHandlers: Map<string, CommandHandler> = new Map();
    private factories = new Map<string, ReturnType<typeof getFactoryDefinition>>();
    private factoryAbortControllers = new Map<string, Map<string, AbortController>>();
    private permissionHandler?: PermissionHandler;
    private mcpAuthHandler?: McpAuthHandler;
    private userInputHandler?: UserInputHandler;
    private elicitationHandler?: ElicitationHandler;
    private exitPlanModeHandler?: ExitPlanModeHandler;
    private autoModeSwitchHandler?: AutoModeSwitchHandler;
    private hooks?: SessionHooks;
    private transformCallbacks?: Map<string, SectionTransformFn>;
    private _rpc: ReturnType<typeof createSessionRpc> | null = null;
    private traceContextProvider?: TraceContextProvider;
    private _capabilities: SessionCapabilities = {};
    private openCanvasInstances: OpenCanvasInstance[] = [];
    private disconnected = false;

    /** @internal Client session API handlers, populated by CopilotClient during create/resume. */
    clientSessionApis: ClientSessionApiHandlers = {};

    /**
     * Friendly factory API for running registered factories by name or handle.
     *
     * @experimental Part of the experimental Agent Factories surface and may
     * change or be removed in future SDK or CLI releases.
     */
    readonly factory: SessionFactoryApi = {
        run: (async (
            nameOrHandle: string | FactoryHandle,
            options?: RunOptions
        ): Promise<unknown> => {
            const name =
                typeof nameOrHandle === "string"
                    ? nameOrHandle
                    : getFactoryDefinition(nameOrHandle).meta.name;
            if (options?.resumeFromRunId !== undefined) {
                return this.factory.resume(options.resumeFromRunId, {
                    limits: options.limits,
                });
            }
            const envelope = await this.rpc.factory.run({
                name,
                args: (options?.args === undefined
                    ? {}
                    : options.args) as FactoryRunRequest["args"],
                options: {
                    limits: options?.limits,
                },
            });

            return toPublicFactoryRunResult(envelope);
        }) as SessionFactoryApi["run"],
        resume: (async (runId: string, options?: Parameters<SessionFactoryApi["resume"]>[1]) => {
            let response;
            try {
                response = await this.rpc.factory.resume({
                    runId,
                    limits: options?.limits,
                });
            } catch (error) {
                if (
                    error instanceof ResponseError &&
                    typeof error.data === "object" &&
                    error.data !== null
                ) {
                    const code = (error.data as { code?: unknown }).code;
                    if (isFactoryResumeErrorCode(code)) {
                        throw new FactoryResumeError(code, error.message);
                    }
                }
                throw error;
            }
            return toPublicFactoryRunResult(response.run);
        }) as SessionFactoryApi["resume"],
        getRun: async (runId) => toPublicFactoryRunResult(await this.rpc.factory.getRun({ runId })),
        waitForRun: (runId, options) => this.waitForFactoryRun(runId, options?.signal),
        listRuns: async () => (await this.rpc.factory.listRuns()).runs,
        getRunDetail: (runId) => this.rpc.factory.getRunDetail({ runId }),
        getRunProgress: (runId, options = {}) =>
            this.rpc.factory.getRunProgress({ runId, ...options }),
        cancel: async (runId) => toPublicFactoryRunResult(await this.rpc.factory.cancel({ runId })),
    };

    /**
     * Resolve when a factory run reaches a terminal status.
     *
     * The subscription is installed *before* the first read so a transition
     * landing between the two cannot be missed, and re-reads are serialized so
     * overlapping invalidation events cannot interleave — the run's revision
     * advances once per operation, so a burst of events is common and must
     * collapse into a single in-flight read. A bounded periodic re-read keeps a
     * dropped invalidation from leaving the wait pending forever.
     */
    private waitForFactoryRun(runId: string, signal?: AbortSignal): Promise<FactoryRunResult> {
        const abortError = (): unknown =>
            signal?.reason ?? new DOMException("Factory run wait was aborted", "AbortError");
        if (signal?.aborted === true) {
            return Promise.reject(abortError());
        }

        return new Promise<FactoryRunResult>((resolve, reject) => {
            let settled = false;
            let reading = false;
            let rereadRequested = false;
            let pollHandle: ReturnType<typeof setInterval> | undefined;
            let unsubscribe: (() => void) | undefined;
            let onAbort: (() => void) | undefined;

            const finish = (complete: () => void): void => {
                if (settled) {
                    return;
                }
                settled = true;
                if (pollHandle !== undefined) {
                    clearInterval(pollHandle);
                }
                unsubscribe?.();
                if (onAbort !== undefined) {
                    signal?.removeEventListener("abort", onAbort);
                }
                complete();
            };

            const read = async (): Promise<void> => {
                if (settled) {
                    return;
                }
                if (reading) {
                    rereadRequested = true;
                    return;
                }
                reading = true;
                try {
                    do {
                        rereadRequested = false;
                        const envelope = await this.rpc.factory.getRun({ runId });
                        if (isFactoryRunTerminal(envelope.status)) {
                            finish(() => resolve(toPublicFactoryRunResult(envelope)));
                            return;
                        }
                    } while (rereadRequested && !settled);
                } catch (error) {
                    finish(() => reject(error));
                } finally {
                    reading = false;
                }
            };

            if (signal !== undefined) {
                onAbort = (): void => finish(() => reject(abortError()));
                signal.addEventListener("abort", onAbort, { once: true });
            }

            unsubscribe = this.on("factory.run_updated", (event) => {
                if (event.data.runId === runId) {
                    void read();
                }
            });

            pollHandle = setInterval(() => void read(), 5_000);
            // The re-read is a safety net, not work the process owes anyone: an
            // outstanding wait must never keep Node alive on its own.
            pollHandle.unref?.();
            void read();
        });
    }

    /**
     * Creates a new CopilotSession instance.
     *
     * @param sessionId - The unique identifier for this session
     * @param connection - The JSON-RPC message connection to the Copilot CLI
     * @param workspacePath - Path to the session workspace directory (when infinite sessions enabled)
     * @param traceContextProvider - Optional callback to get W3C Trace Context for outbound RPCs
     * @internal This constructor is internal. Use {@link CopilotClient.createSession} to create sessions.
     */
    constructor(
        public readonly sessionId: string,
        private connection: MessageConnection,
        private _workspacePath?: string,
        traceContextProvider?: TraceContextProvider,
        options?: { mcpAuthHandler?: McpAuthHandler }
    ) {
        this.traceContextProvider = traceContextProvider;
        this.mcpAuthHandler = options?.mcpAuthHandler;
    }

    /**
     * Typed session-scoped RPC methods.
     */
    get rpc(): ReturnType<typeof createSessionRpc> {
        if (!this._rpc) {
            this._rpc = createSessionRpc(this.connection, this.sessionId);
        }
        return this._rpc;
    }

