diff --git a/apps/vela-gateway/README.md b/apps/vela-gateway/README.md
index 8941b2a..c1818f0 100644
--- a/apps/vela-gateway/README.md
+++ b/apps/vela-gateway/README.md
@@ -1,9 +1,10 @@
 # vela-gateway
 
-This workspace contains the Vela gateway service as a minimal Fastify app.
+This workspace contains the Vela gateway service as a minimal Fastify app with an initial WebSocket session skeleton.
 
 Current status:
 
 - Fastify server boots in the Yarn workspace
 - `/` and `/health` endpoints provide a runnable service baseline
-- WebSocket session orchestration remains a later increment
+- WebSocket session skeleton wiring now exists
+- Full WebSocket session orchestration and behavior remain future work
diff --git a/apps/vela-gateway/package.json b/apps/vela-gateway/package.json
index 1cd96b2..8873714 100644
--- a/apps/vela-gateway/package.json
+++ b/apps/vela-gateway/package.json
@@ -6,7 +6,8 @@
   "scripts": {
     "dev": "node --watch src/index.js",
     "start": "node src/index.js",
-    "build": "node -e \"console.log('vela-gateway: no build step required')\""
+    "build": "node -e \"console.log('vela-gateway: no build step required')\"",
+    "test": "node --test"
   },
 	"dependencies": {
 		"@vela/protocol": "0.0.0",
diff --git a/apps/vela-gateway/src/index.js b/apps/vela-gateway/src/index.js
index c5b8d2d..5fa012a 100644
--- a/apps/vela-gateway/src/index.js
+++ b/apps/vela-gateway/src/index.js
@@ -1,12 +1,294 @@
 const Fastify = require('fastify');
+const crypto = require('node:crypto');
 const {
 	CLIENT_EVENT_TYPES,
 	PROTOCOL_PACKAGE_NAME,
-	SERVER_EVENT_TYPES
+	SERVER_EVENT_TYPES,
+	createMessageEnvelope,
+	isClientEventType,
+	isMessageEnvelope
 } = require('@vela/protocol');
 
