diff --git a/apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx b/apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx
index f16bbd0aa58c..678820bfbed6 100644
--- a/apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx
+++ b/apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx
@@ -2,29 +2,36 @@ import { SourceControlProviderKind } from "@t3tools/contracts";
 import {
   EnvironmentId,
   ProjectId,
+  GitCommandError,
+  GitManagerError,
   ThreadId,
   type ScopedThreadRef,
   type PullRequestDetailView,
   type ThreadPullRequestLink,
 } from "@t3tools/contracts";
+import * as Cause from "effect/Cause";
 import { DEFAULT_CLIENT_SETTINGS } from "@t3tools/contracts/settings";
 import { act, type ReactNode, type ReactElement, type ComponentProps } from "react";
 import { create, type ReactTestRenderer } from "react-test-renderer";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vite-plus/test";
 import { DraftId, useComposerDraftStore } from "~/composerDraftStore";
 
-const { newThread, prepareThread, refresh, Wrapper, Trigger } = vi.hoisted(() => ({
-  newThread: vi.fn(),
-  prepareThread: vi.fn(),
-  refresh: vi.fn(),
-  Wrapper: ({ children }: { children?: ReactNode }) => children,
-  Trigger: ({ children, render }: { children?: ReactNode; render?: ReactElement }) => (
-    <>
-      {render}
-      {children}
-    </>
-  ),
-}));
+const { newThread, prepareThread, refresh, addToast, updateToast, Wrapper, Trigger } = vi.hoisted(
+  () => ({
+    newThread: vi.fn(),
+    prepareThread: vi.fn(),
+    refresh: vi.fn(),
+    addToast: vi.fn(),
+    updateToast: vi.fn(),
+    Wrapper: ({ children }: { children?: ReactNode }) => children,
+    Trigger: ({ children, render }: { children?: ReactNode; render?: ReactElement }) => (
+      <>
+        {render}
+        {children}
+      </>
+    ),
+  }),
+);
 vi.mock("~/state/session", async (original) => ({
   ...(await original<typeof import("~/state/session")>()),
   useEnvironmentScope: () => true,
@@ -79,7 +86,7 @@ vi.mock("~/state/usePullRequestStack", () => ({
     refresh,
   }),
 }));
-vi.mock("../ui/toast", () => ({ toastManager: { add: vi.fn(), update: vi.fn() } }));
+vi.mock("../ui/toast", () => ({ toastManager: { add: addToast, update: updateToast } }));
 vi.mock("../ui/tooltip", () => ({
   TooltipProvider: Wrapper,
   Tooltip: Wrapper,
@@ -232,6 +239,8 @@ beforeEach(() => {
   newThread
     .mockReset()
     .mockResolvedValue({ draftId: newDraftId, threadId: ThreadId.make("new-thread") });
+  addToast.mockReset().mockReturnValue("checkout-toast");
+  updateToast.mockReset();
   prepareThread.mockReset().mockResolvedValue({
     _tag: "Success",
     value: { branch: "feature", worktreePath: "/workspace/pr" },
@@ -358,6 +367,49 @@ describe.each([
   });
 });
 
+const checkoutDiagnostic = "This PR branch is already checked out in the main repo. Use Local.";
+
+it.each([
+  new GitManagerError({
+    cwd: "/server/private-project",
+    operation: "preparePullRequestThread",
+    detail: checkoutDiagnostic,
+  }),
+  new GitCommandError({
+    cwd: "/server/private-project",
+    operation: "GitVcsDriver.createWorktree",
+    command: "git worktree add",
+    detail: checkoutDiagnostic,
+  }),
+])("shows the server detail from a failed checkout ($_tag) without its path", async (error) => {
+  prepareThread.mockResolvedValueOnce({ _tag: "Failure", cause: Cause.fail(error) });
+  await act(async () => {
+    renderer = create(
+      <PullRequestDetailPanel
+        environmentId={threadRef.environmentId}
+        reference={detail}
+        context="page"
+        shortcutsEnabled={false}
+        getShortcutContext={() => ({
+          terminalFocus: false,
+          terminalOpen: false,
+          previewFocus: false,
+          previewOpen: false,
+          isWeb: true,
+          isDesktop: false,
+        })}
+      />,
+    );
+  });
+  await click("In a separate worktree");
+  expect(updateToast).toHaveBeenCalledWith("checkout-toast", {
+    type: "error",
+    title: "Could not prepare the pull request checkout",
+    description: expect.stringContaining(checkoutDiagnostic),
+  });
+  expect(updateToast.mock.lastCall?.[1].description).not.toContain("/server/private-project");
+});
+
 it("changes the title only for the active tab's main scroller", async () => {
   const scrollers = new Map<string, { scrollTop: number; scrollHeight: number }>();
   await act(async () => {
diff --git a/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx b/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
index d68983937f19..b4ebd21585cb 100644
--- a/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
+++ b/apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
@@ -12,6 +12,7 @@ import {
   AuthOrchestrationOperateScope,
   AuthSourceControlWriteScope,
   type EnvironmentId,
+  GitCommandError,
   type PullRequestAction,
   type PullRequestMergeMethod,
   type PullRequestListEntry,
@@ -21,6 +22,7 @@ import {
   resolveEnvironmentMachineKind,
   type ScopedThreadRef,
 } from "@t3tools/contracts";
+import * as Schema from "effect/Schema";
 import {
   ArrowDownUpIcon,
   ArrowLeftIcon,
@@ -238,6 +240,8 @@ const ACTION_FAILURE_HINTS: Record<PullRequestAction, string> = {
 const UPDATE_BRANCH_REBASE_FAILURE_HINT =
   "The host refused it. A rebase stops at the first commit that does not apply cleanly; updating with a merge commit may still work.";
 
