diff --git a/apps/app/src/components/thread/timeline/SelectableMessageProse.events.test.tsx b/apps/app/src/components/thread/timeline/SelectableMessageProse.events.test.tsx
index 923e35e3fd..88d0d2d3de 100644
--- a/apps/app/src/components/thread/timeline/SelectableMessageProse.events.test.tsx
+++ b/apps/app/src/components/thread/timeline/SelectableMessageProse.events.test.tsx
@@ -58,14 +58,19 @@ function waitForAnimationFrame(): Promise<void> {
 }
 
 describe("SelectableMessageProse", () => {
-  it("opts selectable prose out of the compact sidebar swipe gesture", () => {
+  it("keeps selectable prose available to the compact sidebar swipe gesture", () => {
     const { getByText } = render(
       <SelectableMessageProse>Selectable answer text</SelectableMessageProse>,
     );
 
     expect(
-      getByText("Selectable answer text").closest("[data-no-sidebar-swipe]"),
+      getByText("Selectable answer text").closest(
+        "[data-sidebar-swipe-selectable]",
+      ),
     ).not.toBeNull();
+    expect(
+      getByText("Selectable answer text").closest("[data-no-sidebar-swipe]"),
+    ).toBeNull();
   });
 
   it("reports a selection only after pointer release", async () => {
diff --git a/apps/app/src/components/thread/timeline/SelectableMessageProse.tsx b/apps/app/src/components/thread/timeline/SelectableMessageProse.tsx
index 784293000b..7617b91134 100644
--- a/apps/app/src/components/thread/timeline/SelectableMessageProse.tsx
+++ b/apps/app/src/components/thread/timeline/SelectableMessageProse.tsx
@@ -371,10 +371,9 @@ export function SelectableMessageProse({
     <div
       ref={nodeRef}
       className={className}
-      // The compact sidebar listens globally for a right-swipe from the main
-      // inset. A long-press text selection uses the same touch sequence, so
-      // keep sidebar swipe recognition out of selectable message prose.
-      data-no-sidebar-swipe
+      // Let compact-sidebar swipes begin over message prose, but give an
+      // expanded native text selection priority over the same touch sequence.
+      data-sidebar-swipe-selectable
     >
       {children}
     </div>
diff --git a/apps/app/src/components/ui/sidebar.test.tsx b/apps/app/src/components/ui/sidebar.test.tsx
index 2d7af40436..f0657be335 100644
--- a/apps/app/src/components/ui/sidebar.test.tsx
+++ b/apps/app/src/components/ui/sidebar.test.tsx
@@ -1,11 +1,63 @@
+// @vitest-environment jsdom
+
+import { cleanup, fireEvent, render, screen } from "@testing-library/react";
 import { renderToString } from "react-dom/server";
-import { describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { CompactViewportOverrideProvider } from "@bb/shared-ui/hooks/use-compact-viewport";
 import {
+  Sidebar,
+  SidebarInset,
   SidebarProvider,
   SidebarTrigger,
   useOptionalIsSidebarShowing,
 } from "./sidebar";
 
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+});
+
+function createTouch(clientX: number, clientY: number): Touch {
+  return { identifier: 1, clientX, clientY } as Touch;
+}
+
+function createTouchList(...touches: Touch[]): TouchList {
+  const touchList = {
+    length: touches.length,
+    item: (index: number) => touches[index] ?? null,
+  };
+  touches.forEach((touch, index) => {
+    Object.defineProperty(touchList, index, { value: touch });
+  });
+  return touchList as unknown as TouchList;
+}
+
+function fireTouch(
+  target: Element | Document | Window,
+  type: "touchstart" | "touchmove",
+  touch: Touch,
+) {
+  const event = new Event(type, { bubbles: true, cancelable: true });
+  Object.defineProperties(event, {
+    touches: { value: createTouchList(touch) },
+    changedTouches: { value: createTouchList(touch) },
+  });
+  fireEvent(target, event);
+}
+
+function renderSelectableSwipeHarness() {
+  render(
+    <CompactViewportOverrideProvider isCompactViewport>
+      <SidebarProvider>
+        <Sidebar>Sidebar content</Sidebar>
+        <SidebarInset>
+          <div data-sidebar-swipe-selectable>Selectable message prose</div>
+        </SidebarInset>
+      </SidebarProvider>
+    </CompactViewportOverrideProvider>,
+  );
+}
+
 function OptionalSidebarProbe() {
   const isShowing = useOptionalIsSidebarShowing();
   return <div data-sidebar-showing={String(isShowing)} />;
@@ -33,3 +85,39 @@ describe("SidebarTrigger", () => {
     expect(markup).not.toContain('aria-pressed="');
   });
 });
+
+describe("mobile sidebar text-selection arbitration", () => {
+  it("opens from a right swipe that starts over selectable message prose", () => {
+    renderSelectableSwipeHarness();
+    const prose = screen.getByText("Selectable message prose");
+
+    fireTouch(prose, "touchstart", createTouch(120, 160));
+    fireTouch(window, "touchmove", createTouch(260, 164));
+
+    expect(document.querySelector('[data-sidebar="panel"]')).not.toBeNull();
+  });
+
+  it("cancels a pending prose swipe when native text selection begins", () => {
+    let hasSelection = false;
+    let selectionNode: Node | null = null;
+    vi.spyOn(document, "getSelection").mockImplementation(() =>
+      hasSelection
+        ? ({
+            anchorNode: selectionNode,
+            focusNode: selectionNode,
+            isCollapsed: false,
+          } as Selection)
+        : null,
+    );
+    renderSelectableSwipeHarness();
+    const prose = screen.getByText("Selectable message prose");
+    selectionNode = prose.firstChild;
+
+    fireTouch(prose, "touchstart", createTouch(120, 160));
+    hasSelection = true;
+    fireEvent(document, new Event("selectionchange"));
+    fireTouch(window, "touchmove", createTouch(260, 164));
+
+    expect(document.querySelector('[data-sidebar="panel"]')).toBeNull();
+  });
+});
diff --git a/apps/app/src/components/ui/sidebar.tsx b/apps/app/src/components/ui/sidebar.tsx
index f28cca3e1d..00d9ce9226 100644
--- a/apps/app/src/components/ui/sidebar.tsx
+++ b/apps/app/src/components/ui/sidebar.tsx
@@ -51,6 +51,7 @@ type SidebarInsetSwipeSession = {
   lastTimeMs: number;
   velocityX: number;
   isDragging: boolean;
+  selectionRoot: Element | null;
 };
 