    /**
     * Path to the session workspace directory when infinite sessions are enabled.
     * Contains checkpoints/, plan.md, and files/ subdirectories.
     * Undefined if infinite sessions are disabled.
     */
    get workspacePath(): string | undefined {
        return this._workspacePath;
    }

    /**
     * Host capabilities reported when the session was created or resumed.
     * Use this to check feature support before calling capability-gated APIs.
     */
    get capabilities(): SessionCapabilities {
        return this._capabilities;
    }

    /**
     * Interactive UI methods for showing dialogs to the user.
     * Only available when the CLI host supports elicitation
     * (`session.capabilities.ui?.elicitation === true`).
     *
     * @example
     * ```typescript
     * if (session.capabilities.ui?.elicitation) {
     *   const ok = await session.ui.confirm("Deploy to production?");
     * }
     * ```
     */
    get ui(): SessionUiApi {
        return {
            elicitation: (params: ElicitationParams) => this._elicitation(params),
            confirm: (message: string) => this._confirm(message),
            select: (message: string, options: string[]) => this._select(message, options),
            input: (message: string, options?: UiInputOptions) => this._input(message, options),
        };
    }

    /**
     * Sends a message to this session and waits for the response.
     *
     * The message is processed asynchronously. Subscribe to events via {@link on}
     * to receive streaming responses and other session events.
     *
     * @param options - The message options including the prompt and optional attachments
     * @returns A promise that resolves with the message ID of the response
     * @throws Error if the session has been disconnected or the connection fails
     *
     * @example
     * ```typescript
     * const messageId = await session.send({
     *   prompt: "Explain this code",
     *   attachments: [{ type: "file", path: "./src/index.ts" }]
     * });
     * ```
     */
    async send(prompt: string): Promise<string>;
    async send(options: MessageOptions): Promise<string>;
    async send(optionsOrPrompt: MessageOptions | string): Promise<string> {
        const options: MessageOptions =
            typeof optionsOrPrompt === "string" ? { prompt: optionsOrPrompt } : optionsOrPrompt;
        const response = await this.connection.sendRequest("session.send", {
            ...(await getTraceContext(this.traceContextProvider)),
            sessionId: this.sessionId,
            prompt: options.prompt,
            displayPrompt: options.displayPrompt,
            attachments: options.attachments,
            mode: options.mode,
            agentMode: options.agentMode,
            requestHeaders: options.requestHeaders,
        });

        return (response as { messageId: string }).messageId;
    }

    /**
     * Sends a message to this session and waits until the session becomes idle.
     *
     * This is a convenience method that combines {@link send} with waiting for
     * the `session.idle` event. Use this when you want to block until the
     * assistant has finished processing the message.
     *
     * Events are still delivered to handlers registered via {@link on} while waiting.
     *
     * @param options - The message options including the prompt and optional attachments
     * @param timeout - Timeout in milliseconds (default: 60000). Controls how long to wait; does not abort in-flight agent work.
     * @returns A promise that resolves with the final assistant message when the session becomes idle,
     *          or undefined if no assistant message was received
     * @throws Error if the timeout is reached before the session becomes idle
     * @throws Error if the session has been disconnected or the connection fails
     *
     * @example
     * ```typescript
     * // Send and wait for completion with default 60s timeout
     * const response = await session.sendAndWait({ prompt: "What is 2+2?" });
     * console.log(response?.data.content); // "4"
     * ```
     */
    async sendAndWait(prompt: string, timeout?: number): Promise<AssistantMessageEvent | undefined>;
    async sendAndWait(
        options: MessageOptions,
        timeout?: number
    ): Promise<AssistantMessageEvent | undefined>;
    async sendAndWait(
        optionsOrPrompt: MessageOptions | string,
        timeout?: number
    ): Promise<AssistantMessageEvent | undefined> {
        const options: MessageOptions =
            typeof optionsOrPrompt === "string" ? { prompt: optionsOrPrompt } : optionsOrPrompt;
        const effectiveTimeout = timeout ?? 60_000;

        let resolveIdle: () => void;
        let rejectWithError: (error: Error) => void;
        const idlePromise = new Promise<void>((resolve, reject) => {
            resolveIdle = resolve;
            rejectWithError = reject;
        });

        let lastAssistantMessage: AssistantMessageEvent | undefined;

        // Register event handler BEFORE calling send to avoid race condition
        // where session.idle fires before we start listening
        const unsubscribe = this.on((event) => {
            if (event.type === "assistant.message") {
                lastAssistantMessage = event;
            } else if (event.type === "session.idle") {
                resolveIdle();
            } else if (event.type === "session.error") {
                const error = new Error(event.data.message);
                error.stack = event.data.stack;
                rejectWithError(error);
            }
        });

        let timeoutId: ReturnType<typeof setTimeout> | undefined;
        try {
            await this.send(options);

            const timeoutPromise = new Promise<never>((_, reject) => {
                timeoutId = setTimeout(
                    () =>
                        reject(
                            new Error(
                                `Timeout after ${effectiveTimeout}ms waiting for session.idle`
                            )
                        ),
                    effectiveTimeout
                );
            });
            await Promise.race([idlePromise, timeoutPromise]);

            return lastAssistantMessage;
        } finally {
            if (timeoutId !== undefined) {
                clearTimeout(timeoutId);
            }
            unsubscribe();
        }
    }

    /** @internal */
    _markDisconnected(): void {
        this.disconnected = true;
        this.eventHandlers.clear();
        this.typedEventHandlers.clear();
        this.toolHandlers.clear();
        this.permissionHandler = undefined;
        this.userInputHandler = undefined;
        this.elicitationHandler = undefined;
        this.exitPlanModeHandler = undefined;
        this.autoModeSwitchHandler = undefined;
        this.commandHandlers.clear();
        this.canvases.clear();
        this.factories.clear();
        for (const controllersForRun of this.factoryAbortControllers.values()) {
            for (const controller of controllersForRun.values()) {
                controller.abort();
            }
        }
        this.factoryAbortControllers.clear();
        this.transformCallbacks?.clear();
    }

    /**
     * Subscribes to events from this session.
     *
     * Events include assistant messages, tool executions, errors, and session state changes.
     * Multiple handlers can be registered and will all receive events.
     *
     * @param eventType - The specific event type to listen for (e.g., "assistant.message", "session.idle")
     * @param handler - A callback function that receives events of the specified type
     * @returns A function that, when called, unsubscribes the handler
     *
     * @example
     * ```typescript
     * // Listen for a specific event type
     * const unsubscribe = session.on("assistant.message", (event) => {
     *   console.log("Assistant:", event.data.content);
     * });
     *
     * // Later, to stop receiving events:
     * unsubscribe();
     * ```
     */
    on<K extends SessionEventType>(eventType: K, handler: TypedSessionEventHandler<K>): () => void;