+const WEBSOCKET_ROUTE = '/ws';
+const WEBSOCKET_GUID = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11';
+
+function createSessionRecord() {
+	return {
+		id: crypto.randomUUID(),
+		connectedAt: new Date().toISOString(),
+		state: 'idle',
+		audioChunkCount: 0,
+		started: false
+	};
+}
+
+function createWebSocketAcceptValue(key) {
+	return crypto.createHash('sha1').update(`${key}${WEBSOCKET_GUID}`).digest('base64');
+}
+
+function encodeWebSocketFrame(payload, { opcode = 0x1 } = {}) {
+	const body = Buffer.from(payload);
+	const length = body.length;
+
+	if (length >= 65536) {
+		throw new Error('payload too large for minimal websocket implementation');
+	}
+
+	if (length < 126) {
+		return Buffer.concat([Buffer.from([0x80 | opcode, length]), body]);
+	}
+
+	const header = Buffer.alloc(4);
+	header[0] = 0x80 | opcode;
+	header[1] = 126;
+	header.writeUInt16BE(length, 2);
+
+	return Buffer.concat([header, body]);
+}
+
+function decodeWebSocketFrames(buffer) {
+	const messages = [];
+	let offset = 0;
+
+	while (offset + 2 <= buffer.length) {
+		const firstByte = buffer[offset];
+		const secondByte = buffer[offset + 1];
+		const fin = (firstByte & 0x80) !== 0;
+		const opcode = firstByte & 0x0f;
+		const masked = (secondByte & 0x80) !== 0;
+		let payloadLength = secondByte & 0x7f;
+		let headerLength = 2;
+
+		if (!fin) {
+			throw new Error('fragmented websocket frames are not supported');
+		}
+
+		if (payloadLength === 126) {
+			if (offset + 4 > buffer.length) {
+				break;
+			}
+
+			payloadLength = buffer.readUInt16BE(offset + 2);
+			headerLength = 4;
+		} else if (payloadLength === 127) {
+			throw new Error('64-bit websocket payloads are not supported');
+		}
+
+		if (!masked) {
+			throw new Error('client websocket frames must be masked');
+		}
+
+		const maskOffset = offset + headerLength;
+		const payloadOffset = maskOffset + 4;
+		const frameLength = headerLength + 4 + payloadLength;
+
+		if (offset + frameLength > buffer.length) {
+			break;
+		}
+
+		const mask = buffer.subarray(maskOffset, payloadOffset);
+		const payload = Buffer.from(buffer.subarray(payloadOffset, payloadOffset + payloadLength));
+
+		for (let index = 0; index < payload.length; index += 1) {
+			payload[index] ^= mask[index % 4];
+		}
+
+		messages.push({ opcode, payload });
+		offset += frameLength;
+	}
+
+	return {
+		messages,
+		remaining: buffer.subarray(offset)
+	};
+}
+
+function sendSocketMessage(socket, type, payload) {
+	const frame = encodeWebSocketFrame(JSON.stringify(createMessageEnvelope(type, payload)));
+	socket.write(frame);
+}
+
+function sendSocketError(socket, code, message, retryable = true) {
+	sendSocketMessage(socket, 'error', { code, message, retryable });
+}
+
+function updateSessionState(socket, session, nextState) {
+	if (session.state === nextState) {
+		return;
+	}
+
+	session.state = nextState;
+	sendSocketMessage(socket, 'session.state', { value: session.state });
+}
+
+function validateClientMessage(message) {
+	if (!isMessageEnvelope(message)) {
+		return 'message must match the shared envelope shape';
+	}
+
+	if (!isClientEventType(message.type)) {
+		return `unsupported client event type: ${message.type}`;
+	}
+
+	if (!message.payload || typeof message.payload !== 'object' || Array.isArray(message.payload)) {
+		return 'message payload must be an object';
+	}
+
+	if (message.type === 'input_audio.append' && typeof message.payload.chunk !== 'string') {
+		return 'input_audio.append payload.chunk must be a string';
+	}
+
+	return null;
+}
+
+function handleClientMessage(socket, session, rawMessage) {
+	let message;
+
+	try {
+		message = JSON.parse(rawMessage);
+	} catch {
+		sendSocketError(socket, 'invalid_json', 'Message must be valid JSON.');
+		return;
+	}
+
+	const validationError = validateClientMessage(message);
+
+	if (validationError) {
+		sendSocketError(socket, 'invalid_message', validationError);
