fix: only trigger L1-only mode for explicit backend=None at decorator level

Remove buggy check that treated DecoratorConfig.backend defaulting to
None as L1-only mode. Now only @cache(backend=None) triggers L1-only.

For L1-only with presets, use: @cache(backend=None, config=...)

Author: 27Bslash6

src/cachekit/decorators/intent.py

@@ -135,9 +135,6 @@ def decorator(f: F) -> F:
                 if backend is not None:
                     override_dict["backend"] = backend
                 resolved_config = replace(config, **override_dict)
-            # Check if config explicitly specifies backend=None (L1-only mode via config)
-            if not _explicit_l1_only and resolved_config.backend is None:
-                _explicit_l1_only = True
         # Intent-based presets (renamed per Task 6)
         elif _intent == "minimal":  # Renamed from "fast"
             resolved_config = DecoratorConfig.minimal(backend=backend, **manual_overrides)
@@ -160,12 +157,10 @@ def decorator(f: F) -> F:
             # No intent specified - use default DecoratorConfig with overrides
             resolved_config = DecoratorConfig(backend=backend, **manual_overrides)
 
-        # Check if resolved config has backend=None (L1-only mode)
-        # This catches both explicit backend=None in manual_overrides AND backend=None via config presets
-        if not _explicit_l1_only and resolved_config.backend is None:
-            _explicit_l1_only = True
-
         # Delegate to wrapper factory with L1-only mode flag
+        # Note: _explicit_l1_only is ONLY set when backend=None was explicitly passed
+        # via manual_overrides. DecoratorConfig.backend defaults to None, but that
+        # should NOT trigger L1-only mode - it should fall back to the provider.
         return _apply_cache_logic(f, resolved_config, _l1_only_mode=_explicit_l1_only)  # type: ignore[return-value]
 
     # Handle both @cache and @cache() syntax

tests/unit/test_l1_only_mode.py

@@ -109,9 +109,14 @@ def slow_function() -> int:
 
     def test_config_minimal_with_backend_none(self):
         """
-        DecoratorConfig.minimal(backend=None) should also use L1-only mode.
+        Test L1-only mode with DecoratorConfig preset AND backend=None.
 
-        The bug can also occur via config objects that specify backend=None.
+        NOTE: L1-only mode requires backend=None at the decorator level, not in config.
+        This is because DecoratorConfig.backend defaults to None, and we can't
+        distinguish "explicit None" from "default None" in the config.
+
+        Correct usage for L1-only with presets:
+            @cache(backend=None, config=DecoratorConfig.minimal())
         """
         from cachekit.config import DecoratorConfig
         from cachekit.decorators import cache
@@ -121,7 +126,8 @@ def test_config_minimal_with_backend_none(self):
 
             call_count = 0
 
-            @cache(config=DecoratorConfig.minimal(backend=None))
+            # L1-only mode: backend=None passed directly to @cache, config for preset settings
+            @cache(backend=None, config=DecoratorConfig.minimal())
             def minimal_func() -> str:
                 nonlocal call_count
                 call_count += 1