    /**
     * Subscribes to all events from this session.
     *
     * @param handler - A callback function that receives all session events
     * @returns A function that, when called, unsubscribes the handler
     *
     * @example
     * ```typescript
     * const unsubscribe = session.on((event) => {
     *   switch (event.type) {
     *     case "assistant.message":
     *       console.log("Assistant:", event.data.content);
     *       break;
     *     case "session.error":
     *       console.error("Error:", event.data.message);
     *       break;
     *   }
     * });
     *
     * // Later, to stop receiving events:
     * unsubscribe();
     * ```
     */
    on(handler: SessionEventHandler): () => void;

    on<K extends SessionEventType>(
        eventTypeOrHandler: K | SessionEventHandler,
        handler?: TypedSessionEventHandler<K>
    ): () => void {
        // Overload 1: on(eventType, handler) - typed event subscription
        if (typeof eventTypeOrHandler === "string" && handler) {
            const eventType = eventTypeOrHandler;
            if (!this.typedEventHandlers.has(eventType)) {
                this.typedEventHandlers.set(eventType, new Set());
            }
            // Cast is safe: handler receives the correctly typed event at dispatch time
            const storedHandler = handler as (event: SessionEvent) => void;
            this.typedEventHandlers.get(eventType)!.add(storedHandler);
            return () => {
                const handlers = this.typedEventHandlers.get(eventType);
                if (handlers) {
                    handlers.delete(storedHandler);
                }
            };
        }

        // Overload 2: on(handler) - wildcard subscription
        const wildcardHandler = eventTypeOrHandler as SessionEventHandler;
        this.eventHandlers.add(wildcardHandler);
        return () => {
            this.eventHandlers.delete(wildcardHandler);
        };
    }

    /**
     * Dispatches an event to all registered handlers.
     * Also handles broadcast request events internally (external tool calls, permissions).
     *
     * @param event - The session event to dispatch
     * @internal This method is for internal use by the SDK.
     */
    _dispatchEvent(event: SessionEvent): void {
        // Handle broadcast request events internally (fire-and-forget)
        this._handleBroadcastEvent(event);

        // Dispatch to typed handlers for this specific event type
        const typedHandlers = this.typedEventHandlers.get(event.type);
        if (typedHandlers) {
            for (const handler of typedHandlers) {
                try {
                    handler(event as SessionEventPayload<typeof event.type>);
                } catch (_error) {
                    // Handler error
                }
            }
        }

        // Dispatch to wildcard handlers
        for (const handler of this.eventHandlers) {
            try {
                handler(event);
            } catch (_error) {
                // Handler error
            }
        }
    }

    /**
     * Handles broadcast request events by executing local handlers and responding via RPC.
     * Handlers are dispatched as fire-and-forget — rejections propagate as unhandled promise
     * rejections, consistent with standard EventEmitter / event handler semantics.
     * @internal
     */
    private _handleBroadcastEvent(event: SessionEvent): void {
        if (this.disconnected) {
            return;
        }
        if (event.type === "external_tool.requested") {
            const { requestId, toolName } = event.data as {
                requestId: string;
                toolName: string;
                arguments: unknown;
                toolCallId: string;
                sessionId: string;
            };
            const args = (event.data as { arguments: unknown }).arguments;
            const toolCallId = (event.data as { toolCallId: string }).toolCallId;
            const traceparent = (event.data as { traceparent?: string }).traceparent;
            const tracestate = (event.data as { tracestate?: string }).tracestate;
            const handler = this.toolHandlers.get(toolName);
            if (handler) {
                void this._executeToolAndRespond(
                    requestId,
                    toolName,
                    toolCallId,
                    args,
                    handler,
                    traceparent,
                    tracestate
                );
            }
        } else if (event.type === "permission.requested") {
            const { requestId, permissionRequest, resolvedByHook } = event.data as {
                requestId: string;
                permissionRequest: PermissionRequest;
                resolvedByHook?: boolean;
            };
            if (resolvedByHook) {
                return; // Already resolved by a permissionRequest hook; no client action needed.
            }
            if (this.permissionHandler) {
                void this._executePermissionAndRespond(requestId, permissionRequest);
            }
        } else if (event.type === "mcp.oauth_required") {
            const data = event.data as McpAuthRequest | undefined;
            if (!data?.requestId) {
                return;
            }
            if (!this.mcpAuthHandler) {
                console.warn(
                    "Received MCP OAuth request without a registered MCP auth handler. " +
                        `SessionId=${this.sessionId}, RequestId=${data.requestId}`
                );
                return;
            }
            void this._executeMcpAuthAndRespond(data);
        } else if (event.type === "command.execute") {
            const { requestId, commandName, command, args } = event.data as {
                requestId: string;
                command: string;
                commandName: string;
                args: string;
            };
            void this._executeCommandAndRespond(requestId, commandName, command, args);
        } else if (event.type === "elicitation.requested") {
            if (this.elicitationHandler) {
                const { message, requestedSchema, mode, elicitationSource, url, requestId } =
                    event.data;
                void this._handleElicitationRequest(
                    {
                        sessionId: this.sessionId,
                        message,
                        requestedSchema: requestedSchema as ElicitationContext["requestedSchema"],
                        mode,
                        elicitationSource,
                        url,
                    },
                    requestId
                );
            }
        } else if (event.type === "capabilities.changed") {
            this._capabilities = { ...this._capabilities, ...event.data };
        } else if (event.type === "session.canvas.opened") {
            this.upsertOpenCanvasFromEvent(event.data);
        } else if (event.type === "session.canvas.closed") {
            this.removeOpenCanvasFromEvent(event.data);
        }
    }

    private upsertOpenCanvasFromEvent(data: unknown): void {
        if (!isOpenCanvasInstance(data)) {
            console.warn("failed to deserialize session.canvas.opened payload");
            return;
        }
        this.upsertOpenCanvas(data);
    }

    private removeOpenCanvasFromEvent(data: unknown): void {
        if (
            !data ||
            typeof data !== "object" ||
            typeof (data as { instanceId?: unknown }).instanceId !== "string" ||
            (data as { instanceId: string }).instanceId.length === 0
        ) {
            console.warn("failed to deserialize session.canvas.closed payload");
            return;
        }
        this.removeOpenCanvas((data as { instanceId: string }).instanceId);
    }

    private removeOpenCanvas(instanceId: string): void {
        this.openCanvasInstances = this.openCanvasInstances.filter(
            (open) => open.instanceId !== instanceId
        );
    }

    private upsertOpenCanvas(instance: OpenCanvasInstance): void {
        const index = this.openCanvasInstances.findIndex(
            (open) => open.instanceId === instance.instanceId
        );
        if (index >= 0) {
            this.openCanvasInstances[index] = instance;
        } else {
            this.openCanvasInstances.push(instance);
        }
    }

