diff --git a/src/main/ipc/worktrees.test.ts b/src/main/ipc/worktrees.test.ts
index 8e128912517..0fb1a657a5f 100644
--- a/src/main/ipc/worktrees.test.ts
+++ b/src/main/ipc/worktrees.test.ts
@@ -28,7 +28,7 @@ const {
   removeWorktreeMock,
   forceDeleteLocalBranchMock,
   resolveLocalGitUsernameMock,
-  getDefaultBaseRefMock,
+  getBaseRefDefaultMock,
   resolveDefaultBaseRefViaExecMock,
   getDefaultRemoteMock,
   getBranchConflictKindMock,
@@ -77,7 +77,7 @@ const {
   removeWorktreeMock: vi.fn(),
   forceDeleteLocalBranchMock: vi.fn(),
   resolveLocalGitUsernameMock: vi.fn(),
-  getDefaultBaseRefMock: vi.fn(),
+  getBaseRefDefaultMock: vi.fn(),
   resolveDefaultBaseRefViaExecMock: vi.fn(),
   getDefaultRemoteMock: vi.fn(),
   getBranchConflictKindMock: vi.fn(),
@@ -130,7 +130,7 @@ vi.mock('../git/runner', () => ({
 }))
 
 vi.mock('../git/repo', () => ({
-  getDefaultBaseRef: getDefaultBaseRefMock,
+  getBaseRefDefault: getBaseRefDefaultMock,
   resolveDefaultBaseRefViaExec: resolveDefaultBaseRefViaExecMock,
   getDefaultRemote: getDefaultRemoteMock,
   getBranchConflictKind: getBranchConflictKindMock
@@ -299,7 +299,7 @@ describe('registerWorktreeHandlers', () => {
       removeWorktreeMock,
       forceDeleteLocalBranchMock,
       resolveLocalGitUsernameMock,
-      getDefaultBaseRefMock,
+      getBaseRefDefaultMock,
       resolveDefaultBaseRefViaExecMock,
       getDefaultRemoteMock,
       getBranchConflictKindMock,
@@ -400,7 +400,7 @@ describe('registerWorktreeHandlers', () => {
     ])
     store.getAllWorktreeLineage.mockReturnValue({})
     resolveLocalGitUsernameMock.mockResolvedValue('')
-    getDefaultBaseRefMock.mockReturnValue('origin/main')
+    getBaseRefDefaultMock.mockResolvedValue('origin/main')
     resolveDefaultBaseRefViaExecMock.mockResolvedValue('origin/main')
     getDefaultRemoteMock.mockResolvedValue('origin')
     getBranchConflictKindMock.mockResolvedValue(null)
@@ -523,6 +523,7 @@ describe('registerWorktreeHandlers', () => {
 
     await handlers['worktrees:prefetchCreateBase'](null, { repoId: 'repo-1' })
 
+    expect(getBaseRefDefaultMock).toHaveBeenCalledWith('/workspace/repo')
     expect(runtimeStub.resolveRemoteTrackingBase).toHaveBeenCalledWith(
       '/workspace/repo',
       'origin/master'
diff --git a/src/main/runtime/orca-runtime.test.ts b/src/main/runtime/orca-runtime.test.ts
index 2b515e230bb..3b8508c9313 100644
--- a/src/main/runtime/orca-runtime.test.ts
+++ b/src/main/runtime/orca-runtime.test.ts
@@ -41,7 +41,7 @@ import {
   runHook,
   shouldRunSetupForCreate
 } from '../hooks'
-import { getBranchConflictKind, getDefaultBaseRef } from '../git/repo'
+import { getBaseRefDefault, getBranchConflictKind } from '../git/repo'
 import type { OrchestrationDb } from './orchestration/db'
 import type { MessagePriority, MessageRow, MessageType } from './orchestration/types'
 import {
@@ -516,16 +516,23 @@ vi.mock('../github/issues', async (importOriginal) => {
   }
 })
 
-// Why: the CLI create-worktree path calls getDefaultBaseRef to resolve a
-// fallback base branch. Real resolution shells out to `git` against the
-// test's fabricated repo path, which has no refs, so we stub it to a
-// predictable 'origin/main'. The runtime no longer silently fabricates this
-// default, so tests that want the legacy behavior must express it via the mock.
+// Why: CLI worktree creation resolves a default against fabricated repo paths
+// in these tests, so keep the async resolver deterministic.
 vi.mock('../git/repo', async (importOriginal) => {
   const actual = (await importOriginal()) as Record<string, unknown>
+  const actualGetBaseRefDefault = actual.getBaseRefDefault as (
+    path: string,
+    options?: { wslDistro?: string }
+  ) => Promise<string | null>
   return {
     ...actual,
-    getDefaultBaseRef: vi.fn().mockReturnValue('origin/main'),
+    // Why: fabricated local test repos need a deterministic default, while
+    // WSL coverage must still exercise the real async Git-options path.
+    getBaseRefDefault: vi
+      .fn()
+      .mockImplementation((path: string, options?: { wslDistro?: string }) =>
+        options?.wslDistro ? actualGetBaseRefDefault(path, options) : Promise.resolve('origin/main')
+      ),
     getBranchConflictKind: vi.fn().mockResolvedValue(null)
   }
 })
@@ -2825,7 +2832,7 @@ describe('OrcaRuntimeService', () => {
           suggestLocalBaseRefUpdate: true
         }
       )
-      expect(getDefaultBaseRef).toHaveBeenCalled()
+      expect(getBaseRefDefault).toHaveBeenCalled()
     } finally {
       getReposSpy.mockRestore()
       gitSpy.mockRestore()
@@ -5330,7 +5337,7 @@ describe('OrcaRuntimeService', () => {
 
