diff --git a/apps/server/src/git/GitManager.ts b/apps/server/src/git/GitManager.ts
index 8ca0b6b976a9..63a8d0d8bac5 100644
--- a/apps/server/src/git/GitManager.ts
+++ b/apps/server/src/git/GitManager.ts
@@ -764,7 +764,10 @@ export const make = Effect.gen(function* () {
     Effect.gen(function* () {
       const root = yield* fileSystem.realPath(cwd);
       const instructionPath = yield* fileSystem.realPath(path.join(root, fileName));
-      if (!instructionPath.startsWith(`${root}${path.sep}`)) {
+      // A drive root such as `D:\` already ends with a separator, so compare
+      // with path.relative instead of a `${root}${sep}` prefix.
+      const relative = path.relative(root, instructionPath);
+      if (relative === "" || relative.startsWith("..") || path.isAbsolute(relative)) {
         return "";
       }
       const info = yield* fileSystem.stat(instructionPath);
diff --git a/apps/server/src/review/ReviewService.test.ts b/apps/server/src/review/ReviewService.test.ts
index 0802bac2d73a..384b8ad40d12 100644
--- a/apps/server/src/review/ReviewService.test.ts
+++ b/apps/server/src/review/ReviewService.test.ts
@@ -4,8 +4,10 @@ import * as Effect from "effect/Effect";
 import * as FileSystem from "effect/FileSystem";
 import * as Layer from "effect/Layer";
 import * as PlatformError from "effect/PlatformError";
+import { ProjectId } from "@t3tools/contracts";
 
 import * as ServerConfig from "../config.ts";
+import * as ProjectStore from "../orchestration-v2/ProjectStore.ts";
 import * as ServerSettings from "../serverSettings.ts";
 import * as GitVcsDriver from "../vcs/GitVcsDriver.ts";
 import * as VcsDriverRegistry from "../vcs/VcsDriverRegistry.ts";
@@ -17,8 +19,30 @@ function layer(input: {
   readonly detectCalls?: Array<{ readonly cwd: string }>;
   readonly worktreesDirectory?: string;
   readonly previousWorktreesDirectories?: ReadonlyArray<string>;
+  readonly projectRoots?: ReadonlyArray<string> | "unavailable";
 }) {
+  const projectRoots = input.projectRoots ?? [];
   return ReviewService.layer.pipe(
+    Layer.provide(
+      Layer.mock(ProjectStore.ProjectStoreV2)({
+        listShells: () =>
+          projectRoots === "unavailable"
+            ? Effect.fail(
+                new ProjectStore.ProjectStoreV2Error({ operation: "list", cause: "offline" }),
+              )
+            : Effect.succeed(
+                projectRoots.map((workspaceRoot, index) => ({
+                  id: ProjectId.make(`project-${index}`),
+                  title: `Project ${index}`,
+                  workspaceRoot,
+                  defaultModelSelection: null,
+                  scripts: [],
+                  createdAt: "2026-01-01T00:00:00.000Z",
+                  updatedAt: "2026-01-01T00:00:00.000Z",
+                })),
+              ),
+      }),
+    ),
     Layer.provide(
       Layer.mock(VcsDriverRegistry.VcsDriverRegistry)({
         get: () => Effect.die("unexpected VCS registry get"),
@@ -134,6 +158,38 @@ describe("ReviewService", () => {
     }).pipe(Effect.provide(NodeServices.layer)),
   );
 
+  it.effect("allows registered project roots outside the server cwd", () =>
+    Effect.gen(function* () {
+      const fs = yield* FileSystem.FileSystem;
+      const workspaceRoot = yield* fs.makeTempDirectoryScoped({ prefix: "t3-review-workspace-" });
+      const baseDir = yield* fs.makeTempDirectoryScoped({ prefix: "t3-review-base-" });
+      // Stands in for a project on another drive than the server's home cwd.
+      const projectRoot = yield* fs.makeTempDirectoryScoped({ prefix: "t3-review-project-" });
+      const projectChild = `${projectRoot}/packages/app`;
+      yield* fs.makeDirectory(projectChild, { recursive: true });
+      const sibling = `${projectRoot}-sibling`;
+      yield* fs.makeDirectory(sibling);
+      yield* Effect.addFinalizer(() => fs.remove(sibling, { recursive: true }).pipe(Effect.ignore));
+
+      const review = (cwd: string, projectRoots: ReadonlyArray<string> | "unavailable") =>
+        Effect.gen(function* () {
+          const service = yield* ReviewService.ReviewService;
+          return yield* service.getDiffPreview({ cwd });
+        }).pipe(Effect.provide(layer({ workspaceRoot, baseDir, projectRoots })));
+
+      assert.strictEqual((yield* review(projectRoot, [projectRoot])).cwd, projectRoot);
+      assert.strictEqual((yield* review(projectChild, [projectRoot])).cwd, projectChild);
+      for (const [cwd, projectRoots] of [
+        [sibling, [projectRoot]],
+        [projectRoot, []],
+        [projectRoot, "unavailable"],
+      ] as const) {
+        const error = yield* review(cwd, projectRoots).pipe(Effect.flip);
+        assert.strictEqual(error._tag, "VcsRepositoryDetectionError");
+      }
+    }).pipe(Effect.provide(NodeServices.layer)),
+  );
+
   it.effect("allows diff preview cwd inside the configured workspace root", () =>
     Effect.gen(function* () {
       const fs = yield* FileSystem.FileSystem;
diff --git a/apps/server/src/review/ReviewService.ts b/apps/server/src/review/ReviewService.ts
index d8e27c9d6dd7..1bde38b589b4 100644
--- a/apps/server/src/review/ReviewService.ts
+++ b/apps/server/src/review/ReviewService.ts
@@ -16,6 +16,7 @@ import {
 } from "@t3tools/contracts";
 