    /**
     * Executes a tool handler and sends the result back via RPC.
     * @internal
     */
    private async _executeToolAndRespond(
        requestId: string,
        toolName: string,
        toolCallId: string,
        args: unknown,
        handler: ToolHandler,
        traceparent?: string,
        tracestate?: string
    ): Promise<void> {
        try {
            // The built-in tool-search tool receives a snapshot of the session's
            // currently initialized tools so an override can filter the live
            // catalog without issuing its own RPC. Fetch it only for that tool
            // to avoid a round-trip on every tool call; a failed fetch simply
            // leaves the snapshot undefined rather than failing the tool.
            let availableTools: CurrentToolMetadata[] | undefined;
            if (toolName === TOOL_SEARCH_TOOL_NAME) {
                try {
                    const metadata = await this.rpc.tools.getCurrentMetadata();
                    availableTools = metadata.tools ?? undefined;
                } catch {
                    availableTools = undefined;
                }
            }
            const rawResult = await handler(args, {
                sessionId: this.sessionId,
                toolCallId,
                toolName,
                arguments: args,
                availableTools,
                traceparent,
                tracestate,
            });
            let result: ToolResult;
            if (rawResult == null) {
                result = "";
            } else if (typeof rawResult === "string") {
                result = rawResult;
            } else if (isToolResultObject(rawResult)) {
                result = rawResult;
            } else {
                result = JSON.stringify(rawResult);
            }
            if (this.disconnected) {
                return;
            }
            await this.rpc.tools.handlePendingToolCall({ requestId, result });
        } catch (error) {
            if (this.disconnected) {
                return;
            }
            const message = error instanceof Error ? error.message : String(error);
            try {
                await this.rpc.tools.handlePendingToolCall({ requestId, error: message });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
                // Connection lost or RPC error — nothing we can do
            }
        }
    }

    /**
     * Executes a permission handler and sends the result back via RPC.
     * @internal
     */
    private async _executePermissionAndRespond(
        requestId: string,
        permissionRequest: PermissionRequest
    ): Promise<void> {
        try {
            const result = await this.permissionHandler!(permissionRequest, {
                sessionId: this.sessionId,
            });
            if (result.kind === "no-result") {
                return;
            }
            if (this.disconnected) {
                return;
            }
            await this.rpc.permissions.handlePendingPermissionRequest({ requestId, result });
        } catch (_error) {
            if (this.disconnected) {
                return;
            }
            try {
                await this.rpc.permissions.handlePendingPermissionRequest({
                    requestId,
                    result: {
                        kind: "user-not-available",
                    },
                });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
                // Connection lost or RPC error — nothing we can do
            }
        }
    }

    /**
     * Executes an MCP auth handler and sends the result back via RPC.
     * @internal
     */
    private async _executeMcpAuthAndRespond(request: McpAuthRequest): Promise<void> {
        try {
            const result = await this.mcpAuthHandler!(request, { sessionId: this.sessionId });
            const response: McpOauthPendingRequestResponse =
                result && "accessToken" in result
                    ? { kind: "token", ...result }
                    : { kind: "cancelled" };
            await this.rpc.mcp.oauth.handlePendingRequest({
                requestId: request.requestId,
                result: response,
            });
        } catch (_error) {
            try {
                await this.rpc.mcp.oauth.handlePendingRequest({
                    requestId: request.requestId,
                    result: { kind: "cancelled" },
                });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
            }
        }
    }

    /**
     * Executes a command handler and sends the result back via RPC.
     * @internal
     */
    private async _executeCommandAndRespond(
        requestId: string,
        commandName: string,
        command: string,
        args: string
    ): Promise<void> {
        const handler = this.commandHandlers.get(commandName);
        if (!handler) {
            try {
                await this.rpc.commands.handlePendingCommand({
                    requestId,
                    error: `Unknown command: ${commandName}`,
                });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
            }
            return;
        }

        try {
            await handler({ sessionId: this.sessionId, command, commandName, args });
            if (this.disconnected) {
                return;
            }
            await this.rpc.commands.handlePendingCommand({ requestId });
        } catch (error) {
            if (this.disconnected) {
                return;
            }
            const message = error instanceof Error ? error.message : String(error);
            try {
                await this.rpc.commands.handlePendingCommand({ requestId, error: message });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
            }
        }
    }

    /**
     * Registers custom tool handlers for this session.
     *
     * Tools with handlers allow the assistant to execute custom functions automatically.
     * Declaration-only tools are surfaced as events and left pending for the consumer.
     *
     * @param tools - An array of tool definitions with their handlers, or undefined to clear all tools
     * @internal This method is typically called internally when creating a session with tools.
     */
    registerTools(tools?: Tool[]): void {
        this.toolHandlers.clear();
        if (!tools) {
            return;
        }

        for (const tool of tools) {
            if (tool.handler) {
                this.toolHandlers.set(tool.name, tool.handler);
            }
        }
    }

    /**
     * Retrieves a registered tool handler by name.
     *
     * @param name - The name of the tool to retrieve
     * @returns The tool handler if found, or undefined
     * @internal This method is for internal use by the SDK.
     */
    getToolHandler(name: string): ToolHandler | undefined {
        return this.toolHandlers.get(name);
    }

    /**
     * Registers canvas declarations and handlers for this session.
     *
     * @param canvases - Canvases created via `createCanvas`, or undefined to clear all canvases
     * @internal Called by the SDK when creating/resuming a session with `canvases`.
     */
    registerCanvases(canvases?: Canvas[]): void {
        this.canvases.clear();
        if (!canvases || canvases.length === 0) {
            delete this.clientSessionApis.canvas;
            return;
        }
        for (const canvas of canvases) {
            this.canvases.set(canvas.declaration.id, canvas);
        }

        const self = this;
        this.clientSessionApis.canvas = {
            async open(params) {
                const canvas = self.canvases.get(params.canvasId);
                if (!canvas) throw new Error(`No canvas registered with id "${params.canvasId}"`);
                try {
                    return (await canvas.open(params)) ?? {};
                } catch (error) {
                    throw toCanvasRpcError(error);
                }
            },
            async close(params) {
                const canvas = self.canvases.get(params.canvasId);
                if (!canvas) throw new Error(`No canvas registered with id "${params.canvasId}"`);
                try {
                    if (canvas.onClose) {
                        await canvas.onClose(params);
                    }
                } catch (error) {
                    throw toCanvasRpcError(error);
                }
            },
            async invoke(params) {
                const canvas = self.canvases.get(params.canvasId);
                if (!canvas) throw new Error(`No canvas registered with id "${params.canvasId}"`);
                const handler = canvas.actionHandlers.get(params.actionName);
                if (!handler) {
                    throw new CanvasError(
                        "canvas_action_no_handler",
                        "No handler implemented for this canvas action"
                    );
                }
                try {
                    return (await handler(params)) as CanvasActionInvokeResult;
                } catch (error) {
                    throw toCanvasRpcError(error);
                }
            },
        };
    }

