diff --git a/src/agents/subagent-announce-queue.test.ts b/src/agents/subagent-announce-queue.test.ts
index 2ed26841ef9..7f73f8343cb 100644
--- a/src/agents/subagent-announce-queue.test.ts
+++ b/src/agents/subagent-announce-queue.test.ts
@@ -29,6 +29,14 @@ function createRetryingSend() {
   return { send, prompts, waitForSecondAttempt };
 }
 
+function createCollectSendRecorder() {
+  const calls: AnnounceQueueItem[] = [];
+  const send = vi.fn(async (item: AnnounceQueueItem) => {
+    calls.push(item);
+  });
+  return { calls, send };
+}
+
 describe("subagent-announce-queue", () => {
   afterEach(() => {
     vi.useRealTimers();
@@ -122,6 +130,82 @@ describe("subagent-announce-queue", () => {
     expect(sender.prompts[1]).toContain("queued item two");
   });
 
+  it("splits collect-mode batches when target authorization context changes", async () => {
+    const sender = createCollectSendRecorder();
+    const settings = { mode: "collect", debounceMs: 0 } as const;
+    const origin = { channel: "slack", to: "channel:C123", accountId: "acct-1" };
+
+    enqueueAnnounce({
+      key: "announce:test:collect-auth-split",
+      item: {
+        prompt: "first child completed",
+        enqueuedAt: Date.now(),
+        sessionKey: "agent:main:slack:thread:a",
+        origin,
+      },
+      settings,
+      send: sender.send,
+    });
+    enqueueAnnounce({
+      key: "announce:test:collect-auth-split",
+      item: {
+        prompt: "second child completed",
+        enqueuedAt: Date.now(),
+        sessionKey: "agent:main:slack:thread:b",
+        origin,
+      },
+      settings,
+      send: sender.send,
+    });
+
+    await vi.waitFor(() => {
+      expect(sender.send).toHaveBeenCalledTimes(2);
+    });
+    expect(sender.calls.map((call) => call.sessionKey)).toEqual([
+      "agent:main:slack:thread:a",
+      "agent:main:slack:thread:b",
+    ]);
+    expect(sender.calls[0]?.prompt).toContain("first child completed");
+    expect(sender.calls[0]?.prompt).not.toContain("second child completed");
+    expect(sender.calls[1]?.prompt).toContain("second child completed");
+  });
+
+  it("keeps one collect-mode batch when target authorization context matches", async () => {
+    const sender = createCollectSendRecorder();
+    const settings = { mode: "collect", debounceMs: 0 } as const;
+    const origin = { channel: "slack", to: "channel:C123", accountId: "acct-1" };
+
+    enqueueAnnounce({
+      key: "announce:test:collect-auth-match",
+      item: {
+        prompt: "first child completed",
+        enqueuedAt: Date.now(),
+        sessionKey: "agent:main:slack:thread:a",
+        origin,
+      },
+      settings,
+      send: sender.send,
+    });
+    enqueueAnnounce({
+      key: "announce:test:collect-auth-match",
+      item: {
+        prompt: "second child completed",
+        enqueuedAt: Date.now(),
+        sessionKey: "agent:main:slack:thread:a",
+        origin,
+      },
+      settings,
+      send: sender.send,
+    });
+
+    await vi.waitFor(() => {
+      expect(sender.send).toHaveBeenCalledTimes(1);
+    });
+    expect(sender.calls[0]?.sessionKey).toBe("agent:main:slack:thread:a");
+    expect(sender.calls[0]?.prompt).toContain("first child completed");
+    expect(sender.calls[0]?.prompt).toContain("second child completed");
+  });
+
   it("waits until a busy parent session becomes idle before draining", async () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-01-01T00:00:00.000Z"));
diff --git a/src/agents/subagent-announce-queue.ts b/src/agents/subagent-announce-queue.ts
index 4d0d1d19d61..a1b5b653749 100644
--- a/src/agents/subagent-announce-queue.ts
+++ b/src/agents/subagent-announce-queue.ts
@@ -111,6 +111,39 @@ function getAnnounceQueue(
   return created;
 }
 
+function resolveAnnounceAuthorizationKey(item: AnnounceQueueItem): string {
+  return JSON.stringify([item.sessionKey, item.originKey ?? ""]);
+}
+
+function splitCollectItemsByAuthorization(items: AnnounceQueueItem[]): AnnounceQueueItem[][] {
+  if (items.length <= 1) {
+    return items.length === 0 ? [] : [items];
+  }
+
+  const groups: AnnounceQueueItem[][] = [];
+  let currentGroup: AnnounceQueueItem[] = [];
+  let currentKey: string | undefined;
+
+  for (const item of items) {
+    const itemKey = resolveAnnounceAuthorizationKey(item);
+    if (currentGroup.length === 0 || itemKey === currentKey) {
+      currentGroup.push(item);
+      currentKey = itemKey;
+      continue;
+    }
+
+    groups.push(currentGroup);
+    currentGroup = [item];
+    currentKey = itemKey;
+  }
+
+  if (currentGroup.length > 0) {
+    groups.push(currentGroup);
+  }
+
+  return groups;
+}
+
 function hasAnnounceCrossChannelItems(items: AnnounceQueueItem[]): boolean {
   return hasCrossChannelItems(items, (item) => {
     if (!item.origin) {
@@ -171,25 +204,34 @@ function scheduleAnnounceDrain(key: string) {
           }
           const items = queue.items.slice();
           const summary = previewQueueSummaryPrompt({ state: queue, noun: "announce" });
-          const prompt = buildCollectPrompt({
-            title: "[Queued announce messages while agent was busy]",
-            items,
-            summary,
-            renderItem: (item, idx) => `---\nQueued #${idx + 1}\n${item.prompt}`.trim(),
-          });
-          const internalEvents = items.flatMap((item) => item.internalEvents ?? []);
-          const last = items.at(-1);
-          if (!last) {
+          const authGroups = splitCollectItemsByAuthorization(items);
+          if (authGroups.length === 0) {
             break;
           }
-          await queue.send({
-            ...last,
-            prompt,
-            internalEvents: internalEvents.length > 0 ? internalEvents : last.internalEvents,
-          });
-          queue.items.splice(0, items.length);
-          if (summary) {
-            clearQueueSummaryState(queue);
+
+          let pendingSummary = summary;
+          for (const groupItems of authGroups) {
+            const prompt = buildCollectPrompt({
+              title: "[Queued announce messages while agent was busy]",
+              items: groupItems,
+              summary: pendingSummary,
+              renderItem: (item, idx) => `---\nQueued #${idx + 1}\n${item.prompt}`.trim(),
+            });
+            const internalEvents = groupItems.flatMap((item) => item.internalEvents ?? []);
+            const last = groupItems.at(-1);
+            if (!last) {
+              break;
+            }
+            await queue.send({
+              ...last,
+              prompt,
+              internalEvents: internalEvents.length > 0 ? internalEvents : last.internalEvents,
+            });
+            queue.items.splice(0, groupItems.length);
+            if (pendingSummary) {
+              clearQueueSummaryState(queue);
+              pendingSummary = undefined;
+            }
           }
           continue;
         }