feat: add pneumatube gateway bridging smolmail and SMTP via LMTP

tests/test_smtp_server.py

@@ -0,0 +1,60 @@
+import asyncio
+from types import SimpleNamespace
+
+import pytest
+
+from pneumatube.smtp_server import GatewayHandler
+
+
+class _StubBridge:
+    def __init__(self):
+        self.forwarded = []
+
+    def forward(self, username, sender, subject, body):
+        self.forwarded.append(username)
+        if username == "broken":
+            raise RuntimeError("smolmail server unreachable")
+
+    @staticmethod
+    def extract_text(message):
+        return message.get_payload(decode=True).decode("utf-8", "replace")
+
+
+class _InlineWorker:
+    """Runs synchronously: handle_DATA's per-recipient logic doesn't depend
+    on real threading, just on worker.run's (fn, *args) -> result contract."""
+
+    async def run(self, fn, *args):
+        return fn(*args)
+
+
+def _envelope(rcpt_tos):
+    return SimpleNamespace(
+        content=b"Subject: hi\r\n\r\nbody text\r\n",
+        mail_from="sender@realmail.example",
+        rcpt_tos=rcpt_tos,
+    )
+
+
+def test_handle_data_replies_once_per_recipient():
+    bridge = _StubBridge()
+    handler = GatewayHandler(bridge, _InlineWorker(), config=SimpleNamespace())
+    envelope = _envelope(["alice@gateway.example", "broken@gateway.example"])
+
+    reply = asyncio.run(handler.handle_DATA(None, None, envelope))
+    lines = reply.split("\r\n")
+
+    assert len(lines) == 2
+    assert lines[0].startswith("250")
+    assert lines[1].startswith("451")
+    assert bridge.forwarded == ["alice", "broken"]
+
+
+def test_handle_data_all_succeed():
+    bridge = _StubBridge()
+    handler = GatewayHandler(bridge, _InlineWorker(), config=SimpleNamespace())
+    envelope = _envelope(["alice@gateway.example", "bob@gateway.example"])
+
+    reply = asyncio.run(handler.handle_DATA(None, None, envelope))
+
+    assert reply == "250 2.1.5 delivered\r\n250 2.1.5 delivered"