diff --git a/apps/web/src/hooks/useResizableWidth.test.tsx b/apps/web/src/hooks/useResizableWidth.test.tsx
new file mode 100644
index 000000000000..204e8fc7e4dd
--- /dev/null
+++ b/apps/web/src/hooks/useResizableWidth.test.tsx
@@ -0,0 +1,127 @@
+import { act, useLayoutEffect, type PointerEvent } from "react";
+import { create, type ReactTestRenderer } from "react-test-renderer";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vite-plus/test";
+
+import { useResizableWidth } from "./useResizableWidth";
+
+let renderer: ReactTestRenderer;
+let result: ReturnType<typeof useResizableWidth>;
+let captured = false;
+const target = {
+  setPointerCapture: () => {
+    captured = true;
+  },
+  hasPointerCapture: () => captured,
+  releasePointerCapture: () => {
+    captured = false;
+  },
+};
+const style = {
+  cursor: "",
+  userSelect: "",
+  removeProperty(property: string) {
+    if (property === "cursor") this.cursor = "";
+    if (property === "user-select") this.userSelect = "";
+  },
+};
+const setItem = vi.fn();
+const cancelAnimationFrame = vi.fn();
+let events: EventTarget;
+let frame: FrameRequestCallback | undefined;
+
+function pointer(clientX = 100) {
+  return {
+    button: 0,
+    pointerId: 1,
+    clientX,
+    currentTarget: target,
+    preventDefault() {},
+    stopPropagation() {},
+  } as unknown as PointerEvent<HTMLElement>;
+}
+
+function Panel() {
+  const resize = useResizableWidth({
+    storageKey: "test-panel-width",
+    defaultWidth: 400,
+    minWidth: 200,
+    maxWidth: 800,
+    edge: "left",
+  });
+  useLayoutEffect(() => {
+    result = resize;
+  });
+  return null;
+}
+
+beforeEach(async () => {
+  captured = false;
+  frame = undefined;
+  style.cursor = "";
+  style.userSelect = "";
+  events = new EventTarget();
+  vi.stubGlobal("IS_REACT_ACT_ENVIRONMENT", true);
+  vi.stubGlobal("window", {
+    addEventListener: events.addEventListener.bind(events),
+    removeEventListener: events.removeEventListener.bind(events),
+    localStorage: { getItem: () => null, setItem },
+  });
+  vi.stubGlobal("document", { body: { style } });
+  vi.stubGlobal("requestAnimationFrame", (callback: FrameRequestCallback) => {
+    frame = callback;
+    return 42;
+  });
+  vi.stubGlobal("cancelAnimationFrame", cancelAnimationFrame);
+  await act(() => {
+    renderer = create(<Panel />);
+  });
+});
+
+afterEach(async () => {
+  await act(() => renderer.unmount());
+  vi.unstubAllGlobals();
+  vi.clearAllMocks();
+});
+
+describe("panel resize cleanup", () => {
+  it.each(["unmount", "lost capture", "blur", "cancel"])(
+    "clears the cursor and pending resize after %s",
+    async (reason) => {
+      await act(() => {
+        result.handlers.onPointerDown(pointer());
+        result.handlers.onPointerMove(pointer(50));
+      });
+      await act(() => frame?.(0));
+      expect(result.width).toBe(450);
+      // Queue another move to check that interruption cancels pending work too.
+      await act(() => result.handlers.onPointerMove(pointer(25)));
+      expect(style.cursor).toBe("col-resize");
+      expect(style.userSelect).toBe("none");
+      await act(() => {
+        if (reason === "unmount") renderer.unmount();
+        if (reason === "lost capture") result.handlers.onLostPointerCapture(pointer());
+        if (reason === "blur") events.dispatchEvent(new Event("blur"));
+        if (reason === "cancel") result.handlers.onPointerCancel(pointer());
+      });
+      expect(style.cursor).toBe("");
+      expect(style.userSelect).toBe("");
+      expect(captured).toBe(false);
+      expect(cancelAnimationFrame).toHaveBeenCalledWith(42);
+      expect(setItem).not.toHaveBeenCalled();
+      if (reason !== "unmount") expect(result.width).toBe(400);
+    },
+  );
+
+  it("saves the final width when release is followed by lost capture", async () => {
+    await act(() => {
+      result.handlers.onPointerDown(pointer());
+      result.handlers.onPointerMove(pointer(50));
+      result.handlers.onPointerUp(pointer(50));
+      result.handlers.onLostPointerCapture(pointer(50));
+    });
+    expect(result.width).toBe(450);
+    expect(setItem).toHaveBeenCalledExactlyOnceWith("test-panel-width", "450");
+    expect(style.cursor).toBe("");
+    expect(captured).toBe(false);
+  });
+});
diff --git a/apps/web/src/hooks/useResizableWidth.ts b/apps/web/src/hooks/useResizableWidth.ts
index 08c067471f74..7bdb6be339a0 100644
--- a/apps/web/src/hooks/useResizableWidth.ts
+++ b/apps/web/src/hooks/useResizableWidth.ts
@@ -1,5 +1,11 @@
 import * as Schema from "effect/Schema";
-import { type PointerEvent as ReactPointerEvent, useCallback, useRef, useState } from "react";
+import {
+  type PointerEvent as ReactPointerEvent,
+  useCallback,
+  useEffect,
+  useRef,
+  useState,
+} from "react";
 
