csharp.ts

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

/**
 * C# code generator for session-events and RPC types.
 */

import { execFile } from "child_process";
import fs from "fs/promises";
import path from "path";
import { fileURLToPath } from "url";
import { promisify } from "util";
import type { JSONSchema7 } from "json-schema";
import {
    cloneSchemaForCodegen,
    fixNullableRequiredRefsInApiSchema,
    getApiSchemaPath,
    getRpcSchemaTypeName,
    getSessionEventsSchemaPath,
    isCodegenEntrypoint,
    writeGeneratedFile,
    collectExternalSchemaRefNames,
    collectDefinitionCollections,
    collectExperimentalOnlyRpcReferencedDefinitionNames,
    collectReachableDefinitionNames,
    collectRpcMethodReferencedDefinitionNames,
    findSharedSchemaDefinitions,
    postProcessSchema,
    propagateInternalVisibility,
    filterNodeByVisibility,
    resolveRef,
    resolveObjectSchema,
    resolveSchema,
    refTypeName,
    isRpcMethod,
    isIntegerSchemaBoundedToInt32,
    isNodeFullyExperimental,
    isNodeFullyDeprecated,
    isSchemaDeprecated,
    isSchemaExperimental,
    isSchemaInternal,
    isOpaqueJson,
    isOpaqueInProcess,
    isObjectSchema,
    isVoidSchema,
    getNullableInner,
    getEnumValueDescriptions,
    getSessionEventVariantSchemas,
    getSharedSessionEventEnvelopeProperties,
    rewriteSharedDefinitionReferences,
    loadSchemaJson,
    fixBrandCasing,
    REPO_ROOT,
    type ApiSchema,
    type DefinitionCollections,
    type EnumValueDescriptions,
    type RpcMethod,
    type SessionEventEnvelopeProperty,
} from "./utils.js";
import { isOmittableRequest, readLegacyParameters, validateLegacyDefinitions } from "./legacy-parameters.js";

const execFileAsync = promisify(execFile);

// ── C# type rename overrides ────────────────────────────────────────────────
// Map generated class names to shorter public-facing names.
// Applied to base classes AND their derived variants (e.g., FooBar → Bar, FooBazShell → BarShell).
const TYPE_RENAMES: Record<string, string> = {
    PermissionRequestedDataPermissionRequest: "PermissionRequest",
};

const POLYMORPHIC_BASE_PROPERTIES: Record<string, readonly string[]> = {
    PermissionRequest: ["managedApprovalRequired"],
};

/**
 * Public type names declared by hand-written C# sources under `dotnet/src`
 * (excluding `dotnet/src/Generated`). Generated session-event types share the
 * `GitHub.Copilot` namespace with those sources, so a schema definition whose
 * name collides with a hand-written declaration must reuse it — emitting a
 * second class of the same name fails the build (CS0260/CS0102).
 *
 * Populated by {@link collectHandWrittenCSharpTypeNames} before generation.
 */
let handWrittenCSharpTypeNames = new Set<string>();

/**
 * Scan hand-written `.cs` files under `dotnet/src` for top-level public type
 * declarations. The `Generated` directory is skipped so this scanner never
 * reads (or depends on the output of) its own emit.
 */
async function collectHandWrittenCSharpTypeNames(): Promise<Set<string>> {
    const names = new Set<string>();
    const srcDir = path.join(REPO_ROOT, "dotnet", "src");
    const declaration = /^\s*(?:public|internal)\s+(?:(?:abstract|sealed|static|partial|readonly|ref)\s+)*(?:class|record|struct|interface|enum)\s+([A-Za-z_]\w*)/gm;

    const walk = async (dir: string): Promise<void> => {
        let entries;
        try {
            entries = await fs.readdir(dir, { withFileTypes: true });
        } catch {
            return;
        }
        for (const entry of entries) {
            const entryPath = path.join(dir, entry.name);
            if (entry.isDirectory()) {
                if (entry.name === "Generated" || entry.name === "bin" || entry.name === "obj") continue;
                await walk(entryPath);
                continue;
            }
            if (!entry.name.endsWith(".cs")) continue;
            const content = await fs.readFile(entryPath, "utf-8");
            for (const match of content.matchAll(declaration)) names.add(match[1]);
        }
    };

    await walk(srcDir);
    return names;
}

/** Apply rename to a generated class name, checking both exact match and prefix replacement for derived types. */
function applyTypeRename(className: string): string {
    if (TYPE_RENAMES[className]) return TYPE_RENAMES[className];
    for (const [from, to] of Object.entries(TYPE_RENAMES)) {
        if (className.startsWith(from)) {
            return to + className.slice(from.length);
        }
    }
    return className;
}

// ── C# utilities ────────────────────────────────────────────────────────────

function escapeXml(text: string): string {
    return text.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
}

function escapeXmlAttribute(text: string): string {
    return escapeXml(text).replace(/"/g, "&quot;").replace(/'/g, "&apos;");
}

/** Ensures text ends with sentence-ending punctuation. */
function ensureTrailingPunctuation(text: string): string {
    const trimmed = text.trimEnd();
    if (/[.!?]$/.test(trimmed)) return trimmed;
    return `${trimmed}.`;
}

function xmlDocComment(description: string | undefined, indent: string): string[] {
    if (!description) return [];
    const escaped = ensureTrailingPunctuation(escapeXml(description.trim()));
    const lines = escaped.split(/\r?\n/);
    if (lines.length === 1) {
        return [`${indent}/// <summary>${lines[0]}</summary>`];
    }
    return [
        `${indent}/// <summary>`,
        ...lines.map((l) => `${indent}/// ${l}`),
        `${indent}/// </summary>`,
    ];
}

function xmlDocElement(tagName: string, description: string | undefined, indent: string): string[] {
    if (!description) return [];
    const escaped = ensureTrailingPunctuation(escapeXml(description.trim()));
    const lines = escaped.split(/\r?\n/);
    if (lines.length === 1) {
        return [`${indent}/// <${tagName}>${lines[0]}</${tagName}>`];
    }
    return [
        `${indent}/// <${tagName}>`,
        ...lines.map((line) => `${indent}/// ${line}`),
        `${indent}/// </${tagName}>`,
    ];
}

function xmlDocNamedElement(
    tagName: string,
    name: string,
    description: string | undefined,
    indent: string,
    escapeDescription = true
): string[] {
    if (!description) return [];
    const preparedDescription = escapeDescription ? escapeXml(description.trim()) : description.trim();
    const lines = ensureTrailingPunctuation(preparedDescription).split(/\r?\n/);
    const escapedName = escapeXmlAttribute(name);
    if (lines.length === 1) {
        return [`${indent}/// <${tagName} name="${escapedName}">${lines[0]}</${tagName}>`];
    }
    return [
        `${indent}/// <${tagName} name="${escapedName}">`,
        ...lines.map((line) => `${indent}/// ${line}`),
        `${indent}/// </${tagName}>`,
    ];
}

function rpcResultDescription(method: RpcMethod, resultSchema: JSONSchema7 | undefined): string | undefined {
    if (isVoidSchema(resultSchema)) return undefined;
    return method.result?.description ?? resultSchema?.description;
}

function rpcParamsDescription(method: RpcMethod, effectiveParams: JSONSchema7 | undefined): string | undefined {
    return method.params?.description ?? effectiveParams?.description;
}

function fallbackParameterDescription(name: string): string {
    return name === "request" ? "The request parameters." : `The ${name} parameter.`;
}

function pushRpcMethodXmlDocs(
    lines: string[],
    method: RpcMethod,
    indent: string,
    parameterDescriptions: Array<{ name: string; description?: string; escapeDescription?: boolean }>,
    resultSchema: JSONSchema7 | undefined,
    summaryFallback?: string
): void {
    lines.push(...xmlDocComment(method.description ?? summaryFallback ?? `Calls "${method.rpcMethod}".`, indent));
    for (const parameter of parameterDescriptions) {
        lines.push(
            ...xmlDocNamedElement(
                "param",
                parameter.name,
                parameter.description ?? fallbackParameterDescription(parameter.name),
                indent,
                parameter.escapeDescription
            )
        );
    }
    lines.push(...xmlDocElement("returns", rpcResultDescription(method, resultSchema), indent));
}

const CANCELLATION_TOKEN_DESCRIPTION =
    'The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.';

/** Like xmlDocComment but skips XML escaping — use only for codegen-controlled strings that already contain valid XML tags. */
function rawXmlDocSummary(text: string, indent: string): string[] {
    const line = ensureTrailingPunctuation(text.trim());
    return [`${indent}/// <summary>${line}</summary>`];
}

/** Emits a summary (from description or fallback) and, when a real description exists, a remarks line with the fallback. */
function xmlDocCommentWithFallback(description: string | undefined, fallback: string, indent: string): string[] {
    if (description) {
        return [
            ...xmlDocComment(description, indent),
            `${indent}/// <remarks>${ensureTrailingPunctuation(fallback)}</remarks>`,
        ];
    }
    return rawXmlDocSummary(fallback, indent);
}

/** Emits a summary from the schema description, or a fallback naming the property by its JSON key. */
function xmlDocPropertyComment(description: string | undefined, jsonPropName: string, indent: string): string[] {
    if (description) return xmlDocComment(description, indent);
    return rawXmlDocSummary(`Gets or sets the <c>${escapeXml(jsonPropName)}</c> value.`, indent);
}

/** Emits a summary from the schema description, or a generic fallback. */
function xmlDocEnumComment(description: string | undefined, indent: string): string[] {
    if (description) return xmlDocComment(description, indent);
    return rawXmlDocSummary(`Defines the allowed values.`, indent);
}

function xmlDocEnumMemberComment(enumValueDescriptions: EnumValueDescriptions | undefined, value: string): string[] {
    const description = enumValueDescriptions?.[value];
    if (description) return xmlDocComment(description, "    ");
    return rawXmlDocSummary(`Gets the <c>${escapeXml(value)}</c> value.`, "    ");
}

function toPascalCase(name: string): string {
    const parts = splitCSharpIdentifierParts(name);
    if (parts.length > 1) return parts.map(toPascalCasePart).join("");
    return fixBrandCasing(name.charAt(0).toUpperCase() + name.slice(1));
}

function stripDurationMillisecondsSuffix(name: string): string {
    if (name.length > 2 && name.endsWith("Ms") && /[a-z]/.test(name.charAt(name.length - 3))) {
        return name.slice(0, -2);
    }
    return name;
}

function toCSharpPropertyName(propName: string, schema: JSONSchema7): string {
    const normalizedName = propName.replace(/^_+/, "") || propName;
    return toPascalCase(isDurationProperty(schema) ? stripDurationMillisecondsSuffix(normalizedName) : normalizedName);
}

function isSecondsDurationPropertyName(propName: string | undefined): boolean {
    return propName !== undefined && /seconds$/i.test(propName);
}

function typeToClassName(typeName: string): string {
    return splitCSharpIdentifierParts(typeName).map(toPascalCasePart).join("");
}

function splitCSharpIdentifierParts(value: string): string[] {
    return value.split(/[^A-Za-z0-9]+/).filter(Boolean);
}

function toPascalCasePart(value: string): string {
    return fixBrandCasing(value.charAt(0).toUpperCase() + value.slice(1));
}

function toCSharpIdentifier(value: string, fallback: string): string {
    let identifier = splitCSharpIdentifierParts(value).map(toPascalCasePart).join("");
    if (!identifier) {
        identifier = fallback;
    } else if (!/^[A-Za-z_]/.test(identifier)) {
        identifier = `${fallback}${identifier}`;
    }
    return identifier;
}

function uniqueCSharpIdentifier(value: string, used: Set<string>, fallback: string): string {
    const identifier = toCSharpIdentifier(value, fallback);
    if (used.has(identifier)) {
        throw new Error(
            `Generated C# string enum member identifier "${identifier}" is not unique for value "${value}". Add an explicit naming rule instead of stabilizing an arbitrary public member name.`
        );
    }
    used.add(identifier);
    return identifier;
}

function isNonNullableCSharpValueType(typeName: string): boolean {
    return [
        "bool",
        "double",
        "float",
        "Guid",
        "int",
        "long",
        "DateTimeOffset",
        "TimeSpan",
        "JsonElement",
    ].includes(typeName) || generatedEnums.has(typeName) || emittedRpcEnumResultTypes.has(typeName) || externalRpcValueTypes.has(typeName);
}

/**
 * Schemas marked `.asOpaqueJson()` on the runtime side carry
 * `x-opaque-json: true`. These are the only shapes that legitimately surface
 * as opaque JSON in the SDK (mapped to `JsonElement` in C#). Anything else
 * that lacks an idiomatic mapping (untyped fields, non-discriminated unions,
 * etc.) is rejected by the runtime's schema-shape lint, so the codegen
 * treats reaching an unmappable schema here as a bug.
 *
 * The predicate itself lives in {@link "./utils".isOpaqueJson} for reuse.
 */
function failUnmappable(context: string, schema: JSONSchema7): never {
    const summary = JSON.stringify(schema, (key, value) => (key === "description" ? undefined : value)).slice(0, 200);
    throw new Error(
        `C# codegen: cannot map schema to an idiomatic C# type (${context}). ` +
            `On the runtime side, either tighten the Zod schema to a typed shape, or — if it is genuinely free-form JSON — ` +
            `mark it \`.asOpaqueJson()\` so the schema emits \`x-opaque-json: true\` and the codegen maps it to JsonElement. ` +
            `Offending schema (truncated): ${summary}`,
    );
}

function omitUnrepresentableInternalProperties(value: unknown): void {
    if (!value || typeof value !== "object") return;
    if (Array.isArray(value)) {
        value.forEach(omitUnrepresentableInternalProperties);
        return;
    }

    const node = value as Record<string, unknown>;
    const properties = node.properties;
    if (properties && typeof properties === "object" && !Array.isArray(properties)) {
        for (const [name, property] of Object.entries(properties)) {
            if (!property || typeof property !== "object" || Array.isArray(property)) continue;
            const schema = property as JSONSchema7;
            const hasType =
                schema.type !== undefined ||
                schema.$ref !== undefined ||
                schema.anyOf !== undefined ||
                schema.oneOf !== undefined ||
                schema.allOf !== undefined ||
                schema.enum !== undefined ||
                schema.const !== undefined ||
                isOpaqueJson(schema);
            if (isSchemaInternal(schema) && (!hasType || isOpaqueInProcess(schema))) {
                delete (properties as Record<string, unknown>)[name];
            } else {
                omitUnrepresentableInternalProperties(property);
            }
        }
    }

    for (const [name, child] of Object.entries(node)) {
        if (name !== "properties") omitUnrepresentableInternalProperties(child);
    }
}

function requiresArgumentNullCheck(typeName: string, isRequired: boolean): boolean {
    return isRequired && !typeName.endsWith("?") && !isNonNullableCSharpValueType(typeName);
}

async function formatCSharpFile(filePath: string): Promise<void> {
    try {
        const projectFile = path.join(REPO_ROOT, "dotnet/src/GitHub.Copilot.SDK.csproj");
        await execFileAsync("dotnet", ["format", projectFile, "--include", filePath]);
        console.log(`  ✓ Formatted with dotnet format`);
    } catch {
        // dotnet format not available, skip
    }
}

function collectRpcMethods(node: Record<string, unknown>): RpcMethod[] {
    const results: RpcMethod[] = [];
    for (const value of Object.values(node)) {
        if (isRpcMethod(value)) {
            results.push(value);
        } else if (typeof value === "object" && value !== null) {
            results.push(...collectRpcMethods(value as Record<string, unknown>));
        }
    }
    return results;
}

function localRequestVariableName(paramEntries: [string, JSONSchema7Definition][], hasRequestParameter = false): string {
    return hasRequestParameter || paramEntries.some(([name]) => name === "request") ? "rpcRequest" : "request";
}

function schemaTypeToCSharp(schema: JSONSchema7, required: boolean, knownTypes: Map<string, string>, propName?: string): string {
    if (isOpaqueJson(schema)) {
        return required ? "JsonElement" : "JsonElement?";
    }
    const nullableInner = getNullableInner(schema);
    if (nullableInner) {
        // Pass required=true to get the base type, then add "?" for nullable
        return schemaTypeToCSharp(nullableInner, true, knownTypes, propName) + "?";
    }
    if (schema.$ref) {
        const refName = schema.$ref.split("/").pop()!;
        return knownTypes.get(refName) || refName;
    }
    // Titled union schemas (anyOf with a title) — use the title if it's a known generated type
    if (schema.title && schema.anyOf && knownTypes.has(schema.title)) {
        return required ? schema.title : `${schema.title}?`;
    }
    const type = schema.type;
    const format = schema.format;
    // Handle type: ["string", "null"] patterns (nullable string)
    if (Array.isArray(type)) {
        const nonNullTypes = type.filter((t) => t !== "null");
        if (nonNullTypes.length === 1 && nonNullTypes[0] === "string") {
            if (format === "uuid") return "Guid?";
            if (format === "date-time") return "DateTimeOffset?";
            return "string?";
        }
        if (nonNullTypes.length === 1 && nonNullTypes[0] === "boolean") {
            return "bool?";
        }
        if (nonNullTypes.length === 1 && (nonNullTypes[0] === "number" || nonNullTypes[0] === "integer")) {
            if (format === "duration" && !isSecondsDurationPropertyName(propName)) {
                return "TimeSpan?";
            }
            if (nonNullTypes[0] === "integer") {
                const integerType = isIntegerSchemaBoundedToInt32(schema) ? "int" : "long";
                return `${integerType}?`;
            }
            return "double?";
        }
    }
    if (type === "string") {
        if (format === "uuid") return required ? "Guid" : "Guid?";
        if (format === "date-time") return required ? "DateTimeOffset" : "DateTimeOffset?";
        return required ? "string" : "string?";
    }
    if (type === "number" || type === "integer") {
        if (format === "duration" && !isSecondsDurationPropertyName(propName)) {
            return required ? "TimeSpan" : "TimeSpan?";
        }
        if (type === "integer") {
            const integerType = isIntegerSchemaBoundedToInt32(schema) ? "int" : "long";
            return required ? integerType : `${integerType}?`;
        }
        return required ? "double" : "double?";
    }
    if (type === "boolean") return required ? "bool" : "bool?";
    if (type === "array") {
        const items = schema.items as JSONSchema7 | undefined;
        if (!items) failUnmappable(`array without items (propName=${propName ?? "?"})`, schema);
        const itemType = schemaTypeToCSharp(items, true, knownTypes);
        return required ? `${itemType}[]` : `${itemType}[]?`;
    }
    if (type === "object") {
        if (schema.additionalProperties && typeof schema.additionalProperties === "object") {
            const valueType = schemaTypeToCSharp(schema.additionalProperties as JSONSchema7, true, knownTypes);
            return required ? `IDictionary<string, ${valueType}>` : `IDictionary<string, ${valueType}>?`;
        }
        failUnmappable(`object without properties or typed additionalProperties (propName=${propName ?? "?"})`, schema);
    }
    failUnmappable(`unknown/missing type (propName=${propName ?? "?"})`, schema);
}

