Share _signature_cache with uncalled-for (#357)

`docket.execution` had its own `_signature_cache` dict, separate from
the one in `uncalled_for.introspection`. FastMCP clears
`docket.execution._signature_cache` after mutating function signatures
(via `transform_context_annotations`), but `get_dependency_parameters`
reads from uncalled-for's copy — so the stale entry stuck around and
dependency resolution silently returned `{}`.

Now both `_signature_cache` and `_parameter_cache` are re-exported from
uncalled-for, so there's one shared dict for each. Added contract tests
asserting cache identity.

🤖 Generated with Claude Code

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: chrisguidry

src/docket/dependencies/_functional.py

@@ -11,6 +11,11 @@
     SharedContext as SharedContext,
 )
 from uncalled_for.functional import _Depends as _UncalledForDepends
+
+# Re-export _parameter_cache from uncalled-for so that docket and uncalled-for
+# share one cache dict.  FastMCP clears `docket.dependencies._parameter_cache`
+# after mutating function signatures, so this must be the same object that
+# uncalled-for's get_dependency_parameters uses internally.
 from uncalled_for.introspection import (
     _parameter_cache as _parameter_cache,
     get_dependency_parameters,

src/docket/execution.py

@@ -25,6 +25,15 @@
 from ._telemetry import suppress_instrumentation
 from typing_extensions import Self
 
+# Re-export _signature_cache from uncalled-for so that docket and uncalled-for
+# share one cache dict.  FastMCP clears `docket.execution._signature_cache` after
+# mutating function signatures, so this must be the same object that
+# uncalled-for's get_dependency_parameters uses internally.
+from uncalled_for.introspection import (
+    _signature_cache as _signature_cache,
+    get_signature as _uncalled_for_get_signature,
+)
+
 from ._execution_progress import ExecutionProgress, ProgressEvent, StateEvent
 from .annotations import Logged
 from .instrumentation import CACHE_SIZE, message_getter, message_setter
@@ -51,22 +60,8 @@ async def __call__(
     ) -> str: ...  # pragma: no cover
 
 
-_signature_cache: dict[Callable[..., Any], inspect.Signature] = {}
-
-
 def get_signature(function: Callable[..., Any]) -> inspect.Signature:
-    if function in _signature_cache:
-        CACHE_SIZE.set(len(_signature_cache), {"cache": "signature"})
-        return _signature_cache[function]
-
-    signature_attr = getattr(function, "__signature__", None)
-    if isinstance(signature_attr, inspect.Signature):
-        _signature_cache[function] = signature_attr
-        CACHE_SIZE.set(len(_signature_cache), {"cache": "signature"})
-        return signature_attr
-
-    signature = inspect.signature(function)
-    _signature_cache[function] = signature
+    signature = _uncalled_for_get_signature(function)
     CACHE_SIZE.set(len(_signature_cache), {"cache": "signature"})
     return signature
 

tests/test_uncalled_for_contract.py

@@ -201,3 +201,24 @@ def test_failed_dependency_captures_parameter_and_error():
 
     assert failed.parameter == "my_param"
     assert failed.error is error
+
+
+# --- Cache identity ---
+# Docket re-exports _signature_cache and _parameter_cache from uncalled-for.
+# FastMCP clears these caches after mutating function signatures (e.g.
+# transform_context_annotations), so docket's re-exports MUST be the same
+# dict objects that uncalled-for uses internally.
+
+
+def test_signature_cache_is_shared_with_uncalled_for():
+    from docket.execution import _signature_cache  # pyright: ignore[reportPrivateUsage]
+    from uncalled_for.introspection import _signature_cache as uf_cache  # pyright: ignore[reportPrivateUsage]
+
+    assert _signature_cache is uf_cache
+
+
+def test_parameter_cache_is_shared_with_uncalled_for():
+    from docket.dependencies import _parameter_cache  # pyright: ignore[reportPrivateUsage]
+    from uncalled_for.introspection import _parameter_cache as uf_cache  # pyright: ignore[reportPrivateUsage]
+
+    assert _parameter_cache is uf_cache