test: use await import instead of require in rpc-headers test

Avoids the @typescript-eslint/no-var-requires lint error flagged in
review. Dynamic import + jest.resetModules() re-evaluates the module so
the RPC_HEADER_SECRET branch is still exercised per case.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: codyborn

test/unit/util/rpc-headers.test.ts

@@ -1,5 +1,5 @@
 // RPC_HEADERS reads RPC_HEADER_SECRET at module load, so each case sets the env
-// and re-imports the module in isolation.
+// and re-imports the module after resetting the module registry.
 describe('RPC_HEADERS', () => {
   const savedEnv = { ...process.env }
 
@@ -8,26 +8,23 @@ describe('RPC_HEADERS', () => {
     jest.resetModules()
   })
 
-  const loadHeaders = (): { [key: string]: string } => {
-    let headers: { [key: string]: string } = {}
-    jest.isolateModules(() => {
-      headers = require('../../../lib/util/constants').RPC_HEADERS
-    })
-    return headers
+  const loadHeaders = async (): Promise<{ [key: string]: string }> => {
+    jest.resetModules()
+    return (await import('../../../lib/util/constants')).RPC_HEADERS
   }
 
-  it('always sets the service id header', () => {
+  it('always sets the service id header', async () => {
     delete process.env.RPC_HEADER_SECRET
-    expect(loadHeaders()['x-uni-service-id']).toEqual('x_order_service')
+    expect((await loadHeaders())['x-uni-service-id']).toEqual('x_order_service')
   })
 
-  it('adds the x-internal-service-secret header when RPC_HEADER_SECRET is set', () => {
+  it('adds the x-internal-service-secret header when RPC_HEADER_SECRET is set', async () => {
     process.env.RPC_HEADER_SECRET = 'super-secret-value'
-    expect(loadHeaders()['x-internal-service-secret']).toEqual('super-secret-value')
+    expect((await loadHeaders())['x-internal-service-secret']).toEqual('super-secret-value')
   })
 
-  it('omits the x-internal-service-secret header when RPC_HEADER_SECRET is unset', () => {
+  it('omits the x-internal-service-secret header when RPC_HEADER_SECRET is unset', async () => {
     delete process.env.RPC_HEADER_SECRET
-    expect(loadHeaders()).not.toHaveProperty('x-internal-service-secret')
+    expect(await loadHeaders()).not.toHaveProperty('x-internal-service-secret')
   })
 })