    /**
     * Registers factory closures and reverse-RPC handlers for this session.
     *
     * @param factories - Factory handles declared by the joining extension.
     * @internal Called by the SDK when an extension joins a session.
     */
    registerFactories(factories?: FactoryHandle[]): void {
        this.factories.clear();
        if (!factories || factories.length === 0) {
            delete this.clientSessionApis.factory;
            return;
        }

        for (const handle of factories) {
            const definition = getFactoryDefinition(handle);
            if (this.factories.has(definition.meta.name)) {
                throw new Error(
                    `Duplicate factory name "${definition.meta.name}". Factory names must be unique within a joinSession call.`
                );
            }
            this.factories.set(definition.meta.name, definition);
        }

        const self = this;
        this.clientSessionApis.factory = {
            async execute(params) {
                const definition = self.factories.get(params.name);
                if (!definition) {
                    const message = `No factory registered with name "${params.name}"`;
                    throw new ResponseError(ErrorCodes.InvalidParams, message, {
                        code: "factory_not_found",
                        name: params.name,
                    });
                }

                const controller = new AbortController();
                // Keyed by execution token as well as run ID so overlapping
                // attempts for one run stay individually addressable.
                let controllersForRun = self.factoryAbortControllers.get(params.runId);
                if (controllersForRun === undefined) {
                    controllersForRun = new Map();
                    self.factoryAbortControllers.set(params.runId, controllersForRun);
                }
                controllersForRun.set(params.executionToken, controller);
                const progress = new FactoryProgressBuffer(async (lines) => {
                    await self.rpc.factory.log({
                        runId: params.runId,
                        executionToken: params.executionToken,
                        lines,
                    });
                });
                try {
                    const context: FactoryContext = {
                        runId: params.runId,
                        args: params.args as JsonValue,
                        session: self,
                        signal: controller.signal,
                        phase: (title: string) => {
                            throwIfFactoryAborted(controller.signal);
                            progress.enqueue("phase", title);
                        },
                        log: (message: string) => {
                            throwIfFactoryAborted(controller.signal);
                            progress.enqueue("log", message);
                        },
                        agent: async (prompt, options = {}) => {
                            await progress.flush();
                            const response = await awaitFactoryOperation(
                                () =>
                                    self.rpc.factory.agent({
                                        factoryRunId: params.runId,
                                        executionToken: params.executionToken,
                                        prompt,
                                        opts: {
                                            label: options.label,
                                            schema: options.schema,
                                            model: options.model,
                                        },
                                    }),
                                controller.signal
                            );
                            return response.result ?? null;
                        },
                        step: async (
                            key: string,
                            producer: () => Promise<JsonValue> | JsonValue,
                            options: FactoryStepOptions = {}
                        ): Promise<JsonValue> => {
                            await progress.flush();
                            if (options.volatile) {
                                // The flush above is an await point, so an abort can land
                                // between entering step() and running the producer. The
                                // journaled branch is covered by awaitFactoryOperation;
                                // this one has to check for itself, or a cancelled run
                                // would still start new extension work.
                                throwIfFactoryAborted(controller.signal);
                                return producer();
                            }
                            const cached = await awaitFactoryOperation(
                                () =>
                                    self.rpc.factory.journal.get({
                                        runId: params.runId,
                                        executionToken: params.executionToken,
                                        key,
                                    }),
                                controller.signal
                            );
                            if (cached.hit) {
                                if (cached.resultJson === undefined) {
                                    throw new Error(
                                        `step("${key}") journal returned a hit without a result`
                                    );
                                }
                                assertFactoryStepResult(cached.resultJson, key);
                                return cached.resultJson;
                            }

                            // Producers are best-effort at-least-once across crashes or
                            // concurrent callers, so authors must make side effects idempotent.
                            const result = await producer();
                            assertFactoryStepResult(result, key);
                            await awaitFactoryOperation(
                                () =>
                                    self.rpc.factory.journal.put({
                                        runId: params.runId,
                                        executionToken: params.executionToken,
                                        key,
                                        resultJson:
                                            result as FactoryJournalPutRequest["resultJson"],
                                    }),
                                controller.signal
                            );
                            return result;
                        },
                        parallel: runFactoryParallel,
                        pipeline: runFactoryPipeline,
                        factory: async () => {
                            throw new Error("nested factories are not supported");
                        },
                    };
                    const result = await definition.run(context);
                    if (result === undefined) {
                        return {};
                    }
                    assertFactoryResult(result);
                    return { result } as FactoryExecuteResult;
                } finally {
                    try {
                        await progress.close();
                    } finally {
                        const controllersForRun = self.factoryAbortControllers.get(params.runId);
                        if (controllersForRun?.get(params.executionToken) === controller) {
                            controllersForRun.delete(params.executionToken);
                            if (controllersForRun.size === 0) {
                                self.factoryAbortControllers.delete(params.runId);
                            }
                        }
                    }
                }
            },
            async abort(params) {
                const controllersForRun = self.factoryAbortControllers.get(params.runId);
                if (controllersForRun !== undefined) {
                    const reason = new DOMException("Factory run was aborted", "AbortError");
                    for (const controller of controllersForRun.values()) {
                        controller.abort(reason);
                    }
                }
                return {};
            },
        };
    }

    /**
     * Registers per-provider {@link BearerTokenProvider} callbacks for BYOK providers
     * configured with managed-identity / on-demand bearer-token auth.
     *
     * The runtime never receives the callback itself; the SDK strips it from the
     * provider config and instead sends `hasBearerTokenProvider: true`. When the
     * runtime needs a token it issues a session-scoped `providerToken.getToken`
     * request, which this handler routes to the matching per-provider callback.
     *
     * @param providers - Map of provider name → callback, or undefined/empty to clear.
     * @internal This method is called internally when creating/resuming a session.
     */
    registerBearerTokenProviders(providers?: Map<string, BearerTokenProvider>): void {
        this.bearerTokenProviders.clear();
        if (!providers || providers.size === 0) {
            delete this.clientSessionApis.providerToken;
            return;
        }
        for (const [name, callback] of providers) {
            this.bearerTokenProviders.set(name, callback);
        }

        const self = this;
        this.clientSessionApis.providerToken = {
            async getToken(params) {
                const callback = self.bearerTokenProviders.get(params.providerName);
                if (!callback) {
                    throw new Error(
                        `No bearer-token provider registered for provider "${params.providerName}"`
                    );
                }
                const token = await callback({
                    providerName: params.providerName,
                    sessionId: params.sessionId,
                });
                return { token };
            },
        };
    }

    /**
     * Registers command handlers for this session.
     *
     * @param commands - An array of command definitions with handlers, or undefined to clear
     * @internal This method is typically called internally when creating/resuming a session.
     */
    registerCommands(commands?: { name: string; handler: CommandHandler }[]): void {
        this.commandHandlers.clear();
        if (!commands) {
            return;
        }
        for (const cmd of commands) {
            this.commandHandlers.set(cmd.name, cmd.handler);
        }
    }

    /**
     * Registers the elicitation handler for this session.
     *
     * @param handler - The handler to invoke when the server dispatches an elicitation request
     * @internal This method is typically called internally when creating/resuming a session.
     */
    registerElicitationHandler(handler?: ElicitationHandler): void {
        this.elicitationHandler = handler;
    }

    /**
     * Registers the exit-plan-mode handler for this session.
     *
     * @param handler - The handler to invoke when the server dispatches an exit-plan-mode request
     * @internal This method is typically called internally when creating/resuming a session.
     */
    registerExitPlanModeHandler(handler?: ExitPlanModeHandler): void {
        this.exitPlanModeHandler = handler;
    }