/** Tracks whether any TimeSpan property was emitted so the converter can be generated. */


/**
 * Emit C# data-annotation attributes for a JSON Schema property.
 * Returns an array of attribute lines (without trailing newlines).
 */
function emitDataAnnotations(schema: JSONSchema7, indent: string, csharpType: string): string[] {
    const attrs: string[] = [];
    const format = schema.format;

    // [Url] + [StringSyntax(StringSyntaxAttribute.Uri)] for format: "uri"
    if (format === "uri") {
        attrs.push(`${indent}[Url]`);
        attrs.push(`${indent}[StringSyntax(StringSyntaxAttribute.Uri)]`);
    }

    // [StringSyntax(StringSyntaxAttribute.Regex)] and [RegularExpression] for format: "regex"
    if (format === "regex") {
        attrs.push(`${indent}[StringSyntax(StringSyntaxAttribute.Regex)]`);
        if (typeof schema.pattern === "string") {
            attrs.push(`${indent}[RegularExpression("${escapeCSharpStringLiteral(schema.pattern)}")]`);
        }
    }

    // [Base64String] for base64-encoded string properties
    if (format === "byte" || (schema as Record<string, unknown>).contentEncoding === "base64") {
        attrs.push(`${indent}[Base64String]`);
    }

    // [RegularExpression] for pattern constraints on non-regex-format properties
    if (format !== "regex" && typeof schema.pattern === "string") {
        attrs.push(`${indent}[RegularExpression("${escapeCSharpStringLiteral(schema.pattern)}")]`);
    }

    // [MinLength] / [MaxLength] for string constraints
    if (typeof schema.minLength === "number" || typeof schema.maxLength === "number") {
        attrs.push(
            `${indent}[UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Safe for generated string properties: JSON Schema minLength/maxLength map to string length validation, not reflection over trimmed Count members")]`
        );
    }
    if (typeof schema.minLength === "number") {
        attrs.push(`${indent}[MinLength(${schema.minLength})]`);
    }
    if (typeof schema.maxLength === "number") {
        attrs.push(`${indent}[MaxLength(${schema.maxLength})]`);
    }

    return attrs;
}

/**
 * Returns true when a TimeSpan-typed property needs a [JsonConverter] attribute.
 *
 * NOTE: The runtime schema generally uses `format: "duration"` on numeric (integer/number)
 * fields to mean "a duration value expressed in milliseconds". This differs from the JSON
 * Schema spec, where `format: "duration"` denotes an ISO 8601 duration string (e.g.
 * "PT1H30M"). The generator and runtime agree on this convention, so we map millisecond
 * fields to TimeSpan with a milliseconds-based JSON converter rather than expecting ISO
 * 8601 strings. Seconds-suffixed fields stay numeric because their wire value is seconds.
 */
function isDurationProperty(schema: JSONSchema7): boolean {
    const nullableInner = getNullableInner(schema);
    if (nullableInner) {
        return isDurationProperty(nullableInner);
    }

    if (schema.format === "duration") {
        const t = schema.type;
        if (t === "number" || t === "integer") return true;
        if (Array.isArray(t)) {
            const nonNull = (t as string[]).filter((x) => x !== "null");
            if (nonNull.length === 1 && (nonNull[0] === "number" || nonNull[0] === "integer")) return true;
        }
    }
    return false;
}

function isMillisecondsDurationProperty(propName: string | undefined, schema: JSONSchema7): boolean {
    return isDurationProperty(schema) && !isSecondsDurationPropertyName(propName);
}


const COPYRIGHT = `/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *--------------------------------------------------------------------------------------------*/`;

const EXPERIMENTAL_ATTRIBUTE = "[Experimental(global::GitHub.Copilot.Diagnostics.Experimental)]";
const EDITOR_BROWSABLE_NEVER_ATTRIBUTE = "[EditorBrowsable(EditorBrowsableState.Never)]";
const OBSOLETE_ATTRIBUTE = `#if NET5_0_OR_GREATER
[Obsolete("This member is deprecated and will be removed in a future version.", DiagnosticId = "GHCP001")]
#else
[Obsolete("This member is deprecated and will be removed in a future version.")]
#endif`;
const STRING_ENUM_RESERVED_MEMBER_NAMES = new Set(["Value", "Equals", "GetHashCode", "ToString", "Converter"]);

function experimentalAttribute(indent = ""): string {
    return `${indent}${EXPERIMENTAL_ATTRIBUTE}`;
}

function pushExperimentalAttribute(lines: string[], indent = ""): void {
    lines.push(experimentalAttribute(indent));
}

function obsoleteAttributes(indent = ""): string[] {
    return [
        `${indent}${EDITOR_BROWSABLE_NEVER_ATTRIBUTE}`,
        ...OBSOLETE_ATTRIBUTE.split("\n").map((line) => line.startsWith("#") ? line : `${indent}${line}`),
    ];
}

function obsoleteAttributeBlock(indent = ""): string {
    return obsoleteAttributes(indent).join("\n");
}

function pushObsoleteAttributes(lines: string[], indent = ""): void {
    lines.push(...obsoleteAttributes(indent));
}

/**
 * Emit the `[JsonInclude]` attribute for an internally-marked property and
 * return the C# access modifier to use for the property declaration.
 *
 * `[JsonInclude]` is required because System.Text.Json only auto-(de)serialises
 * public members by default; without it, the `internal` setter would silently
 * be skipped.
 */
function pushCSharpInternalAttribute(lines: string[], schema: JSONSchema7, indent = "    "): "public" | "internal" {
    const propInternal = isSchemaInternal(schema);
    if (propInternal) lines.push(`${indent}[JsonInclude]`);
    return propInternal ? "internal" : "public";
}

// ══════════════════════════════════════════════════════════════════════════════
// SESSION EVENTS
// ══════════════════════════════════════════════════════════════════════════════

interface EventVariant {
    typeName: string;
    className: string;
    dataClassName: string;
    dataSchema: JSONSchema7;
    dataDescription?: string;
    eventDeprecated: boolean;
    eventExperimental: boolean;
    dataExperimental: boolean;
}

let generatedEnums = new Map<string, { enumName: string; values: string[] }>();

/** Schema definitions available during session event generation (for $ref resolution). */
let sessionDefinitions: DefinitionCollections = { definitions: {}, $defs: {} };

/** Emits a schema enum as a string-backed value type that preserves unknown runtime values. */
function getOrCreateEnum(
    parentClassName: string,
    propName: string,
    values: string[],
    enumOutput: string[],
    description?: string,
    enumValueDescriptions?: EnumValueDescriptions,
    explicitName?: string,
    deprecated?: boolean,
    experimental?: boolean
): string {
    const enumName = explicitName ?? `${parentClassName}${propName}`;
    const existing = generatedEnums.get(enumName);
    if (existing) return existing.enumName;
    generatedEnums.set(enumName, { enumName, values });

    const lines: string[] = [];
    lines.push(...xmlDocEnumComment(description, ""));
    if (experimental) pushExperimentalAttribute(lines);
    if (deprecated) pushObsoleteAttributes(lines);
    lines.push(`[JsonConverter(typeof(Converter))]`);
    lines.push(`[DebuggerDisplay("{Value,nq}")]`);
    lines.push(`public readonly struct ${enumName} : IEquatable<${enumName}>`);
    lines.push(`{`);
    lines.push(`    private readonly string? _value;`, "");
    lines.push(`    /// <summary>Initializes a new instance of the <see cref="${enumName}"/> struct.</summary>`);
    lines.push(`    /// <param name="value">The value to associate with this <see cref="${enumName}"/>.</param>`);
    lines.push(`    [JsonConstructor]`);
    lines.push(`    public ${enumName}(string value)`);
    lines.push(`    {`);
    lines.push(`        ArgumentException.ThrowIfNullOrWhiteSpace(value);`);
    lines.push(`        _value = value;`);
    lines.push(`    }`, "");
    lines.push(`    /// <summary>Gets the value associated with this <see cref="${enumName}"/>.</summary>`);
    lines.push(`    public string Value => _value ?? string.Empty;`, "");
    const usedMemberNames = new Set(STRING_ENUM_RESERVED_MEMBER_NAMES);
    for (const value of values) {
        const memberName = uniqueCSharpIdentifier(value, usedMemberNames, "Value");
        lines.push(...xmlDocEnumMemberComment(enumValueDescriptions, value));
        lines.push(`    public static ${enumName} ${memberName} { get; } = new("${escapeCSharpStringLiteral(value)}");`, "");
    }
    lines.push(`    /// <summary>Returns a value indicating whether two <see cref="${enumName}"/> instances are equivalent.</summary>`);
    lines.push(`    public static bool operator ==(${enumName} left, ${enumName} right) => left.Equals(right);`, "");
    lines.push(`    /// <summary>Returns a value indicating whether two <see cref="${enumName}"/> instances are not equivalent.</summary>`);
    lines.push(`    public static bool operator !=(${enumName} left, ${enumName} right) => !(left == right);`, "");
    lines.push(`    /// <inheritdoc />`);
    lines.push(`    public override bool Equals(object? obj) => obj is ${enumName} other && Equals(other);`, "");
    lines.push(`    /// <inheritdoc />`);
    lines.push(`    public bool Equals(${enumName} other) => string.Equals(Value, other.Value, StringComparison.OrdinalIgnoreCase);`, "");
    lines.push(`    /// <inheritdoc />`);
    lines.push(`    public override int GetHashCode() => StringComparer.OrdinalIgnoreCase.GetHashCode(Value);`, "");
    lines.push(`    /// <inheritdoc />`);
    lines.push(`    public override string ToString() => Value;`, "");
    lines.push(`    /// <summary>Provides a <see cref="JsonConverter{${enumName}}"/> for serializing <see cref="${enumName}"/> instances.</summary>`);
    lines.push(`    [EditorBrowsable(EditorBrowsableState.Never)]`);
    lines.push(`    public sealed class Converter : JsonConverter<${enumName}>`);
    lines.push(`    {`);
    lines.push(`        /// <inheritdoc />`);
    lines.push(`        public override ${enumName} Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)`);
    lines.push(`        {`);
    lines.push(`            return new(GeneratedStringEnumJson.ReadValue(ref reader, typeToConvert));`);
    lines.push(`        }`, "");
    lines.push(`        /// <inheritdoc />`);
    lines.push(`        public override void Write(Utf8JsonWriter writer, ${enumName} value, JsonSerializerOptions options)`);
    lines.push(`        {`);
    lines.push(`            GeneratedStringEnumJson.WriteValue(writer, value.Value, typeof(${enumName}));`);
    lines.push(`        }`);
    lines.push(`    }`);
    lines.push(`}`, "");
    enumOutput.push(lines.join("\n"));
    return enumName;
}

function extractEventVariants(schema: JSONSchema7): EventVariant[] {
    const definitionCollections = collectDefinitionCollections(schema as Record<string, unknown>);
    return getSessionEventVariantSchemas(schema, definitionCollections)
        .map((variant) => {
            const typeSchema = variant.properties!.type as JSONSchema7;
            const typeName = typeSchema?.const as string;
            if (!typeName) throw new Error("Variant must have type.const");
            const baseName = typeToClassName(typeName);
            const dataSchema =
                resolveObjectSchema(variant.properties!.data as JSONSchema7, definitionCollections) ??
                resolveSchema(variant.properties!.data as JSONSchema7, definitionCollections) ??
                (variant.properties!.data as JSONSchema7);
            return {
                typeName,
                className: `${baseName}Event`,
                dataClassName: `${baseName}Data`,
                dataSchema,
                dataDescription: dataSchema?.description,
                eventDeprecated: isSchemaDeprecated(variant),
                eventExperimental: isSchemaExperimental(variant),
                dataExperimental: isSchemaExperimental(dataSchema),
            };
        });
}

interface DiscriminatorVariant {
    value: unknown;
    schema: JSONSchema7;
}

interface DiscriminatorInfo {
    property: string;
    mapping: Map<string, DiscriminatorVariant>;
}

/**
 * Find a discriminator property shared by all variants in an anyOf.
 */
function findDiscriminator(variants: JSONSchema7[]): DiscriminatorInfo | null {
    if (variants.length === 0) return null;
    const firstVariant = variants[0];
    if (!firstVariant.properties) return null;

    for (const [propName, propSchema] of Object.entries(firstVariant.properties).sort(([a], [b]) => a.localeCompare(b))) {
        if (typeof propSchema !== "object") continue;
        const schema = propSchema as JSONSchema7;
        if (schema.const === undefined) continue;

        const mapping = new Map<string, DiscriminatorVariant>();
        let isValidDiscriminator = true;

        for (const variant of variants) {
            if (!variant.properties) { isValidDiscriminator = false; break; }
            const variantProp = variant.properties[propName];
            if (typeof variantProp !== "object") { isValidDiscriminator = false; break; }
            const variantSchema = variantProp as JSONSchema7;
            if (variantSchema.const === undefined) { isValidDiscriminator = false; break; }
            const key = String(variantSchema.const);
            if (mapping.has(key)) { isValidDiscriminator = false; break; }
            mapping.set(key, { value: variantSchema.const, schema: variant });
        }

        if (isValidDiscriminator && mapping.size === variants.length) {
            return { property: propName, mapping };
        }
    }
    return null;
}

/** Callback that resolves the C# type for a property schema within a polymorphic class. */
type PropertyTypeResolver = (
    propSchema: JSONSchema7,
    parentClassName: string,
    propName: string,
    isRequired: boolean,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[]
) => string;

interface DiscriminatedUnionGenerationOptions {
    sealLeafTypes?: boolean;
}

function isBooleanDiscriminator(discriminatorInfo: DiscriminatorInfo): boolean {
    return Array.from(discriminatorInfo.mapping.values()).every((variant) => typeof variant.value === "boolean");
}

function escapeCSharpStringLiteral(value: string): string {
    return value.replace(/\\/g, "\\\\").replace(/"/g, '\\"');
}

function generateDiscriminatedUnionClass(
    baseClassName: string,
    discriminatorInfo: DiscriminatorInfo,
    variants: JSONSchema7[],
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[],
    description?: string,
    propertyResolver?: PropertyTypeResolver,
    experimental = false,
    options: DiscriminatedUnionGenerationOptions = {}
): string {
    if (isBooleanDiscriminator(discriminatorInfo)) {
        return generateFlattenedBooleanDiscriminatedClass(baseClassName, discriminatorInfo, knownTypes, nestedClasses, enumOutput, description, propertyResolver, experimental, options);
    }

    return generatePolymorphicClasses(baseClassName, discriminatorInfo.property, variants, knownTypes, nestedClasses, enumOutput, description, propertyResolver, experimental, options);
}

function generateFlattenedBooleanDiscriminatedClass(
    baseClassName: string,
    discriminatorInfo: DiscriminatorInfo,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[],
    description?: string,
    propertyResolver?: PropertyTypeResolver,
    experimental = false,
    options: DiscriminatedUnionGenerationOptions = {}
): string {
    const resolver = propertyResolver ?? resolveSessionPropertyType;
    const renamedBase = applyTypeRename(baseClassName);
    const lines: string[] = [];
    const flattenedProperties = new Map<string, { schema: JSONSchema7; requiredCount: number; variantCount: number }>();
    const variants = Array.from(discriminatorInfo.mapping.values()).map((variant) => variant.schema);

    for (const variant of variants) {
        const required = new Set(variant.required || []);
        for (const [propName, propSchema] of Object.entries(variant.properties || {})) {
            if (typeof propSchema !== "object" || propName === discriminatorInfo.property) continue;

            const existing = flattenedProperties.get(propName);
            if (existing) {
                existing.variantCount++;
                if (required.has(propName)) existing.requiredCount++;
                continue;
            }

            flattenedProperties.set(propName, {
                schema: propSchema as JSONSchema7,
                requiredCount: required.has(propName) ? 1 : 0,
                variantCount: 1,
            });
        }
    }

    lines.push(...xmlDocCommentWithFallback(description, `Data type discriminated by <c>${escapeXml(discriminatorInfo.property)}</c>.`, ""));
    if (experimental) pushExperimentalAttribute(lines);
    lines.push(`public ${options.sealLeafTypes ? "sealed " : ""}partial class ${renamedBase}`);
    lines.push(`{`);
    lines.push(`    /// <summary>The boolean discriminator.</summary>`);
    lines.push(`    [JsonPropertyName("${discriminatorInfo.property}")]`);
    lines.push(`    public bool ${toPascalCase(discriminatorInfo.property)} { get; set; }`);

    const propertyEntries = Array.from(flattenedProperties.entries()).sort(([a], [b]) => a.localeCompare(b));
    for (const [propName, info] of propertyEntries) {
        const isReq = info.variantCount === variants.length && info.requiredCount === variants.length;
        const csharpName = toCSharpPropertyName(propName, info.schema);
        const csharpType = resolver(info.schema, renamedBase, csharpName, isReq, knownTypes, nestedClasses, enumOutput);

