Major refactor: API, providers, messaging, and Anthropic protocol

Consolidates the incremental refactor work into a single change set: modular web tools (api/web_tools), native Anthropic request building and SSE block policy, OpenAI conversion and error handling, provider transports and rate limiting, messaging handler and tree queue, safe logging, smoke tests, and broad test coverage.

tests/api/test_dependencies.py

@@ -16,7 +16,7 @@ from api.dependencies import (
 )
 from config.nim import NimSettings
 from providers.deepseek import DeepSeekProvider
-from providers.exceptions import UnknownProviderTypeError
+from providers.exceptions import ServiceUnavailableError, UnknownProviderTypeError
 from providers.lmstudio import LMStudioProvider
 from providers.nvidia_nim import NvidiaNimProvider
 from providers.ollama import OllamaProvider
@@ -40,7 +40,7 @@ def _make_mock_settings(**overrides):
     mock.nim = NimSettings()
     mock.http_read_timeout = 300.0
     mock.http_write_timeout = 10.0
-    mock.http_connect_timeout = 2.0
+    mock.http_connect_timeout = 10.0
     mock.enable_model_thinking = True
     for key, value in overrides.items():
         setattr(mock, key, value)
@@ -434,18 +434,17 @@ def test_resolve_provider_per_app_uses_separate_registries() -> None:
         assert p1 is not p2
 
 
-def test_resolve_provider_lazily_installs_registry() -> None:
-    """If app has no provider_registry, one is created on app.state."""
+def test_resolve_provider_missing_registry_raises_service_unavailable() -> None:
+    """HTTP apps must install app.state.provider_registry (e.g. via AppRuntime)."""
     with patch("api.dependencies.get_settings") as mock_settings:
         mock_settings.return_value = _make_mock_settings()
         settings = _make_mock_settings()
         app = SimpleNamespace(state=State())
         assert getattr(app.state, "provider_registry", None) is None
-        resolve_provider("nvidia_nim", app=cast(Starlette, app), settings=settings)
-        reg = app.state.provider_registry
-        assert reg is not None
-        p2 = resolve_provider("nvidia_nim", app=cast(Starlette, app), settings=settings)
-        assert p2 is reg.get("nvidia_nim", settings)  # same registry instance
+        with pytest.raises(
+            ServiceUnavailableError, match="Provider registry is not configured"
+        ):
+            resolve_provider("nvidia_nim", app=cast(Starlette, app), settings=settings)
 
 
 def test_resolve_provider_unrelated_value_error_is_not_unknown_provider_log() -> None: