feat: add responses api, websocket support, and fast mode

tests/test_fast_mode.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import unittest
+
+from chatmock.fast_mode import parse_optional_bool, resolve_service_tier, supports_priority_service_tier
+
+
+class FastModeTests(unittest.TestCase):
+    def test_parse_optional_bool(self) -> None:
+        self.assertTrue(parse_optional_bool(True))
+        self.assertTrue(parse_optional_bool("true"))
+        self.assertFalse(parse_optional_bool(False))
+        self.assertFalse(parse_optional_bool("off"))
+        self.assertIsNone(parse_optional_bool("maybe"))
+
+    def test_priority_allowlist_uses_normalized_model_ids(self) -> None:
+        self.assertTrue(supports_priority_service_tier("gpt5.4"))
+        self.assertFalse(supports_priority_service_tier("gpt-5.3-codex"))
+
+    def test_explicit_fast_mode_true_errors_for_unsupported_model(self) -> None:
+        resolution = resolve_service_tier(
+            "gpt-5.3-codex",
+            request_fast_mode=True,
+            server_fast_mode=False,
+        )
+        self.assertIsNone(resolution.service_tier)
+        self.assertIsNotNone(resolution.error_message)
+
+    def test_server_default_fast_mode_falls_back_on_unsupported_model(self) -> None:
+        resolution = resolve_service_tier(
+            "gpt-5.3-codex",
+            server_fast_mode=True,
+        )
+        self.assertIsNone(resolution.service_tier)
+        self.assertIsNone(resolution.error_message)
+        self.assertIsNotNone(resolution.warning_message)
+
+    def test_request_fast_mode_false_overrides_server_default(self) -> None:
+        resolution = resolve_service_tier(
+            "gpt-5.4",
+            request_fast_mode=False,
+            server_fast_mode=True,
+        )
+        self.assertIsNone(resolution.service_tier)
+        self.assertIsNone(resolution.error_message)
+
+
+if __name__ == "__main__":
+    unittest.main()