[steps] Fix resolving steps sharing a cache folder and running unresolved

docs/internal/steps/expansion_design.md

@@ -51,8 +51,8 @@ class StudyLoader(Step):
 - **Chain resolution**: When this step appears inside a larger Chain, `with_input()` resolves
   it so the built chain integrates into the parent chain.
 
-- **UID consistency**: `_exca_uid_dict_override` on Step delegates to the resolved Chain
-  representation, so `StudyLoader(transforms=[T1])` and `Chain([StudyLoader(), T1])`
+- **UID consistency**: `_exca_uid_dict_override` on Step exports the resolution,
+  so `StudyLoader(transforms=[T1])` and `Chain([StudyLoader(), T1])`
   produce the same UID.
 
 ### How caching works
@@ -103,6 +103,8 @@ return `self` from `_resolve_step()`, so re-resolution is a no-op.
 ### 5. UID consistency via `_exca_uid_dict_override`
 
 `utils.py` is updated to support `None` return (opt-out). Step's override:
-- Fast path `None` if `"has_resolve"` not in `_step_flags`
 - `None` if `_resolve_step()` returns `self`
-- Otherwise delegates to the returned Step's `_exca_uid_dict_override()`
+- Otherwise the resolution's uid export
+
+`ConfigExporter` applies overrides recursively: nested resolutions affect cache
+keys and `uid.yaml`; `full-uid.yaml`/`config.yaml` retain declared configs.

exca/steps/base.py

@@ -299,12 +299,10 @@ def _make_paths(self, aligned: tp.Sequence[Step]) -> backends.StepPaths:
         return paths
 
     def _exca_uid_dict_override(self) -> dict[str, tp.Any] | None:
-        if "has_resolve" not in self._step_flags:
-            return None
         built = utils.resolved_step(self)
         if built is self:
             return None
-        return built._exca_uid_dict_override()
+        return exca.utils.ConfigExporter(uid=True, exclude_defaults=True).apply(built)
 
     def lookup(
         self,

exca/steps/helpers.py

@@ -199,10 +199,11 @@ def _run_items(self, batch: items.StepItems) -> items.StepItems:
                 f"a step), got {self.infra!r}"
             )
         cbatches = []
-        for child in self.steps:
-            uids = [identity.materialize_uid(child, v) for v in batch]
+        for variant in self.steps:
+            resolved = utils.resolved_step(variant)
+            uids = [identity.materialize_uid(resolved, v) for v in batch]
             child_batch = items.StepItems(source=dict(zip(uids, batch)), uids=uids)
-            cbatches.append(self.infra._prepare(child, child_batch))
+            cbatches.append(self.infra._prepare(resolved, child_batch))
         with self.infra._claim(cbatches) as claimed:
             if claimed.ready:
                 self.infra._execute(claimed.ready)

exca/steps/test_steps.py

@@ -18,7 +18,7 @@
 
 import exca
 
-from . import backends, conftest, identity, items, utils
+from . import backends, conftest, helpers, identity, items, utils
 from .base import Chain, Step
 
 # =============================================================================
@@ -450,6 +450,33 @@ def test_resolve_step_uid_consistency() -> None:
     assert step_uid == chain_uid
 
 
+class _ResolvesToMult(Step):
+    def _run(self, value: float) -> float:
+        return value
+
+    def _resolve_step(self) -> Step:
+        return conftest.Mult(infra=self.infra)
+
+
+class _StepWithBody(Step):
+    body: Step
+
+    def _run(self, value: float) -> float:
+        return value
+
+
+def test_nested_resolution_drives_uid() -> None:
+    resolving_uid = identity.step_uid([_StepWithBody(body=_ResolvesToMult())])
+    assert resolving_uid == identity.step_uid([_StepWithBody(body=conftest.Mult())])
+
+
+def test_parallel_caches_the_resolved_step_result(tmp_path: Path) -> None:
+    infra: tp.Any = {"backend": "Cached", "folder": tmp_path}
+    sweep = helpers.Parallel(steps=[_ResolvesToMult()], infra=infra)
+    sweep.run(5.0)
+    assert sweep.steps[0].lookup(5.0).result() == 10.0
+
+
 def test_resolve_step_runtime_checks(tmp_path: Path) -> None:
     force_infra: tp.Any = {"backend": "Cached", "folder": tmp_path, "mode": "force"}
     chain_infra: tp.Any = {"backend": "Cached", "folder": tmp_path}