diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 50eea7fc6d2..89e9e2e6123 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -424,8 +424,12 @@ jobs:
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
-      - name: Test Windows PowerShell CLI boundary
-        run: pnpm exec vitest run --config config/vitest.config.ts src/main/cli/wsl-cli-powershell-boundary.test.ts
+      - name: Test Windows-specific boundaries
+        run: >-
+          pnpm exec vitest run --config config/vitest.config.ts
+          src/main/cli/wsl-cli-powershell-boundary.test.ts
+          src/main/orca-profiles/profile-index-store.test.ts
+          src/shared/secure-file-fsync-flags.test.ts
 
       - name: Build package inputs
         run: pnpm run build:release
diff --git a/src/shared/secure-file-fsync-flags.test.ts b/src/shared/secure-file-fsync-flags.test.ts
new file mode 100644
index 00000000000..1c167bffdad
--- /dev/null
+++ b/src/shared/secure-file-fsync-flags.test.ts
@@ -0,0 +1,52 @@
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
+import type * as NodeFs from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+const openedPaths = vi.hoisted(() => [] as { path: string; flags: string | number }[])
+
+vi.mock('node:fs', async () => {
+  const actual = await vi.importActual<typeof NodeFs>('node:fs')
+  return {
+    ...actual,
+    openSync: (path: NodeFs.PathLike, flags: string | number, mode?: NodeFs.Mode) => {
+      openedPaths.push({ path: String(path), flags })
+      return actual.openSync(path, flags, mode)
+    }
+  }
+})
+
+import { bestEffortFsyncDirectorySync, fsyncFileSync } from './secure-file'
+
+const createdPaths: string[] = []
+
+afterEach(() => {
+  openedPaths.length = 0
+  for (const path of createdPaths.splice(0)) {
+    rmSync(path, { recursive: true, force: true })
+  }
+})
+
+describe('secure file fsync flags', () => {
+  it('opens files read/write before fsync', () => {
+    const directory = mkdtempSync(join(tmpdir(), 'orca-file-fsync-'))
+    createdPaths.push(directory)
+    const path = join(directory, 'record.json')
+    writeFileSync(path, '{}')
+
+    fsyncFileSync(path)
+
+    expect(openedPaths).toEqual([{ path, flags: 'r+' }])
+  })
+
+  const posixIt = process.platform === 'win32' ? it.skip : it
+  posixIt('opens directories read-only before fsync', () => {
+    const directory = mkdtempSync(join(tmpdir(), 'orca-directory-fsync-'))
+    createdPaths.push(directory)
+
+    bestEffortFsyncDirectorySync(directory)
+
+    expect(openedPaths).toEqual([{ path: directory, flags: 'r' }])
+  })
+})
diff --git a/src/shared/secure-file.ts b/src/shared/secure-file.ts
index e3c38c70e09..7b2f646c540 100644
--- a/src/shared/secure-file.ts
+++ b/src/shared/secure-file.ts
@@ -133,8 +133,8 @@ export function writeSecureFile(
   }
 }
 
-export function fsyncFileSync(path: string): void {
-  const descriptor = openSync(path, 'r')
+function fsyncPathSync(path: string, flags: 'r' | 'r+'): void {
+  const descriptor = openSync(path, flags)
   try {
     fsyncSync(descriptor)
   } finally {
@@ -142,12 +142,17 @@ export function fsyncFileSync(path: string): void {
   }
 }
 
+export function fsyncFileSync(path: string): void {
+  // FlushFileBuffers requires a write-capable handle on Windows.
+  fsyncPathSync(path, 'r+')
+}
+
 export function bestEffortFsyncDirectorySync(directory: string): void {
   if (process.platform === 'win32') {
     return
   }
   try {
-    fsyncFileSync(directory)
+    fsyncPathSync(directory, 'r')
   } catch (error) {
     if (
       error instanceof Error &&