feat(09-01): build enhanced event batcher with granular event coalescing

- Add createDomainEventBatcher with entity type+ID dedup within 50ms window
- Domain-changed overrides all granular events in same batch
- More than 10 unique entities triggers full refresh fallback
- Delete action preserved during coalescing (last-write-wins otherwise)
- Unknown event types trigger full refresh as safety fallback
- Legacy createEventBatcher preserved for backward compatibility
- Add 12 comprehensive tests for all coalescing behaviors

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/renderer/lib/ipc-batcher.ts

@@ -1,3 +1,7 @@
+import type { DesktopEvent } from "@shared/types";
+
+// --- Legacy simple batcher -- kept for backward compatibility ---
+
 type BatchCallback = () => void;
 
 export function createEventBatcher(callback: BatchCallback, windowMs = 50) {
@@ -28,3 +32,94 @@ export function createEventBatcher(callback: BatchCallback, windowMs = 50) {
 
   return { schedule, flush, dispose };
 }
+
+// --- Enhanced batcher for granular events ---
+
+export interface GranularEventEntry {
+  type: string;
+  entityId: string;
+  action: string;
+}
+
+const MAX_GRANULAR_EVENTS = 10;
+
+export function entityKeyFromEvent(event: DesktopEvent): GranularEventEntry | null {
+  switch (event.type) {
+    case "task-updated":
+      return { type: "task-updated", entityId: event.taskId, action: event.action };
+    case "run-updated":
+      return { type: "run-updated", entityId: event.runId, action: event.action };
+    case "approval-updated":
+      return { type: "approval-updated", entityId: event.approvalId, action: event.action };
+    case "agent-updated":
+      return { type: "agent-updated", entityId: event.agentId, action: event.action };
+    case "budget-changed":
+      return { type: "budget-changed", entityId: event.companyId, action: "changed" };
+    default:
+      return null;
+  }
+}
+
+export function createDomainEventBatcher(
+  onFullRefresh: () => void,
+  onGranularBatch: (events: GranularEventEntry[]) => void,
+  windowMs = 50,
+  maxGranular = MAX_GRANULAR_EVENTS,
+) {
+  let timer: ReturnType<typeof setTimeout> | null = null;
+  let hasDomainChanged = false;
+  const pending = new Map<string, GranularEventEntry>();
+
+  function push(event: DesktopEvent) {
+    if (event.type === "domain-changed") {
+      hasDomainChanged = true;
+    } else {
+      const entry = entityKeyFromEvent(event);
+      if (entry) {
+        const key = `${entry.type}:${entry.entityId}`;
+        const existing = pending.get(key);
+        // If any event in window has action "deleted", preserve that action
+        if (existing && existing.action === "deleted" && entry.action !== "deleted") {
+          // Keep the delete -- it takes priority
+        } else {
+          pending.set(key, entry);
+        }
+      } else {
+        // Unknown event type -- treat as domain-changed for safety (per D-05)
+        hasDomainChanged = true;
+      }
+    }
+    if (timer === null) {
+      timer = setTimeout(flushInternal, windowMs);
+    }
+  }
+
+  function flushInternal() {
+    timer = null;
+    if (hasDomainChanged || pending.size > maxGranular) {
+      onFullRefresh();
+    } else if (pending.size > 0) {
+      onGranularBatch([...pending.values()]);
+    }
+    hasDomainChanged = false;
+    pending.clear();
+  }
+
+  function flush() {
+    if (timer !== null) {
+      clearTimeout(timer);
+      flushInternal();
+    }
+  }
+
+  function dispose() {
+    if (timer !== null) {
+      clearTimeout(timer);
+      timer = null;
+    }
+    hasDomainChanged = false;
+    pending.clear();
+  }
+
+  return { push, flush, dispose };
+}