diff --git a/desktop/src/features/home/lib/inboxViewHelpers.test.mjs b/desktop/src/features/home/lib/inboxViewHelpers.test.mjs
index c2eb0ce5f..ba7f371d2 100644
--- a/desktop/src/features/home/lib/inboxViewHelpers.test.mjs
+++ b/desktop/src/features/home/lib/inboxViewHelpers.test.mjs
@@ -3,6 +3,7 @@ import test from "node:test";
 
 import {
   getContextMessageDepth,
+  getInboxDefaultReplyParentEventId,
   getReactionTargetId,
   isInboxThreadContextEvent,
   matchesInboxFilter,
@@ -184,6 +185,44 @@ test("getContextMessageDepth does not loop forever on a cycle", () => {
   assert.equal(getContextMessageDepth(a, map), 1);
 });
 
+// --- getInboxDefaultReplyParentEventId ---
+
+function feedItem(id, tags = []) {
+  return {
+    id,
+    pubkey: "x",
+    createdAt: 0,
+    kind: 9,
+    tags,
+    content: "",
+    category: "activity",
+    channelId: "channel-a",
+    channelName: "bugs",
+  };
+}
+
+test("getInboxDefaultReplyParentEventId uses the selected item's parent for reply rows", () => {
+  assert.equal(
+    getInboxDefaultReplyParentEventId(
+      feedItem("latest-reply", [
+        ["h", "channel-a"],
+        ["e", "thread-root", "", "root"],
+        ["e", "parent-comment", "", "reply"],
+      ]),
+    ),
+    "parent-comment",
+  );
+});
+
+test("getInboxDefaultReplyParentEventId falls back to the selected item for roots", () => {
+  assert.equal(
+    getInboxDefaultReplyParentEventId(
+      feedItem("thread-root", [["h", "channel-a"]]),
+    ),
+    "thread-root",
+  );
+});
+
 // --- isInboxThreadContextEvent ---
 
 function channelEvent(id, tags = []) {
diff --git a/desktop/src/features/home/lib/inboxViewHelpers.ts b/desktop/src/features/home/lib/inboxViewHelpers.ts
index 94dcf871f..043fcd2e9 100644
--- a/desktop/src/features/home/lib/inboxViewHelpers.ts
+++ b/desktop/src/features/home/lib/inboxViewHelpers.ts
@@ -99,3 +99,14 @@ export function getReactionTargetId(tags: string[][]) {
 
   return null;
 }
+
+export function getInboxDefaultReplyParentEventId(item: FeedItem): string {
+  const thread = getThreadReference(item.tags);
+
+  // Inbox rows are grouped by thread and surface the latest activity. If the
+  // latest activity is itself a reply, sending from the bottom composer should
+  // continue the selected item's parent thread, not create a new child under
+  // that latest activity. Explicit per-message reply targets still override
+  // this default in InboxDetailPane.
+  return thread.parentId ?? thread.rootId ?? item.id;
+}
diff --git a/desktop/src/features/home/ui/InboxDetailPane.tsx b/desktop/src/features/home/ui/InboxDetailPane.tsx
index dd45d879f..e10c60aff 100644
--- a/desktop/src/features/home/ui/InboxDetailPane.tsx
+++ b/desktop/src/features/home/ui/InboxDetailPane.tsx
@@ -12,6 +12,7 @@ import {
   type InboxDisplayMessage,
   InboxMessageRow,
 } from "@/features/home/ui/InboxMessageRow";
+import { getInboxDefaultReplyParentEventId } from "@/features/home/lib/inboxViewHelpers";
 import { getThreadReference } from "@/features/messages/lib/threading";
 import type { TimelineMessage } from "@/features/messages/types";
 import { MessageComposer } from "@/features/messages/ui/MessageComposer";
@@ -210,7 +211,8 @@ export function InboxDetailPane({
         ];
   const replyTarget =
     displayMessages.find((message) => message.id === replyTargetId) ?? null;
-  const composerParentEventId = replyTarget?.id ?? item.id;
+  const composerParentEventId =
+    replyTarget?.id ?? getInboxDefaultReplyParentEventId(item.item);
   const composerReplyTarget =
     replyTarget && replyTarget.id !== item.id
       ? {
diff --git a/desktop/tests/e2e/smoke.spec.ts b/desktop/tests/e2e/smoke.spec.ts
index 7e47b76ae..d2b05f153 100644
--- a/desktop/tests/e2e/smoke.spec.ts
+++ b/desktop/tests/e2e/smoke.spec.ts
@@ -185,6 +185,80 @@ test("inbox feed shows channel and agent activity sections", async ({
   );
 });
 
+test("inbox composer replies to the selected thread parent, not the latest comment", async ({
+  page,
+}) => {
+  await page.goto("/");
+
+  const { firstReplyId, latestReplyId, latestReplyContent } =
+    await page.evaluate(() => {
+      const emitMessage = window.__BUZZ_E2E_EMIT_MOCK_MESSAGE__;
+      const pushFeedItem = window.__BUZZ_E2E_PUSH_MOCK_FEED_ITEM__;
+      if (!emitMessage || !pushFeedItem) {
+        throw new Error("Mock Buzz bridge helpers are unavailable.");
+      }
+
+      const root = emitMessage({
+        channelName: "general",
+        content: "Inbox parent target root",
+      });
+      const firstReply = emitMessage({
+        channelName: "general",
+        content: "Inbox parent target first reply",
+        parentEventId: root.id,
+      });
+      const latestReply = emitMessage({
+        channelName: "general",
+        content: "Inbox parent target latest reply",
+        parentEventId: firstReply.id,
+      });
+
+      pushFeedItem({
+        id: latestReply.id,
+        kind: latestReply.kind,
+        pubkey: latestReply.pubkey,
+        content: latestReply.content,
+        created_at: latestReply.created_at,
+        channel_id: "9a1657ac-f7aa-5db0-b632-d8bbeb6dfb50",
+        channel_name: "general",
+        tags: latestReply.tags,
+        category: "activity",
+      });
+
+      return {
+        firstReplyId: firstReply.id,
+        latestReplyId: latestReply.id,
+        latestReplyContent: latestReply.content,
+      };
+    });
+
+  const reply = `Inbox parent-target reply ${Date.now()}`;
+  const inboxList = page.getByTestId("home-inbox-list");
+  await expect(inboxList).toContainText(latestReplyContent);
+  await inboxList.getByText(latestReplyContent).click();
+  await expect(page.getByTestId("home-inbox-detail")).toContainText(
+    latestReplyContent,
+  );
+
+  await page.getByTestId("message-input").fill(reply);
+  await page.getByTestId("send-message").click();
+  await expect(page.getByTestId("home-inbox-detail")).toContainText(reply);
+
+  const sendPayload = await page.evaluate((content) => {
+    const entry = [...(window.__BUZZ_E2E_COMMAND_LOG__ ?? [])]
+      .reverse()
+      .find(
+        (candidate) =>
+          candidate.command === "send_channel_message" &&
+          (candidate.payload as { content?: string }).content === content,
+      );
+    return entry?.payload as { parentEventId?: string | null } | undefined;
+  }, reply);
+
+  expect(sendPayload?.parentEventId).toBe(firstReplyId);
+  expect(sendPayload?.parentEventId).not.toBe(latestReplyId);
+});
+
 test("opens a mocked forum activity item from the inbox feed", async ({
   page,
 }) => {