feat: add sender/recipient accept gates, security+stress test harnesses, nix flake, and docs

tests/test_lookup_server.py

@@ -8,22 +8,27 @@ from pneumatube.lookup_server import _lookup
 
 
 class _StubBridge:
-    def __init__(self, known):
+    def __init__(self, known, accepted=None):
         self.known = known
+        self.accepted = known if accepted is None else accepted
 
     def user_exists(self, username):
         if username == "broken":
             return None
         return username in self.known
 
+    def recipient_accepted_gateway(self, username):
+        return username in self.accepted
+
 
 class _InlineWorker:
     async def run(self, fn, *args):
         return fn(*args)
 
 
-def _config():
-    return SimpleNamespace(email_domain="gateway.example")
+def _config(**overrides):
+    defaults = {"email_domain": "gateway.example", "require_accepted_recipient": True}
+    return SimpleNamespace(**{**defaults, **overrides})
 
 
 def test_lookup_known_user_returns_ok():
@@ -52,3 +57,20 @@ def test_lookup_other_domain_has_no_opinion():
     bridge = _StubBridge({"alice"})
     reply = asyncio.run(_lookup(bridge, _InlineWorker(), _config(), "alice@other.example"))
     assert reply == "500 not found"
+
+
+def test_lookup_rejects_unaccepted_recipient_by_default():
+    bridge = _StubBridge({"alice"}, accepted=set())
+    reply = asyncio.run(_lookup(bridge, _InlineWorker(), _config(), "alice@gateway.example"))
+    code, _, text = reply.partition(" ")
+    assert code == "200"
+    assert unquote(text) == "550 5.7.1 recipient has not accepted mail from this gateway"
+
+
+def test_lookup_allows_unaccepted_recipient_when_disabled():
+    bridge = _StubBridge({"alice"}, accepted=set())
+    config = _config(require_accepted_recipient=False)
+    reply = asyncio.run(_lookup(bridge, _InlineWorker(), config, "alice@gateway.example"))
+    code, _, text = reply.partition(" ")
+    assert code == "200"
+    assert unquote(text) == "OK"