diff --git a/apps/web/src/components/ChatView.tsx b/apps/web/src/components/ChatView.tsx
index 3c8a0a1529..ae239f210c 100644
--- a/apps/web/src/components/ChatView.tsx
+++ b/apps/web/src/components/ChatView.tsx
@@ -52,7 +52,11 @@ import { projectSearchEntriesQueryOptions } from "~/lib/projectReactQuery";
 import { serverConfigQueryOptions, serverQueryKeys } from "~/lib/serverReactQuery";
 
 import { isElectron } from "../env";
-import { parseDiffRouteSearch, stripDiffSearchParams } from "../diffRouteSearch";
+import {
+  clearDiffSearchParams,
+  parseDiffRouteSearch,
+  stripDiffSearchParams,
+} from "../diffRouteSearch";
 import {
   type ComposerSlashCommand,
   type ComposerTrigger,
@@ -1400,7 +1404,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
       replace: true,
       search: (previous) => {
         const rest = stripDiffSearchParams(previous);
-        return diffOpen ? rest : { ...rest, diff: "1" };
+        return diffOpen ? clearDiffSearchParams(previous) : { ...rest, diff: "1" };
       },
     });
   }, [diffOpen, navigate, threadId]);
diff --git a/apps/web/src/diffRouteSearch.test.ts b/apps/web/src/diffRouteSearch.test.ts
index ef00874bd2..fc971c548f 100644
--- a/apps/web/src/diffRouteSearch.test.ts
+++ b/apps/web/src/diffRouteSearch.test.ts
@@ -1,6 +1,10 @@
 import { describe, expect, it } from "vitest";
 
-import { parseDiffRouteSearch } from "./diffRouteSearch";
+import {
+  clearDiffSearchParams,
+  parseDiffRouteSearch,
+  stripDiffSearchParams,
+} from "./diffRouteSearch";
 
 describe("parseDiffRouteSearch", () => {
   it("parses valid diff search values", () => {
@@ -72,3 +76,40 @@ describe("parseDiffRouteSearch", () => {
     });
   });
 });
+
+describe("stripDiffSearchParams", () => {
+  it("removes diff search keys", () => {
+    const stripped = stripDiffSearchParams({
+      diff: "1",
+      diffFilePath: "src/app.ts",
+      diffTurnId: "turn-1",
+      project: "demo",
+    });
+
+    expect(stripped).toEqual({ project: "demo" });
+    expect("diff" in stripped).toBe(false);
+    expect("diffTurnId" in stripped).toBe(false);
+    expect("diffFilePath" in stripped).toBe(false);
+  });
+});
+
+describe("clearDiffSearchParams", () => {
+  it("keeps explicit undefined tombstones for diff keys", () => {
+    const cleared = clearDiffSearchParams({
+      diff: "1",
+      diffFilePath: "src/app.ts",
+      diffTurnId: "turn-1",
+      project: "demo",
+    });
+
+    expect(cleared).toEqual({
+      diff: undefined,
+      diffFilePath: undefined,
+      diffTurnId: undefined,
+      project: "demo",
+    });
+    expect("diff" in cleared).toBe(true);
+    expect("diffTurnId" in cleared).toBe(true);
+    expect("diffFilePath" in cleared).toBe(true);
+  });
+});
diff --git a/apps/web/src/diffRouteSearch.ts b/apps/web/src/diffRouteSearch.ts
index f310b74b78..450b41cd2c 100644
--- a/apps/web/src/diffRouteSearch.ts
+++ b/apps/web/src/diffRouteSearch.ts
@@ -1,9 +1,9 @@
 import { TurnId } from "@t3tools/contracts";
 
 export interface DiffRouteSearch {
-  diff?: "1";
-  diffTurnId?: TurnId;
-  diffFilePath?: string;
+  diff?: "1" | undefined;
+  diffTurnId?: TurnId | undefined;
+  diffFilePath?: string | undefined;
 }
 
 function isDiffOpenValue(value: unknown): boolean {
@@ -25,6 +25,22 @@ export function stripDiffSearchParams<T extends Record<string, unknown>>(
   return rest as Omit<T, "diff" | "diffTurnId" | "diffFilePath">;
 }
 
+export function clearDiffSearchParams<T extends Record<string, unknown>>(
+  params: T,
+): Omit<T, "diff" | "diffTurnId" | "diffFilePath"> & {
+  diff: undefined;
+  diffTurnId: undefined;
+  diffFilePath: undefined;
+} {
+  const rest = stripDiffSearchParams(params);
+  return {
+    ...rest,
+    diff: undefined,
+    diffTurnId: undefined,
+    diffFilePath: undefined,
+  };
+}
+
 export function parseDiffRouteSearch(search: Record<string, unknown>): DiffRouteSearch {
   const diff = isDiffOpenValue(search.diff) ? "1" : undefined;
   const diffTurnIdRaw = diff ? normalizeSearchString(search.diffTurnId) : undefined;
diff --git a/apps/web/src/routes/_chat.$threadId.tsx b/apps/web/src/routes/_chat.$threadId.tsx
index b85aeab0d9..e610d7b7db 100644
--- a/apps/web/src/routes/_chat.$threadId.tsx
+++ b/apps/web/src/routes/_chat.$threadId.tsx
@@ -5,6 +5,7 @@ import { Suspense, lazy, type ReactNode, useCallback, useEffect } from "react";
 import ChatView from "../components/ChatView";
 import { useComposerDraftStore } from "../composerDraftStore";
 import {
+  clearDiffSearchParams,
   type DiffRouteSearch,
   parseDiffRouteSearch,
   stripDiffSearchParams,
@@ -133,10 +134,17 @@ const DiffPanelInlineSidebar = (props: {
       className="w-auto min-h-0 flex-none bg-transparent"
       style={{ "--sidebar-width": DIFF_INLINE_DEFAULT_WIDTH } as React.CSSProperties}
     >
+      {diffOpen ? (
+        <div
+          aria-hidden="true"
+          className="fixed inset-0 z-[15] bg-transparent"
+          onClick={onCloseDiff}
+        />
+      ) : null}
       <Sidebar
         side="right"
         collapsible="offcanvas"
-        className="border-l border-border bg-card text-foreground"
+        className="z-20 border-l border-border bg-card text-foreground"
         resizable={{
           minWidth: DIFF_INLINE_SIDEBAR_MIN_WIDTH,
           shouldAcceptWidth: shouldAcceptInlineSidebarWidth,
@@ -171,7 +179,7 @@ function ChatThreadRouteView() {
       to: "/$threadId",
       params: { threadId },
       search: (previous) => {
-        return stripDiffSearchParams(previous);
+        return clearDiffSearchParams(previous);
       },
     });
   }, [navigate, threadId]);