        lines.push("");
        lines.push(...xmlDocPropertyComment(info.schema.description, propName, "    "));
        lines.push(...emitDataAnnotations(info.schema, "    ", csharpType));
        if (isSchemaDeprecated(info.schema)) pushObsoleteAttributes(lines, "    ");
        if (isSchemaExperimental(info.schema)) pushExperimentalAttribute(lines, "    ");
        if (isMillisecondsDurationProperty(propName, info.schema)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
        if (!isReq) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
        const propVisibility = pushCSharpInternalAttribute(lines, info.schema);
        lines.push(`    [JsonPropertyName("${propName}")]`);
        const reqMod = isReq && !csharpType.endsWith("?") ? "required " : "";
        lines.push(`    ${propVisibility} ${reqMod}${csharpType} ${csharpName} { get; set; }`);
    }

    lines.push(`}`);
    return lines.join("\n");
}

/**
 * Generate a polymorphic base class and derived classes for a discriminated union.
 */
function generatePolymorphicClasses(
    baseClassName: string,
    discriminatorProperty: string,
    variants: JSONSchema7[],
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[],
    description?: string,
    propertyResolver?: PropertyTypeResolver,
    experimental = false,
    options: DiscriminatedUnionGenerationOptions = {}
): string {
    const resolver = propertyResolver ?? resolveSessionPropertyType;
    const lines: string[] = [];
    const discriminatorInfo = findDiscriminator(variants)!;
    const renamedBase = applyTypeRename(baseClassName);
    const baseProperties = new Set(POLYMORPHIC_BASE_PROPERTIES[renamedBase] ?? []);

    lines.push(...xmlDocCommentWithFallback(description, `Polymorphic base type discriminated by <c>${escapeXml(discriminatorProperty)}</c>.`, ""));
    if (experimental) pushExperimentalAttribute(lines);
    lines.push(`[JsonPolymorphic(`);
    lines.push(`    TypeDiscriminatorPropertyName = "${discriminatorProperty}",`);
    lines.push(`    UnknownDerivedTypeHandling = JsonUnknownDerivedTypeHandling.FallBackToBaseType)]`);

    for (const { value } of discriminatorInfo.mapping.values()) {
        const constValue = String(value);
        const derivedClassName = applyTypeRename(`${baseClassName}${toPascalCase(constValue)}`);
        lines.push(`[JsonDerivedType(typeof(${derivedClassName}), "${escapeCSharpStringLiteral(constValue)}")]`);
    }

    lines.push(`public partial class ${renamedBase}`);
    lines.push(`{`);
    lines.push(`    /// <summary>The type discriminator.</summary>`);
    lines.push(`    [JsonPropertyName("${discriminatorProperty}")]`);
    lines.push(`    public virtual string ${toPascalCase(discriminatorProperty)} { get; set; } = string.Empty;`);
    for (const propName of baseProperties) {
        const propSchema = variants
            .map((variant) => variant.properties?.[propName])
            .find((property): property is JSONSchema7 => typeof property === "object");
        if (!propSchema) continue;

        const csharpName = toCSharpPropertyName(propName, propSchema);
        const csharpType = resolver(
            propSchema,
            renamedBase,
            csharpName,
            false,
            knownTypes,
            nestedClasses,
            enumOutput
        );
        lines.push("");
        lines.push(...xmlDocPropertyComment(propSchema.description, propName, "    "));
        lines.push(...emitDataAnnotations(propSchema, "    ", csharpType));
        if (isSchemaDeprecated(propSchema)) pushObsoleteAttributes(lines, "    ");
        if (isSchemaExperimental(propSchema)) pushExperimentalAttribute(lines, "    ");
        lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
        const propVisibility = pushCSharpInternalAttribute(lines, propSchema);
        lines.push(`    [JsonPropertyName("${propName}")]`);
        lines.push(`    ${propVisibility} virtual ${csharpType} ${csharpName} { get; set; }`);
    }
    lines.push(`}`);
    lines.push("");

    for (const { value, schema } of discriminatorInfo.mapping.values()) {
        const constValue = String(value);
        const derivedClassName = applyTypeRename(`${baseClassName}${toPascalCase(constValue)}`);
        const derivedCode = generateDerivedClass(
            derivedClassName,
            renamedBase,
            discriminatorProperty,
            constValue,
            schema,
            knownTypes,
            nestedClasses,
            enumOutput,
            resolver,
            experimental,
            options,
            baseProperties
        );
        nestedClasses.set(derivedClassName, derivedCode);
    }

    return lines.join("\n");
}

/**
 * Generate a derived class for a discriminated union variant.
 */
function generateDerivedClass(
    className: string,
    baseClassName: string,
    discriminatorProperty: string,
    discriminatorValue: string,
    schema: JSONSchema7,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[],
    propertyResolver: PropertyTypeResolver,
    experimental = false,
    options: DiscriminatedUnionGenerationOptions = {},
    baseProperties: ReadonlySet<string> = new Set()
): string {
    const lines: string[] = [];
    const required = new Set(schema.required || []);

    lines.push(...xmlDocCommentWithFallback(schema.description, `The <c>${escapeXml(discriminatorValue)}</c> variant of <see cref="${baseClassName}"/>.`, ""));
    if (experimental || isSchemaExperimental(schema)) pushExperimentalAttribute(lines);
    if (isSchemaDeprecated(schema)) pushObsoleteAttributes(lines);
    lines.push(`public ${options.sealLeafTypes ? "sealed " : ""}partial class ${className} : ${baseClassName}`);
    lines.push(`{`);
    lines.push(`    /// <inheritdoc />`);
    lines.push(`    [JsonIgnore]`);
    lines.push(`    public override string ${toPascalCase(discriminatorProperty)} => "${discriminatorValue}";`);
    lines.push("");

    if (schema.properties) {
        for (const [propName, propSchema] of Object.entries(schema.properties).sort(([a], [b]) => a.localeCompare(b))) {
            if (typeof propSchema !== "object") continue;
            if (propName === discriminatorProperty) continue;

            const isReq = required.has(propName);
            const prop = propSchema as JSONSchema7;
            const csharpName = toCSharpPropertyName(propName, prop);
            const csharpType = propertyResolver(prop, className, csharpName, isReq, knownTypes, nestedClasses, enumOutput);

            if (baseProperties.has(propName)) {
                lines.push(`    /// <inheritdoc />`);
                if (!isReq) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
                lines.push(`    [JsonPropertyName("${propName}")]`);
                lines.push(`    public override ${csharpType} ${csharpName}`);
                lines.push(`    {`);
                lines.push(`        get => base.${csharpName};`);
                lines.push(`        set => base.${csharpName} = value;`);
                lines.push(`    }`, "");
                continue;
            }

            lines.push(...xmlDocPropertyComment(prop.description, propName, "    "));
            lines.push(...emitDataAnnotations(prop, "    ", csharpType));
            if (isSchemaDeprecated(prop)) pushObsoleteAttributes(lines, "    ");
            if (isSchemaExperimental(prop)) pushExperimentalAttribute(lines, "    ");
            if (isMillisecondsDurationProperty(propName, prop)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
            if (!isReq) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
            const propVisibility = pushCSharpInternalAttribute(lines, prop);
            lines.push(`    [JsonPropertyName("${propName}")]`);
            const reqMod = isReq && !csharpType.endsWith("?") ? "required " : "";
            lines.push(`    ${propVisibility} ${reqMod}${csharpType} ${csharpName} { get; set; }`, "");
        }
    }

    if (lines[lines.length - 1] === "") lines.pop();
    lines.push(`}`);
    return lines.join("\n");
}

interface JsonUnionVariant {
    typeName: string;
    propertyName: string;
    schema?: JSONSchema7;
    matchExpression?: string;
}

function getUnionMembers(schema: JSONSchema7): JSONSchema7[] | undefined {
    return (schema.anyOf ?? schema.oneOf) as JSONSchema7[] | undefined;
}

function getNonNullUnionMembers(schema: JSONSchema7): JSONSchema7[] {
    return (getUnionMembers(schema) ?? []).filter((s) => typeof s === "object" && s !== null && (s as JSONSchema7).type !== "null");
}

function getVariantSchema(variant: JSONSchema7, definitions: DefinitionCollections): JSONSchema7 | undefined {
    if (variant.$ref) {
        const resolved = resolveRef(variant.$ref, definitions);
        return typeof resolved === "object" && resolved !== null ? resolved : undefined;
    }

    const resolved = resolveObjectSchema(variant, definitions) ?? resolveSchema(variant, definitions) ?? variant;
    return typeof resolved === "object" && resolved !== null ? resolved : undefined;
}

function getJsonUnionMatchExpression(variant: JsonUnionVariant, variants: JsonUnionVariant[]): string | undefined {
    const required = new Set(variant.schema?.required ?? []);
    if (required.size === 0) return undefined;

    const otherRequired = new Set<string>();
    for (const other of variants) {
        if (other === variant) continue;
        for (const property of other.schema?.required ?? []) {
            otherRequired.add(property);
        }
    }

    const present = [...required].filter((property) => !otherRequired.has(property));
    if (present.length === 0) return undefined;

    const absent = new Set<string>();
    for (const other of variants) {
        if (other === variant) continue;
        for (const property of other.schema?.required ?? []) {
            if (!required.has(property)) absent.add(property);
        }
    }

    return [
        "element.ValueKind == JsonValueKind.Object",
        ...present.map((property) => `element.TryGetProperty("${escapeCSharpStringLiteral(property)}", out _)`),
        ...[...absent].sort().map((property) => `!element.TryGetProperty("${escapeCSharpStringLiteral(property)}", out _)`),
    ].join(" && ");
}

function generateJsonUnionClass(className: string, variants: JsonUnionVariant[], description: string | undefined, jsonContextType: string, isInternal: boolean, experimental = false): string {
    const lines: string[] = [];
    lines.push(...xmlDocCommentWithFallback(description, `JSON union data type for <c>${escapeXml(className)}</c>.`, ""));
    if (experimental) pushExperimentalAttribute(lines);
    lines.push(`[JsonConverter(typeof(Converter))]`);
    lines.push(`${isInternal ? "internal" : "public"} sealed partial class ${className}`);
    lines.push(`{`);

    for (const variant of variants) {
        lines.push(`    /// <summary>Gets the value when this instance contains <see cref="${variant.typeName}"/>.</summary>`);
        lines.push(`    public ${variant.typeName}? ${variant.propertyName} { get; }`, "");
    }

    for (const variant of variants) {
        lines.push(`    /// <summary>Initializes a new instance of the <see cref="${className}"/> class from <see cref="${variant.typeName}"/>.</summary>`);
        lines.push(`    public ${className}(${variant.typeName} value)`);
        lines.push(`    {`);
        lines.push(`        ArgumentNullException.ThrowIfNull(value);`);
        lines.push(`        ${variant.propertyName} = value;`);
        lines.push(`    }`, "");
        lines.push(`    /// <summary>Converts <see cref="${variant.typeName}"/> to <see cref="${className}"/>.</summary>`);
        lines.push(`    public static implicit operator ${className}(${variant.typeName} value) => new(value);`, "");
    }

    lines.push(`    /// <summary>Provides a <see cref="JsonConverter{${className}}"/> for serializing <see cref="${className}"/> instances.</summary>`);
    lines.push(`    [EditorBrowsable(EditorBrowsableState.Never)]`);
    lines.push(`    public sealed class Converter : JsonConverter<${className}>`);
    lines.push(`    {`);
    lines.push(`        /// <inheritdoc />`);
    lines.push(`        public override ${className} Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)`);
    lines.push(`        {`);
    lines.push(`            if (reader.TokenType == JsonTokenType.Null)`);
    lines.push(`            {`);
    lines.push(`                throw new JsonException("Expected JSON object for ${escapeCSharpStringLiteral(className)}.");`);
    lines.push(`            }`);
    lines.push(``);
    lines.push(`            using var document = JsonDocument.ParseValue(ref reader);`);
    lines.push(`            var element = document.RootElement;`);

    const fallbackVariants: JsonUnionVariant[] = [];
    for (const variant of variants) {
        const matchExpression = variant.matchExpression ?? getJsonUnionMatchExpression(variant, variants);
        if (!matchExpression) {
            fallbackVariants.push(variant);
            continue;
        }

        const valueName = variant.propertyName.charAt(0).toLowerCase() + variant.propertyName.slice(1);
        const deserializeExpression = `JsonSerializer.Deserialize(element, ${jsonContextType}.Default.${variant.typeName})`;
        lines.push(`            if (${matchExpression})`);
        lines.push(`            {`);
        lines.push(`                var ${valueName} = ${deserializeExpression};`);
        lines.push(`                return ${valueName} is null ? throw new JsonException("Expected ${escapeCSharpStringLiteral(variant.typeName)} value.") : new ${className}(${valueName});`);
        lines.push(`            }`);
    }

    for (const variant of fallbackVariants) {
        const valueName = variant.propertyName.charAt(0).toLowerCase() + variant.propertyName.slice(1);
        const deserializeExpression = `JsonSerializer.Deserialize(element, ${jsonContextType}.Default.${variant.typeName})`;
        lines.push(``);
        lines.push(`            try`);
        lines.push(`            {`);
        lines.push(`                var ${valueName} = ${deserializeExpression};`);
        lines.push(`                if (${valueName} is not null) return new ${className}(${valueName});`);
        lines.push(`            }`);
        lines.push(`            catch (JsonException)`);
        lines.push(`            {`);
        lines.push(`            }`);
    }

    lines.push(``);
    lines.push(`            throw new JsonException("JSON value did not match any ${escapeCSharpStringLiteral(className)} variant.");`);
    lines.push(`        }`, "");
    lines.push(`        /// <inheritdoc />`);
    lines.push(`        public override void Write(Utf8JsonWriter writer, ${className} value, JsonSerializerOptions options)`);
    lines.push(`        {`);
    for (const variant of variants) {
        const valueName = variant.propertyName.charAt(0).toLowerCase() + variant.propertyName.slice(1);
        const serializeExpression = `JsonSerializer.Serialize(writer, ${valueName}, ${jsonContextType}.Default.${variant.typeName});`;
        lines.push(`            if (value.${variant.propertyName} is { } ${valueName})`);
        lines.push(`            {`);
        lines.push(`                ${serializeExpression}`);
        lines.push(`                return;`);
        lines.push(`            }`);
    }
    lines.push(``);
    lines.push(`            throw new JsonException("No ${escapeCSharpStringLiteral(className)} variant value is set.");`);
    lines.push(`        }`);
    lines.push(`    }`);
    lines.push(`}`);
    return lines.join("\n");
}

function toUnionVariantPropertyName(typeName: string, usedNames: Set<string>): string {
    const shortName = typeName.split(".").pop() ?? typeName;
    return uniqueCSharpIdentifier(shortName, usedNames, "Value");
}

function tryGenerateSessionJsonUnionType(
    schema: JSONSchema7,
    parentClassName: string,
    propName: string,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[]
): string | undefined {
    const members = getNonNullUnionMembers(schema);
    if (members.length <= 1) return undefined;

    const className = (schema.title as string) ?? `${parentClassName}${propName}`;
    if (nestedClasses.has(className)) return className;

    const usedNames = new Set<string>();
    const variants: JsonUnionVariant[] = [];
    for (const member of members) {
        const memberSchema = getVariantSchema(member, sessionDefinitions);
        const typeName = member.$ref
            ? typeToClassName(refTypeName(member.$ref, sessionDefinitions))
            : ((memberSchema?.title as string | undefined) ?? `${className}Variant${variants.length + 1}`);
        if (!memberSchema || !isObjectSchema(memberSchema)) return undefined;

        if (!nestedClasses.has(typeName)) {
            nestedClasses.set(typeName, generateNestedClass(typeName, memberSchema, knownTypes, nestedClasses, enumOutput));
        }
        variants.push({
            typeName,
            propertyName: toUnionVariantPropertyName(typeName, usedNames),
            schema: memberSchema,
        });
    }

    nestedClasses.set(className, generateJsonUnionClass(className, variants, schema.description, "SessionEventsJsonContext", isSchemaInternal(schema)));
    return className;
}

function generateNestedClass(
    className: string,
    schema: JSONSchema7,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[]
): string {
    const required = new Set(schema.required || []);
    const lines: string[] = [];
    lines.push(...xmlDocCommentWithFallback(schema.description, `Nested data type for <c>${className}</c>.`, ""));
    if (isSchemaExperimental(schema)) pushExperimentalAttribute(lines);
    if (isSchemaDeprecated(schema)) pushObsoleteAttributes(lines);
    lines.push(`${isSchemaInternal(schema) ? "internal" : "public"} sealed partial class ${className}`, `{`);

    for (const [propName, propSchema] of Object.entries(schema.properties || {}).sort(([a], [b]) => a.localeCompare(b))) {
        if (typeof propSchema !== "object") continue;
        const prop = propSchema as JSONSchema7;
        const isReq = required.has(propName);
        const csharpName = toCSharpPropertyName(propName, prop);
        const csharpType = resolveSessionPropertyType(prop, className, csharpName, isReq, knownTypes, nestedClasses, enumOutput);

        lines.push(...xmlDocPropertyComment(prop.description, propName, "    "));
        lines.push(...emitDataAnnotations(prop, "    ", csharpType));
        if (isSchemaDeprecated(prop)) pushObsoleteAttributes(lines, "    ");
        if (isSchemaExperimental(prop)) pushExperimentalAttribute(lines, "    ");
        if (isMillisecondsDurationProperty(propName, prop)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
        if (!isReq) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
        const propVisibility = pushCSharpInternalAttribute(lines, prop);
        lines.push(`    [JsonPropertyName("${propName}")]`);
        const reqMod = isReq && !csharpType.endsWith("?") ? "required " : "";
        lines.push(`    ${propVisibility} ${reqMod}${csharpType} ${csharpName} { get; set; }`, "");
    }
    if (lines[lines.length - 1] === "") lines.pop();
    lines.push(`}`);
    return lines.join("\n");
}