+const isGitCommandError = Schema.is(GitCommandError);
+
 const TABS: ReadonlyArray<{ value: DetailTab; label: string }> = [
   { value: "summary", label: "Summary" },
   { value: "guide", label: "Guide" },
@@ -1322,13 +1326,16 @@ export function PullRequestDetailPanel({
     if (prepared._tag === "Failure") {
       setHandoff(null);
       // The server says what to do about it — that the branch is already checked out in the main
-      // repository, say — and that sentence is the only way out of the failure.
-      const detailMessage =
-        prepareThread.error instanceof Error ? prepareThread.error.message : null;
+      // repository, say — and that sentence is the only way out of the failure. A failed git
+      // command's message also names the server's project directory, so only its detail is shown.
+      const failure = squashAtomCommandFailure(prepared);
       toastManager.update(toastId, {
         type: "error",
         title: "Could not prepare the pull request checkout",
-        ...(detailMessage ? { description: detailMessage } : {}),
+        description: readableFailure(
+          isGitCommandError(failure) ? failure.detail : failure,
+          "Check that the branch still exists and is not checked out elsewhere, then try again.",
+        ),
       });
       return;
     }
diff --git a/apps/web/src/components/pullRequest/usePullRequestActions.ts b/apps/web/src/components/pullRequest/usePullRequestActions.ts
index 3ca753df2b82..75311b5e1ac0 100644
--- a/apps/web/src/components/pullRequest/usePullRequestActions.ts
+++ b/apps/web/src/components/pullRequest/usePullRequestActions.ts
@@ -7,14 +7,16 @@ import { useAtomCommand } from "~/state/use-atom-command";
  */
 import { scopeProjectRef } from "@t3tools/client-runtime/environment";
 import { squashAtomCommandFailure } from "@t3tools/client-runtime/state/runtime";
-import type {
-  EnvironmentId,
-  ProjectId,
-  PullRequestAction,
-  PullRequestDetail,
-  PullRequestMergeMethod,
-  PullRequestRef,
+import {
+  GitCommandError,
+  type EnvironmentId,
+  type ProjectId,
+  type PullRequestAction,
+  type PullRequestDetail,
+  type PullRequestMergeMethod,
+  type PullRequestRef,
 } from "@t3tools/contracts";
+import * as Schema from "effect/Schema";
 import { useCallback, useRef, useState } from "react";
 import { resolveProjectSettings } from "@t3tools/shared/projectSettings";
 import { useClientSettings, useEnvironmentSettings } from "~/hooks/useSettings";
@@ -38,6 +40,8 @@ import { handoffPrompt, handoffReviewComments, readableFailure } from "./pullReq
 import { pullRequestEntryKey, type EnvironmentPullRequestEntry } from "./pullRequestList.logic";
 
 /** Resolve on demand so hidden quick actions do not rebuild the legacy project grouping. */
+const isGitCommandError = Schema.is(GitCommandError);
+
 export function usePullRequestDefaultMergeMethodResolver(
   environmentId: EnvironmentId,
   projectId: ProjectId,
@@ -394,13 +398,16 @@ export function usePullRequestHandoffs({
     if (prepared._tag === "Failure") {
       setHandoff(null);
       // The server says what to do about it — that the branch is already checked out in the main
-      // repository, say — and that sentence is the only way out of the failure.
-      const detailMessage =
-        prepareThread.error instanceof Error ? prepareThread.error.message : null;
+      // repository, say — and that sentence is the only way out of the failure. A failed git
+      // command's message also names the server's project directory, so only its detail is shown.
+      const failure = squashAtomCommandFailure(prepared);
       toastManager.update(toastId, {
         type: "error",
         title: "Could not prepare the pull request checkout",
-        ...(detailMessage ? { description: detailMessage } : {}),
+        description: readableFailure(
+          isGitCommandError(failure) ? failure.detail : failure,
+          "Check that the branch still exists and is not checked out elsewhere, then try again.",
+        ),
       });
       return;
     }