+		return;
+	}
+
+	switch (message.type) {
+		case 'session.start':
+			session.started = true;
+			sendSocketMessage(socket, 'session.ready', { sessionId: session.id });
+			sendSocketMessage(socket, 'session.state', { value: session.state });
+			break;
+		case 'input_audio.append':
+			session.audioChunkCount += 1;
+			updateSessionState(socket, session, 'listening');
+			break;
+		case 'input_audio.commit':
+			session.audioChunkCount = 0;
+			updateSessionState(socket, session, 'idle');
+			break;
+		case 'response.cancel':
+			session.audioChunkCount = 0;
+			updateSessionState(socket, session, 'idle');
+			break;
+		default:
+			sendSocketError(socket, 'unhandled_message', `No handler is implemented for ${message.type}.`);
+	}
+}
+
+function registerWebSocketSessionRoute(app) {
+	app.get(WEBSOCKET_ROUTE, async (_request, reply) => {
+		reply.code(426);
+		return {
+			service: 'vela-gateway',
+			transport: 'websocket',
+			route: WEBSOCKET_ROUTE,
+			protocol: PROTOCOL_PACKAGE_NAME,
+			messageEnvelope: 'MessageEnvelope<{type, payload}>',
+			note: 'Connect with a WebSocket client to establish an ephemeral session.'
+		};
+	});
+
+	app.server.on('upgrade', (request, socket) => {
+		const origin = `http://${request.headers.host ?? 'localhost'}`;
+		const { pathname } = new URL(request.url ?? '/', origin);
+
+		if (pathname !== WEBSOCKET_ROUTE) {
+			socket.destroy();
+			return;
+		}
+
+		if ((request.headers.upgrade ?? '').toLowerCase() !== 'websocket') {
+			socket.destroy();
+			return;
+		}
+
+		const websocketKey = request.headers['sec-websocket-key'];
+
+		if (typeof websocketKey !== 'string') {
+			socket.destroy();
+			return;
+		}
+
+		const session = createSessionRecord();
+		app.websocketSessions.set(session.id, session);
+
+		socket.write(
+			[
+				'HTTP/1.1 101 Switching Protocols',
+				'Upgrade: websocket',
+				'Connection: Upgrade',
+				`Sec-WebSocket-Accept: ${createWebSocketAcceptValue(websocketKey)}`,
+				'\r\n'
+			].join('\r\n')
+		);
+
+		app.log.info({ sessionId: session.id, route: WEBSOCKET_ROUTE }, 'websocket session connected');
+		sendSocketMessage(socket, 'session.ready', { sessionId: session.id });
+		sendSocketMessage(socket, 'session.state', { value: session.state });
+
+		let frameBuffer = Buffer.alloc(0);
+		let closed = false;
+
+		const cleanup = () => {
+			if (closed) {
+				return;
+			}
+
+			closed = true;
+			app.websocketSessions.delete(session.id);
+			app.log.info({ sessionId: session.id }, 'websocket session disconnected');
+		};
+
+		socket.on('data', (chunk) => {
+			frameBuffer = Buffer.concat([frameBuffer, chunk]);
+
+			try {
+				const decoded = decodeWebSocketFrames(frameBuffer);
+				frameBuffer = decoded.remaining;
+
+				for (const message of decoded.messages) {
+					if (message.opcode === 0x8) {
+						socket.end(encodeWebSocketFrame('', { opcode: 0x8 }));
+						return;
+					}
+
+					if (message.opcode === 0x9) {
+						socket.write(encodeWebSocketFrame(message.payload, { opcode: 0xA }));
+						continue;
+					}
+
+					if (message.opcode !== 0x1) {
+						sendSocketError(socket, 'unsupported_message', 'Only text messages are supported.');
+						continue;
+					}
+
+					handleClientMessage(socket, session, message.payload.toString('utf8'));
+				}
+			} catch (error) {
+				app.log.warn({ err: error, sessionId: session.id }, 'closing malformed websocket session');
+				sendSocketError(socket, 'invalid_frame', error.message, false);
+				socket.end(encodeWebSocketFrame('', { opcode: 0x8 }));
+			}
+		});
+
+		socket.on('end', cleanup);
+		socket.on('close', cleanup);
+		socket.on('error', (error) => {
+			app.log.warn({ err: error, sessionId: session.id }, 'websocket session socket error');
+			cleanup();
+		});
+	});
+}
+
 function buildServer() {
 	const app = Fastify({ logger: true });
+	app.decorate('websocketSessions', new Map());
 
