diff --git a/frontend/src/components/workspace/messages/message-list.tsx b/frontend/src/components/workspace/messages/message-list.tsx
index b5a5cff19..36565a31e 100644
--- a/frontend/src/components/workspace/messages/message-list.tsx
+++ b/frontend/src/components/workspace/messages/message-list.tsx
@@ -212,6 +212,7 @@ export function MessageList({
   canRegenerate = false,
   canBranch = false,
   enableSidecarActions = true,
+  sidecarSurface = false,
   initialScroll = "smooth",
   resizeScroll = "smooth",
 }: {
@@ -235,6 +236,7 @@ export function MessageList({
   canRegenerate?: boolean;
   canBranch?: boolean;
   enableSidecarActions?: boolean;
+  sidecarSurface?: boolean;
   initialScroll?: ConversationProps["initial"];
   resizeScroll?: ConversationProps["resize"];
 }) {
@@ -417,10 +419,18 @@ export function MessageList({
     if (!selectionToolbar) {
       return;
     }
-    sidecar?.addContextToConversation(selectionToolbar.context);
+    // On the sidecar surface, "add to conversation" targets the side chat's
+    // own composer (activeReferences) rather than the main composer's quotes,
+    // so the selected snippet is attached to the conversation the user is
+    // actually reading.
+    if (sidecarSurface) {
+      sidecar?.openContext(selectionToolbar.context);
+    } else {
+      sidecar?.addContextToConversation(selectionToolbar.context);
+    }
     window.getSelection()?.removeAllRanges();
     setSelectionToolbar(null);
-  }, [selectionToolbar, sidecar]);
+  }, [selectionToolbar, sidecar, sidecarSurface]);
 
   const handleAskSelectionInSidecar = useCallback(() => {
     if (!selectionToolbar) {
@@ -873,17 +883,19 @@ export function MessageList({
             <MessageCircleIcon className="size-3.5" />
             {t.sidecar.addToConversation}
           </Button>
-          <Button
-            className="h-8 rounded-full px-2.5 text-xs"
-            size="sm"
-            type="button"
-            variant="ghost"
-            onClick={handleAskSelectionInSidecar}
-            onMouseDown={(event) => event.preventDefault()}
-          >
-            <MessageSquarePlusIcon className="size-3.5" />
-            {t.sidecar.askInSideChat}
-          </Button>
+          {!sidecarSurface && (
+            <Button
+              className="h-8 rounded-full px-2.5 text-xs"
+              size="sm"
+              type="button"
+              variant="ghost"
+              onClick={handleAskSelectionInSidecar}
+              onMouseDown={(event) => event.preventDefault()}
+            >
+              <MessageSquarePlusIcon className="size-3.5" />
+              {t.sidecar.askInSideChat}
+            </Button>
+          )}
           <Button
             aria-label={t.common.close}
             className="size-8 rounded-full"
diff --git a/frontend/src/components/workspace/sidecar/sidecar-panel.tsx b/frontend/src/components/workspace/sidecar/sidecar-panel.tsx
index 2d449ab86..009dd15b8 100644
--- a/frontend/src/components/workspace/sidecar/sidecar-panel.tsx
+++ b/frontend/src/components/workspace/sidecar/sidecar-panel.tsx
@@ -478,6 +478,7 @@ export function SidecarPanel({ className }: { className?: string }) {
             loadMoreHistory={loadMoreHistory}
             isHistoryLoading={isHistoryLoading}
             tokenUsageInlineMode={tokenUsageInlineMode}
+            sidecarSurface
             initialScroll="instant"
             resizeScroll="instant"
           />
diff --git a/frontend/tests/e2e/sidecar-chat.spec.ts b/frontend/tests/e2e/sidecar-chat.spec.ts
index b40264608..cc8e7823a 100644
--- a/frontend/tests/e2e/sidecar-chat.spec.ts
+++ b/frontend/tests/e2e/sidecar-chat.spec.ts
@@ -105,6 +105,32 @@ async function selectTextAndClickToolbarButton(
   throw lastError;
 }
 
+async function expectSidecarSelectionToolbarActions(page: Page, text: string) {
+  let lastError: unknown;
+  for (let attempt = 0; attempt < 3; attempt += 1) {
+    try {
+      await selectTextOnPage(page, text, "sidecar-message-list");
+      const labels = await page.evaluate(() =>
+        Array.from(
+          document.querySelectorAll<HTMLButtonElement>(
+            "[data-sidecar-selection-toolbar] button",
+          ),
+        ).map((button) => button.textContent?.trim() ?? ""),
+      );
+      expect(labels.some((label) => /add to conversation/i.test(label))).toBe(
+        true,
+      );
+      expect(labels.some((label) => /ask in side chat/i.test(label))).toBe(
+        false,
+      );
+      return;
+    } catch (error) {
+      lastError = error;
+    }
+  }
+  throw lastError;
+}
+
 async function expectComposerHeightsEqual(page: Page) {
   const metrics = await page.evaluate(() => {
     const findFormByPlaceholder = (pattern: RegExp) => {
@@ -943,30 +969,16 @@ test.describe("Side chat", () => {
         .first(),
     ).toBeVisible();
 
+    // Selecting text inside the side chat itself only offers "Add to
+    // conversation" (no "Ask in side chat"), and the snippet attaches to the
+    // side chat's own composer rather than the main composer's quotes.
+    await expectSidecarSelectionToolbarActions(page, "Hello from DeerFlow!");
     await selectTextAndClickToolbarButton(
       page,
       "Hello from DeerFlow!",
       "Add to conversation",
       "sidecar-message-list",
     );
-    await expect(
-      mainInputForm.getByTestId("conversation-quote-attachment"),
-    ).toContainText("1 selected text fragment");
-    await expect(sidecarReference).toBeHidden();
-    await mainInputForm
-      .getByTestId("conversation-quote-attachment")
-      .getByRole("button", { name: /clear selected references/i })
-      .click();
-    await expect(
-      mainInputForm.getByTestId("conversation-quote-attachment"),
-    ).toBeHidden();
-
-    await selectTextAndClickToolbarButton(
-      page,
-      "Hello from DeerFlow!",
-      "Ask in side chat",
-      "sidecar-message-list",
-    );
     await expect(sidecarReference).toContainText("1 selected text fragment");
     await expect(
       mainInputForm.getByTestId("conversation-quote-attachment"),