fix: auth plugin loginAs injection broken in 4.x (#5502)

* fix: return plugin-injected functions directly from container instead of wrapping in non-callable Proxy

The 4.x ESM migration changed Container.support(name) to always go through
the proxy, which wraps values in lazyLoad() — a Proxy designed for page
objects (property access), not callable functions. This broke the auth
plugin's loginAs/login injection since the returned Proxy has no apply trap.

Also fixes missing-key detection in inject.js (was never firing because
lazyLoad always returns a truthy Proxy).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* revert: inject.js missing-key check change that broke I injection

The `!(key in objects)` check used the proxy's `has` trap which doesn't
include keys added directly to container.support (like the Actor `I`
from createActor). Reverting to the original `!objects[key]` check.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: DavertMik <davert@testomat.io>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

lib/container.js

@@ -150,7 +150,9 @@ class Container {
     if (!name) {
       return container.proxySupport
     }
-    // Always return the proxy to ensure MetaStep creation works
+    if (typeof container.support[name] === 'function') {
+      return container.support[name]
+    }
     return container.proxySupport[name]
   }
 
@@ -600,6 +602,8 @@ function createSupportObjects(config) {
         let value
         if (container.sharedKeys.has(prop) && prop in container.support) {
           value = container.support[prop]
+        } else if (prop in container.support && typeof container.support[prop] === 'function') {
+          value = container.support[prop]
         } else {
           value = lazyLoad(prop)
         }
@@ -614,6 +618,9 @@ function createSupportObjects(config) {
         if (container.sharedKeys.has(key) && key in container.support) {
           return container.support[key]
         }
+        if (key in container.support && typeof container.support[key] === 'function') {
+          return container.support[key]
+        }
         return lazyLoad(key)
       },
     },

test/unit/container_test.js

@@ -287,6 +287,17 @@ describe('Container', () => {
       expect(container.support('userPage')).is.ok
       expect(container.support('userPage').login).is.eql('#login')
     })
+
+    it('should be able to add and retrieve a function as a support object', async () => {
+      await container.create({})
+      const loginFunction = async name => `logged in as ${name}`
+      container.append({ support: { loginAs: loginFunction } })
+      expect(container.support('I')).is.ok
+      const loginAs = container.support('loginAs')
+      expect(loginAs).to.be.a('function')
+      const result = await loginAs('admin')
+      expect(result).to.eql('logged in as admin')
+    })
   })
 
   describe('TypeScript support', () => {