 	app.get('/', async () => ({
 		service: 'vela-gateway',
@@ -21,6 +303,7 @@ function buildServer() {
 	}));
 
 	app.get('/health', async () => ({ status: 'ok' }));
+	registerWebSocketSessionRoute(app);
 
 	return app;
 }
diff --git a/apps/vela-gateway/test/websocket-session.test.js b/apps/vela-gateway/test/websocket-session.test.js
new file mode 100644
index 0000000..8a3a577
--- /dev/null
+++ b/apps/vela-gateway/test/websocket-session.test.js
@@ -0,0 +1,328 @@
+const assert = require('node:assert/strict');
+const crypto = require('node:crypto');
+const net = require('node:net');
+const test = require('node:test');
+
+const {
+	CLIENT_EVENT_TYPES,
+	PROTOCOL_PACKAGE_NAME,
+	SERVER_EVENT_TYPES
+} = require('@vela/protocol');
+
+const { buildServer } = require('../src/index.js');
+
+function encodeMaskedTextFrame(payload) {
+	const body = Buffer.from(payload);
+	const mask = crypto.randomBytes(4);
+	const length = body.length;
+	let header;
+
+	if (length < 126) {
+		header = Buffer.from([0x81, 0x80 | length]);
+	} else {
+		header = Buffer.alloc(4);
+		header[0] = 0x81;
+		header[1] = 0x80 | 126;
+		header.writeUInt16BE(length, 2);
+	}
+
+	const maskedBody = Buffer.from(body);
+
+	for (let index = 0; index < maskedBody.length; index += 1) {
+		maskedBody[index] ^= mask[index % 4];
+	}
+
+	return Buffer.concat([header, mask, maskedBody]);
+}
+
+function encodeMaskedCloseFrame() {
+	return Buffer.from([0x88, 0x80, 0x00, 0x00, 0x00, 0x00]);
+}
+
+function decodeServerFrames(buffer) {
+	const messages = [];
+	let offset = 0;
+
+	while (offset + 2 <= buffer.length) {
+		const firstByte = buffer[offset];
+		const secondByte = buffer[offset + 1];
+		const opcode = firstByte & 0x0f;
+		let payloadLength = secondByte & 0x7f;
+		let headerLength = 2;
+
+		if ((secondByte & 0x80) !== 0) {
+			throw new Error('server frames must not be masked');
+		}
+
+		if (payloadLength === 126) {
+			if (offset + 4 > buffer.length) {
+				break;
+			}
+
+			payloadLength = buffer.readUInt16BE(offset + 2);
+			headerLength = 4;
+		} else if (payloadLength === 127) {
+			throw new Error('64-bit payloads are not supported in tests');
+		}
+
+		const frameLength = headerLength + payloadLength;
+
+		if (offset + frameLength > buffer.length) {
+			break;
+		}
+
+		const payload = buffer.subarray(offset + headerLength, offset + frameLength);
+		messages.push({ opcode, payload: payload.toString('utf8') });
+		offset += frameLength;
+	}
+
+	return {
+		messages,
+		remaining: buffer.subarray(offset)
+	};
+}
+
+async function startServer() {
+	const app = buildServer();
+	await app.listen({ port: 0, host: '127.0.0.1' });
+	const address = app.server.address();
+
+	return {
+		app,
+		port: address.port,
+		async close() {
+			await app.close();
+		}
+	};
+}
+
+function waitForCondition(check, timeout = 1000) {
+	return new Promise((resolve, reject) => {
+		const start = Date.now();
+
+		const poll = () => {
+			if (check()) {
+				resolve();
+				return;
+			}
+
+			if (Date.now() - start >= timeout) {
+				reject(new Error('timed out waiting for condition'));
+				return;
+			}
+
+			setTimeout(poll, 10);
+		};
+
+		poll();
+	});
+}
+
+async function connectWebSocket(port) {
+	const socket = net.createConnection({ host: '127.0.0.1', port });
+	let handshakeComplete = false;
+	let handshakeBuffer = Buffer.alloc(0);
+	let frameBuffer = Buffer.alloc(0);
+	const queue = [];
+	const waiters = [];
+
+	const pushMessage = (message) => {
+		if (waiters.length > 0) {
+			waiters.shift()(message);
+			return;
+		}
+
+		queue.push(message);
+	};
+
+	socket.on('data', (chunk) => {
+		let data = chunk;
+
+		if (!handshakeComplete) {
+			handshakeBuffer = Buffer.concat([handshakeBuffer, chunk]);
+			const separatorIndex = handshakeBuffer.indexOf('\r\n\r\n');
+
+			if (separatorIndex === -1) {
+				return;
+			}
+
+			handshakeComplete = true;
+			const response = handshakeBuffer.subarray(0, separatorIndex).toString('utf8');
+			assert.match(response, /101 Switching Protocols/);
+			data = handshakeBuffer.subarray(separatorIndex + 4);
+			handshakeBuffer = Buffer.alloc(0);
+		}
+
+		if (data.length === 0) {
+			return;
+		}
+
+		frameBuffer = Buffer.concat([frameBuffer, data]);
+
+		const decoded = decodeServerFrames(frameBuffer);
+		frameBuffer = decoded.remaining;
+
+		for (const message of decoded.messages) {
+			if (message.opcode === 0x1) {
+				pushMessage(JSON.parse(message.payload));
+			} else {
+				pushMessage({ opcode: message.opcode, payload: message.payload });
+			}
+		}
+	});
+
+	await new Promise((resolve, reject) => {
