diff --git a/apps/web/src/components/AppSidebarLayout.tsx b/apps/web/src/components/AppSidebarLayout.tsx
index f7b3209f661ac..6c24323299c95 100644
--- a/apps/web/src/components/AppSidebarLayout.tsx
+++ b/apps/web/src/components/AppSidebarLayout.tsx
@@ -37,6 +37,7 @@ import {
   usePanelNavigationSuppression,
 } from "../panelAnimations";
 import { BackgroundThreadAnnouncer } from "./BackgroundThreadAnnouncer";
+import { createSidebarProjectScopeSession } from "./Sidebar.logic";
 import LegacyThreadSidebar from "./LegacySidebar";
 import ThreadSidebar from "./Sidebar";
 import { SidebarBrandWidthProbe } from "./sidebar/SidebarChrome";
@@ -379,6 +380,9 @@ export function AppSidebarLayout({ children }: { children: ReactNode }) {
     observedKey: null,
     pendingKey: null,
   }));
+  // The shell swaps its tree across the mobile breakpoint and remounts the
+  // sidebar. This outlives that so a Scratch scope picked this session stays.
+  const [projectScopeSession] = useState(() => createSidebarProjectScopeSession());
   const { active: panelAnimationsActive, durationMs: panelAnimationDurationMs } =
     usePanelAnimationSettings();
   const pathname = useLocation({ select: (location) => location.pathname });
@@ -443,7 +447,10 @@ export function AppSidebarLayout({ children }: { children: ReactNode }) {
           {legacySidebarEnabled ? (
             <LegacyThreadSidebar routeReveal={sidebarRouteReveal} />
           ) : (
-            <ThreadSidebar routeReveal={sidebarRouteReveal} />
+            <ThreadSidebar
+              routeReveal={sidebarRouteReveal}
+              projectScopeSession={projectScopeSession}
+            />
           )}
           <SidebarRail onDoubleClick={resetSidebarWidth} />
         </Sidebar>
diff --git a/apps/web/src/components/Sidebar.logic.test.ts b/apps/web/src/components/Sidebar.logic.test.ts
index a66540ff4fdf3..917d732d13c94 100644
--- a/apps/web/src/components/Sidebar.logic.test.ts
+++ b/apps/web/src/components/Sidebar.logic.test.ts
@@ -20,7 +20,11 @@ import {
   resolveThreadStatusPill,
   resolveWorkingStartedAt,
   searchSidebarThreads,
+  createSidebarProjectScopeSession,
+  markSidebarProjectScopeChosen,
+  shouldClearPersistedSidebarProjectScope,
   shouldRecedeSidebarThread,
+  sidebarProjectScopeWasRestored,
   sortInboxThreadsByReturn,
   resolveSidebarDropTarget,
   planSidebarThreadDrop,
@@ -1352,3 +1356,156 @@ describe("resolveSidebarRouteReveal", () => {
     ).toEqual({ pendingKey: hiddenKey, widensScope: false });
   });
 });
+
+describe("shouldClearPersistedSidebarProjectScope", () => {
+  const local = EnvironmentId.make("env-local");
+  const remote = EnvironmentId.make("env-remote");
+  const remoteScratchRoot = "/home/user/.t3/scratch";
+  const scratchWorkspaceRootFor = (environmentId: EnvironmentId) =>
+    environmentId === remote ? remoteScratchRoot : "/Users/me/.t3/scratch";
+  const scratchGroup = {
+    memberProjects: [{ environmentId: remote, workspaceRoot: `${remoteScratchRoot}/` }],
+  };
+  const repoGroup = {
+    memberProjects: [{ environmentId: remote, workspaceRoot: "/home/user/src/t3code" }],
+  };
+
+  it("keeps the scope until project snapshots are ready", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: false,
+        restored: true,
+        scopedGroup: null,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: false,
+        restored: true,
+        scopedGroup: scratchGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("keeps an empty scope", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: null,
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: null,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("clears a scope whose catalog group is gone", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: "missing-project",
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: null,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(true);
+  });
+
+  it("clears a restored scope that resolves to a scratch workspace", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: scratchGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(true);
+  });
+
+  it("keeps a scratch scope the user picked in this session", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: true,
+        restored: false,
+        scopedGroup: scratchGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("clears a scratch scope restored into a new session", () => {
+    const session = createSidebarProjectScopeSession();
+    expect(sidebarProjectScopeWasRestored(session)).toBe(true);
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: true,
+        restored: sidebarProjectScopeWasRestored(session),
+        scopedGroup: scratchGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(true);
+  });
+
+  it("keeps a scratch scope the user chose when the sidebar remounts", () => {
+    const session = createSidebarProjectScopeSession();
+    markSidebarProjectScopeChosen(session);
+    // A remount reads the layout's session again; it does not start a new one.