    /**
     * Registers the auto-mode-switch handler for this session.
     *
     * @param handler - The handler to invoke when the server dispatches an auto-mode-switch request
     * @internal This method is typically called internally when creating/resuming a session.
     */
    registerAutoModeSwitchHandler(handler?: AutoModeSwitchHandler): void {
        this.autoModeSwitchHandler = handler;
    }

    /**
     * Handles an elicitation.requested broadcast event.
     * Invokes the registered handler and responds via handlePendingElicitation RPC.
     * @internal
     */
    async _handleElicitationRequest(context: ElicitationContext, requestId: string): Promise<void> {
        if (!this.elicitationHandler) {
            return;
        }
        try {
            const result = await this.elicitationHandler(context);
            await this.rpc.ui.handlePendingElicitation({ requestId, result });
        } catch {
            // Handler failed — attempt to cancel so the request doesn't hang
            try {
                await this.rpc.ui.handlePendingElicitation({
                    requestId,
                    result: { action: "cancel" },
                });
            } catch (rpcError) {
                if (!(rpcError instanceof ConnectionError || rpcError instanceof ResponseError)) {
                    throw rpcError;
                }
                // Connection lost or RPC error — nothing we can do
            }
        }
    }

    /**
     * Handles an exitPlanMode.request callback from the runtime.
     * @internal
     */
    async _handleExitPlanModeRequest(request: ExitPlanModeRequest): Promise<ExitPlanModeResult> {
        if (!this.exitPlanModeHandler) {
            return { approved: true };
        }

        return await this.exitPlanModeHandler(request, { sessionId: this.sessionId });
    }

    /**
     * Handles an autoModeSwitch.request callback from the runtime.
     * @internal
     */
    async _handleAutoModeSwitchRequest(
        request: AutoModeSwitchRequest
    ): Promise<AutoModeSwitchResponse> {
        if (!this.autoModeSwitchHandler) {
            return "no";
        }

        return await this.autoModeSwitchHandler(request, { sessionId: this.sessionId });
    }

    /**
     * Sets the host capabilities for this session.
     *
     * @param capabilities - The capabilities object from the create/resume response
     * @internal This method is typically called internally when creating/resuming a session.
     */
    setCapabilities(capabilities?: SessionCapabilities): void {
        this._capabilities = capabilities ?? {};
    }

    /**
     * Snapshot of canvas instances currently known to be open for this session.
     * Populated from the `session.resume` response and live `session.canvas.opened`
     * and `session.canvas.closed` events. Returns a defensive copy — mutating the
     * returned array has no effect on the session.
     */
    get openCanvases(): OpenCanvasInstance[] {
        return [...this.openCanvasInstances];
    }

    /**
     * Sets the open-canvas snapshot for this session.
     *
     * @param instances - The `openCanvases` array from the `session.resume` response.
     * @internal This method is typically called internally when resuming a session.
     */
    setOpenCanvases(instances: OpenCanvasInstance[]): void {
        this.openCanvasInstances = [...instances];
    }

    private assertElicitation(): void {
        if (!this._capabilities.ui?.elicitation) {
            throw new Error(
                "Elicitation is not supported by the host. " +
                    "Check session.capabilities.ui?.elicitation before calling UI methods."
            );
        }
    }

    private async _elicitation(params: ElicitationParams): Promise<ElicitationResult> {
        this.assertElicitation();
        return this.rpc.ui.elicitation({
            message: params.message,
            requestedSchema: params.requestedSchema,
        });
    }

    private async _confirm(message: string): Promise<boolean> {
        this.assertElicitation();
        const result = await this.rpc.ui.elicitation({
            message,
            requestedSchema: {
                type: "object",
                properties: {
                    confirmed: { type: "boolean", default: true },
                },
                required: ["confirmed"],
            },
        });
        return result.action === "accept" && (result.content?.confirmed as boolean) === true;
    }

    private async _select(message: string, options: string[]): Promise<string | null> {
        this.assertElicitation();
        const result = await this.rpc.ui.elicitation({
            message,
            requestedSchema: {
                type: "object",
                properties: {
                    selection: { type: "string", enum: options },
                },
                required: ["selection"],
            },
        });
        if (result.action === "accept" && result.content?.selection != null) {
            return result.content.selection as string;
        }
        return null;
    }

    private async _input(message: string, options?: UiInputOptions): Promise<string | null> {
        this.assertElicitation();
        const field: Record<string, unknown> = { type: "string" as const };
        if (options?.title) field.title = options.title;
        if (options?.description) field.description = options.description;
        if (options?.minLength != null) field.minLength = options.minLength;
        if (options?.maxLength != null) field.maxLength = options.maxLength;
        if (options?.format) field.format = options.format;
        if (options?.default != null) field.default = options.default;

        const result = await this.rpc.ui.elicitation({
            message,
            requestedSchema: {
                type: "object",
                properties: {
                    value: field as ElicitationParams["requestedSchema"]["properties"][string],
                },
                required: ["value"],
            },
        });
        if (result.action === "accept" && result.content?.value != null) {
            return result.content.value as string;
        }
        return null;
    }

    /**
     * Registers a handler for permission requests.
     *
     * When the assistant needs permission to perform certain actions (e.g., file operations),
     * this handler is called to approve or deny the request.
     *
     * @param handler - The permission handler function, or undefined to remove the handler
     * @internal This method is typically called internally when creating a session.
     */
    registerPermissionHandler(handler?: PermissionHandler): void {
        this.permissionHandler = handler;
    }

    /**
     * Registers a user input handler for ask_user requests.
     *
     * When the agent needs input from the user (via ask_user tool),
     * this handler is called to provide the response.
     *
     * @param handler - The user input handler function, or undefined to remove the handler
     * @internal This method is typically called internally when creating a session.
     */
    registerUserInputHandler(handler?: UserInputHandler): void {
        this.userInputHandler = handler;
    }

    /**
     * Registers hook handlers for session lifecycle events.
     *
     * Hooks allow custom logic to be executed at various points during
     * the session lifecycle (before/after tool use, session start/end, etc.).
     *
     * @param hooks - The hook handlers object, or undefined to remove all hooks
     * @internal This method is typically called internally when creating a session.
     */
    registerHooks(hooks?: SessionHooks): void {
        this.hooks = hooks;
    }

    /**
     * Registers transform callbacks for system message sections.
     *
     * @param callbacks - Map of section ID to transform callback, or undefined to clear
     * @internal This method is typically called internally when creating a session.
     */
    registerTransformCallbacks(callbacks?: Map<string, SectionTransformFn>): void {
        this.transformCallbacks = callbacks;
    }