+		socket.once('connect', resolve);
+		socket.once('error', reject);
+		socket.write(
+			[
+				'GET /ws HTTP/1.1',
+				'Host: 127.0.0.1',
+				'Upgrade: websocket',
+				'Connection: Upgrade',
+				'Sec-WebSocket-Version: 13',
+				`Sec-WebSocket-Key: ${crypto.randomBytes(16).toString('base64')}`,
+				'\r\n'
+			].join('\r\n')
+		);
+	});
+
+	return {
+		socket,
+		nextMessage(timeout = 1000) {
+			if (queue.length > 0) {
+				return Promise.resolve(queue.shift());
+			}
+
+			return new Promise((resolve, reject) => {
+				const timer = setTimeout(() => {
+					const waiterIndex = waiters.indexOf(onMessage);
+					if (waiterIndex >= 0) {
+						waiters.splice(waiterIndex, 1);
+					}
+					reject(new Error('timed out waiting for websocket message'));
+				}, timeout);
+
+				const onMessage = (message) => {
+					clearTimeout(timer);
+					resolve(message);
+				};
+
+				waiters.push(onMessage);
+			});
+		},
+		sendJson(message) {
+			socket.write(encodeMaskedTextFrame(JSON.stringify(message)));
+		},
+		sendText(payload) {
+			socket.write(encodeMaskedTextFrame(payload));
+		},
+		async close() {
+			await new Promise((resolve) => {
+				socket.once('close', resolve);
+				socket.write(encodeMaskedCloseFrame());
+			});
+		}
+	};
+}
+
+test('http routes stay available and preserve the root response contract', async () => {
+	const server = await startServer();
+
+	try {
+		const rootResponse = await server.app.inject({ method: 'GET', url: '/' });
+		assert.equal(rootResponse.statusCode, 200);
+		assert.deepEqual(rootResponse.json(), {
+			service: 'vela-gateway',
+			status: 'ok',
+			transport: 'http',
+			next: 'websocket session skeleton',
+			protocol: {
+				package: PROTOCOL_PACKAGE_NAME,
+				clientEventCount: CLIENT_EVENT_TYPES.length,
+				serverEventCount: SERVER_EVENT_TYPES.length
+			}
+		});
+
+		const healthResponse = await server.app.inject({ method: 'GET', url: '/health' });
+		assert.equal(healthResponse.statusCode, 200);
+		assert.deepEqual(healthResponse.json(), { status: 'ok' });
+
+		const wsDocResponse = await server.app.inject({ method: 'GET', url: '/ws' });
+		assert.equal(wsDocResponse.statusCode, 426);
+		assert.equal(wsDocResponse.json().route, '/ws');
+	} finally {
+		await server.close();
+	}
+});
+
+test('websocket connect creates and cleans up an ephemeral session', async () => {
+	const server = await startServer();
+
+	try {
+		const client = await connectWebSocket(server.port);
+		const readyMessage = await client.nextMessage();
+		assert.equal(readyMessage.type, 'session.ready');
+		assert.equal(typeof readyMessage.payload.sessionId, 'string');
+		assert.equal(server.app.websocketSessions.size, 1);
+
+		const stateMessage = await client.nextMessage();
+		assert.deepEqual(stateMessage, {
+			type: 'session.state',
+			payload: { value: 'idle' }
+		});
+
+		await client.close();
+		await waitForCondition(() => server.app.websocketSessions.size === 0);
+		assert.equal(server.app.websocketSessions.size, 0);
+	} finally {
+		await server.close();
+	}
+});
+
+test('websocket handles valid and invalid client messages safely', async () => {
+	const server = await startServer();
+
+	try {
+		const client = await connectWebSocket(server.port);
+		await client.nextMessage();
+		await client.nextMessage();
+
+		client.sendJson({ type: 'input_audio.append', payload: { chunk: 'Zm9v' } });
+		assert.deepEqual(await client.nextMessage(), {
+			type: 'session.state',
+			payload: { value: 'listening' }
+		});
+
+		client.sendJson({ type: 'input_audio.commit', payload: {} });
+		assert.deepEqual(await client.nextMessage(), {
+			type: 'session.state',
+			payload: { value: 'idle' }
+		});
+
+		client.sendText('{bad json');
+		assert.deepEqual(await client.nextMessage(), {
+			type: 'error',
+			payload: {
+				code: 'invalid_json',
+				message: 'Message must be valid JSON.',
+				retryable: true
+			}
+		});
+
+		client.sendJson({ type: 'unknown.event', payload: {} });
+		assert.deepEqual(await client.nextMessage(), {
+			type: 'error',
+			payload: {
+				code: 'invalid_message',
+				message: 'unsupported client event type: unknown.event',
+				retryable: true
+			}
+		});
+
+		assert.equal(server.app.websocketSessions.size, 1);
+		await client.close();
+	} finally {
+		await server.close();
+	}
+});
diff --git a/docs/architecture.md b/docs/architecture.md
index ba355e3..f612609 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -65,7 +65,7 @@ The current implementation is a minimal SvelteKit app with a single starter page
 - Fastify (Node)
 - WebSocket-based session layer
 
