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

chatmock/fast_mode.py

@@ -0,0 +1,92 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+from .model_registry import normalize_model_name
+
+
+PRIORITY_SUPPORTED_MODELS = frozenset(
+    (
+        "gpt-5.4",
+        "gpt-5.2",
+        "gpt-5.1",
+        "gpt-5",
+        "gpt-5.1-codex",
+        "gpt-5-codex",
+    )
+)
+
+_TRUE_STRINGS = {"1", "true", "yes", "on"}
+_FALSE_STRINGS = {"0", "false", "no", "off"}
+
+
+def parse_optional_bool(value: Any) -> bool | None:
+    if isinstance(value, bool):
+        return value
+    if isinstance(value, str):
+        normalized = value.strip().lower()
+        if normalized in _TRUE_STRINGS:
+            return True
+        if normalized in _FALSE_STRINGS:
+            return False
+    return None
+
+
+def supports_priority_service_tier(model: str | None) -> bool:
+    return normalize_model_name(model) in PRIORITY_SUPPORTED_MODELS
+
+
+@dataclass(frozen=True)
+class ServiceTierResolution:
+    service_tier: str | None
+    error_message: str | None = None
+    warning_message: str | None = None
+    used_server_default: bool = False
+
+
+def resolve_service_tier(
+    model: str | None,
+    *,
+    request_fast_mode: Any = None,
+    request_service_tier: Any = None,
+    server_fast_mode: bool = False,
+) -> ServiceTierResolution:
+    explicit_fast_mode = parse_optional_bool(request_fast_mode)
+
+    tier: str | None = None
+    explicit_request = False
+    used_server_default = False
+
+    if explicit_fast_mode is not None:
+        tier = "priority" if explicit_fast_mode else None
+        explicit_request = True
+    elif isinstance(request_service_tier, str) and request_service_tier.strip():
+        tier = request_service_tier.strip().lower()
+        explicit_request = True
+    elif server_fast_mode:
+        tier = "priority"
+        used_server_default = True
+
+    if tier == "priority" and not supports_priority_service_tier(model):
+        normalized = normalize_model_name(model)
+        message = (
+            f"Fast mode is not supported for model '{normalized}'. "
+            "Use a supported GPT-5 priority-processing model or disable fast mode for this request."
+        )
+        if explicit_request:
+            return ServiceTierResolution(
+                service_tier=None,
+                error_message=message,
+                used_server_default=used_server_default,
+            )
+        return ServiceTierResolution(
+            service_tier=None,
+            warning_message=message,
+            used_server_default=used_server_default,
+        )
+
+    return ServiceTierResolution(
+        service_tier=tier,
+        used_server_default=used_server_default,
+    )