function resolveSessionPropertyType(
    propSchema: JSONSchema7,
    parentClassName: string,
    propName: string,
    isRequired: boolean,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[]
): string {
    if (isOpaqueJson(propSchema)) {
        return isRequired ? "JsonElement" : "JsonElement?";
    }
    // Handle $ref by resolving against schema definitions
    if (propSchema.$ref) {
        const className = typeToClassName(refTypeName(propSchema.$ref, sessionDefinitions));
        const refSchema = resolveRef(propSchema.$ref, sessionDefinitions);
        if (!refSchema) {
            return isRequired ? className : `${className}?`;
        }

        if (refSchema.enum && Array.isArray(refSchema.enum)) {
            const enumName = getOrCreateEnum(className, "", refSchema.enum as string[], enumOutput, refSchema.description, getEnumValueDescriptions(refSchema), undefined, isSchemaDeprecated(refSchema), isSchemaExperimental(refSchema));
            return isRequired ? enumName : `${enumName}?`;
        }

        if (refSchema.type === "object" && refSchema.properties) {
            if (!nestedClasses.has(className)) {
                nestedClasses.set(className, generateNestedClass(className, refSchema, knownTypes, nestedClasses, enumOutput));
            }
            return isRequired ? className : `${className}?`;
        }

        return resolveSessionPropertyType(refSchema, parentClassName, propName, isRequired, knownTypes, nestedClasses, enumOutput);
    }
    if (propSchema.anyOf) {
        const simpleNullable = getNullableInner(propSchema);
        if (simpleNullable) {
            return resolveSessionPropertyType(simpleNullable, parentClassName, propName, false, knownTypes, nestedClasses, enumOutput);
        }
        // Discriminated union: anyOf with multiple object variants sharing a const discriminator
        const nonNull = propSchema.anyOf.filter((s) => typeof s === "object" && s !== null && (s as JSONSchema7).type !== "null");
        if (nonNull.length > 1) {
            // Resolve $ref variants to their actual schemas
            const variants = (nonNull as JSONSchema7[]).map((v) => {
                if (v.$ref) {
                    const resolved = resolveRef(v.$ref, sessionDefinitions);
                    return resolved ?? v;
                }
                return v;
            });
            const discriminatorInfo = findDiscriminator(variants);
            if (discriminatorInfo) {
                const hasNull = propSchema.anyOf.length > nonNull.length;
                const baseClassName = (propSchema.title as string) ?? `${parentClassName}${propName}`;
                const renamedBase = applyTypeRename(baseClassName);
                const polymorphicCode = generateDiscriminatedUnionClass(baseClassName, discriminatorInfo, variants, knownTypes, nestedClasses, enumOutput, propSchema.description, undefined, isSchemaExperimental(propSchema), { sealLeafTypes: true });
                nestedClasses.set(renamedBase, polymorphicCode);
                return isRequired && !hasNull ? renamedBase : `${renamedBase}?`;
            }
        }
        const unionType = tryGenerateSessionJsonUnionType(propSchema, parentClassName, propName, knownTypes, nestedClasses, enumOutput);
        if (unionType) return isRequired ? unionType : `${unionType}?`;
        failUnmappable(`anyOf without discriminator (${parentClassName}.${propName})`, propSchema);
    }
    if (propSchema.oneOf) {
        const unionType = tryGenerateSessionJsonUnionType(propSchema, parentClassName, propName, knownTypes, nestedClasses, enumOutput);
        if (unionType) return isRequired ? unionType : `${unionType}?`;
        failUnmappable(`oneOf without discriminator (${parentClassName}.${propName})`, propSchema);
    }
    if (propSchema.enum && Array.isArray(propSchema.enum)) {
        const enumName = getOrCreateEnum(parentClassName, propName, propSchema.enum as string[], enumOutput, propSchema.description, getEnumValueDescriptions(propSchema), propSchema.title as string | undefined, isSchemaDeprecated(propSchema), isSchemaExperimental(propSchema));
        return isRequired ? enumName : `${enumName}?`;
    }
    if (propSchema.type === "object" && propSchema.properties) {
        const nestedClassName = (propSchema.title as string) ?? `${parentClassName}${propName}`;
        nestedClasses.set(nestedClassName, generateNestedClass(nestedClassName, propSchema, knownTypes, nestedClasses, enumOutput));
        return isRequired ? nestedClassName : `${nestedClassName}?`;
    }
    if (propSchema.type === "array" && propSchema.items) {
        const items = propSchema.items as JSONSchema7;
        const itemType = resolveSessionPropertyType(
            items,
            parentClassName,
            `${propName}Item`,
            true,
            knownTypes,
            nestedClasses,
            enumOutput
        );
        return isRequired ? `${itemType}[]` : `${itemType}[]?`;
    }
    if (propSchema.type === "object" && propSchema.additionalProperties && typeof propSchema.additionalProperties === "object") {
        const valueSchema = propSchema.additionalProperties as JSONSchema7;
        const valueType = resolveSessionPropertyType(
            valueSchema,
            parentClassName,
            `${propName}Value`,
            true,
            knownTypes,
            nestedClasses,
            enumOutput
        );
        return isRequired ? `IDictionary<string, ${valueType}>` : `IDictionary<string, ${valueType}>?`;
    }
    return schemaTypeToCSharp(propSchema, isRequired, knownTypes, propName);
}

function generateDataClass(variant: EventVariant, knownTypes: Map<string, string>, nestedClasses: Map<string, string>, enumOutput: string[]): string {
    const unionMembers = variant.dataSchema.anyOf ?? variant.dataSchema.oneOf;
    if (unionMembers) {
        const members = unionMembers
            .filter((member): member is JSONSchema7 => typeof member === "object")
            .map((member) => resolveObjectSchema(member, sessionDefinitions) ?? member)
            .filter((member) => member.type !== "null");
        const discriminator = findDiscriminator(members);
        if (!discriminator) {
            failUnmappable(`event payload union (${variant.dataClassName})`, variant.dataSchema);
        }
        return generateDiscriminatedUnionClass(
            variant.dataClassName, discriminator, members, knownTypes, nestedClasses, enumOutput,
            variant.dataDescription, undefined, variant.dataExperimental, { sealLeafTypes: true }
        );
    }
    const dataVisibility = isSchemaInternal(variant.dataSchema) ? "internal" : "public";
    const lines: string[] = [];
    if (variant.dataDescription) {
        lines.push(...xmlDocComment(variant.dataDescription, ""));
    } else {
        lines.push(...rawXmlDocSummary(`Event payload for <see cref="${variant.className}"/>.`, ""));
    }
    if (variant.dataExperimental || isSchemaExperimental(variant.dataSchema)) {
        pushExperimentalAttribute(lines);
    }
    if (isSchemaDeprecated(variant.dataSchema)) {
        pushObsoleteAttributes(lines);
    }
    if (!variant.dataSchema?.properties) {
        lines.push(`${dataVisibility} sealed partial class ${variant.dataClassName} { }`);
        return lines.join("\n");
    }

    const required = new Set(variant.dataSchema.required || []);
    lines.push(`${dataVisibility} sealed partial class ${variant.dataClassName}`, `{`);

    for (const [propName, propSchema] of Object.entries(variant.dataSchema.properties).sort(([a], [b]) => a.localeCompare(b))) {
        if (typeof propSchema !== "object") continue;
        const isReq = required.has(propName);
        const prop = propSchema as JSONSchema7;
        const csharpName = toCSharpPropertyName(propName, prop);
        const csharpType = resolveSessionPropertyType(prop, variant.dataClassName, csharpName, isReq, knownTypes, nestedClasses, enumOutput);

        lines.push(...xmlDocPropertyComment(prop.description, propName, "    "));
        lines.push(...emitDataAnnotations(prop, "    ", csharpType));
        if (isSchemaDeprecated(prop)) pushObsoleteAttributes(lines, "    ");
        if (isSchemaExperimental(prop)) pushExperimentalAttribute(lines, "    ");
        if (isMillisecondsDurationProperty(propName, prop)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
        if (!isReq) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
        const propVisibility = pushCSharpInternalAttribute(lines, prop);
        lines.push(`    [JsonPropertyName("${propName}")]`);
        const reqMod = isReq && !csharpType.endsWith("?") ? "required " : "";
        lines.push(`    ${propVisibility} ${reqMod}${csharpType} ${csharpName} { get; set; }`, "");
    }
    if (lines[lines.length - 1] === "") lines.pop();
    lines.push(`}`);
    return lines.join("\n");
}

function emitSessionEventEnvelopeProperty(
    property: SessionEventEnvelopeProperty,
    knownTypes: Map<string, string>,
    nestedClasses: Map<string, string>,
    enumOutput: string[]
): string[] {
    const csharpName = toCSharpPropertyName(property.name, property.schema);
    const csharpType = resolveSessionPropertyType(
        property.schema,
        "SessionEvent",
        csharpName,
        property.required,
        knownTypes,
        nestedClasses,
        enumOutput
    );
    const lines: string[] = [];

    lines.push(...xmlDocPropertyComment(property.schema.description, property.name, "    "));
    lines.push(...emitDataAnnotations(property.schema, "    ", csharpType));
    if (isSchemaDeprecated(property.schema)) pushObsoleteAttributes(lines, "    ");
    if (isSchemaExperimental(property.schema)) pushExperimentalAttribute(lines, "    ");
    if (isMillisecondsDurationProperty(property.name, property.schema)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
    if (!property.required) lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]`);
    const propVisibility = pushCSharpInternalAttribute(lines, property.schema);
    lines.push(`    [JsonPropertyName("${property.name}")]`);
    lines.push(`    ${propVisibility} ${csharpType} ${csharpName} { get; set; }`, "");

    return lines;
}

export function generateSessionEventsCode(schema: JSONSchema7): string {
    generatedEnums.clear();
    sessionDefinitions = collectDefinitionCollections(schema as Record<string, unknown>);
    const variants = extractEventVariants(schema).filter((variant) => !isSchemaInternal(variant.dataSchema));
    const knownTypes = new Map<string, string>();
    const nestedClasses = new Map<string, string>();
    const enumOutput: string[] = [];
    const envelopeProperties = getSharedSessionEventEnvelopeProperties(schema, sessionDefinitions);

    const lines: string[] = [];
    lines.push(`${COPYRIGHT}

// AUTO-GENERATED FILE - DO NOT EDIT
// Generated from: session-events.schema.json

#pragma warning disable CS0612 // Type or member is obsolete
#pragma warning disable CS0618 // Type or member is obsolete (with message)

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.Json.Serialization.Metadata;

namespace GitHub.Copilot;
`);

    // Base class with XML doc
    lines.push(`/// <summary>`);
    lines.push(`/// Provides the base class from which all session events derive.`);
    lines.push(`/// </summary>`);
    lines.push(`[DebuggerDisplay("{DebuggerDisplay,nq}")]`);
    lines.push(`[JsonPolymorphic(`, `    TypeDiscriminatorPropertyName = "type",`, `    IgnoreUnrecognizedTypeDiscriminators = true)]`);
    for (const variant of [...variants].sort((a, b) => a.typeName.localeCompare(b.typeName))) {
        lines.push(`[JsonDerivedType(typeof(${variant.className}), "${variant.typeName}")]`);
    }
    lines.push(`public partial class SessionEvent`, `{`);
    for (const property of envelopeProperties) {
        lines.push(...emitSessionEventEnvelopeProperty(property, knownTypes, nestedClasses, enumOutput));
    }
    lines.push(`    /// <summary>`, `    /// The event type discriminator.`, `    /// </summary>`);
    lines.push(`    [JsonIgnore]`, `    public virtual string Type => "unknown";`, "");
    lines.push(`    /// <summary>Deserializes a JSON string into a <see cref="SessionEvent"/>.</summary>`);
    lines.push(`    public static SessionEvent FromJson(string json) =>`, `        SessionEventJsonConverter.Deserialize(json);`, "");
    lines.push(`    /// <summary>Serializes this event to a JSON string.</summary>`);
    lines.push(`    public string ToJson() =>`, `        JsonSerializer.Serialize(this, SessionEventsJsonContext.Default.SessionEvent);`, "");
    lines.push(`    [DebuggerBrowsable(DebuggerBrowsableState.Never)]`, `    private string DebuggerDisplay => ToJson();`);
    lines.push(`}`, "");

    lines.push(`internal sealed partial class SessionEventJsonConverter : JsonConverter<SessionEvent>`, `{`);
    lines.push(`    internal static SessionEventJsonConverter Default { get; } = new();`, "");
    lines.push(`    public override SessionEvent? Read(`, `        ref Utf8JsonReader reader,`, `        Type typeToConvert,`, `        JsonSerializerOptions options)`, `    {`);
    lines.push(`        // Preserve the reader's position for deserialization.`);
    lines.push(`        var probe = reader;`);
    lines.push(`        JsonTypeInfo typeInfo = ReadEventTypeInfo(ref probe);`);
    lines.push(`        return ToSessionEvent(JsonSerializer.Deserialize(ref reader, typeInfo));`, `    }`, "");
    lines.push(`    private static JsonTypeInfo? GetEventTypeInfo(ReadOnlySpan<byte> type)`, `    {`);
    lines.push(`        switch (type.Length)`, `        {`);
    const variantsByByteLength = new Map<number, typeof variants>();
    for (const variant of [...variants].sort((a, b) => a.typeName.localeCompare(b.typeName))) {
        const byteLength = Buffer.byteLength(variant.typeName, "utf8");
        const group = variantsByByteLength.get(byteLength) ?? [];
        group.push(variant);
        variantsByByteLength.set(byteLength, group);
    }
    for (const [byteLength, group] of [...variantsByByteLength].sort(([a], [b]) => a - b)) {
        lines.push(`            case ${byteLength}:`);
        for (const variant of group) {
            lines.push(`                if (type.SequenceEqual("${escapeCSharpStringLiteral(variant.typeName)}"u8))`);
            lines.push(`                    return SessionEventsJsonContext.Default.${variant.className};`);
        }
        lines.push(`                break;`);
    }
    lines.push(`        }`, `        return null;`, `    }`, "");
    lines.push(`    public override void Write(`, `        Utf8JsonWriter writer,`, `        SessionEvent value,`, `        JsonSerializerOptions options) =>`, `        JsonSerializer.Serialize(writer, value, SessionEventsJsonContext.Default.SessionEvent);`, "");
    lines.push(`    private static SessionEvent ToSessionEvent(object? value) =>`);
    lines.push(`        value as SessionEvent ?? ((SessionEventEnvelope?)value)?.ToSessionEvent()!;`, "");
    lines.push(`    private static JsonTypeInfo ReadEventTypeInfo(ref Utf8JsonReader reader)`, `    {`);
    lines.push(`        if (reader.TokenType == JsonTokenType.Null)`, `        {`, `            return SessionEventsJsonContext.Default.SessionEventEnvelope;`, `        }`, "");
    lines.push(`        if (reader.TokenType != JsonTokenType.StartObject)`, `        {`);
    lines.push(`            throw new JsonException("Expected a session event object.");`, `        }`, "");
    lines.push(`        JsonTypeInfo? typeInfo = null;`);
    lines.push(`        bool foundDiscriminator = false;`);
    lines.push(`        while (reader.Read() && reader.TokenType == JsonTokenType.PropertyName)`, `        {`);
    lines.push(`            bool isDiscriminator = reader.ValueIsEscaped`);
    lines.push(`                ? ReadString(ref reader) == "type"`);
    lines.push(`                : reader.ValueTextEquals("type"u8);`);
    lines.push(`            if (isDiscriminator)`, `            {`);
    lines.push(`                if (foundDiscriminator)`, `                {`);
    lines.push(`                    throw new JsonException("Duplicate session event type discriminator.");`, `                }`);
    lines.push(`                foundDiscriminator = true;`);
    lines.push(`                reader.Read();`);
    lines.push(`                if (reader.TokenType == JsonTokenType.String)`, `                {`);
    lines.push(`                    if (reader.HasValueSequence || reader.ValueIsEscaped)`, `                    {`);
    lines.push(`                        typeInfo = GetEventTypeInfo(StrictUtf8.GetBytes(ReadString(ref reader)));`, `                    }`);
    lines.push(`                    else`, `                    {`);
    lines.push(`                        typeInfo = GetEventTypeInfo(reader.ValueSpan);`);
    lines.push(`                        if (typeInfo is null)`, `                        {`);
    lines.push(`                            // Validate unknown discriminator text too, including invalid UTF-8.`);
    lines.push(`                            _ = ReadString(ref reader);`, `                        }`, `                    }`, `                }`);
    lines.push(`                else if (reader.TokenType != JsonTokenType.Number || !reader.TryGetInt32(out _))`, `                {`);
    lines.push(`                    throw new JsonException("Expected a string or integer session event type discriminator.");`, `                }`, `            }`);
    lines.push(`            else`, `            {`);
    lines.push(`                bool isMetadata = reader.HasValueSequence || reader.ValueIsEscaped`);
    lines.push(`                    ? ReadString(ref reader) is { Length: > 0 } propertyName && propertyName[0] == '$'`);
    lines.push(`                    : !reader.ValueSpan.IsEmpty && reader.ValueSpan[0] == (byte)'$';`);
    lines.push(`                if (isMetadata)`, `                {`);
    lines.push(`                    throw new JsonException("Unexpected session event metadata property.");`, `                }`);
    lines.push(`                reader.Read();`);
    lines.push(`                reader.Skip();`, `            }`, `        }`, "");
    lines.push(`        return typeInfo ?? SessionEventsJsonContext.Default.SessionEventEnvelope;`, `    }`);
    lines.push(`}`, "");

    lines.push(`internal sealed class SessionEventJsonTypeInfoResolver : IJsonTypeInfoResolver`, `{`);
    lines.push(`    internal static SessionEventJsonTypeInfoResolver Default { get; } = new();`, "");
    lines.push(`    public JsonTypeInfo? GetTypeInfo(Type type, JsonSerializerOptions options)`, `    {`);
    lines.push(`        if (type != typeof(SessionEvent))`, `        {`, `            return null;`, `        }`, "");
    lines.push(`        JsonTypeInfo typeInfo = JsonMetadataServices.CreateValueInfo<SessionEvent>(`, `            options,`, `            SessionEventJsonConverter.Default);`);
    lines.push(`        typeInfo.PolymorphismOptions = null;`);
    lines.push(`        return typeInfo;`, `    }`);
    lines.push(`}`, "");

    lines.push(`internal sealed class SessionEventEnvelope`, `{`);
    for (const property of envelopeProperties) {
        lines.push(...emitSessionEventEnvelopeProperty(property, knownTypes, nestedClasses, enumOutput));
    }
    lines.push(`    internal SessionEvent ToSessionEvent() => new()`, `    {`);
    for (const property of envelopeProperties) {
        const csharpName = toCSharpPropertyName(property.name, property.schema);
        lines.push(`        ${csharpName} = ${csharpName},`);
    }
    lines.push(`    };`, `}`, "");