+    expect(sidebarProjectScopeWasRestored(session)).toBe(false);
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${remote}:${remoteScratchRoot}`,
+        snapshotsReady: true,
+        restored: sidebarProjectScopeWasRestored(session),
+        scopedGroup: scratchGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("keeps a scope that resolves to a normal project", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: "github.com/pingdotgg/t3code",
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: repoGroup,
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("compares each member with its own environment scratch root", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: `${local}:${remoteScratchRoot}`,
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: {
+          memberProjects: [{ environmentId: local, workspaceRoot: remoteScratchRoot }],
+        },
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+
+  it("keeps a group that still contains a non-scratch checkout", () => {
+    expect(
+      shouldClearPersistedSidebarProjectScope({
+        scopeKey: "github.com/pingdotgg/t3code",
+        snapshotsReady: true,
+        restored: true,
+        scopedGroup: {
+          memberProjects: [...scratchGroup.memberProjects, ...repoGroup.memberProjects],
+        },
+        scratchWorkspaceRootFor,
+      }),
+    ).toBe(false);
+  });
+});
diff --git a/apps/web/src/components/Sidebar.logic.ts b/apps/web/src/components/Sidebar.logic.ts
index 475ca41271143..cfb284bcaba24 100644
--- a/apps/web/src/components/Sidebar.logic.ts
+++ b/apps/web/src/components/Sidebar.logic.ts
@@ -1,4 +1,5 @@
 import { resolveThreadWorkingStartedAt } from "@t3tools/client-runtime/state/models";
+import { isScratchProject } from "@t3tools/client-runtime/state/projects";
 import { backgroundWorkHoldsCompletion } from "@t3tools/shared/orchestrationV2PendingBackgroundWork";
 import { threadPullRequestSearchTerms } from "@t3tools/shared/threadPullRequests";
 import * as React from "react";
@@ -560,6 +561,59 @@ export function isSidebarSubagentThread(thread: Pick<SidebarThreadSummary, "line
   return thread.lineage.relationshipToParent === "subagent";
 }
 
+// The thread sidebar remounts when the viewport crosses the mobile breakpoint.
+// AppSidebarLayout holds this, so a Scratch pick in the page session is not
+// read back as restored state and cleared.
+export interface SidebarProjectScopeSession {
+  userChose: boolean;
+}
+
+export function createSidebarProjectScopeSession(): SidebarProjectScopeSession {
+  return { userChose: false };
+}
+
+export function markSidebarProjectScopeChosen(session: SidebarProjectScopeSession): void {
+  session.userChose = true;
+}
+
+export function sidebarProjectScopeWasRestored(session: SidebarProjectScopeSession): boolean {
+  return !session.userChose;
+}
+
+// Scratch is a real catalog project, so a key that points only at it never
+// looks missing and keeps filtering the sidebar. A pick in this session stays;
+// a missing group is cleared once snapshots are ready.
+export function shouldClearPersistedSidebarProjectScope(input: {
+  readonly scopeKey: string | null;
+  readonly snapshotsReady: boolean;
+  /** False when the user chose this scope during the current page session. */
+  readonly restored: boolean;
+  readonly scopedGroup: {
+    readonly memberProjects: ReadonlyArray<{
+      readonly environmentId: EnvironmentId;
+      readonly workspaceRoot: string;
+    }>;
+  } | null;
+  readonly scratchWorkspaceRootFor: (environmentId: EnvironmentId) => string | null | undefined;
+}): boolean {
+  if (input.scopeKey === null || !input.snapshotsReady) {
+    return false;
+  }
+  const group = input.scopedGroup;
+  if (group === null) {
+    return true;
+  }
+  if (!input.restored) {
+    return false;
+  }
+  return (
+    group.memberProjects.length > 0 &&
+    group.memberProjects.every((member) =>
+      isScratchProject(member, input.scratchWorkspaceRootFor(member.environmentId)),
+    )
+  );
+}
+
 // Subagent threads have no sidebar row, so an open subagent is represented by
 // its nearest non-subagent ancestor. A broken chain (missing parent, cycle,
 // other environment) resolves to the thread itself, which then matches no row.
