fix: shard Dispatcher DO per session instead of global singleton (#83)

* fix: shard Dispatcher DO per session instead of global singleton

* fix: use random UUID fallback for missing sessionId, soften locality comment

* worker: pass sessionId as query param on dispatcher DO upgrade

* worker: rename dispatcher URL query param sessionId -> meetingId to dodge CF auto-redaction

* worker: drop dispatcher URL session identifier (redacted by CF; DO reads ctx.id.name instead)

Author: rpurdel

worker/index.ts

@@ -229,10 +229,11 @@ async function handleWebSocketWithDispatcher(
 	containerWs.accept();
 
 	// Connect to Dispatcher DO via WebSocket (preferred - avoids subrequest limit)
+	// Each session gets its own DO instance for isolation.
 	let dispatcherWs: WebSocket | null = null;
 	if (env.DISPATCHER_DO) {
 		try {
-			const doId = env.DISPATCHER_DO.idFromName('global');
+			const doId = env.DISPATCHER_DO.idFromName(sessionId);
 			const stub = env.DISPATCHER_DO.get(doId);
 
 			const upgradeRequest = new Request('http://dispatcher/websocket', {
@@ -291,7 +292,7 @@ async function handleWebSocketWithDispatcher(
 		if (!env.DISPATCHER_DO || (sessionClosed && !allowDuringClose)) return null;
 
 		try {
-			const doId = env.DISPATCHER_DO.idFromName('global');
+			const doId = env.DISPATCHER_DO.idFromName(sessionId);
 			const stub = env.DISPATCHER_DO.get(doId);
 
 			const upgradeRequest = new Request('http://dispatcher/websocket', {
@@ -511,7 +512,7 @@ export default {
 		const useDispatcher = useDispatcherParam !== null
 			? useDispatcherParam === 'true'
 			: env.USE_DISPATCHER === 'true';
-		const sessionId = url.searchParams.get('sessionId') || 'unknown';
+		const sessionId = url.searchParams.get('sessionId') || crypto.randomUUID();
 
 		// Select which container instance to use based on routing strategy
 		const containerInstanceId = await selectContainerInstance(request, env);