discovery: generate capability JSON from the registry

A capability is a descriptor plus what the endpoint declares (device/Capability.ts), and its discovery object is
generated from the two. The new API is bridge.addDevice({ endpointId, name, categories, ... }) and
device.add(PowerController, options): both throw a DeclarationError that names the endpoint, the interface and
the instance (device/validate.ts), and leave the bridge and the device as they were. AlexaInterface is the same
Capability with the 1.x methods on it; it, ActionMapping and the enums moved to src/compat/, Device to src/device/.

What a 1.x caller can observe:
- every endpoint ends with { type: "AlexaInterface", interface: "Alexa", version: "3" } (alexa-interface.html);
  new Alex2MQTT(..., { alexaInterface: false }) leaves it out
- the fields of a capability object come in the order of Amazon's examples; their content is unchanged
- addCapability() with a name that is not an interface throws (1.5.2 announced it with the version "UNKNOWN")
- ActionMapping takes the payload as an object; a JSON string is parsed (1.5.2 sent the string), any other throws
- what Alexa would reject in a 1.x declaration is not refused: device.check() lists it and the bridge logs each
  line once, as "warning: ..." through the log hook, when it answers a discovery
- a device whose JSON cannot be built is left out of the answer and reported as an error event
- PowerController and EndpointHealth are the descriptors and keep ON/OFF and OK/UNREACHABLE; PowerState is new

Tests: six zoo devices declared the 1.x way give the JSON that Alexa accepted from 1.5.2 on 2026-09-28, plus the
Alexa capability. npm test: 85 pass (was 57) in 10-12 s, also on Node 18.20.8 and 20.20.2.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/registry/index.ts

@@ -45,8 +45,8 @@ export const registry = {
 export { Alexa, BrightnessController, EndpointHealth, PowerController, TemperatureSensor };
 export { DeclarationError, defineInterface } from "./types.js";
 export type {
-  AnyDescriptor, CapabilityExtras, Declared, DirectiveDescriptor, EndpointView, EventDescriptor, InterfaceDescriptor,
-  Label, PropertyDescriptor,
+  ActionsToDirective, AnyDescriptor, CapabilityExtras, Declared, DirectiveDescriptor, EndpointView, EventDescriptor,
+  InterfaceDescriptor, Label, PropertyDescriptor, Semantics, StatesToRange, StatesToValue,
 } from "./types.js";
 export { s, SchemaError } from "./schema.js";
 export type { Infer, Schema, Temperature, TimeInterval } from "./schema.js";

src/registry/interfaces/stubs.ts

@@ -84,6 +84,21 @@ const TABLE: readonly Row[] = [
   ["Alexa.WakeOnLANController", "1", [], "alexa-wakeonlancontroller.html"],
 ];
 
+// What 1.5.2 added to the capability object of three of them
+const EXTRAS: Record<string, AnyDescriptor["discovery"]> = {
+  // No properties object; supportsDeactivation and proactivelyReported on the capability itself
+  "Alexa.SceneController": ({ proactivelyReported }) => ({
+    properties: false,
+    topLevel: { supportsDeactivation: true, proactivelyReported },
+  }),
+  "Alexa.ThermostatController": () => ({
+    configuration: { supportedModes: ["HEAT", "COOL", "AUTO", "OFF"], supportsScheduling: false },
+  }),
+  "Alexa.ModeController": ({ options }) => (options.supportedModes?.length > 0
+    ? { configuration: { ordered: true, supportedModes: options.supportedModes } }
+    : {}),
+};
+
 function kindOf(namespace: string): AnyDescriptor["kind"] {
   if (namespace.endsWith("Sensor")) return "sensor";
   if (namespace.endsWith("EventSource")) return "eventSource";
@@ -100,6 +115,7 @@ function stub([namespace, version, properties, page]: Row): AnyDescriptor {
     instanced: false,
     properties: Object.fromEntries(properties.map((name) => [name, { name, value: s.unknown() }])),
     directives: {},
+    discovery: EXTRAS[namespace],
   };
 }
 

