diff --git a/config/scripts/run-internal-dev-setup.mjs b/config/scripts/run-internal-dev-setup.mjs
new file mode 100644
index 000000000..6bd3733dc
--- /dev/null
+++ b/config/scripts/run-internal-dev-setup.mjs
@@ -0,0 +1,64 @@
+#!/usr/bin/env node
+import { accessSync, constants, existsSync } from 'node:fs'
+import { spawnSync } from 'node:child_process'
+import { resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+function isExecutable(filePath, platform, access = accessSync) {
+  if (platform === 'win32') {
+    return true
+  }
+
+  try {
+    access(filePath, constants.X_OK)
+    return true
+  } catch {
+    return false
+  }
+}
+
+function quoteWindowsArg(value) {
+  return `"${value.replace(/"/g, '""')}"`
+}
+
+function spawnOptionalSetup(spawn, setupPath, worktreePath, platform, env) {
+  if (platform === 'win32') {
+    spawn(
+      env.ComSpec || 'cmd.exe',
+      ['/d', '/s', '/c', `call ${quoteWindowsArg(setupPath)} ${quoteWindowsArg(worktreePath)}`],
+      {
+        stdio: 'inherit',
+        windowsVerbatimArguments: true
+      }
+    )
+    return
+  }
+
+  spawn(setupPath, [worktreePath], {
+    stdio: 'inherit'
+  })
+}
+
+export function runInternalDevSetup({
+  env = process.env,
+  cwd = process.cwd(),
+  platform = process.platform,
+  exists = existsSync,
+  access = accessSync,
+  spawn = spawnSync
+} = {}) {
+  const setupPath = env.ORCA_INTERNAL_DEV_SETUP?.trim()
+  if (!setupPath || !exists(setupPath) || !isExecutable(setupPath, platform, access)) {
+    return 0
+  }
+
+  // Why: this hook is an optional local accelerator; failures should not block
+  // creating a worktree or running the normal dependency install.
+  spawnOptionalSetup(spawn, setupPath, env.ORCA_WORKTREE_PATH || cwd, platform, env)
+
+  return 0
+}
+
+if (process.argv[1] && resolve(fileURLToPath(import.meta.url)) === resolve(process.argv[1])) {
+  process.exit(runInternalDevSetup())
+}
diff --git a/config/scripts/run-internal-dev-setup.test.mjs b/config/scripts/run-internal-dev-setup.test.mjs
new file mode 100644
index 000000000..b00073156
--- /dev/null
+++ b/config/scripts/run-internal-dev-setup.test.mjs
@@ -0,0 +1,85 @@
+import { describe, expect, it, vi } from 'vitest'
+import { runInternalDevSetup } from './run-internal-dev-setup.mjs'
+
+describe('runInternalDevSetup', () => {
+  it('does nothing when ORCA_INTERNAL_DEV_SETUP is unset', () => {
+    const spawn = vi.fn()
+
+    expect(runInternalDevSetup({ env: {}, exists: vi.fn(), spawn })).toBe(0)
+    expect(spawn).not.toHaveBeenCalled()
+  })
+
+  it('does nothing when the configured setup path does not exist', () => {
+    const spawn = vi.fn()
+
+    expect(
+      runInternalDevSetup({
+        env: { ORCA_INTERNAL_DEV_SETUP: '/tmp/missing' },
+        exists: () => false,
+        spawn
+      })
+    ).toBe(0)
+    expect(spawn).not.toHaveBeenCalled()
+  })
+
+  it('skips non-executable setup paths on POSIX', () => {
+    const spawn = vi.fn()
+
+    expect(
+      runInternalDevSetup({
+        env: { ORCA_INTERNAL_DEV_SETUP: '/tmp/setup' },
+        platform: 'linux',
+        exists: () => true,
+        access: () => {
+          throw new Error('EACCES')
+        },
+        spawn
+      })
+    ).toBe(0)
+    expect(spawn).not.toHaveBeenCalled()
+  })
+
+  it('runs the optional setup with the worktree path and ignores its exit status', () => {
+    const spawn = vi.fn(() => ({ status: 1 }))
+
+    expect(
+      runInternalDevSetup({
+        env: {
+          ORCA_INTERNAL_DEV_SETUP: '/tmp/setup',
+          ORCA_WORKTREE_PATH: '/tmp/worktree'
+        },
+        platform: 'linux',
+        exists: () => true,
+        access: () => undefined,
+        spawn
+      })
+    ).toBe(0)