 import { getLocalStorageItem, setLocalStorageItem } from "./useLocalStorage";
 
@@ -24,6 +30,7 @@ export interface ResizableWidthHandlers {
   readonly onPointerMove: (event: ReactPointerEvent<HTMLElement>) => void;
   readonly onPointerUp: (event: ReactPointerEvent<HTMLElement>) => void;
   readonly onPointerCancel: (event: ReactPointerEvent<HTMLElement>) => void;
+  readonly onLostPointerCapture: (event: ReactPointerEvent<HTMLElement>) => void;
 }
 
 /**
@@ -75,6 +82,8 @@ export function useResizableWidth(options: UseResizableWidthOptions): {
   const releasePointer = useCallback((pointerId: number) => {
     const state = dragStateRef.current;
     if (!state) return;
+    // Clear first because releasing capture can trigger another cleanup.
+    dragStateRef.current = null;
     if (state.rafId !== null) {
       cancelAnimationFrame(state.rafId);
     }
@@ -87,12 +96,27 @@ export function useResizableWidth(options: UseResizableWidthOptions): {
     }
     document.body.style.removeProperty("cursor");
     document.body.style.removeProperty("user-select");
-    dragStateRef.current = null;
   }, []);
 
+  const cancelDrag = useCallback(() => {
+    const state = dragStateRef.current;
+    if (!state) return;
+    releasePointer(state.pointerId);
+    setWidth(state.startWidth);
+  }, [releasePointer]);
+
+  useEffect(() => {
+    window.addEventListener("blur", cancelDrag);
+    return () => {
+      window.removeEventListener("blur", cancelDrag);
+      const state = dragStateRef.current;
+      if (state) releasePointer(state.pointerId);
+    };
+  }, [cancelDrag, releasePointer]);
+
   const onPointerDown = useCallback(
     (event: ReactPointerEvent<HTMLElement>) => {
-      if (event.button !== 0) return;
+      if (event.button !== 0 || dragStateRef.current) return;
       event.preventDefault();
       event.stopPropagation();
       const target = event.currentTarget;
@@ -155,14 +179,19 @@ export function useResizableWidth(options: UseResizableWidthOptions): {
       const state = dragStateRef.current;
       if (!state || state.pointerId !== event.pointerId) return;
       // Don't persist a cancelled drag; revert to the start width.
-      releasePointer(event.pointerId);
-      setWidth(state.startWidth);
+      cancelDrag();
     },
-    [releasePointer],
+    [cancelDrag],
   );
 
   return {
     width: clampedWidth,
-    handlers: { onPointerDown, onPointerMove, onPointerUp, onPointerCancel },
+    handlers: {
+      onPointerDown,
+      onPointerMove,
+      onPointerUp,
+      onPointerCancel,
+      onLostPointerCapture: onPointerCancel,
+    },
   };
 }