feat(service): add wait_for_approval and return the cache for a login with no prompt

A pair code shown in a log line never answers a prompt, so the server read that login as anonymous and kept the session cache.

tests/core/test_service_wait_for_approval.py

@@ -0,0 +1,34 @@
+import logging
+from types import SimpleNamespace
+
+import pytest
+
+from unshackle.core.api.input_bridge import InputBridge
+from unshackle.core.service import Service
+
+
+def _service(bridge=None):
+    return SimpleNamespace(log=logging.getLogger("test"), _input_bridge=bridge)
+
+
+def test_returns_the_first_value_check_gives():
+    answers = iter([None, None, "token"])
+    assert Service.wait_for_approval(_service(), "enter code", lambda: next(answers), timeout=5, interval=0) == "token"
+
+
+def test_times_out_when_check_never_gives_a_value():
+    with pytest.raises(TimeoutError):
+        Service.wait_for_approval(_service(), "enter code", lambda: None, timeout=0.05, interval=0.01)
+
+
+def test_stops_when_the_remote_session_is_cancelled():
+    bridge = InputBridge()
+    calls = []
+
+    def check():
+        calls.append(1)
+        bridge.cancel()
+
+    with pytest.raises(RuntimeError):
+        Service.wait_for_approval(_service(bridge), "enter code", check, timeout=5, interval=0)
+    assert len(calls) == 1