diff --git a/src/wf_core/models/input_bindings.py b/src/wf_core/models/input_bindings.py
index 744b5fbe..85749e77 100644
--- a/src/wf_core/models/input_bindings.py
+++ b/src/wf_core/models/input_bindings.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from collections.abc import Mapping
+from collections.abc import Iterator, Mapping
 from typing import Annotated, Literal, TypeAliasType
 
 from pydantic import BaseModel, ConfigDict, Field, field_validator
@@ -103,6 +103,22 @@ type InputExpression = Annotated[
 ]
 
 
+def walk_expression_paths(
+    expression: InputExpression,
+) -> Iterator[tuple[GraphSourcePath, str]]:
+    """Yield graph path leaves with their stable expression locations."""
+    if isinstance(expression, PathExpression):
+        yield expression.path, "path"
+    elif isinstance(expression, ArrayExpression):
+        for index, item in enumerate(expression.items):
+            for path, suffix in walk_expression_paths(item):
+                yield path, f"items[{index}].{suffix}"
+    elif isinstance(expression, ObjectExpression):
+        for field, item in expression.fields.items():
+            for path, suffix in walk_expression_paths(item):
+                yield path, f"fields.{field}.{suffix}"
+
+
 class OccurrenceExpression(BaseModel):
     """Reference one typed schedule-occurrence field.
 
diff --git a/src/wf_core/runtime/input_sources.py b/src/wf_core/runtime/input_sources.py
index cdde45cf..7f9b80c3 100644
--- a/src/wf_core/runtime/input_sources.py
+++ b/src/wf_core/runtime/input_sources.py
@@ -16,7 +16,7 @@ runtime values); budget parity there comes from the same model-level
 
 from __future__ import annotations
 
-from collections.abc import Iterator, Mapping, Sequence
+from collections.abc import Mapping, Sequence
 from typing import Any, Protocol
 
 from wf_core.errors import WorkflowExecutionError
@@ -227,23 +227,3 @@ def resolve_schedule_input_bindings(
             raise WorkflowExecutionError(f"{label} {location}: {exc}") from exc
     return payload
 
-
-def walk_expression_paths(
-    expression: InputExpression,
-) -> Iterator[tuple[GraphSourcePath, str]]:
-    """Yield ``(graph path, location)`` leaves in one shared traversal order.
-
-    Locations use the same ``items[i]`` / ``fields.name`` / ``path`` suffix
-    shape as :func:`wf_core.validation.steps._validate_expression_sources`,
-    so validation and runtime traverse leaves in the same order.
-    """
-    if isinstance(expression, PathExpression):
-        yield expression.path, "path"
-    elif isinstance(expression, ArrayExpression):
-        for index, item in enumerate(expression.items):
-            for path, suffix in walk_expression_paths(item):
-                yield path, f"items[{index}].{suffix}"
-    elif isinstance(expression, ObjectExpression):
-        for field, item in expression.fields.items():
-            for path, suffix in walk_expression_paths(item):
-                yield path, f"fields.{field}.{suffix}"
diff --git a/src/wf_core/validation/steps.py b/src/wf_core/validation/steps.py
index a76003ea..f86b1737 100644
--- a/src/wf_core/validation/steps.py
+++ b/src/wf_core/validation/steps.py
@@ -10,7 +10,11 @@ from wf_core.models.conditions import (
     PathOperand,
     VariadicCondition,
 )
-from wf_core.models.input_bindings import InputExpression, InputExpressionBinding
+from wf_core.models.input_bindings import (
+    InputExpression,
+    InputExpressionBinding,
+    walk_expression_paths,
+)
 from wf_core.models.schemas import NodeDef
 from wf_core.models.steps import (
     ConditionNode,
@@ -33,7 +37,6 @@ from wf_core.paths import (
     is_valid_destination_path,
     is_valid_source_path,
 )
-from wf_core.runtime.input_sources import walk_expression_paths
 from wf_core.validation.issues import ValidationIssueCode, ValidationReport
 
 
@@ -247,7 +250,7 @@ def _validate_expression_sources(
     """Validate every graph path leaf while keeping one top-level target atomic.
 
     Leaf traversal order is the canonical order defined by
-    :func:`wf_core.runtime.input_sources.walk_expression_paths`.
+    :func:`wf_core.models.input_bindings.walk_expression_paths`.
     """
     for path, suffix in walk_expression_paths(expression):
         _validate_source_path(
diff --git a/src/wf_scheduling/dispatch.py b/src/wf_scheduling/dispatch.py
index 69f488f2..fb7425e3 100644
--- a/src/wf_scheduling/dispatch.py
+++ b/src/wf_scheduling/dispatch.py
@@ -14,7 +14,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 from datetime import datetime
-from typing import Protocol, Union
+from typing import Protocol
 
 from wf_artifacts.runs.models import RunAdmission
 from wf_core import RunState
@@ -32,7 +32,7 @@ class StillRunning:
     """Dispatched with an unknown outcome; the run stays admitted."""
 