   it('treats SSH worktree drift as unknown without local git probes', async () => {
     vi.mocked(listWorktrees).mockClear()
-    vi.mocked(getDefaultBaseRef).mockClear()
+    vi.mocked(getBaseRefDefault).mockClear()
     const remoteStore = {
       ...store,
       getRepos: () => [
@@ -5366,7 +5373,7 @@ describe('OrcaRuntimeService', () => {
     }
 
     expect(gitProvider.listWorktrees).toHaveBeenCalledWith('/remote/repo')
-    expect(getDefaultBaseRef).not.toHaveBeenCalled()
+    expect(getBaseRefDefault).not.toHaveBeenCalled()
     expect(listWorktrees).not.toHaveBeenCalled()
   })
 
diff --git a/src/main/runtime/orca-runtime.ts b/src/main/runtime/orca-runtime.ts
index b7e4c1d2c30..a4dea13dd80 100644
--- a/src/main/runtime/orca-runtime.ts
+++ b/src/main/runtime/orca-runtime.ts
@@ -599,7 +599,6 @@ import type {
 } from '../../shared/github-project-types'
 import {
   getBaseRefDefault,
-  getDefaultBaseRef,
   getDefaultRemote,
   getBranchConflictKind,
   isGitRepo,
@@ -14249,7 +14248,7 @@ export class OrcaRuntimeService {
       resolveDefaultBaseRef: () =>
         hasLocalWorktreeGitOptions
           ? resolveDefaultBaseRefViaExec((argv) => gitExecFileAsync(argv, localGitExecOptions))
-          : Promise.resolve(getDefaultBaseRef(repo.path)),
+          : getBaseRefDefault(repo.path),
       isBaseUsable: async (baseBranchCandidate) => {
         const remoteTrackingBase = await this.resolveRemoteTrackingBase(
           repo.path,
@@ -14280,10 +14279,8 @@ export class OrcaRuntimeService {
       }
     })
     if (!baseBranch) {
-      // Why: getDefaultBaseRef returns null when no suitable ref exists.
-      // Don't fabricate 'origin/main' — passing it to addWorktree would
-      // produce an opaque git failure. Surface a clear error so the CLI
-      // caller can pick an explicit --base ref.
+      // Why: a null default means no suitable ref exists; fail clearly instead
+      // of handing Git a fabricated origin/main ref.
       throw new Error(
         'Could not resolve a default base ref for this repo. Pass an explicit --base and try again.'
       )
diff --git a/src/main/worktree-create-base-prefetch.ts b/src/main/worktree-create-base-prefetch.ts
index 42add57be66..8653c6866eb 100644
--- a/src/main/worktree-create-base-prefetch.ts
+++ b/src/main/worktree-create-base-prefetch.ts
@@ -2,7 +2,7 @@ import { isFolderRepo } from '../shared/repo-kind'
 import type { Repo } from '../shared/types'
 import { hasLocalCommitObject, isFullGitObjectId } from './git/commit-object-ref'
 import { hasWorktreeBaseCommitRef } from './git/worktree-base-ref-probe'
-import { getDefaultBaseRef } from './git/repo'
+import { getBaseRefDefault } from './git/repo'
 import { getSshGitProvider } from './providers/ssh-git-dispatch'
 import { prefetchRemoteWorktreeCreateBase } from './ipc/worktree-remote'
 import { resolveWorktreeCreateBase } from './worktree-create-base'
@@ -48,7 +48,7 @@ async function prefetchLocalWorktreeCreateBase(
   const resolvedBaseBranch = await resolveWorktreeCreateBase({
     requestedBaseBranch: baseBranch,
     repoWorktreeBaseRef: repo.worktreeBaseRef,
-    resolveDefaultBaseRef: async () => getDefaultBaseRef(repo.path),
+    resolveDefaultBaseRef: () => getBaseRefDefault(repo.path),
     isBaseUsable: async (baseBranchCandidate) => {
       const remoteTrackingBase = await runtime.resolveRemoteTrackingBase(
         repo.path,