 const sidebarMobileWidthStyle: SidebarMobileWidthStyle = {
@@ -152,11 +153,13 @@ function createSidebarInsetSwipeSession({
   id,
   startX,
   startY,
+  selectionRoot,
 }: {
   kind: "pointer" | "touch";
   id: number;
   startX: number;
   startY: number;
+  selectionRoot: Element | null;
 }): SidebarInsetSwipeSession {
   const nowMs = Date.now();
   return {
@@ -170,6 +173,7 @@ function createSidebarInsetSwipeSession({
     lastTimeMs: nowMs,
     velocityX: 0,
     isDragging: false,
+    selectionRoot,
   };
 }
 
@@ -218,6 +222,26 @@ function isInsideHorizontalScrollRegion(target: Element): boolean {
   return false;
 }
 
+function getSidebarSwipeSelectionRoot(
+  target: EventTarget | null,
+): Element | null {
+  return target instanceof Element
+    ? target.closest("[data-sidebar-swipe-selectable]")
+    : null;
+}
+
+function hasExpandedTextSelectionWithin(root: Element): boolean {
+  const selection = root.ownerDocument.getSelection();
+  if (selection === null || selection.isCollapsed) {
+    return false;
+  }
+
+  return (
+    (selection.anchorNode !== null && root.contains(selection.anchorNode)) ||
+    (selection.focusNode !== null && root.contains(selection.focusNode))
+  );
+}
+
 function shouldIgnoreSidebarSwipeTarget(target: EventTarget | null): boolean {
   if (!(target instanceof Element)) {
     return false;
@@ -242,6 +266,14 @@ function shouldIgnoreSidebarSwipeTarget(target: EventTarget | null): boolean {
     return true;
   }
 
+  const selectionRoot = getSidebarSwipeSelectionRoot(target);
+  if (
+    selectionRoot !== null &&
+    hasExpandedTextSelectionWithin(selectionRoot)
+  ) {
+    return true;
+  }
+
   return isInsideHorizontalScrollRegion(target);
 }
 
@@ -1002,6 +1034,7 @@ const SidebarInset = React.forwardRef<
         id: touch.identifier,
         startX: touch.clientX,
         startY: touch.clientY,
+        selectionRoot: getSidebarSwipeSelectionRoot(event.target),
       });
 
       const removeListeners = () => {
@@ -1046,6 +1079,7 @@ const SidebarInset = React.forwardRef<
         id: event.pointerId,
         startX: event.clientX,
         startY: event.clientY,
+        selectionRoot: getSidebarSwipeSelectionRoot(event.target),
       });
 
       const removeListeners = () => {
@@ -1064,6 +1098,17 @@ const SidebarInset = React.forwardRef<
   );
 
   React.useEffect(() => {
+    const cancelSwipeForTextSelection = () => {
+      const selectionRoot = swipeSessionRef.current?.selectionRoot;
+      if (
+        selectionRoot !== null &&
+        selectionRoot !== undefined &&
+        hasExpandedTextSelectionWithin(selectionRoot)
+      ) {
+        clearSwipeSession();
+      }
+    };
+
     document.addEventListener("pointerdown", startPointerSwipe, {
       capture: true,
       passive: true,
@@ -1072,6 +1117,7 @@ const SidebarInset = React.forwardRef<
       capture: true,
       passive: true,
     });
+    document.addEventListener("selectionchange", cancelSwipeForTextSelection);
     return () => {
       document.removeEventListener("pointerdown", startPointerSwipe, {
         capture: true,
@@ -1079,8 +1125,12 @@ const SidebarInset = React.forwardRef<
       document.removeEventListener("touchstart", startTouchSwipe, {
         capture: true,
       });
+      document.removeEventListener(
+        "selectionchange",
+        cancelSwipeForTextSelection,
+      );
     };
-  }, [startPointerSwipe, startTouchSwipe]);
+  }, [clearSwipeSession, startPointerSwipe, startTouchSwipe]);
 
   const handleWheelSwipe = React.useCallback(
     (event: WheelEvent) => {