 
-DispatchResult = Union[Stopped, StillRunning]
+DispatchResult = Stopped | StillRunning
 
 
 class RunDispatcher(Protocol):
diff --git a/src/wf_scheduling/poll.py b/src/wf_scheduling/poll.py
index d7100069..109dff27 100644
--- a/src/wf_scheduling/poll.py
+++ b/src/wf_scheduling/poll.py
@@ -17,7 +17,7 @@ contains no fixture input, fixture environments, or canned results.
 from __future__ import annotations
 
 from datetime import datetime, timezone
-from typing import Any
+from typing import Any, cast
 
 from wf_scheduling.calendar import (
     CronSource,
@@ -31,7 +31,7 @@ from wf_scheduling.history import (
     HistoryEntry,
     HistoryRecorder,
 )
-from wf_scheduling.models import PendingCandidate
+from wf_scheduling.models import OccurrenceKind, PendingCandidate
 from wf_scheduling.ownership import (
     SchedulerOwnership,
     SecondOwnerError,
@@ -258,7 +258,7 @@ class Scheduler:
     def _record(
         self,
         *,
-        kind: str,
+        kind: OccurrenceKind,
         sched_id: str,
         intended: datetime | None = None,
         run_id: str | None = None,
@@ -275,7 +275,7 @@ class Scheduler:
         self.history.record(
             HistoryEntry(
                 schedule_id=sched_id,
-                kind=kind,  # type: ignore[arg-type]
+                kind=kind,
                 resolved_at=intended,
                 run_id=run_id,
                 revision=revision,
@@ -504,13 +504,16 @@ class Scheduler:
             run_id=run_id,
         )
         self.run_store.clear_executing(run_id)
-        kind = {
-            StoredRunStatus.COMPLETED: "completed",
-            StoredRunStatus.INTERRUPTED: "interrupted",
-            StoredRunStatus.FAILED: "failed",
-        }[stopped.status]
+        kind = cast(
+            OccurrenceKind,
+            {
+                StoredRunStatus.COMPLETED: "completed",
+                StoredRunStatus.INTERRUPTED: "interrupted",
+                StoredRunStatus.FAILED: "failed",
+            }[stopped.status],
+        )
         self._record(
-            kind=kind,  # type: ignore[arg-type]
+            kind=kind,
             sched_id=admission.schedule_id,
             intended=_admission_intended(self.run_store, run_id),
             run_id=run_id,
@@ -563,13 +566,16 @@ class Scheduler:
             run_id=run_id,
         )
         self.run_store.clear_executing(run_id)
-        kind = {
-            StoredRunStatus.COMPLETED: "completed",
-            StoredRunStatus.INTERRUPTED: "interrupted",
-            StoredRunStatus.FAILED: "failed",
-        }[stopped.status]
+        kind = cast(
+            OccurrenceKind,
+            {
+                StoredRunStatus.COMPLETED: "completed",
+                StoredRunStatus.INTERRUPTED: "interrupted",
+                StoredRunStatus.FAILED: "failed",
+            }[stopped.status],
+        )
         self._record(
-            kind=kind,  # type: ignore[arg-type]
+            kind=kind,
             sched_id=admission.schedule_id,
             intended=_admission_intended(self.run_store, run_id),
             run_id=run_id,
@@ -597,11 +603,14 @@ class Scheduler:
         history. Returns whether an entry was appended.
         """
         self._require_ownership()
-        kind = {
-            "completed": "completed",
-            "interrupted": "interrupted",
-            "failed": "failed",
-        }.get(status_value)
+        kind = cast(
+            OccurrenceKind | None,
+            {
+                "completed": "completed",
+                "interrupted": "interrupted",
+                "failed": "failed",
+            }.get(status_value),
+        )
         if kind is None:
             return False
         try:
@@ -614,7 +623,7 @@ class Scheduler:
         if self.history.has_terminal(sched_id, run_id, kind, checkpoint_id):
             return False
         self._record(
-            kind=kind,  # type: ignore[arg-type]
+            kind=kind,
             sched_id=sched_id,
             intended=admission.scheduled_at,
             run_id=run_id,
diff --git a/src/wf_scheduling/recovery.py b/src/wf_scheduling/recovery.py
index 7eb1a489..791b5a7d 100644
--- a/src/wf_scheduling/recovery.py
+++ b/src/wf_scheduling/recovery.py
@@ -62,6 +62,7 @@ from wf_scheduling.history import (
     HistoryEntry,
     HistoryRecorder,
 )
+from wf_scheduling.models import OccurrenceKind
 from wf_scheduling.ownership import (
     SchedulerOwnership,
     SecondOwnerError,
@@ -676,7 +677,7 @@ def _reconcile_terminal(
     history: HistoryRecorder,
     sched_id: str | None,
     run_id: str,
-    kind: str,
+    kind: OccurrenceKind,
     checkpoint_id: str | None,
     intended: datetime | None,
     revision: int | None,
@@ -697,7 +698,7 @@ def _reconcile_terminal(
     history.record(
         HistoryEntry(
             schedule_id=sched_id,
-            kind=kind,  # type: ignore[arg-type]
+            kind=kind,
             resolved_at=intended,
             run_id=run_id,
             revision=revision,