 import * as ServerConfig from "../config.ts";
+import * as ProjectStore from "../orchestration-v2/ProjectStore.ts";
 import * as GitVcsDriver from "../vcs/GitVcsDriver.ts";
 import * as VcsDriverRegistry from "../vcs/VcsDriverRegistry.ts";
 import * as ServerSettings from "../serverSettings.ts";
@@ -42,6 +43,7 @@ export const make = Effect.gen(function* () {
   const vcsRegistry = yield* VcsDriverRegistry.VcsDriverRegistry;
   const git = yield* GitVcsDriver.GitVcsDriver;
   const settings = yield* ServerSettings.ServerSettingsService;
+  const projectStore = yield* ProjectStore.ProjectStoreV2;
 
   const canonicalizePath = (value: string) => {
     const resolvedPath = path.resolve(value);
@@ -97,6 +99,19 @@ export const make = Effect.gen(function* () {
       return;
     }
 
+    // Registered projects can live outside the server cwd, which is the home
+    // directory in packaged desktop builds, e.g. a repository on another
+    // Windows drive. Unreadable or unresolvable project roots grant nothing.
+    const projects = yield* projectStore.listShells().pipe(Effect.orElseSucceed(() => []));
+    for (const project of projects) {
+      const root = yield* canonicalizePath(project.workspaceRoot).pipe(
+        Effect.orElseSucceed(() => null),
+      );
+      if (root !== null && isWithinRoot(candidate, root)) {
+        return;
+      }
+    }
+
     return yield* new VcsRepositoryDetectionError({
       operation,
       cwd,
diff --git a/apps/server/src/server.ts b/apps/server/src/server.ts
index 98a541409380..0707410e065e 100644
--- a/apps/server/src/server.ts
+++ b/apps/server/src/server.ts
@@ -373,6 +373,7 @@ const layerProjectCloneTracker = ProjectCloneTracker.layer.pipe(
 );
 
 const layerReview = ReviewService.layer.pipe(
+  Layer.provide(ProjectStore.layer),
   Layer.provideMerge(GitVcsDriver.layer),
   Layer.provideMerge(layerVcsDriverRegistry),
 );
diff --git a/apps/web/src/components/DiffPanel.tsx b/apps/web/src/components/DiffPanel.tsx
index 633094738e9e..0c7a4a28988d 100644
--- a/apps/web/src/components/DiffPanel.tsx
+++ b/apps/web/src/components/DiffPanel.tsx
@@ -339,7 +339,7 @@ export default function DiffPanel({
     },
     { enabled: isGitRepo && selectedTurn !== undefined },
   );
-  const primaryBranchDiffPreview = useEnvironmentQuery(
+  const branchDiffPreview = useEnvironmentQuery(
     canReadFiles && selectedRunId === null && activeThread && activeCwd
       ? reviewEnvironment.diffPreview({
           environmentId: activeThread.environmentId,
@@ -351,26 +351,6 @@ export default function DiffPanel({
         })
       : null,
   );
-  const shouldRetryBranchDiffAtEnvironmentCwd =
-    selectedRunId === null &&
-    primaryBranchDiffPreview.error?.includes("configured workspace root") === true &&
-    serverConfig?.cwd !== undefined &&
-    serverConfig.cwd !== activeCwd;
-  const fallbackBranchDiffPreview = useEnvironmentQuery(
-    canReadFiles && shouldRetryBranchDiffAtEnvironmentCwd && activeThread && serverConfig
-      ? reviewEnvironment.diffPreview({
-          environmentId: activeThread.environmentId,
-          input: {
-            cwd: serverConfig.cwd,
-            ...(selectedBaseRef ? { baseRef: selectedBaseRef } : {}),
-            ignoreWhitespace: diffIgnoreWhitespace,
-          },
-        })
-      : null,
-  );
-  const branchDiffPreview = shouldRetryBranchDiffAtEnvironmentCwd
-    ? fallbackBranchDiffPreview
-    : primaryBranchDiffPreview;
   const canRefreshGitDiff =
     isGitRepo && selectedRunId === null && activeThread != null && activeCwd != null;
   const activeThreadRefreshKey = routeThreadRef