fix(email): don't probe IMAP for send-only (SMTP-only) accounts (#4830)

An account configured with SMTP only (no imap_host) has no inbox, but the
inbox list path still called _imap_connect, which handed an empty host to
imaplib. imaplib.IMAP4("", 993) silently dials localhost:993 and fails with
"[Errno 111] Connection refused", so the email panel's poll logged a
"Failed to list emails" ERROR every ~60s and surfaced a scary error in the UI.

_imap_connect now fails fast with a typed EmailNotConfiguredError (subclass of
RuntimeError, so existing broad handlers keep working) when no imap_host is set,
and the inbox list returns an empty result for that case instead of an error.
SMTP send is unaffected.

tests/test_email_send_only_no_inbox.py

@@ -0,0 +1,75 @@
+"""A send-only (SMTP-only) account has no inbox to read.
+
+`_imap_connect` must fail fast with a clear, typed error instead of handing an
+empty host to imaplib — `imaplib.IMAP4("", 993)` silently dials localhost:993
+and surfaces a confusing "[Errno 111] Connection refused" on every inbox poll.
+"""
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+
+_tmp_data = Path(tempfile.mkdtemp(prefix="odysseus-email-send-only-test-"))
+os.environ.setdefault("DATA_DIR", str(_tmp_data))
+os.environ.setdefault("DATABASE_URL", f"sqlite:///{_tmp_data / 'app.db'}")
+
+import routes.email_helpers as helpers
+from routes.email_helpers import EmailNotConfiguredError, _imap_connect
+
+
+_SEND_ONLY_CFG = {
+    "account_id": "acct-send-only",
+    "account_name": "send-only",
+    "smtp_host": "smtp.example.org",
+    "smtp_port": 465,
+    "smtp_user": "noreply@example.org",
+    "smtp_password": "secret",
+    "imap_host": "",          # <- the send-only marker
+    "imap_port": 993,
+    "imap_user": "",
+    "imap_password": "",
+    "imap_starttls": True,
+    "from_address": "noreply@example.org",
+}
+
+
+def test_not_configured_error_is_runtime_error():
+    # Subclassing RuntimeError keeps existing broad `except Exception` handlers
+    # working while letting the inbox poll catch this case specifically.
+    assert issubclass(EmailNotConfiguredError, RuntimeError)
+
+
+def test_imap_connect_send_only_raises_and_never_dials(monkeypatch):
+    monkeypatch.setattr(helpers, "_get_email_config", lambda *a, **k: dict(_SEND_ONLY_CFG))
+
+    def _boom(*a, **k):  # opening a connection means we dialed an empty host
+        raise AssertionError("send-only account must not open an IMAP connection")
+
+    monkeypatch.setattr(helpers, "_open_imap_connection", _boom)
+
+    with pytest.raises(EmailNotConfiguredError):
+        _imap_connect("acct-send-only")
+
+
+def test_imap_connect_with_host_still_connects(monkeypatch):
+    # Guard must not regress normal accounts: a configured imap_host still
+    # reaches _open_imap_connection.
+    cfg = dict(_SEND_ONLY_CFG, imap_host="imap.example.org", imap_user="u", imap_password="p")
+    monkeypatch.setattr(helpers, "_get_email_config", lambda *a, **k: cfg)
+
+    opened = {}
+
+    class _FakeConn:
+        def login(self, user, password):
+            opened["login"] = (user, password)
+
+    def _fake_open(host, port, *, starttls, timeout):
+        opened["host"] = host
+        return _FakeConn()
+
+    monkeypatch.setattr(helpers, "_open_imap_connection", _fake_open)
+
+    conn = _imap_connect("acct-with-imap")
+    assert opened["host"] == "imap.example.org"
+    assert isinstance(conn, _FakeConn)