    // Event classes with XML docs
    for (const variant of variants) {
        const remarksLine = `/// <remarks>Represents the <c>${escapeXml(variant.typeName)}</c> event.</remarks>`;
        if (variant.dataDescription) {
            lines.push(...xmlDocComment(variant.dataDescription, ""));
            lines.push(remarksLine);
        } else {
            lines.push(`/// <summary>Represents the <c>${escapeXml(variant.typeName)}</c> event.</summary>`);
        }
        if (variant.eventExperimental) {
            pushExperimentalAttribute(lines);
        }
        if (variant.eventDeprecated) {
            pushObsoleteAttributes(lines);
        }
        lines.push(`public sealed partial class ${variant.className} : SessionEvent`, `{`);
        lines.push(`    /// <inheritdoc />`);
        lines.push(`    [JsonIgnore]`, `    public override string Type => "${variant.typeName}";`, "");
        lines.push(`    /// <summary>The <c>${escapeXml(variant.typeName)}</c> event payload.</summary>`);
        lines.push(
            `    [JsonPropertyName("data")]`,
            `    public required ${variant.dataClassName} Data { get; set; }`,
            `}`,
            ""
        );
    }

    // Data classes
    for (const variant of variants) {
        lines.push(generateDataClass(variant, knownTypes, nestedClasses, enumOutput), "");
    }

    // Nested classes. A name already declared by a hand-written source is skipped:
    // that declaration is the one the namespace keeps, and the generated property
    // simply binds to it.
    for (const [name, code] of nestedClasses) {
        if (handWrittenCSharpTypeNames.has(name)) continue;
        lines.push(code, "");
    }

    // Enums
    for (const code of enumOutput) lines.push(code);

    // JsonSerializerContext
    const types = ["SessionEvent", "SessionEventEnvelope", ...variants.flatMap((v) => [v.className, v.dataClassName]), ...nestedClasses.keys()].sort();
    lines.push(`[JsonSourceGenerationOptions(`, `    JsonSerializerDefaults.Web,`, `    AllowOutOfOrderMetadataProperties = true,`, `    NumberHandling = JsonNumberHandling.AllowReadingFromString,`, `    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull)]`);
    for (const t of types) lines.push(`[JsonSerializable(typeof(${t}))]`);
    lines.push(`[JsonSerializable(typeof(JsonElement))]`);
    lines.push(`internal sealed partial class SessionEventsJsonContext : JsonSerializerContext;`);

    return lines.join("\n");
}

export async function generateSessionEvents(schemaPath?: string): Promise<void> {
    console.log("C#: generating session-events...");
    const resolvedPath = schemaPath ?? (await getSessionEventsSchemaPath());
    const schema = cloneSchemaForCodegen((await loadSchemaJson(resolvedPath)) as JSONSchema7);
    const processed = propagateInternalVisibility(postProcessSchema(schema));
    handWrittenCSharpTypeNames = await collectHandWrittenCSharpTypeNames();
    const code = generateSessionEventsCode(processed);
    const outPath = await writeGeneratedFile("dotnet/src/Generated/SessionEvents.cs", code);
    console.log(`  ✓ ${outPath}`);
    await formatCSharpFile(outPath);
}

// ══════════════════════════════════════════════════════════════════════════════
// RPC TYPES
// ══════════════════════════════════════════════════════════════════════════════

let emittedRpcClassSchemas = new Map<string, string>();
const nonSessionRequestTypeNames = new Set<string>();
let emittedRpcEnumResultTypes = new Set<string>();
let experimentalRpcTypes = new Set<string>();
let nonExperimentalRpcTypes = new Set<string>();
let rpcKnownTypes = new Map<string, string>();
let rpcEnumOutput: string[] = [];
let externalRpcValueTypes = new Set<string>();
let rpcRootJsonSerializableTypes = new Set<string>();

/** Schema definitions available during RPC generation (for $ref resolution). */
let rpcDefinitions: DefinitionCollections = { definitions: {}, $defs: {} };

function singularPascal(s: string): string {
    const p = toPascalCase(s);
    if (p.endsWith("ies")) return `${p.slice(0, -3)}y`;
    if (/(xes|zes|ches|shes|sses)$/i.test(p)) return p.slice(0, -2);
    if (p.endsWith("s") && !/(ss|us|is)$/i.test(p)) return p.slice(0, -1);
    return p;
}

function getMethodResultSchema(method: RpcMethod): JSONSchema7 | undefined {
    return resolveSchema(method.result, rpcDefinitions) ?? method.result ?? undefined;
}

function resultTypeName(method: RpcMethod): string {
    return getCSharpSchemaTypeName(getMethodResultSchema(method), `${typeToClassName(method.rpcMethod)}Result`);
}

function getCSharpSchemaTypeName(schema: JSONSchema7 | null | undefined, fallback: string): string {
    if (schema?.$ref) return typeToClassName(refTypeName(schema.$ref, rpcDefinitions));
    return getRpcSchemaTypeName(schema, fallback);
}

/** Returns the C# type for a method's result, accounting for nullable anyOf wrappers and opaque JSON. */
function resolvedResultTypeName(method: RpcMethod): string {
    const schema = getMethodResultSchema(method);
    if (!schema) return resultTypeName(method);
    if (isOpaqueJson(schema)) return "object";
    const inner = getNullableInner(schema);
    if (inner) {
        if (isOpaqueJson(inner)) return "object?";
        // Nullable wrapper: resolve the inner $ref type name with "?" suffix
        const innerName = inner.$ref
            ? typeToClassName(refTypeName(inner.$ref, rpcDefinitions))
            : getRpcSchemaTypeName(inner, resultTypeName(method));
        return `${innerName}?`;
    }
    return resultTypeName(method);
}

/** Returns the ValueTask<T> or ValueTask string for an incoming-handler's result type. */
function handlerTaskType(method: RpcMethod): string {
    const schema = getMethodResultSchema(method);
    return !isVoidSchema(schema) ? `ValueTask<${resolvedResultTypeName(method)}>` : "ValueTask";
}

/** Returns the Task<T> or Task string for an outgoing-call wrapper's result type. */
function resultTaskType(method: RpcMethod): string {
    const schema = getMethodResultSchema(method);
    return !isVoidSchema(schema) ? `Task<${resolvedResultTypeName(method)}>` : "Task";
}

function paramsTypeName(method: RpcMethod): string {
    return getCSharpSchemaTypeName(resolveMethodParamsSchema(method), `${typeToClassName(method.rpcMethod)}Request`);
}

function resolveMethodParamsSchema(method: RpcMethod): JSONSchema7 | undefined {
    return (
        resolveObjectSchema(method.params, rpcDefinitions) ??
        resolveSchema(method.params, rpcDefinitions) ??
        method.params ??
        undefined
    );
}

type RpcParameterEntry = [string, JSONSchema7 | boolean];

function legacyParameterEntries(
    method: RpcMethod,
    params: JSONSchema7 | undefined,
    entries: RpcParameterEntry[],
    session = false,
): RpcParameterEntry[] | undefined {
    const resolved = method.params ? resolveSchema(method.params, rpcDefinitions) : undefined;
    const legacy = readLegacyParameters(params, method.rpcMethod, {
        implicit: session ? ["sessionId"] : [],
        optional: isOmittableRequest(method.params),
        nullable: !!((method.params && getNullableInner(method.params)) || (resolved && getNullableInner(resolved))),
    });
    if (!legacy) return undefined;
    const properties = new Map(entries);
    let optionalSeen = false;
    return legacy.legacy.map((name) => {
        const property = properties.get(name);
        if (!property || typeof property !== "object") {
            throw new Error(`Invalid x-legacy-parameters for ${method.rpcMethod}: non-object property ${name}`);
        }
        // C# positional parameters with defaults must follow the required ones.
        if (legacy.required.has(name)) {
            if (optionalSeen) {
                throw new Error(`Invalid x-legacy-parameters for ${method.rpcMethod}: required parameters must precede optional parameters`);
            }
        } else {
            optionalSeen = true;
        }
        return [name, property];
    });
}

function emitRequestObjectMethod(
    name: string,
    method: RpcMethod,
    requestClassName: string,
    wireRequestClassName: string,
    assignments: string[] | undefined,
    resultClassName: string,
    lines: string[],
    indent: string,
    groupExperimental: boolean,
    groupDeprecated: boolean,
    requiredMembers: string[],
): void {
    const resultSchema = getMethodResultSchema(method);
    const taskType = isVoidSchema(resultSchema) ? "Task" : `Task<${resultClassName}>`;
    const visibility = method.visibility === "internal" ? "internal" : "public";
    const session = assignments !== undefined;
    lines.push("");
    pushRpcMethodXmlDocs(lines, method, indent, [
        { name: "request", description: rpcParamsDescription(method, resolveMethodParamsSchema(method)) },
        { name: "cancellationToken", description: CANCELLATION_TOKEN_DESCRIPTION, escapeDescription: false },
    ], resultSchema);
    if (method.stability === "experimental" && !groupExperimental) pushExperimentalAttribute(lines, indent);
    if (method.deprecated && !groupDeprecated) pushObsoleteAttributes(lines, indent);
    lines.push(`${indent}${visibility} async ${taskType} ${name}Async(${requestClassName} request, CancellationToken cancellationToken = default)`);
    lines.push(`${indent}{`, `${indent}    ArgumentNullException.ThrowIfNull(request);`);
    for (const member of requiredMembers) {
        lines.push(`${indent}    ArgumentNullException.ThrowIfNull(request.${member});`);
    }
    if (session) {
        lines.push(`${indent}    _session.ThrowIfDisposed();`);
        lines.push(`${indent}    var wireRequest = new ${wireRequestClassName} { ${assignments.join(", ")} };`);
    }
    const invocation = `CopilotClient.InvokeRpcAsync${isVoidSchema(resultSchema) ? "" : `<${resultClassName}>`}`;
    lines.push(`${indent}    ${isVoidSchema(resultSchema) ? "" : "return "}await ${invocation}(${session ? "_session.Rpc" : "_rpc"}, "${method.rpcMethod}", [${session ? "wireRequest" : "request"}], cancellationToken);`);
    lines.push(`${indent}}`);
}

function stableStringify(value: unknown): string {
    if (Array.isArray(value)) {
        return `[${value.map((item) => stableStringify(item)).join(",")}]`;
    }
    if (value && typeof value === "object") {
        const entries = Object.entries(value as Record<string, unknown>).sort(([a], [b]) => a.localeCompare(b));
        return `{${entries.map(([key, entryValue]) => `${JSON.stringify(key)}:${stableStringify(entryValue)}`).join(",")}}`;
    }
    return JSON.stringify(value);
}

// Match literal values before deserialization: an optional discriminator must not swallow another variant.
function getRpcUnionMatchExpression(schema: JSONSchema7, seenRefs: ReadonlySet<string> = new Set()): string | undefined {
    if (schema.$ref) {
        if (seenRefs.has(schema.$ref)) return undefined;
        seenRefs = new Set([...seenRefs, schema.$ref]);
    }
    const resolved = resolveSchema(schema, rpcDefinitions) ?? schema;
    const members = getUnionMembers(resolved);
    if (members) {
        const expressions = members.map((member) => getRpcUnionMatchExpression(member, seenRefs));
        return expressions.every((expression) => expression !== undefined)
            ? `(${expressions.join(" || ")})`
            : undefined;
    }

    const expressions: string[] = [];
    for (const [name, property] of Object.entries(resolved.properties ?? {})) {
        if (typeof property !== "object") continue;
        const propSchema = resolveSchema(property, rpcDefinitions) ?? property;
        const values = propSchema.const !== undefined ? [propSchema.const] : propSchema.enum;
        if (!values?.length || !values.every((value) => typeof value === "string")) continue;
        const propertyName = escapeCSharpStringLiteral(name);
        const present = `element.TryGetProperty("${propertyName}", out _)`;
        const value = `element.GetProperty("${propertyName}")`;
        const matches = values.map((entry) => `${value}.GetString() == "${escapeCSharpStringLiteral(entry as string)}"`);
        const match = `${present} && ${value}.ValueKind == JsonValueKind.String && (${matches.join(" || ")})`;
        expressions.push(resolved.required?.includes(name) ? `(${match})` : `(!${present} || (${match}))`);
    }
    return expressions.length > 0
        ? `element.ValueKind == JsonValueKind.Object && ${expressions.join(" && ")}`
        : undefined;
}

function resolveRpcType(schema: JSONSchema7, isRequired: boolean, parentClassName: string, propName: string, classes: string[]): string {
    if (isOpaqueJson(schema)) {
        return isRequired ? "JsonElement" : "JsonElement?";
    }
    if (schema.type === "object" && schema.additionalProperties === true &&
        (!schema.properties || Object.keys(schema.properties).length === 0)) {
        return isRequired ? "IDictionary<string, JsonElement>" : "IDictionary<string, JsonElement>?";
    }
    // Handle $ref by resolving against schema definitions and generating the referenced class
    if (schema.$ref) {
        const typeName = typeToClassName(refTypeName(schema.$ref, rpcDefinitions));
        const refSchema = resolveRef(schema.$ref, rpcDefinitions);
        if (!refSchema) {
            return isRequired ? typeName : `${typeName}?`;
        }

        if (refSchema.enum && Array.isArray(refSchema.enum)) {
            const enumName = getOrCreateEnum(typeName, "", refSchema.enum as string[], rpcEnumOutput, refSchema.description, getEnumValueDescriptions(refSchema), undefined, isSchemaDeprecated(refSchema), isSchemaExperimental(refSchema) || experimentalRpcTypes.has(typeName));
            return isRequired ? enumName : `${enumName}?`;
        }

        if (refSchema.type === "object" && refSchema.properties) {
            const cls = emitRpcClass(typeName, refSchema, "public", classes);
            if (cls) classes.push(cls);
            return isRequired ? typeName : `${typeName}?`;
        }

        return resolveRpcType({ ...refSchema, title: refSchema.title ?? typeName }, isRequired, parentClassName, propName, classes);
    }
    const unionVariants = schema.anyOf ?? schema.oneOf;
    // Keep the same polymorphic API even when a discriminated union has only one variant.
    if (unionVariants) {
        const nonNull = getNonNullUnionMembers(schema);
        if (nonNull.length > 0) {
            const variants = (nonNull as JSONSchema7[]).map((v) => {
                if (v.$ref) {
                    const resolved = resolveRef(v.$ref, rpcDefinitions);
                    return resolved ?? v;
                }
                return v;
            });
            const discriminatorInfo = findDiscriminator(variants);
            if (discriminatorInfo) {
                const hasNull = unionVariants.length > nonNull.length;
                const baseClassName = (schema.title as string) ?? `${parentClassName}${propName}`;
                if (!emittedRpcClassSchemas.has(baseClassName)) {
                    emittedRpcClassSchemas.set(baseClassName, "polymorphic");
                    const nestedMap = new Map<string, string>();
                    const rpcPropertyResolver: PropertyTypeResolver = (propSchema, parentClass, pName, isReq, _kt, nestedCls, enumOut) => {
                        const nestedRpcClasses: string[] = [];
                        const result = resolveRpcType(propSchema, isReq, parentClass, pName, nestedRpcClasses);
                        for (const cls of nestedRpcClasses) {
                            nestedCls.set(cls.match(/class (\w+)/)?.[1] ?? cls.slice(0, 40), cls);
                        }
                        return result;
                    };
                    const polymorphicCode = generateDiscriminatedUnionClass(baseClassName, discriminatorInfo, variants, rpcKnownTypes, nestedMap, rpcEnumOutput, schema.description, rpcPropertyResolver, isSchemaExperimental(schema) || experimentalRpcTypes.has(baseClassName));
                    classes.push(polymorphicCode);
                    for (const nested of nestedMap.values()) classes.push(nested);
                }
                return isRequired && !hasNull ? baseClassName : `${baseClassName}?`;
            }
        }
    }
    // Preserve nullable references without introducing another wrapper around their declared type.
    const nullableInner = getNullableInner(schema);
    if (nullableInner) {
        return resolveRpcType(nullableInner, false, parentClassName, propName, classes);
    }
    if (unionVariants && getNonNullUnionMembers(schema).length > 0) {
        const members = getNonNullUnionMembers(schema);
        const matchExpressions = members.map((member) => getRpcUnionMatchExpression(member));
        if (matchExpressions.every((expression) => expression !== undefined)) {
            const className = schema.title ?? `${parentClassName}${propName}`;
            if (!emittedRpcClassSchemas.has(className)) {
                emittedRpcClassSchemas.set(className, "union");
                const usedNames = new Set<string>();
                const variants = members.map((member, index) => {
                    const typeName = resolveRpcType(member, true, className, `Variant${index + 1}`, classes);
                    return {
                        typeName,
                        propertyName: toUnionVariantPropertyName(typeName, usedNames),
                        matchExpression: matchExpressions[index],
                    };
                });
                classes.push(generateJsonUnionClass(className, variants, schema.description, "RpcJsonContext", isSchemaInternal(schema), isSchemaExperimental(schema) || experimentalRpcTypes.has(className)));
            }
            return isRequired && members.length === unionVariants.length ? className : `${className}?`;
        }
    }
    // Handle enums (string unions like "interactive" | "plan" | "autopilot")
    if (schema.enum && Array.isArray(schema.enum)) {
        const explicitName = schema.title as string | undefined;
        const generatedEnumName = explicitName ?? `${parentClassName}${propName}`;
        const enumName = getOrCreateEnum(
            parentClassName,
            propName,
            schema.enum as string[],
            rpcEnumOutput,
            schema.description,
            getEnumValueDescriptions(schema),
            explicitName,
            isSchemaDeprecated(schema),
            isSchemaExperimental(schema) || experimentalRpcTypes.has(generatedEnumName),
        );
        return isRequired ? enumName : `${enumName}?`;
    }
    if (schema.type === "object" && schema.properties) {
        const className = (schema.title as string) ?? `${parentClassName}${propName}`;
        classes.push(emitRpcClass(className, schema, "public", classes));
        return isRequired ? className : `${className}?`;
    }
    if (schema.type === "array" && schema.items) {
        const items = schema.items as JSONSchema7;
        if (items.type === "object" && items.properties) {
            const itemClass = (items.title as string) ?? `${parentClassName}${singularPascal(propName)}`;
            classes.push(emitRpcClass(itemClass, items, "public", classes));
            return isRequired ? `IList<${itemClass}>` : `IList<${itemClass}>?`;
        }
        const itemType = resolveRpcType(items, true, parentClassName, `${propName}Item`, classes);
        return isRequired ? `IList<${itemType}>` : `IList<${itemType}>?`;
    }
    if (schema.type === "object" && schema.additionalProperties && typeof schema.additionalProperties === "object") {
        const vs = schema.additionalProperties as JSONSchema7;
        const valueType = resolveRpcType(vs, true, parentClassName, `${propName}Value`, classes);
        return isRequired ? `IDictionary<string, ${valueType}>` : `IDictionary<string, ${valueType}>?`;
    }
    return schemaTypeToCSharp(schema, isRequired, rpcKnownTypes, propName);
}

