refactor: Remove dead lastEventId from subscription schemas and document at-most-once delivery

Strip the unused .input(z.object({ lastEventId })) from all 6 subscription
procedures — the parameter was never consumed by eventBusIterable. Remove the
now-unused zod import. Add at-most-once delivery JSDoc to the EventBus interface
to make the real guarantee explicit. Add compliance comment above
onConversationUpdate noting what to wire when a conversation view is built.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/server/events/types.ts

@@ -684,6 +684,14 @@ export type DomainEventType = DomainEventMap['type'];
  *
  * All modules communicate through this interface.
  * Can be swapped for external systems (RabbitMQ, WebSocket forwarding) later.
+ *
+ * **Delivery guarantee: at-most-once.**
+ *
+ * Events emitted while a client is disconnected are permanently lost.
+ * Reconnecting clients receive only events emitted after reconnection.
+ * React Query's `refetchOnWindowFocus` and `refetchOnReconnect` compensate
+ * for missed mutations since the system uses query invalidation rather
+ * than incremental state.
  */
 export interface EventBus {
   /**

apps/server/trpc/routers/subscription.ts

@@ -2,7 +2,6 @@
  * Subscription Router — SSE event streams
  */
 
-import { z } from 'zod';
 import type { ProcedureBuilder } from '../trpc.js';
 import {
   eventBusIterable,
@@ -17,42 +16,40 @@ import {
 export function subscriptionProcedures(publicProcedure: ProcedureBuilder) {
   return {
     onEvent: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, ALL_EVENT_TYPES, signal);
       }),
 
     onAgentUpdate: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, AGENT_EVENT_TYPES, signal);
       }),
 
     onTaskUpdate: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, TASK_EVENT_TYPES, signal);
       }),
 
     onPageUpdate: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, PAGE_EVENT_TYPES, signal);
       }),
 
     onPreviewUpdate: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, PREVIEW_EVENT_TYPES, signal);
       }),
 
+    // NOTE: No frontend view currently displays inter-agent conversation data.
+    // When a conversation view is added, add to its useLiveUpdates call:
+    //   { prefix: 'conversation:', invalidate: ['<query-key>'] }
+    // and add the relevant mutation(s) to INVALIDATION_MAP in apps/web/src/lib/invalidation.ts.
     onConversationUpdate: publicProcedure
-      .input(z.object({ lastEventId: z.string().nullish() }).optional())
       .subscription(async function* (opts) {
         const signal = opts.signal ?? new AbortController().signal;
         yield* eventBusIterable(opts.ctx.eventBus, CONVERSATION_EVENT_TYPES, signal);