    /**
     * Handles a systemMessage.transform request from the runtime.
     * Dispatches each section to its registered transform callback.
     *
     * @param sections - Map of section IDs to their current rendered content
     * @returns A promise that resolves with the transformed sections
     * @internal This method is for internal use by the SDK.
     */
    async _handleSystemMessageTransform(
        sections: Record<string, { content: string }>
    ): Promise<{ sections: Record<string, { content: string }> }> {
        const result: Record<string, { content: string }> = {};

        for (const [sectionId, { content }] of Object.entries(sections)) {
            const callback = this.transformCallbacks?.get(sectionId);
            if (callback) {
                try {
                    const transformed = await callback(content);
                    result[sectionId] = { content: transformed };
                } catch (_error) {
                    // Callback failed — return original content
                    result[sectionId] = { content };
                }
            } else {
                // No callback for this section — pass through unchanged
                result[sectionId] = { content };
            }
        }

        return { sections: result };
    }

    /**
     * Handles a user input request from the Copilot CLI.
     *
     * @param request - The user input request data from the CLI
     * @returns A promise that resolves with the user's response
     * @internal This method is for internal use by the SDK.
     */
    async _handleUserInputRequest(request: unknown): Promise<UserInputResponse> {
        if (!this.userInputHandler) {
            // No handler registered, throw error
            throw new Error("User input requested but no handler registered");
        }

        try {
            const result = await this.userInputHandler(request as UserInputRequest, {
                sessionId: this.sessionId,
            });
            return result;
        } catch (error) {
            // Handler failed, rethrow
            throw error;
        }
    }

    /**
     * Handles a hooks invocation from the Copilot CLI.
     *
     * @param hookType - The type of hook being invoked
     * @param input - The input data for the hook
     * @returns A promise that resolves with the hook output, or undefined
     * @internal This method is for internal use by the SDK.
     */
    async _handleHooksInvoke(hookType: string, input: unknown): Promise<unknown> {
        if (!this.hooks) {
            return undefined;
        }

        // All hook inputs share BaseHookInput, which exposes `timestamp` as a Date.
        // The wire format sends it as Unix epoch ms (number), so we deserialize
        // here, at the one place that knows the input is a hook payload. Bad data
        // is left alone — the user-facing handler types still cast unknown to the
        // specific HookInput, so a runtime type mismatch surfaces as a normal
        // TypeError in user code rather than being silently masked.
        const normalized = deserializeHookInput(input);

        type GenericHandler = (
            input: unknown,
            invocation: { sessionId: string }
        ) => Promise<unknown> | unknown;

        const handlerMap: Record<string, GenericHandler | undefined> = {
            preToolUse: this.hooks.onPreToolUse as GenericHandler | undefined,
            preMcpToolCall: this.hooks.onPreMcpToolCall as GenericHandler | undefined,
            postToolUse: this.hooks.onPostToolUse as GenericHandler | undefined,
            postToolUseFailure: this.hooks.onPostToolUseFailure as GenericHandler | undefined,
            userPromptSubmitted: this.hooks.onUserPromptSubmitted as GenericHandler | undefined,
            sessionStart: this.hooks.onSessionStart as GenericHandler | undefined,
            sessionEnd: this.hooks.onSessionEnd as GenericHandler | undefined,
            errorOccurred: this.hooks.onErrorOccurred as GenericHandler | undefined,
            agentStop: this.hooks.onAgentStop as GenericHandler | undefined,
        };

        const handler = handlerMap[hookType];
        if (!handler) {
            return undefined;
        }

        try {
            const result = await handler(normalized, { sessionId: this.sessionId });
            return result;
        } catch (_error) {
            // Hook failed, return undefined
            return undefined;
        }
    }

    /**
     * Retrieves all events and messages from this session's history.
     *
     * This returns the complete conversation history including user messages,
     * assistant responses, tool executions, and other session events.
     *
     * @returns A promise that resolves with an array of all session events
     * @throws Error if the session has been disconnected or the connection fails
     *
     * @example
     * ```typescript
     * const events = await session.getEvents();
     * for (const event of events) {
     *   if (event.type === "assistant.message") {
     *     console.log("Assistant:", event.data.content);
     *   }
     * }
     * ```
     */
    async getEvents(): Promise<SessionEvent[]> {
        const response = await this.connection.sendRequest("session.getMessages", {
            sessionId: this.sessionId,
        });

        return (response as { events: SessionEvent[] }).events;
    }

    /**
     * Disconnects this session and releases all in-memory resources (event handlers,
     * tool handlers, permission handlers).
     *
     * Session state on disk (conversation history, planning state, artifacts) is
     * preserved, so the conversation can be resumed later by calling
     * {@link CopilotClient.resumeSession} with the session ID. To permanently
     * remove all session data including files on disk, use
     * {@link CopilotClient.deleteSession} instead.
     *
     * After calling this method, the session object can no longer be used.
     *
     * @returns A promise that resolves when the session is disconnected
     * @throws Error if the connection fails
     *
     * @example
     * ```typescript
     * // Clean up when done — session can still be resumed later
     * await session.disconnect();
     * ```
     */
    async disconnect(): Promise<void> {
        if (this.disconnected) {
            return;
        }
        await this.connection.sendRequest("session.destroy", {
            sessionId: this.sessionId,
        });
        this._markDisconnected();
    }

    /** Enables `await using session = ...` syntax for automatic cleanup. */
    async [Symbol.asyncDispose](): Promise<void> {
        return this.disconnect();
    }

    /**
     * Aborts the currently processing message in this session.
     *
     * Use this to cancel a long-running request. The session remains valid
     * and can continue to be used for new messages.
     *
     * @returns A promise that resolves when the abort request is acknowledged
     * @throws Error if the session has been disconnected or the connection fails
     *
     * @example
     * ```typescript
     * // Start a long-running request
     * const messagePromise = session.send({ prompt: "Write a very long story..." });
     *
     * // Abort after 5 seconds
     * setTimeout(async () => {
     *   await session.abort();
     * }, 5000);
     * ```
     */
    async abort(): Promise<void> {
        await this.connection.sendRequest("session.abort", {
            sessionId: this.sessionId,
        });
    }

    /**
     * Change the model for this session.
     * The new model takes effect for the next message. Conversation history is preserved.
     *
     * @param model - Model ID to switch to
     * @param options - Optional settings for the new model
     *
     * @example
     * ```typescript
     * await session.setModel("gpt-5.4");
     * await session.setModel("claude-sonnet-4.6", { reasoningEffort: "high" });
     * ```
     */
    async setModel(
        model: string,
        options?: {
            reasoningEffort?: ReasoningEffort;
            reasoningSummary?: ReasoningSummary;
            contextTier?: ContextTier;
            modelCapabilities?: ModelCapabilitiesOverride;
        }
    ): Promise<void> {
        await this.rpc.model.switchTo({ modelId: model, ...options });
    }