+    expect(spawn).toHaveBeenCalledWith('/tmp/setup', ['/tmp/worktree'], {
+      stdio: 'inherit'
+    })
+  })
+
+  it('uses cmd.exe with explicit quoting so .cmd setup shims receive paths with spaces', () => {
+    const spawn = vi.fn(() => ({ status: 0 }))
+
+    expect(
+      runInternalDevSetup({
+        env: {
+          ORCA_INTERNAL_DEV_SETUP: 'C:\\tools\\setup.cmd',
+          ORCA_WORKTREE_PATH: 'C:\\repo\\worktree'
+        },
+        platform: 'win32',
+        exists: () => true,
+        spawn
+      })
+    ).toBe(0)
+    expect(spawn).toHaveBeenCalledWith(
+      'cmd.exe',
+      ['/d', '/s', '/c', 'call "C:\\tools\\setup.cmd" "C:\\repo\\worktree"'],
+      {
+        stdio: 'inherit',
+        windowsVerbatimArguments: true
+      }
+    )
+  })
+})
diff --git a/orca.yaml b/orca.yaml
index 5dad55e82..6b7ccd6f1 100644
--- a/orca.yaml
+++ b/orca.yaml
@@ -1,5 +1,4 @@
 scripts:
   setup: |
-    [ -n "$ORCA_INTERNAL_DEV_SETUP" ] && [ -x "$ORCA_INTERNAL_DEV_SETUP" ] && \
-      "$ORCA_INTERNAL_DEV_SETUP" "$ORCA_WORKTREE_PATH" || true
+    node config/scripts/run-internal-dev-setup.mjs
     pnpm install
diff --git a/src/main/hooks-runner.test.ts b/src/main/hooks-runner.test.ts
index cb8e1b8c9..da98c8ddb 100644
--- a/src/main/hooks-runner.test.ts
+++ b/src/main/hooks-runner.test.ts
@@ -185,33 +185,45 @@ describe('createIssueCommandRunnerScript', () => {
 
   it('writes a POSIX runner under the worktree git dir for long issue commands', async () => {
     const fs = await import('fs')
+    const originalPlatform = process.platform
 
     execFileSyncMock.mockReturnValue(
       '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh'
     )
-
-    const { createIssueCommandRunnerScript } = await import('./hooks')
-    const result = createIssueCommandRunnerScript(
-      makeRepo(),
-      '/test/repo-feature',
-      'codex exec "long command"\nclaude -p "review it"'
-    )
-
-    expect(result).toEqual({
-      runnerScriptPath: '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
-      envVars: expect.objectContaining({
-        ORCA_ROOT_PATH: '/test/repo',
-        ORCA_WORKTREE_PATH: '/test/repo-feature'
-      })
+    Object.defineProperty(process, 'platform', {
+      configurable: true,
+      value: 'linux'
     })
-    expect(vi.mocked(fs.writeFileSync)).toHaveBeenCalledWith(
-      '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
-      '#!/usr/bin/env bash\nset -e\ncodex exec "long command"\nclaude -p "review it"\n',
-      'utf-8'
-    )
-    expect(vi.mocked(fs.chmodSync)).toHaveBeenCalledWith(
-      '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
-      0o755
-    )
+
+    try {
+      const { createIssueCommandRunnerScript } = await import('./hooks')
+      const result = createIssueCommandRunnerScript(
+        makeRepo(),
+        '/test/repo-feature',
+        'codex exec "long command"\nclaude -p "review it"'
+      )
+
+      expect(result).toEqual({
+        runnerScriptPath: '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
+        envVars: expect.objectContaining({
+          ORCA_ROOT_PATH: '/test/repo',
+          ORCA_WORKTREE_PATH: '/test/repo-feature'
+        })
+      })
+      expect(vi.mocked(fs.writeFileSync)).toHaveBeenCalledWith(
+        '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
+        '#!/usr/bin/env bash\nset -e\ncodex exec "long command"\nclaude -p "review it"\n',
+        'utf-8'
+      )
+      expect(vi.mocked(fs.chmodSync)).toHaveBeenCalledWith(
+        '/test/repo/.git/worktrees/feature/orca/issue-command-runner.sh',
+        0o755
+      )
+    } finally {
+      Object.defineProperty(process, 'platform', {
+        configurable: true,
+        value: originalPlatform
+      })
+    }
   })
 })