src/registry/resources.ts

@@ -0,0 +1,47 @@
+// Friendly names: what the user calls an instance, a mode or a preset (resources-and-assets.html).
+import { ASSETS, RESERVED_WORDS } from "./catalog.js";
+import type { AssetId } from "./catalog.js";
+import { at, s, SchemaError } from "./schema.js";
+import type { Schema } from "./schema.js";
+import type { Label } from "./types.js";
+
+/** A friendly name as text, in one locale. */
+export function text(name: string, locale = "en-US"): Label {
+  return { "@type": "text", value: { text: name, locale } };
+}
+
+/** A friendly name from the global Alexa catalog: one id, several names, every language Alexa speaks. */
+export function asset(assetId: AssetId): Label {
+  return { "@type": "asset", value: { assetId } };
+}
+
+const LOCALE = /^[a-z]{2}-[A-Z]{2}$/;
+const textValue = s.object({
+  text: s.string({ min: 1 }),
+  locale: s.string({ pattern: LOCALE, expects: "a locale like en-US" }),
+});
+const assetValue = s.object({ assetId: s.oneOf(ASSETS, "an id of the global Alexa catalog, like Alexa.Setting.Opening") });
+const typed = s.object({ "@type": s.enum("text", "asset"), value: s.unknown() });
+const reserved: readonly string[] = RESERVED_WORDS;
+
+/** One friendly name. An asset has to be in the catalog, a text must not be a word Alexa keeps for itself. */
+export const label: Schema<Label> = {
+  expects: "a friendly name, from text() or asset()",
+  parse(input, path = "") {
+    const { "@type": type, value } = typed.parse(input, path);
+    if (type === "asset") return { "@type": type, value: assetValue.parse(value, at(path, "value")) };
+    const named = textValue.parse(value, at(path, "value"));
+    if (reserved.includes(named.text.trim().toLowerCase())) {
+      throw new SchemaError(at(path, "value.text"), `${JSON.stringify(named.text)} is a reserved word, not to be used as a friendly name`);
+    }
+    return { "@type": type, value: named };
+  },
+};
+
+/** The friendly names of an instance, a mode or a preset: at least one. */
+export const labels = s.array(label, { min: 1 });
+
+/** What the user is shown for a friendly name: the text, or the id of the asset. */
+export function shownAs(name: Label): string {
+  return name["@type"] === "text" ? name.value.text : name.value.assetId;
+}

src/registry/schema.ts

@@ -65,11 +65,13 @@ function shown(input: unknown): string {
   return text.length > 60 ? `${text.slice(0, 57)}...` : text;
 }
 
-function mismatch(path: string, expects: string, input: unknown): SchemaError {
+/** The error of a value that is not what a schema expects. */
+export function mismatch(path: string, expects: string, input: unknown): SchemaError {
   return new SchemaError(path, `expected ${expects}, got ${shown(input)}`);
 }
 
-const at = (path: string, key: string): string => (path ? `${path}.${key}` : key);
+/** The path of a key of the object at path. */
+export const at = (path: string, key: string): string => (path ? `${path}.${key}` : key);
 
 function isRecord(input: unknown): input is Record<string, unknown> {
   return typeof input === "object" && input !== null && !Array.isArray(input);
@@ -117,7 +119,12 @@ function literal<V extends string | number | boolean | null>(value: V): Schema<V
 }
 
 function enumeration<V extends readonly string[]>(...values: V): EnumSchema<V[number]> {
-  return { ...schema<V[number]>(values.join(" | "), (input) => values.includes(input as string)), values };
+  return oneOf(values, values.join(" | "));
+}
+
+/** One of a list too long to print in an error message: expects says what the list is. */
+function oneOf<V extends string>(values: readonly V[], expects: string): EnumSchema<V> {
+  return { ...schema<V>(expects, (input) => values.includes(input as V)), values };
 }
 
 function unknown(): Schema<unknown> {
@@ -229,6 +236,7 @@ export const s = {
   boolean,
   literal,
   enum: enumeration,
+  oneOf,
   unknown,
   optional,
   nullable,

src/registry/types.ts

@@ -10,6 +10,33 @@ export type Label =
   | { "@type": "text"; value: { text: string; locale: string } }
   | { "@type": "asset"; value: { assetId: string } };
 
+/** Phrases ("open", "lower") mapped to one directive (alexa-discovery-objects.html, "ActionMappings object"). */
+export interface ActionsToDirective {
+  "@type": "ActionsToDirective";
+  actions: string[];
+  directive: { name: string; payload?: Record<string, unknown> };
+}
+
+/** States ("open", "closed") mapped to a value of the property (same page, "StateMappings object"). */
+export interface StatesToValue {
+  "@type": "StatesToValue";
+  states: string[];
+  value: unknown;
+}
+
+/** States mapped to a range of values of the property. */
+export interface StatesToRange {
+  "@type": "StatesToRange";
+  states: string[];
+  range: { minimumValue: number; maximumValue: number };
+}
+
+/** The semantics object of a generic controller: at least one of the two lists. */
+export interface Semantics {
+  actionMappings?: ActionsToDirective[];
+  stateMappings?: Array<StatesToValue | StatesToRange>;
+}
+
 export interface PropertyDescriptor<V> {
   name: string;
   value: Schema<V>;
@@ -48,7 +75,7 @@ export interface CapabilityExtras {
 }
 
 /** A capability as declared on an endpoint: what discovery() and validate() of its descriptor are given. */
-export interface Declared<O = Record<string, unknown>> {
+export interface Declared<O = unknown> {
   readonly endpointId: string;
   readonly namespace: string;
   /** "" when the interface is declared without an instance. */
@@ -67,7 +94,7 @@ export interface EndpointView {
   readonly friendlyName: string;
   readonly description: string;
   readonly displayCategories: readonly string[];
-  /** The other capabilities of the endpoint. */
+  /** The capabilities declared on the endpoint before this one. */
   readonly capabilities: readonly Declared[];
 }