    /**
     * Log a message to the session timeline.
     * The message appears in the session event stream and is visible to SDK consumers
     * and (for non-ephemeral messages) persisted to the session event log on disk.
     *
     * @param message - Human-readable message text
     * @param options - Optional log level and ephemeral flag
     *
     * @example
     * ```typescript
     * await session.log("Processing started");
     * await session.log("Disk usage high", { level: "warning" });
     * await session.log("Connection failed", { level: "error" });
     * await session.log("Debug info", { ephemeral: true });
     * ```
     */
    async log(
        message: string,
        options?: { level?: "info" | "warning" | "error"; ephemeral?: boolean }
    ): Promise<void> {
        await this.rpc.log({ message, ...options });
    }
}

/**
 * Type guard that checks whether a value is a {@link ToolResultObject}.
 * A valid object must have a string `textResultForLlm` and a recognized `resultType`.
 */
function isToolResultObject(value: unknown): value is ToolResultObject {
    if (typeof value !== "object" || value === null) {
        return false;
    }

    if (
        !("textResultForLlm" in value) ||
        typeof (value as ToolResultObject).textResultForLlm !== "string"
    ) {
        return false;
    }

    if (!("resultType" in value) || typeof (value as ToolResultObject).resultType !== "string") {
        return false;
    }

    const allowedResultTypes: Array<ToolResultObject["resultType"]> = [
        "success",
        "failure",
        "rejected",
        "denied",
        "timeout",
    ];

    return allowedResultTypes.includes((value as ToolResultObject).resultType);
}

/** Convert a canvas handler error into a ResponseError with a structured data envelope. */
function toCanvasRpcError(error: unknown): ResponseError<unknown> {
    if (error instanceof ResponseError) return error;
    const code = error instanceof CanvasError ? error.code : "canvas_handler_error";
    const message = error instanceof Error ? error.message : String(error);
    return new ResponseError(ErrorCodes.InternalError, message, { code, message });
}

type FactoryResultValidationCategory =
    | "unsupported_type"
    | "non_finite_number"
    | "negative_zero"
    | "cyclic_value"
    | "nested_undefined"
    | "unsupported_object";

interface StrictJsonValidationContext {
    code: "factory_result_not_json" | "factory_step_not_json";
    label: string;
    allowTopLevelUndefined: boolean;
}

function strictJsonValidationError(
    context: StrictJsonValidationContext,
    category: FactoryResultValidationCategory,
    message: string,
    path: string
): ResponseError<{ code: string; category: FactoryResultValidationCategory; path: string }> {
    return new ResponseError(ErrorCodes.InternalError, message, {
        code: context.code,
        category,
        path,
    });
}

function assertStrictJson(
    value: unknown,
    context: StrictJsonValidationContext
): asserts value is JsonValue | undefined {
    const ancestors = new Set<object>();

    const visit = (current: unknown, path: string, allowUndefined: boolean): void => {
        if (current === undefined) {
            if (allowUndefined) {
                return;
            }
            throw strictJsonValidationError(
                context,
                "nested_undefined",
                `${context.label} contains nested undefined at ${path}`,
                path
            );
        }
        if (current === null || typeof current === "boolean" || typeof current === "string") {
            return;
        }
        if (typeof current === "number") {
            if (!Number.isFinite(current)) {
                throw strictJsonValidationError(
                    context,
                    "non_finite_number",
                    `${context.label} contains a non-finite number at ${path}`,
                    path
                );
            }
            // JSON serializes -0 as "0", so a journaled -0 would come back as 0
            // after a resume and break the lossless replay guarantee.
            if (Object.is(current, -0)) {
                throw strictJsonValidationError(
                    context,
                    "negative_zero",
                    `${context.label} contains negative zero at ${path}; normalize it to 0`,
                    path
                );
            }
            return;
        }
        if (
            typeof current === "function" ||
            typeof current === "symbol" ||
            typeof current === "bigint"
        ) {
            throw strictJsonValidationError(
                context,
                "unsupported_type",
                `${context.label} contains a function, symbol, or BigInt at ${path}`,
                path
            );
        }
        if (typeof current !== "object") {
            throw strictJsonValidationError(
                context,
                "unsupported_type",
                `${context.label} contains a function, symbol, or BigInt at ${path}`,
                path
            );
        }
        if (ancestors.has(current)) {
            throw strictJsonValidationError(
                context,
                "cyclic_value",
                `${context.label} contains a cyclic reference at ${path}`,
                path
            );
        }

        ancestors.add(current);
        try {
            if (Array.isArray(current)) {
                const keys = Reflect.ownKeys(current);
                if (
                    keys.length !== current.length + 1 ||
                    keys.some(
                        (key) =>
                            key !== "length" &&
                            (typeof key !== "string" ||
                                !/^(0|[1-9]\d*)$/.test(key) ||
                                Number(key) >= current.length)
                    )
                ) {
                    throw strictJsonValidationError(
                        context,
                        "unsupported_object",
                        `${context.label} contains a non-JSON array property at ${path}`,
                        path
                    );
                }
                for (let index = 0; index < current.length; index++) {
                    const descriptor = Object.getOwnPropertyDescriptor(current, String(index));
                    if (
                        descriptor === undefined ||
                        !descriptor.enumerable ||
                        !("value" in descriptor)
                    ) {
                        throw strictJsonValidationError(
                            context,
                            "unsupported_object",
                            `${context.label} contains a non-JSON array property at ${path}[${index}]`,
                            `${path}[${index}]`
                        );
                    }
                    visit(descriptor.value, `${path}[${index}]`, false);
                }
                return;
            }

            const prototype = Object.getPrototypeOf(current);
            if (prototype !== Object.prototype && prototype !== null) {
                throw strictJsonValidationError(
                    context,
                    "unsupported_object",
                    `${context.label} contains a non-JSON object at ${path}`,
                    path
                );
            }
            for (const key of Reflect.ownKeys(current)) {
                if (typeof key === "symbol") {
                    throw strictJsonValidationError(
                        context,
                        "unsupported_type",
                        `${context.label} contains a function, symbol, or BigInt at ${path}`,
                        path
                    );
                }
                const propertyPath = /^[A-Za-z_$][\w$]*$/.test(key)
                    ? `${path}.${key}`
                    : `${path}[${JSON.stringify(key)}]`;
                const descriptor = Object.getOwnPropertyDescriptor(current, key);
                if (
                    descriptor === undefined ||
                    !descriptor.enumerable ||
                    !("value" in descriptor)
                ) {
                    throw strictJsonValidationError(
                        context,
                        "unsupported_object",
                        `${context.label} contains a non-JSON property at ${propertyPath}`,
                        propertyPath
                    );
                }
                visit(descriptor.value, propertyPath, false);
            }
        } finally {
            ancestors.delete(current);
        }
    };

    visit(value, "$", context.allowTopLevelUndefined);
}

function assertFactoryResult(value: unknown): asserts value is JsonValue | undefined {
    assertStrictJson(value, {
        code: "factory_result_not_json",
        label: "Factory result",
        allowTopLevelUndefined: true,
    });
}

function assertFactoryStepResult(value: unknown, key: string): asserts value is JsonValue {
    assertStrictJson(value, {
        code: "factory_step_not_json",
        label: `Factory step "${key}" result`,
        allowTopLevelUndefined: false,
    });
}