function emitRpcClass(
    className: string,
    schema: JSONSchema7,
    visibility: "public" | "internal",
    extraClasses: string[],
    inlineTypeParentName: string = className,
    preserveRequiredNulls = false,
    requiredMembers = false
): string {
    const effectiveSchema =
        resolveObjectSchema(schema, rpcDefinitions) ??
        resolveSchema(schema, rpcDefinitions) ??
        schema;
    // Visibility is driven by the JSON Schema definition itself (set via
    // `.asInternal()` on the originating Zod schema). The runtime schema
    // generator enforces that no public method references an internal type,
    // so it's safe to upgrade callers' default to internal here.
    if (
        (schema as Record<string, unknown>).visibility === "internal" ||
        (effectiveSchema as Record<string, unknown>).visibility === "internal"
    ) {
        visibility = "internal";
    }
    const schemaKey = stableStringify(effectiveSchema);
    const existingSchema = emittedRpcClassSchemas.get(className);
    if (existingSchema) {
        if (existingSchema !== schemaKey) {
            throw new Error(
                `Conflicting RPC class name "${className}" for different schemas. Add a schema title/withTypeName to disambiguate.`
            );
        }
        return "";
    }

    emittedRpcClassSchemas.set(className, schemaKey);

    const requiredSet = new Set(effectiveSchema.required || []);
    const lines: string[] = [];
    lines.push(...xmlDocComment(schema.description || effectiveSchema.description || `RPC data type for ${className.replace(/(Request|Result|Params)$/, "")} operations.`, ""));
    if (experimentalRpcTypes.has(className) || isSchemaExperimental(schema) || isSchemaExperimental(effectiveSchema)) {
        pushExperimentalAttribute(lines);
    }
    if (isSchemaDeprecated(schema) || isSchemaDeprecated(effectiveSchema)) {
        pushObsoleteAttributes(lines);
    }
    lines.push(`${visibility} sealed class ${className}`, `{`);

    const props = Object.entries(effectiveSchema.properties || {}).sort(([a], [b]) => a.localeCompare(b));
    for (let i = 0; i < props.length; i++) {
        const [propName, propSchema] = props[i];
        if (typeof propSchema !== "object") continue;
        const prop = propSchema as JSONSchema7;
        const isReq = requiredSet.has(propName);
        const csharpName = toCSharpPropertyName(propName, prop);
        const csharpType = resolveRpcType(prop, isReq, inlineTypeParentName, csharpName, extraClasses);

        lines.push(...xmlDocPropertyComment(prop.description, propName, "    "));
        lines.push(...emitDataAnnotations(prop, "    ", csharpType));
        if (isSchemaDeprecated(prop)) pushObsoleteAttributes(lines, "    ");
        if (isSchemaExperimental(prop)) pushExperimentalAttribute(lines, "    ");
        if (isMillisecondsDurationProperty(propName, prop)) lines.push(`    [JsonConverter(typeof(MillisecondsTimeSpanConverter))]`);
        const propVisibility = pushCSharpInternalAttribute(lines, prop);
        lines.push(`    [JsonPropertyName("${propName}")]`);
        if (preserveRequiredNulls && isReq && csharpType.endsWith("?")) {
            lines.push(`    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]`);
        }

        let defaultVal = "";
        let propAccessors = "{ get; set; }";
        let requiredModifier = "";
        if (requiredMembers && isReq && !csharpType.endsWith("?")) {
            // Legacy-parameter request types require their mandatory inputs rather than
            // defaulting them to empty values.
            requiredModifier = "required ";
        } else if (isReq && !csharpType.endsWith("?")) {
            if (csharpType === "string") defaultVal = " = string.Empty;";
            else if (csharpType.startsWith("IList<")) {
                propAccessors = "{ get => field ??= []; set; }";
            } else if (csharpType.startsWith("IDictionary<")) {
                const concreteType = csharpType.replace("IDictionary<", "Dictionary<");
                propAccessors = `{ get => field ??= new ${concreteType}(); set; }`;
            } else if (emittedRpcClassSchemas.has(csharpType)) {
                propAccessors = "{ get => field ??= new(); set; }";
            } else if (!isNonNullableCSharpValueType(csharpType)) {
                defaultVal = " = null!;";
            }
        }
        lines.push(`    ${propVisibility} ${requiredModifier}${csharpType} ${csharpName} ${propAccessors}${defaultVal}`);
        if (i < props.length - 1) lines.push("");
    }
    lines.push(`}`);
    return lines.join("\n");
}

function emitRpcResultType(typeName: string, schema: JSONSchema7, visibility: "public" | "internal", classes: string[]): string {
    if (isObjectSchema(schema)) {
        const resultClass = emitRpcClass(typeName, schema, visibility, classes);
        if (resultClass) classes.push(resultClass);
        return typeName;
    }

    const resultType = resolveRpcType(schema, true, typeName, "", classes);
    if (resultType.includes("<") || resultType.endsWith("[]")) {
        rpcRootJsonSerializableTypes.add(resultType.replace(/\?$/, ""));
    }
    return resultType;
}

/**
 * Emit ServerRpc as an instance class (like SessionRpc but without sessionId).
 */
function emitServerRpcClasses(node: Record<string, unknown>, classes: string[]): string[] {
    const result: string[] = [];

    // Find top-level groups (e.g. "models", "tools", "account")
    const groups = Object.entries(node).filter(([, v]) => typeof v === "object" && v !== null && !isRpcMethod(v));
    // Find top-level methods (e.g. "ping")
    const topLevelMethods = Object.entries(node).filter(([, v]) => isRpcMethod(v));

    // ServerRpc class
    const srLines: string[] = [];
    srLines.push(`/// <summary>Provides server-scoped RPC methods (no session required).</summary>`);
    srLines.push(`public sealed class ServerRpc`);
    srLines.push(`{`);
    srLines.push(`    private readonly JsonRpc _rpc;`);
    srLines.push("");
    srLines.push(`    internal ServerRpc(JsonRpc rpc)`);
    srLines.push(`    {`);
    srLines.push(`        _rpc = rpc;`);
    srLines.push(`    }`);

    // Top-level methods (like ping)
    for (const [key, value] of topLevelMethods) {
        if (!isRpcMethod(value)) continue;
        emitServerInstanceMethod(key, value, srLines, classes, "    ", false, false);
    }

    // Group properties
    for (const [groupName] of groups) {
        const propertyName = toPascalCase(groupName);
        srLines.push("");
        srLines.push(`    /// <summary>${propertyName} APIs.</summary>`);
        srLines.push(
            `    public Server${propertyName}Api ${propertyName} =>`,
            `        field ??`,
            `        Interlocked.CompareExchange(ref field, new(_rpc), null) ??`,
            `        field;`
        );
    }

    srLines.push(`}`);
    result.push(srLines.join("\n"));

    // Per-group API classes
    for (const [groupName, groupNode] of groups) {
        result.push(...emitServerApiClass(`Server${toPascalCase(groupName)}Api`, groupNode as Record<string, unknown>, classes));
    }

    return result;
}

function emitServerApiClass(className: string, node: Record<string, unknown>, classes: string[]): string[] {
    const parts: string[] = [];
    const lines: string[] = [];
    const displayName = className.replace(/^Server/, "").replace(/Api$/, "");
    const subGroups = Object.entries(node).filter(([, v]) => typeof v === "object" && v !== null && !isRpcMethod(v));

    lines.push(`/// <summary>Provides server-scoped ${displayName} APIs.</summary>`);
    const groupExperimental = isNodeFullyExperimental(node);
    const groupDeprecated = isNodeFullyDeprecated(node);
    if (groupExperimental) {
        pushExperimentalAttribute(lines);
    }
    if (groupDeprecated) {
        pushObsoleteAttributes(lines);
    }
    lines.push(`public sealed class ${className}`);
    lines.push(`{`);
    lines.push(`    private readonly JsonRpc _rpc;`);
    lines.push("");
    lines.push(`    internal ${className}(JsonRpc rpc)`);
    lines.push(`    {`);
    lines.push(`        _rpc = rpc;`);
    lines.push(`    }`);

    for (const [key, value] of Object.entries(node)) {
        if (!isRpcMethod(value)) continue;
        emitServerInstanceMethod(key, value, lines, classes, "    ", groupExperimental, groupDeprecated);
    }

    for (const [subGroupName] of subGroups) {
        const subClassName = className.replace(/Api$/, "") + toPascalCase(subGroupName) + "Api";
        const propertyName = toPascalCase(subGroupName);
        lines.push("");
        lines.push(`    /// <summary>${propertyName} APIs.</summary>`);
        lines.push(
            `    public ${subClassName} ${propertyName} =>`,
            `        field ??`,
            `        Interlocked.CompareExchange(ref field, new(_rpc), null) ??`,
            `        field;`
        );
    }

    lines.push(`}`);
    parts.push(lines.join("\n"));

    for (const [subGroupName, subGroupNode] of subGroups) {
        const subClassName = className.replace(/Api$/, "") + toPascalCase(subGroupName) + "Api";
        parts.push(...emitServerApiClass(subClassName, subGroupNode as Record<string, unknown>, classes));
    }

    return parts;
}

function emitServerInstanceMethod(
    name: string,
    method: RpcMethod,
    lines: string[],
    classes: string[],
    indent: string,
    groupExperimental: boolean,
    groupDeprecated: boolean
): void {
    const methodName = toPascalCase(name);
    const isInternal = method.visibility === "internal";
    const methodVisibility = isInternal ? "internal" : "public";
    const resultSchema = getMethodResultSchema(method);
    let resultClassName = !isVoidSchema(resultSchema) ? resultTypeName(method) : "";
    if (!isVoidSchema(resultSchema) && method.stability === "experimental" && !nonExperimentalRpcTypes.has(resultClassName)) {
        experimentalRpcTypes.add(resultClassName);
    }
    if (!isVoidSchema(resultSchema)) {
        resultClassName = emitRpcResultType(resultClassName, resultSchema!, methodVisibility, classes);
    }

    const effectiveParams = resolveMethodParamsSchema(method);
    const paramEntries = effectiveParams?.properties ? Object.entries(effectiveParams.properties) : [];
    const requiredSet = new Set(effectiveParams?.required || []);
    const legacyEntries = legacyParameterEntries(method, effectiveParams, paramEntries);

    // Sort so required params come before optional (C# requires defaults at end)
    paramEntries.sort((a, b) => {
        const aReq = requiredSet.has(a[0]) ? 0 : 1;
        const bReq = requiredSet.has(b[0]) ? 0 : 1;
        return aReq - bReq;
    });

    let requestClassName: string | null = null;
    if (paramEntries.length > 0) {
        requestClassName = paramsTypeName(method);
        if (method.stability === "experimental" && !nonExperimentalRpcTypes.has(requestClassName)) {
            experimentalRpcTypes.add(requestClassName);
        }
        const reqClass = emitRpcClass(requestClassName, effectiveParams!, legacyEntries ? methodVisibility : "internal", classes, requestClassName, true, !!legacyEntries);
        if (reqClass) classes.push(reqClass);
    }

    const sigParams: string[] = [];
    const bodyAssignments: string[] = [];
    const argumentNullChecks: string[] = [];
    const requiredMemberNames: string[] = [];
    const parameterDescriptions: Array<{ name: string; description?: string; escapeDescription?: boolean }> = [];

    for (const [pName, pSchema] of legacyEntries ?? paramEntries) {
        if (typeof pSchema !== "object") continue;
        const isReq = requiredSet.has(pName);
        const jsonSchema = pSchema as JSONSchema7;
        const csharpName = requestClassName
            ? toCSharpPropertyName(pName, jsonSchema)
            : toPascalCase(pName);
        const naturalType = requestClassName
            ? resolveRpcType(jsonSchema, isReq, requestClassName, csharpName, classes)
            : schemaTypeToCSharp(jsonSchema, isReq, rpcKnownTypes, csharpName);
        // Boundary special-case: if the natural type is JsonElement/JsonElement?
        // or a list of JsonElement (i.e. the schema is opaque-JSON, possibly
        // wrapped in an array), accept object/IList<object?> at the public
        // surface for ergonomics and convert at the call site. DTO fields
        // keep the JsonElement form.
        const opaqueRequired = naturalType === "JsonElement";
        const opaqueOptional = naturalType === "JsonElement?";
        const opaqueListRequired = naturalType === "IList<JsonElement>";
        const opaqueListOptional = naturalType === "IList<JsonElement>?";
        const opaque = opaqueRequired || opaqueOptional || opaqueListRequired || opaqueListOptional;
        const csType = opaqueRequired
            ? "object"
            : opaqueOptional
                ? "object?"
                : opaqueListRequired
                    ? "IList<object?>"
                    : opaqueListOptional
                        ? "IList<object?>?"
                        : naturalType;
        sigParams.push(`${csType} ${pName}${isReq ? "" : " = null"}`);
        const assignedValue = opaqueRequired
            ? `CopilotClient.ToJsonElementForWire(${pName})!.Value`
            : opaqueOptional
                ? `CopilotClient.ToJsonElementForWire(${pName})`
                : opaqueListRequired
                    ? `${pName}.Select(static v => CopilotClient.ToJsonElementForWire(v)!.Value).ToList()`
                    : opaqueListOptional
                        ? `${pName}?.Select(static v => CopilotClient.ToJsonElementForWire(v)!.Value).ToList()`
                        : pName;
        bodyAssignments.push(`${csharpName} = ${assignedValue}`);
        if (opaqueRequired || opaqueListRequired || (!opaque && requiresArgumentNullCheck(csType, isReq))) {
            argumentNullChecks.push(`${indent}    ArgumentNullException.ThrowIfNull(${pName});`);
        }
        if (opaqueListRequired || (!opaque && requiresArgumentNullCheck(csType, isReq))) {
            requiredMemberNames.push(csharpName);
        }
        parameterDescriptions.push({ name: pName, description: jsonSchema.description });
    }
    sigParams.push("CancellationToken cancellationToken = default");
    parameterDescriptions.push({
        name: "cancellationToken",
        description: CANCELLATION_TOKEN_DESCRIPTION,
        escapeDescription: false,
    });

    const taskType = !isVoidSchema(resultSchema) ? `Task<${resultClassName}>` : "Task";
    const localRequestName = localRequestVariableName(paramEntries);
    lines.push("");
    pushRpcMethodXmlDocs(lines, method, indent, parameterDescriptions, resultSchema);
    if (method.stability === "experimental" && !groupExperimental) {
        pushExperimentalAttribute(lines, indent);
    }
    if (method.deprecated && !groupDeprecated) {
        pushObsoleteAttributes(lines, indent);
    }
    lines.push(`${indent}${methodVisibility} async ${taskType} ${methodName}Async(${sigParams.join(", ")})`);
    lines.push(`${indent}{`);
    lines.push(...argumentNullChecks);
    if (argumentNullChecks.length > 0) {
        lines.push("");
    }
    if (requestClassName && bodyAssignments.length > 0) {
        lines.push(`${indent}    var ${localRequestName} = new ${requestClassName} { ${bodyAssignments.join(", ")} };`);
        if (!isVoidSchema(resultSchema)) {
            lines.push(`${indent}    return await CopilotClient.InvokeRpcAsync<${resultClassName}>(_rpc, "${method.rpcMethod}", [${localRequestName}], cancellationToken);`);
        } else {
            lines.push(`${indent}    await CopilotClient.InvokeRpcAsync(_rpc, "${method.rpcMethod}", [${localRequestName}], cancellationToken);`);
        }
    } else {
        if (!isVoidSchema(resultSchema)) {
            lines.push(`${indent}    return await CopilotClient.InvokeRpcAsync<${resultClassName}>(_rpc, "${method.rpcMethod}", [], cancellationToken);`);
        } else {
            lines.push(`${indent}    await CopilotClient.InvokeRpcAsync(_rpc, "${method.rpcMethod}", [], cancellationToken);`);
        }
    }
    lines.push(`${indent}}`);
    if (legacyEntries && requestClassName) {
        emitRequestObjectMethod(methodName, method, requestClassName, requestClassName, undefined, resultClassName, lines, indent, groupExperimental, groupDeprecated, requiredMemberNames);
    }
}

function emitSessionRpcClasses(node: Record<string, unknown>, classes: string[]): string[] {
    const result: string[] = [];
    const groups = Object.entries(node).filter(([, v]) => typeof v === "object" && v !== null && !isRpcMethod(v));
    const topLevelMethods = Object.entries(node).filter(([, v]) => isRpcMethod(v));

    const srLines = [`/// <summary>Provides typed session-scoped RPC methods.</summary>`, `public sealed class SessionRpc`, `{`, `    private readonly CopilotSession _session;`, ""];
    srLines.push(`    internal SessionRpc(CopilotSession session)`, `    {`, `        _session = session;`);
    srLines.push(`    }`);
    srLines.push("", `    internal CopilotSession Session => _session;`);
    for (const [groupName] of groups) {
        const propertyName = toPascalCase(groupName);
        srLines.push(
            "",
            `    /// <summary>${propertyName} APIs.</summary>`,
            `    public ${propertyName}Api ${propertyName} =>`,
            `        field ??`,
            `        Interlocked.CompareExchange(ref field, new(_session), null) ??`,
            `        field;`
        );
    }