diff --git a/apps/web/src/components/Sidebar.tsx b/apps/web/src/components/Sidebar.tsx
index 72f90e27a8e3a..32dd958d31445 100644
--- a/apps/web/src/components/Sidebar.tsx
+++ b/apps/web/src/components/Sidebar.tsx
@@ -175,7 +175,11 @@ import {
   resolveSidebarDropVerb,
   resolveSidebarThreadSection,
   searchSidebarThreads,
+  markSidebarProjectScopeChosen,
+  shouldClearPersistedSidebarProjectScope,
   shouldCreateNewThreadInCurrentProject,
+  sidebarProjectScopeWasRestored,
+  type SidebarProjectScopeSession,
   shouldNavigateAfterThreadPark,
   sidebarListItemId,
   sidebarThreadKeyAtY,
@@ -779,7 +783,13 @@ function readRouteThreadKey(router: AnyRouter): string | null {
   return ref === null ? null : scopedThreadKey(ref);
 }
 
-export default function Sidebar({ routeReveal }: { routeReveal: SidebarRouteReveal }) {
+export default function Sidebar({
+  routeReveal,
+  projectScopeSession,
+}: {
+  routeReveal: SidebarRouteReveal;
+  projectScopeSession: SidebarProjectScopeSession;
+}) {
   const {
     projects,
     serverConfigs,
@@ -895,6 +905,7 @@ export default function Sidebar({ routeReveal }: { routeReveal: SidebarRouteReve
   const projectScopeFilter = useComboboxFilter();
   const allProjectSnapshotsReady = useAllEnvironmentProjectSnapshotsReady();
   const allProjectConfigsReady = useAtomValue(environmentProjects.projectConfigsReadyAtom);
+  const projectCatalogReady = allProjectSnapshotsReady && allProjectConfigsReady;
   const headerSearchRef = useRef<HTMLDivElement | null>(null);
   // Safari may click after Ctrl+click opens settings; suppress that selection until the picker reopens.
   const suppressNextScopeChangeRef = useRef(false);
@@ -947,7 +958,9 @@ export default function Sidebar({ routeReveal }: { routeReveal: SidebarRouteReve
   const routeThreadKey = routeThreadRef ? scopedThreadKey(routeThreadRef) : null;
 
   // A selection made under one scope can hold threads the next scope hides.
+  // A scope loaded with the page can be cleared. A pick in this session is kept.
   const setProjectScopeKey = (key: string | null) => {
+    markSidebarProjectScopeChosen(projectScopeSession);
     clearSelection();
     setPersistedProjectScopeKey(key);
   };
@@ -957,7 +970,7 @@ export default function Sidebar({ routeReveal }: { routeReveal: SidebarRouteReve
     groups: projectGroups,
     key: persistedProjectScopeKey,
     settings: projectGroupingSettings,
-    canClearMissingScope: allProjectSnapshotsReady && allProjectConfigsReady,
+    canClearMissingScope: projectCatalogReady,
   });
   const chosenProjectGroup =
     chosenProjectScopeKey === null
@@ -1008,6 +1021,34 @@ export default function Sidebar({ routeReveal }: { routeReveal: SidebarRouteReve
     clearSelection();
     setPersistedProjectScopeKey(null);
   }, [clearSelection, revealWidensScope, setPersistedProjectScopeKey]);
+  // A restored Scratch scope is a real group, so the missing-project read leaves
+  // its stored key in place and the sidebar stays filtered. Clear that key once
+  // the catalog is ready. Pass the resolved key: a missing project stays stored
+  // until it returns. A Scratch scope picked in this session stays.
+  useEffect(() => {
+    if (
+      !shouldClearPersistedSidebarProjectScope({
+        scopeKey: chosenProjectScopeKey,
+        snapshotsReady: projectCatalogReady,
+        restored: sidebarProjectScopeWasRestored(projectScopeSession),
+        scopedGroup: chosenProjectGroup,
+        scratchWorkspaceRootFor: (environmentId) =>
+          serverConfigs.get(environmentId)?.scratchWorkspaceRoot,
+      })
+    ) {
+      return;
+    }
+    clearSelection();
+    setPersistedProjectScopeKey(null);
+  }, [
+    chosenProjectGroup,
+    chosenProjectScopeKey,
+    clearSelection,
+    projectCatalogReady,
+    projectScopeSession,
+    serverConfigs,
+    setPersistedProjectScopeKey,
+  ]);
   const revealActiveRow = useActiveRowReveal(routeReveal, routeRowThreadKey);
   const showProjectEnvironments = projectGroupsSpanEnvironments(projectGroups);
   const scratchMachineLabelFor = (