diff --git a/cli/src/api/apiMachine.test.ts b/cli/src/api/apiMachine.test.ts
index 321990f0..4204c412 100644
--- a/cli/src/api/apiMachine.test.ts
+++ b/cli/src/api/apiMachine.test.ts
@@ -18,7 +18,7 @@ vi.mock('../modules/common/opencodeModels', () => ({
     listOpencodeModelsForCwd: listOpencodeModelsForCwdMock
 }))
 
-import { ApiMachineClient } from './apiMachine'
+import { ApiMachineClient, normalizeWindowsDriveRoot } from './apiMachine'
 import type { Machine } from './types'
 
 function makeMachine(id: string): Machine {
@@ -37,6 +37,18 @@ function makeMachine(id: string): Machine {
     }
 }
 
+describe('normalizeWindowsDriveRoot', () => {
+    it('restores the trailing separator when Windows realpath returns a bare drive', () => {
+        expect(normalizeWindowsDriveRoot('C:')).toBe('C:\\')
+        expect(normalizeWindowsDriveRoot('D:')).toBe('D:\\')
+    })
+
+    it('leaves non-drive-root paths unchanged', () => {
+        expect(normalizeWindowsDriveRoot('C:\\Users')).toBe('C:\\Users')
+        expect(normalizeWindowsDriveRoot('/tmp/workspace')).toBe('/tmp/workspace')
+    })
+})
+
 async function callListOpencodeModels(client: ApiMachineClient, machineId: string, cwd: string): Promise<unknown> {
     // Reach into the private rpc handler manager to dispatch a request.
     // Mirrors how the on-socket 'rpc-request' listener invokes handleRequest.
@@ -137,7 +149,7 @@ describe('ApiMachineClient listOpencodeModelsForCwd handler', () => {
             })
             // The handler realpaths the cwd (security: prevents symlink escape),
             // so on macOS /var/folders/... resolves to /private/var/folders/...
-            expect(listOpencodeModelsForCwdMock).toHaveBeenCalledWith(realpathSync(secondWorkspaceRoot))
+            expect(listOpencodeModelsForCwdMock).toHaveBeenCalledWith(realpathSync.native(secondWorkspaceRoot))
         } finally {
             rmSync(secondWorkspaceRoot, { recursive: true, force: true })
             client.shutdown()
diff --git a/cli/src/api/apiMachine.ts b/cli/src/api/apiMachine.ts
index 4225ff6a..07e24153 100644
--- a/cli/src/api/apiMachine.ts
+++ b/cli/src/api/apiMachine.ts
@@ -41,6 +41,14 @@ interface ListMachineDirectoryRequest {
     path: string
 }
 
+export function normalizeWindowsDriveRoot(path: string): string {
+    return /^[A-Za-z]:$/.test(path) ? `${path}\\` : path
+}
+
+function canonicalRealpathSync(path: string): string {
+    return normalizeWindowsDriveRoot(realpathSync.native(path))
+}
+
 function normalizeWorkspaceRoots(paths?: string[]): string[] | undefined {
     if (!paths?.length) {
         return undefined
@@ -48,9 +56,9 @@ function normalizeWorkspaceRoots(paths?: string[]): string[] | undefined {
 
     const normalized = Array.from(new Set(paths.map((path) => {
         try {
-            return realpathSync(path)
+            return canonicalRealpathSync(path)
         } catch {
-            return resolvePath(path)
+            return normalizeWindowsDriveRoot(resolvePath(path))
         }
     })))
 
@@ -232,7 +240,7 @@ export class ApiMachineClient {
     private async resolveForWorkspaceCheck(path: string): Promise<string> {
         const absolute = resolvePath(path)
         try {
-            return await realpath(absolute)
+            return normalizeWindowsDriveRoot(await realpath(absolute))
         } catch {
             const missing: string[] = []
             let cursor = absolute
@@ -240,12 +248,12 @@ export class ApiMachineClient {
                 missing.unshift(basename(cursor))
                 cursor = dirname(cursor)
                 try {
-                    return join(await realpath(cursor), ...missing)
+                    return join(normalizeWindowsDriveRoot(await realpath(cursor)), ...missing)
                 } catch {
                     // keep walking to the nearest existing parent
                 }
             }
-            return absolute
+            return normalizeWindowsDriveRoot(absolute)
         }
     }