    // Emit top-level session RPC methods directly on the SessionRpc class
    const topLevelLines: string[] = [];
    for (const [key, value] of topLevelMethods) {
        emitSessionMethod(key, value as RpcMethod, topLevelLines, classes, "    ", false, false);
    }
    srLines.push(...topLevelLines);

    srLines.push(`}`);
    result.push(srLines.join("\n"));

    for (const [groupName, groupNode] of groups) {
        result.push(...emitSessionApiClass(`${toPascalCase(groupName)}Api`, groupNode as Record<string, unknown>, classes));
    }
    return result;
}

function hasSessionRequestEnvelope(schema: JSONSchema7 | undefined): boolean {
    if (!schema?.title || !schema.properties?.sessionId) return false;
    if (!nonSessionRequestTypeNames.has(schema.title)) return false;
    const definition = rpcDefinitions.definitions?.[schema.title] ?? rpcDefinitions.$defs?.[schema.title];
    if (!definition || typeof definition !== "object") return false;
    const canonical = resolveObjectSchema(definition, rpcDefinitions);
    if (!canonical?.properties || canonical.properties.sessionId) return false;

    // Runtime session params can inherit the canonical request's title while
    // adding only the transport sessionId. Separate shared envelopes without
    // renaming existing session-only wire types used by handwritten SDK code.
    const withoutSession: JSONSchema7 = {
        ...schema,
        properties: Object.fromEntries(Object.entries(schema.properties).filter(([name]) => name !== "sessionId")),
        required: schema.required?.filter((name) => name !== "sessionId"),
    };
    return stableStringify(withoutSession) === stableStringify(canonical);
}

function emitSessionMethod(key: string, method: RpcMethod, lines: string[], classes: string[], indent: string, groupExperimental: boolean, groupDeprecated: boolean): void {
    const methodName = toPascalCase(key);
    const isInternal = method.visibility === "internal";
    const methodVisibility = isInternal ? "internal" : "public";
    const resultSchema = getMethodResultSchema(method);
    let resultClassName = !isVoidSchema(resultSchema) ? resultTypeName(method) : "";
    if (!isVoidSchema(resultSchema) && method.stability === "experimental" && !nonExperimentalRpcTypes.has(resultClassName)) {
        experimentalRpcTypes.add(resultClassName);
    }
    if (!isVoidSchema(resultSchema)) {
        resultClassName = emitRpcResultType(resultClassName, resultSchema!, methodVisibility, classes);
    }

    const effectiveParams = resolveMethodParamsSchema(method);
    const paramEntries = (effectiveParams?.properties ? Object.entries(effectiveParams.properties) : []).filter(([k]) => k !== "sessionId");
    const requiredSet = new Set(effectiveParams?.required || []);
    const legacyEntries = legacyParameterEntries(method, effectiveParams, paramEntries, true);
    const useRequestParameter =
        paramEntries.length > 0 &&
        !!getNullableInner(method.params) &&
        paramEntries.every(([name]) => !requiredSet.has(name));

    // Sort so required params come before optional (C# requires defaults at end)
    paramEntries.sort((a, b) => {
        const aReq = requiredSet.has(a[0]) ? 0 : 1;
        const bReq = requiredSet.has(b[0]) ? 0 : 1;
        return aReq - bReq;
    });

    const requestClassName = paramsTypeName(method);
    const wireRequestClassName = useRequestParameter || legacyEntries || hasSessionRequestEnvelope(effectiveParams)
        ? `${requestClassName}WithSession`
        : requestClassName;
    if (method.stability === "experimental" && !nonExperimentalRpcTypes.has(requestClassName)) {
        experimentalRpcTypes.add(requestClassName);
        if (wireRequestClassName !== requestClassName && !nonExperimentalRpcTypes.has(wireRequestClassName)) {
            experimentalRpcTypes.add(wireRequestClassName);
        }
    }
    if (effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0) {
        if (useRequestParameter || legacyEntries) {
            const publicParams: JSONSchema7 = {
                ...effectiveParams,
                properties: Object.fromEntries(paramEntries),
                required: effectiveParams.required?.filter((name) => name !== "sessionId"),
            };
            const publicReqClass = emitRpcClass(requestClassName, publicParams, methodVisibility, classes, requestClassName, true, !!legacyEntries);
            if (publicReqClass) classes.push(publicReqClass);
            // The wire wrapper carries the same properties as the public request
            // type plus `sessionId`, so both must reuse the same inline types.
            const wireReqClass = emitRpcClass(
                wireRequestClassName,
                effectiveParams,
                "internal",
                classes,
                requestClassName,
                true
            );
            if (wireReqClass) classes.push(wireReqClass);
        } else {
            const reqClass = emitRpcClass(wireRequestClassName, effectiveParams, "internal", classes, requestClassName, true);
            if (reqClass) classes.push(reqClass);
        }
    }

    const sigParams: string[] = [];
    const bodyAssignments = [`SessionId = _session.SessionId`];
    const argumentNullChecks: string[] = [];
    const requiredMemberNames: string[] = [];
    const parameterDescriptions: Array<{ name: string; description?: string; escapeDescription?: boolean }> = [];

    if (useRequestParameter) {
        sigParams.push(`${requestClassName}? request = null`);
        parameterDescriptions.push({ name: "request", description: rpcParamsDescription(method, effectiveParams) });
        for (const [pName, pSchema] of paramEntries) {
            if (typeof pSchema !== "object") continue;
            const csharpName = toCSharpPropertyName(pName, pSchema as JSONSchema7);
            bodyAssignments.push(`${csharpName} = request?.${csharpName}`);
        }
    } else {
        for (const [pName, pSchema] of legacyEntries ?? paramEntries) {
            if (typeof pSchema !== "object") continue;
            const isReq = requiredSet.has(pName);
            const jsonSchema = pSchema as JSONSchema7;
            const csharpName = toCSharpPropertyName(pName, jsonSchema);
            const naturalType = resolveRpcType(jsonSchema, isReq, requestClassName, csharpName, classes);
            const opaqueRequired = naturalType === "JsonElement";
            const opaqueOptional = naturalType === "JsonElement?";
            const opaqueListRequired = naturalType === "IList<JsonElement>";
            const opaqueListOptional = naturalType === "IList<JsonElement>?";
            const opaque = opaqueRequired || opaqueOptional || opaqueListRequired || opaqueListOptional;
            const csType = opaqueRequired
                ? "object"
                : opaqueOptional
                    ? "object?"
                    : opaqueListRequired
                        ? "IList<object?>"
                        : opaqueListOptional
                            ? "IList<object?>?"
                            : naturalType;
            sigParams.push(`${csType} ${pName}${isReq ? "" : " = null"}`);
            const assignedValue = opaqueRequired
                ? `CopilotClient.ToJsonElementForWire(${pName})!.Value`
                : opaqueOptional
                    ? `CopilotClient.ToJsonElementForWire(${pName})`
                    : opaqueListRequired
                        ? `${pName}.Select(static v => CopilotClient.ToJsonElementForWire(v)!.Value).ToList()`
                        : opaqueListOptional
                            ? `${pName}?.Select(static v => CopilotClient.ToJsonElementForWire(v)!.Value).ToList()`
                            : pName;
            bodyAssignments.push(`${csharpName} = ${assignedValue}`);
            if (opaqueRequired || opaqueListRequired || (!opaque && requiresArgumentNullCheck(csType, isReq))) {
                argumentNullChecks.push(`${indent}    ArgumentNullException.ThrowIfNull(${pName});`);
            }
            if (opaqueListRequired || (!opaque && requiresArgumentNullCheck(csType, isReq))) {
                requiredMemberNames.push(csharpName);
            }
            parameterDescriptions.push({ name: pName, description: jsonSchema.description });
        }
    }
    sigParams.push("CancellationToken cancellationToken = default");
    parameterDescriptions.push({
        name: "cancellationToken",
        description: CANCELLATION_TOKEN_DESCRIPTION,
        escapeDescription: false,
    });

    const taskType = !isVoidSchema(resultSchema) ? `Task<${resultClassName}>` : "Task";
    const localRequestName = localRequestVariableName(paramEntries, useRequestParameter);
    lines.push("");
    pushRpcMethodXmlDocs(lines, method, indent, parameterDescriptions, resultSchema);
    if (method.stability === "experimental" && !groupExperimental) {
        pushExperimentalAttribute(lines, indent);
    }
    if (method.deprecated && !groupDeprecated) {
        pushObsoleteAttributes(lines, indent);
    }
    lines.push(`${indent}${methodVisibility} async ${taskType} ${methodName}Async(${sigParams.join(", ")})`);
    lines.push(`${indent}{`);
    lines.push(...argumentNullChecks);
    lines.push(`${indent}    _session.ThrowIfDisposed();`);
    lines.push("");
    lines.push(`${indent}    var ${localRequestName} = new ${wireRequestClassName} { ${bodyAssignments.join(", ")} };`);
    if (!isVoidSchema(resultSchema)) {
        lines.push(`${indent}    return await CopilotClient.InvokeRpcAsync<${resultClassName}>(_session.Rpc, "${method.rpcMethod}", [${localRequestName}], cancellationToken);`, `${indent}}`);
    } else {
        lines.push(`${indent}    await CopilotClient.InvokeRpcAsync(_session.Rpc, "${method.rpcMethod}", [${localRequestName}], cancellationToken);`, `${indent}}`);
    }
    if (legacyEntries) {
        const assignments = ["SessionId = _session.SessionId", ...paramEntries.flatMap(([name, schema]) =>
            typeof schema === "object" ? [`${toCSharpPropertyName(name, schema)} = request.${toCSharpPropertyName(name, schema)}`] : [])];
        emitRequestObjectMethod(methodName, method, requestClassName, wireRequestClassName, assignments, resultClassName, lines, indent, groupExperimental, groupDeprecated, requiredMemberNames);
    }
}

function emitSessionApiClass(className: string, node: Record<string, unknown>, classes: string[]): string[] {
    const parts: string[] = [];
    const displayName = className.replace(/Api$/, "");
    const groupExperimental = isNodeFullyExperimental(node);
    const groupDeprecated = isNodeFullyDeprecated(node);
    const experimentalAttr = groupExperimental ? `${experimentalAttribute()}\n` : "";
    const deprecatedAttr = groupDeprecated ? `${obsoleteAttributeBlock()}\n` : "";
    const subGroups = Object.entries(node).filter(([, v]) => typeof v === "object" && v !== null && !isRpcMethod(v));

    const lines = [`/// <summary>Provides session-scoped ${displayName} APIs.</summary>`, `${experimentalAttr}${deprecatedAttr}public sealed class ${className}`, `{`, `    private readonly CopilotSession _session;`, ""];
    lines.push(`    internal ${className}(CopilotSession session)`, `    {`, `        _session = session;`);
    lines.push(`    }`);

    for (const [key, value] of Object.entries(node)) {
        if (!isRpcMethod(value)) continue;
        emitSessionMethod(key, value, lines, classes, "    ", groupExperimental, groupDeprecated);
    }

    for (const [subGroupName] of subGroups) {
        const subClassName = className.replace(/Api$/, "") + toPascalCase(subGroupName) + "Api";
        const propertyName = toPascalCase(subGroupName);
        lines.push("");
        lines.push(`    /// <summary>${propertyName} APIs.</summary>`);
        lines.push(
            `    public ${subClassName} ${propertyName} =>`,
            `        field ??`,
            `        Interlocked.CompareExchange(ref field, new(_session), null) ??`,
            `        field;`
        );
    }

    lines.push(`}`);
    parts.push(lines.join("\n"));

    for (const [subGroupName, subGroupNode] of subGroups) {
        const subClassName = className.replace(/Api$/, "") + toPascalCase(subGroupName) + "Api";
        parts.push(...emitSessionApiClass(subClassName, subGroupNode as Record<string, unknown>, classes));
    }

    return parts;
}

function collectClientGroups(node: Record<string, unknown>): Array<{ groupName: string; groupNode: Record<string, unknown>; methods: RpcMethod[] }> {
    const groups: Array<{ groupName: string; groupNode: Record<string, unknown>; methods: RpcMethod[] }> = [];
    for (const [groupName, groupNode] of Object.entries(node)) {
        if (typeof groupNode === "object" && groupNode !== null) {
            groups.push({
                groupName,
                groupNode: groupNode as Record<string, unknown>,
                methods: collectRpcMethods(groupNode as Record<string, unknown>),
            });
        }
    }
    return groups;
}

function clientHandlerInterfaceName(groupName: string): string {
    return `I${toPascalCase(groupName)}Handler`;
}

function clientHandlerMethodName(rpcMethod: string): string {
    const parts = rpcMethod.split(".");
    return `${toPascalCase(parts[parts.length - 1])}Async`;
}

function emitClientSessionApiRegistration(clientSchema: Record<string, unknown>, classes: string[]): string[] {
    const lines: string[] = [];
    const groups = collectClientGroups(clientSchema);

    for (const { methods } of groups) {
        for (const method of methods) {
            const resultSchema = getMethodResultSchema(method);
            if (!isVoidSchema(resultSchema) && !isOpaqueJson(resultSchema)) {
                emitRpcResultType(resultTypeName(method), resultSchema!, "public", classes);
            }

            const effectiveParams = resolveMethodParamsSchema(method);
            if (effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0) {
                const paramsClass = emitRpcClass(paramsTypeName(method), effectiveParams, "public", classes);
                if (paramsClass) classes.push(paramsClass);
            }
        }
    }

    for (const { groupName, groupNode, methods } of groups) {
        const interfaceName = clientHandlerInterfaceName(groupName);
        const groupExperimental = isNodeFullyExperimental(groupNode);
        const groupDeprecated = isNodeFullyDeprecated(groupNode);
        lines.push(`/// <summary>Handles \`${groupName}\` client session API methods.</summary>`);
        if (groupExperimental) {
            pushExperimentalAttribute(lines);
        }
        if (groupDeprecated) {
            pushObsoleteAttributes(lines);
        }
        lines.push(`public interface ${interfaceName}`);
        lines.push(`{`);
        for (const method of methods) {
            const effectiveParams = resolveMethodParamsSchema(method);
            const hasParams = !!effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0;
            const resultSchema = getMethodResultSchema(method);
            const taskType = resultTaskType(method);
            pushRpcMethodXmlDocs(
                lines,
                method,
                "    ",
                [
                    ...(hasParams ? [{ name: "request", description: rpcParamsDescription(method, effectiveParams) }] : []),
                    { name: "cancellationToken", description: CANCELLATION_TOKEN_DESCRIPTION, escapeDescription: false },
                ],
                resultSchema,
                `Handles "${method.rpcMethod}".`
            );
            if (method.stability === "experimental" && !groupExperimental) {
                pushExperimentalAttribute(lines, "    ");
            }
            if (method.deprecated && !groupDeprecated) {
                pushObsoleteAttributes(lines, "    ");
            }
            if (hasParams) {
                lines.push(`    ${taskType} ${clientHandlerMethodName(method.rpcMethod)}(${paramsTypeName(method)} request, CancellationToken cancellationToken = default);`);
            } else {
                lines.push(`    ${taskType} ${clientHandlerMethodName(method.rpcMethod)}(CancellationToken cancellationToken = default);`);
            }
        }
        lines.push(`}`);
        lines.push("");
    }

    lines.push(`/// <summary>Provides all client session API handler groups for a session.</summary>`);
    lines.push(`public sealed class ClientSessionApiHandlers`);
    lines.push(`{`);
    for (const { groupName } of groups) {
        lines.push(`    /// <summary>Optional handler for ${toPascalCase(groupName)} client session API methods.</summary>`);
        lines.push(`    public ${clientHandlerInterfaceName(groupName)}? ${toPascalCase(groupName)} { get; set; }`);
        lines.push("");
    }
    if (lines[lines.length - 1] === "") lines.pop();
    lines.push(`}`);
    lines.push("");

    lines.push(`/// <summary>Registers client session API handlers on a JSON-RPC connection.</summary>`);
    lines.push(`internal static class ClientSessionApiRegistration`);
    lines.push(`{`);
    lines.push(`    /// <summary>`);
    lines.push(`    /// Registers handlers for server-to-client session API calls.`);
    lines.push(`    /// Each incoming call includes a <c>sessionId</c> in its params object,`);
    lines.push(`    /// which is used to resolve the session's handler group.`);
    lines.push(`    /// </summary>`);
    lines.push(`    public static void RegisterClientSessionApiHandlers(JsonRpc rpc, Func<string, ClientSessionApiHandlers> getHandlers)`);
    lines.push(`    {`);
    for (const { groupName, methods } of groups) {
        for (const method of methods) {
            const handlerProperty = toPascalCase(groupName);
            const handlerMethod = clientHandlerMethodName(method.rpcMethod);
            const effectiveParams = resolveMethodParamsSchema(method);
            const hasParams = !!effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0;
            const resultSchema = getMethodResultSchema(method);
            const paramsClass = paramsTypeName(method);
            const taskType = handlerTaskType(method);