-The current implementation is a minimal Fastify service with `/` and `/health` HTTP endpoints. The WebSocket session layer is a later increment.
+The current implementation is a minimal Fastify service with `/`, `/health`, and a documented `/ws` WebSocket session endpoint. The gateway keeps one ephemeral in-memory session record per live socket connection and removes it on disconnect.
 
 #### Responsibilities
 
@@ -77,6 +77,14 @@ The current implementation is a minimal Fastify service with `/` and `/health` H
 - TTS orchestration
 - event streaming
 
+#### Current WebSocket skeleton
+
+- `GET /ws` documents the route for plain HTTP clients and returns `426 Upgrade Required`
+- WebSocket upgrades on `/ws` create an ephemeral session immediately
+- the gateway sends `session.ready` followed by `session.state` (`idle`) when the socket is established
+- valid minimal client events can move the session between `idle` and `listening`
+- invalid JSON, invalid envelopes, and malformed frames are handled defensively so the process stays up
+
 ## Voice Pipeline
 
 ```text
diff --git a/docs/backlog.md b/docs/backlog.md
index 2881d77..f2282c3 100644
--- a/docs/backlog.md
+++ b/docs/backlog.md
@@ -34,7 +34,7 @@ Prove the end-to-end interaction model with mocked or stubbed providers.
 - [x] bootstrap `vela-ui` as a runnable SvelteKit app in the Yarn workspace
 - [x] bootstrap `vela-gateway` as a runnable Fastify app in the Yarn workspace
 - create a minimal UI with mic control, state indicator, transcript, and response text
-- create a gateway WebSocket session skeleton
+- [x] create a gateway WebSocket session skeleton
 - implement mocked STT flow for partial and final transcript events
 - implement mocked LLM response streaming
 - implement stubbed audio playback or placeholder TTS output
@@ -180,5 +180,6 @@ Polish the system after the core voice loop is reliable.
 
 - `apps/vela-ui` now boots as a minimal SvelteKit app with a starter page
 - `apps/vela-gateway` now boots as a minimal Fastify app with `/` and `/health` endpoints
+- `apps/vela-gateway` now exposes a minimal `/ws` WebSocket session skeleton with ephemeral in-memory sessions and defensive message handling
 - `apps/vela-protocol` now provides the shared WebSocket event contract for the UI and gateway
 - backend framework choice is now concrete: Fastify
diff --git a/docs/integrations.md b/docs/integrations.md
index fd37191..c092447 100644
--- a/docs/integrations.md
+++ b/docs/integrations.md
@@ -4,7 +4,16 @@
 
 - `vela-ui` is implemented as a SvelteKit application
 - `vela-gateway` is implemented as a Fastify service
-- current integration work beyond the gateway HTTP baseline remains future implementation
+- `vela-gateway` now exposes `/ws` as the minimal WebSocket session entrypoint using the shared `@vela/protocol` contract
+- current integration work beyond the gateway WebSocket/session baseline remains future implementation
+
+## Gateway Session Contract
+
+- transport: WebSocket on `/ws`
+- session storage: in-memory only, one ephemeral record per live connection
+- message format: `@vela/protocol` `MessageEnvelope<{ type, payload }>`
+- current server behavior: acknowledge connect with `session.ready` and `session.state`
+- safety baseline: invalid JSON, invalid envelopes, and malformed frames return protocol errors or close that socket without taking down the service
 
 ## STT (Speech-to-Text)
 
diff --git a/docs/protocol.md b/docs/protocol.md
index d6fce51..fa2f346 100644
--- a/docs/protocol.md
+++ b/docs/protocol.md
@@ -5,6 +5,12 @@
 The shared code-level contract lives in the Yarn workspace package `@vela/protocol` so both the
 gateway and UI import the same event names and envelope shape.
 
+Current gateway baseline:
+
+- WebSocket endpoint: `/ws`
+- the gateway sends `session.ready` and `session.state` immediately after a successful socket upgrade
+- the gateway accepts JSON text messages only in the shared envelope shape
+
 ## WebSocket Message Envelope
 
 Every WebSocket message uses one envelope format:
@@ -40,6 +46,17 @@ type ClientEvent =
 - `input_audio.commit` marks the current buffered user turn as ready for downstream processing
 - `response.cancel` interrupts the active listen/think/speak flow
 
+### Current skeleton behavior
+
+- on connect, the gateway creates an ephemeral in-memory session and emits `session.ready` plus `session.state`
+- `session.start` is accepted as an idempotent session acknowledgment and re-sends readiness/state
+- `input_audio.append` updates the ephemeral session record and moves the session to `listening`
+- `input_audio.commit` resets the minimal buffered state and returns the session to `idle`
+- `response.cancel` resets the minimal session state back to `idle`
+- malformed JSON produces `error` with code `invalid_json`
+- invalid envelopes or unsupported client event names produce `error` with code `invalid_message`
+- malformed WebSocket frames are rejected without crashing the gateway process
+
 ### Server → Client
 
 ```ts