            if (hasParams) {
                lines.push(`        rpc.SetLocalRpcMethod("${method.rpcMethod}", (Func<${paramsClass}, CancellationToken, ${taskType}>)(async (request, cancellationToken) =>`);
                lines.push(`        {`);
                lines.push(`            var handler = getHandlers(request.SessionId).${handlerProperty};`);
                lines.push(`            if (handler is null) throw new InvalidOperationException($"No ${groupName} handler registered for session: {request.SessionId}");`);
                if (!isVoidSchema(resultSchema)) {
                    lines.push(`            return await handler.${handlerMethod}(request, cancellationToken);`);
                } else {
                    lines.push(`            await handler.${handlerMethod}(request, cancellationToken);`);
                }
                lines.push(`        }), singleObjectParam: true);`);
            } else {
                lines.push(`        rpc.SetLocalRpcMethod("${method.rpcMethod}", (Func<CancellationToken, ${taskType}>)(_ =>`);
                lines.push(`            throw new InvalidOperationException("No params provided for ${method.rpcMethod}")));`);
            }
        }
    }
    lines.push(`    }`);
    lines.push(`}`);

    return lines;
}

/**
 * Emit C# handler interfaces + a process-wide registration for client
 * *global* API groups.
 *
 * Unlike client-session APIs, these methods carry no implicit `sessionId`
 * dispatch key. The SDK consumer registers a single process-wide handler set
 * via `RegisterClientGlobalApiHandlers`; the runtime dispatcher routes each
 * incoming call to the registered handler regardless of which (if any)
 * runtime session triggered it.
 */
function emitClientGlobalApiRegistration(clientSchema: Record<string, unknown>, classes: string[]): string[] {
    const lines: string[] = [];
    const groups = collectClientGroups(clientSchema);

    for (const { methods } of groups) {
        for (const method of methods) {
            const resultSchema = getMethodResultSchema(method);
            if (!isVoidSchema(resultSchema) && !isOpaqueJson(resultSchema)) {
                emitRpcResultType(resultTypeName(method), resultSchema!, "public", classes);
            }

            const effectiveParams = resolveMethodParamsSchema(method);
            if (effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0) {
                const paramsClass = emitRpcClass(paramsTypeName(method), effectiveParams, "public", classes);
                if (paramsClass) classes.push(paramsClass);
            }
        }
    }

    for (const { groupName, groupNode, methods } of groups) {
        const interfaceName = clientHandlerInterfaceName(groupName);
        const groupExperimental = isNodeFullyExperimental(groupNode);
        const groupDeprecated = isNodeFullyDeprecated(groupNode);
        lines.push(`/// <summary>Handles \`${groupName}\` client global API methods.</summary>`);
        if (groupExperimental) {
            pushExperimentalAttribute(lines);
        }
        if (groupDeprecated) {
            pushObsoleteAttributes(lines);
        }
        lines.push(`public interface ${interfaceName}`);
        lines.push(`{`);
        for (const method of methods) {
            const effectiveParams = resolveMethodParamsSchema(method);
            const hasParams = !!effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0;
            const resultSchema = getMethodResultSchema(method);
            const taskType = resultTaskType(method);
            pushRpcMethodXmlDocs(
                lines,
                method,
                "    ",
                [
                    ...(hasParams ? [{ name: "request", description: rpcParamsDescription(method, effectiveParams) }] : []),
                    { name: "cancellationToken", description: CANCELLATION_TOKEN_DESCRIPTION, escapeDescription: false },
                ],
                resultSchema,
                `Handles "${method.rpcMethod}".`
            );
            if (method.stability === "experimental" && !groupExperimental) {
                pushExperimentalAttribute(lines, "    ");
            }
            if (method.deprecated && !groupDeprecated) {
                pushObsoleteAttributes(lines, "    ");
            }
            if (hasParams) {
                lines.push(`    ${taskType} ${clientHandlerMethodName(method.rpcMethod)}(${paramsTypeName(method)} request, CancellationToken cancellationToken = default);`);
            } else {
                lines.push(`    ${taskType} ${clientHandlerMethodName(method.rpcMethod)}(CancellationToken cancellationToken = default);`);
            }
        }
        lines.push(`}`);
        lines.push("");
    }

    lines.push(`/// <summary>Provides all client global API handler groups for a connection.</summary>`);
    lines.push(`public sealed class ClientGlobalApiHandlers`);
    lines.push(`{`);
    for (const { groupName } of groups) {
        lines.push(`    /// <summary>Optional handler for ${toPascalCase(groupName)} client global API methods.</summary>`);
        lines.push(`    public ${clientHandlerInterfaceName(groupName)}? ${toPascalCase(groupName)} { get; set; }`);
        lines.push("");
    }
    if (lines[lines.length - 1] === "") lines.pop();
    lines.push(`}`);
    lines.push("");

    lines.push(`/// <summary>Registers client global API handlers on a JSON-RPC connection.</summary>`);
    lines.push(`internal static class ClientGlobalApiRegistration`);
    lines.push(`{`);
    lines.push(`    /// <summary>`);
    lines.push(`    /// Registers handlers for server-to-client global API calls.`);
    lines.push(`    /// Unlike client session APIs, these methods carry no implicit`);
    lines.push(`    /// <c>sessionId</c> dispatch key — a single set of handlers serves the`);
    lines.push(`    /// entire connection.`);
    lines.push(`    /// </summary>`);
    lines.push(`    public static void RegisterClientGlobalApiHandlers(JsonRpc rpc, ClientGlobalApiHandlers handlers)`);
    lines.push(`    {`);
    for (const { groupName, methods } of groups) {
        for (const method of methods) {
            const handlerProperty = toPascalCase(groupName);
            const handlerMethod = clientHandlerMethodName(method.rpcMethod);
            const effectiveParams = resolveMethodParamsSchema(method);
            const hasParams = !!effectiveParams?.properties && Object.keys(effectiveParams.properties).length > 0;
            const resultSchema = getMethodResultSchema(method);
            const paramsClass = paramsTypeName(method);
            const taskType = handlerTaskType(method);

            if (hasParams) {
                lines.push(`        rpc.SetLocalRpcMethod("${method.rpcMethod}", (Func<${paramsClass}, CancellationToken, ${taskType}>)(async (request, cancellationToken) =>`);
                lines.push(`        {`);
                lines.push(`            var handler = handlers.${handlerProperty} ?? throw new InvalidOperationException("No ${groupName} client-global handler registered");`);
                if (!isVoidSchema(resultSchema)) {
                    lines.push(`            return await handler.${handlerMethod}(request, cancellationToken);`);
                } else {
                    lines.push(`            await handler.${handlerMethod}(request, cancellationToken);`);
                }
                lines.push(`        }), singleObjectParam: true);`);
            } else {
                lines.push(`        rpc.SetLocalRpcMethod("${method.rpcMethod}", (Func<CancellationToken, ${taskType}>)(async cancellationToken =>`);
                lines.push(`        {`);
                lines.push(`            var handler = handlers.${handlerProperty} ?? throw new InvalidOperationException("No ${groupName} client-global handler registered");`);
                if (!isVoidSchema(resultSchema)) {
                    lines.push(`            return await handler.${handlerMethod}(cancellationToken);`);
                } else {
                    lines.push(`            await handler.${handlerMethod}(cancellationToken);`);
                }
                lines.push(`        }));`);
            }
        }
    }
    lines.push(`    }`);
    lines.push(`}`);

    return lines;
}

export function generateRpcCode(
    schema: ApiSchema,
    externalJsonSerializableRefs: Map<string, Set<string>> = new Map(),
    externalValueTypes: Set<string> = new Set()
): string {
    schema = cloneSchemaForCodegen(schema);
    omitUnrepresentableInternalProperties(schema);
    emittedRpcClassSchemas.clear();
    nonSessionRequestTypeNames.clear();
    emittedRpcEnumResultTypes.clear();
    experimentalRpcTypes.clear();
    nonExperimentalRpcTypes.clear();
    rpcKnownTypes.clear();
    rpcEnumOutput = [];
    rpcRootJsonSerializableTypes.clear();
    generatedEnums.clear(); // Clear shared enum deduplication map
    externalRpcValueTypes = new Set([...externalValueTypes].map(typeToClassName));
    rpcDefinitions = collectDefinitionCollections(schema as Record<string, unknown>);
    // Response classes gain settable properties, so object initialisers are unchanged.
    validateLegacyDefinitions(rpcDefinitions);
    for (const method of [
        ...collectRpcMethods(schema.server || {}),
        ...collectRpcMethods(filterNodeByVisibility(schema.clientSession || {}, "public") || {}),
        ...collectRpcMethods(filterNodeByVisibility(schema.clientGlobal || {}, "public") || {}),
    ]) {
        nonSessionRequestTypeNames.add(paramsTypeName(method));
    }
    const allMethods = [
        ...collectRpcMethods(schema.server || {}),
        ...collectRpcMethods(schema.session || {}),
        ...collectRpcMethods(schema.clientSession || {}),
        ...collectRpcMethods(schema.clientGlobal || {}),
    ];
    for (const name of collectRpcMethodReferencedDefinitionNames(
        allMethods.filter((method) => method.stability !== "experimental"),
        rpcDefinitions
    )) {
        nonExperimentalRpcTypes.add(typeToClassName(name));
    }
    for (const name of collectExperimentalOnlyRpcReferencedDefinitionNames(allMethods, rpcDefinitions)) {
        experimentalRpcTypes.add(typeToClassName(name));
    }
    for (const defs of [rpcDefinitions.definitions, rpcDefinitions.$defs]) {
        for (const [name, def] of Object.entries(defs ?? {})) {
            if (typeof def === "object" && def !== null && isSchemaExperimental(def as JSONSchema7)) {
                experimentalRpcTypes.add(typeToClassName(name));
            }
        }
    }
    const classes: string[] = [];

    let serverRpcParts: string[] = [];
    if (schema.server) serverRpcParts = emitServerRpcClasses(schema.server, classes);

    let sessionRpcParts: string[] = [];
    if (schema.session) sessionRpcParts = emitSessionRpcClasses(schema.session, classes);

    // Client handler surfaces (interfaces, handler properties, RPC registration)
    // are only generated for public methods. Internal client methods (e.g.
    // `hooks.invoke`) are runtime transport plumbing and must not surface any
    // generated code — including their request/result DTOs, which would
    // otherwise leak as `internal` types referenced by a `public` handler
    // interface (CS0050/CS0051 inconsistent accessibility).
    let clientSessionParts: string[] = [];
    if (schema.clientSession) {
        const publicClientSession = filterNodeByVisibility(schema.clientSession, "public");
        if (publicClientSession) clientSessionParts = emitClientSessionApiRegistration(publicClientSession, classes);
    }

    let clientGlobalParts: string[] = [];
    if (schema.clientGlobal) {
        const publicClientGlobal = filterNodeByVisibility(schema.clientGlobal, "public");
        if (publicClientGlobal) clientGlobalParts = emitClientGlobalApiRegistration(publicClientGlobal, classes);
    }

    const lines: string[] = [];
    lines.push(`${COPYRIGHT}

// AUTO-GENERATED FILE - DO NOT EDIT
// Generated from: api.schema.json

#pragma warning disable CS0612 // Type or member is obsolete
#pragma warning disable CS0618 // Type or member is obsolete (with message)

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading;

namespace GitHub.Copilot.Rpc;
`);

    for (const cls of classes) if (cls) lines.push(cls, "");
    for (const enumCode of rpcEnumOutput) lines.push(enumCode, "");
    for (const part of serverRpcParts) lines.push(part, "");
    for (const part of sessionRpcParts) lines.push(part, "");
    if (clientSessionParts.length > 0) lines.push(...clientSessionParts, "");
    if (clientGlobalParts.length > 0) lines.push(...clientGlobalParts, "");

    // Add JsonSerializerContext for AOT/trimming support
    const typeNames = [
        ...new Set([...emittedRpcClassSchemas.keys(), ...emittedRpcEnumResultTypes, ...rpcRootJsonSerializableTypes]),
    ].sort();
    if (typeNames.length > 0) {
        lines.push(`[JsonSourceGenerationOptions(`);
        lines.push(`    JsonSerializerDefaults.Web,`);
        lines.push(`    AllowOutOfOrderMetadataProperties = true,`);
        lines.push(`    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull)]`);
        for (const t of ["bool", "double", "int", "long", "string"]) lines.push(`[JsonSerializable(typeof(${t}))]`);
        for (const [schemaFile, names] of externalJsonSerializableRefs) {
            if (schemaFile !== "session-events.schema.json") continue;
            for (const name of [...names].sort()) {
                const typeName = typeToClassName(name);
                lines.push(`[JsonSerializable(typeof(GitHub.Copilot.${typeName}), TypeInfoPropertyName = "SessionEvents${typeName}")]`);
            }
        }
        for (const t of typeNames) lines.push(`[JsonSerializable(typeof(${t}))]`);
        lines.push(`internal partial class RpcJsonContext : JsonSerializerContext;`);
    }

    return lines.join("\n");
}

export async function generateRpc(schemaPath?: string, sessionEventsSchema?: JSONSchema7): Promise<void> {
    console.log("C#: generating RPC types...");
    const resolvedPath = schemaPath ?? (await getApiSchemaPath());
    handWrittenCSharpTypeNames = await collectHandWrittenCSharpTypeNames();
    let schema = fixNullableRequiredRefsInApiSchema(cloneSchemaForCodegen((await loadSchemaJson(resolvedPath)) as ApiSchema));
    let sessionEventsCode: string | undefined;
    if (sessionEventsSchema) {
        sessionEventsCode = generateSessionEventsCode(sessionEventsSchema);
        const sharedDefinitions = findSharedSchemaDefinitions(
            schema as unknown as Record<string, unknown>,
            sessionEventsSchema as unknown as Record<string, unknown>
        );
        const reachableDefinitions = collectReachableDefinitionNames(sessionEventsSchema as unknown as Record<string, unknown>);
        for (const name of [...sharedDefinitions]) {
            const typeName = typeToClassName(name);
            const declarationPattern = new RegExp(
                `\\bpublic\\s+(?:(?:sealed|abstract|partial|readonly)\\s+)*(?:class|struct|enum)\\s+${typeName}\\b`
            );
            if (
                !reachableDefinitions.has(name) ||
                (!declarationPattern.test(sessionEventsCode) && !handWrittenCSharpTypeNames.has(typeName))
            ) {
                sharedDefinitions.delete(name);
            }
        }
        schema = rewriteSharedDefinitionReferences(schema, sharedDefinitions, "session-events.schema.json");
    }
    const externalJsonSerializableRefs = new Map<string, Set<string>>();
    const externalValueTypes = new Set<string>();
    if (sessionEventsSchema && sessionEventsCode) {
        const externalRefs = collectExternalSchemaRefNames(schema);
        const sessionEventRefs = externalRefs.get("session-events.schema.json");
        if (sessionEventRefs && sessionEventRefs.size > 0) {
            const reachableDefinitions = collectReachableDefinitionNames(
                sessionEventsSchema as unknown as Record<string, unknown>,
                sessionEventRefs
            );
            const emittedDefinitions = new Set<string>();
            for (const name of reachableDefinitions) {
                const typeName = typeToClassName(name);
                const declarationPattern = new RegExp(`\\bpublic\\s+(?:(?:sealed|abstract|partial|readonly)\\s+)*(?:class|struct)\\s+${typeName}\\b`);
                // A hand-written declaration also lives in `GitHub.Copilot`, so the
                // reference resolves even though the generated file skipped it.
                if (declarationPattern.test(sessionEventsCode) || handWrittenCSharpTypeNames.has(typeName)) {
                    emittedDefinitions.add(name);
                }
                const valueTypeDeclarationPattern = new RegExp(`\\bpublic\\s+(?:(?:readonly)\\s+)?struct\\s+${typeName}\\b`);
                if (valueTypeDeclarationPattern.test(sessionEventsCode)) {
                    externalValueTypes.add(name);
                }
            }
            externalJsonSerializableRefs.set(
                "session-events.schema.json",
                emittedDefinitions
            );
        }
    }
    const code = generateRpcCode(schema, externalJsonSerializableRefs, externalValueTypes);
    const outPath = await writeGeneratedFile("dotnet/src/Generated/Rpc.cs", code);
    console.log(`  ✓ ${outPath}`);
    await formatCSharpFile(outPath);
}

// ══════════════════════════════════════════════════════════════════════════════
// MAIN
// ══════════════════════════════════════════════════════════════════════════════

async function generate(sessionSchemaPath?: string, apiSchemaPath?: string): Promise<void> {
    await generateSessionEvents(sessionSchemaPath);
    try {
        const resolvedSessionPath = sessionSchemaPath ?? (await getSessionEventsSchemaPath());
        const sessionSchema = propagateInternalVisibility(postProcessSchema(cloneSchemaForCodegen((await loadSchemaJson(resolvedSessionPath)) as JSONSchema7)));
        await generateRpc(apiSchemaPath, sessionSchema);
    } catch (err) {
        if ((err as NodeJS.ErrnoException).code === "ENOENT" && !apiSchemaPath) {
            console.log("C#: skipping RPC (api.schema.json not found)");
        } else {
            throw err;
        }
    }
}

const __filename = fileURLToPath(import.meta.url);

if (isCodegenEntrypoint(process.argv[1], __filename)) {
    const sessionArg = process.argv[2] || undefined;
    const apiArg = process.argv[3] || undefined;
    generate(sessionArg, apiArg).catch((err) => {
        console.error("C# generation failed:", err);
        process.exit(1);
    });
}