added some good stuff

src/wf_authoring/builder.py

@@ -15,9 +15,12 @@ from wf_core import (
     StateSchema,
     Workflow,
 )
+from wf_core.errors import WorkflowExecutionError
 from wf_core.model import Condition as CoreCondition
 
 from .dsl import Expr, GraphPath, PathArg, compile_condition
+from .nodes.callables import SyncRegistryHandler
+from .nodes.registry import build_registry
 from .schemas import SchemaLike, StateSchemaLike, schema_ref_from, state_schema_from
 from .spec import NodeSpec
 
@@ -98,7 +101,7 @@ class WorkflowBuilder:
     input_schema: SchemaLike
     state_schema: StateSchemaLike
     output_schema: SchemaLike
-    start: str
+    start: str | None = None
     node_specs: dict[str, NodeSpec[Any, Any]] = field(default_factory=dict)
     nodes: list[Any] = field(default_factory=list)
     edges: list[Edge] = field(default_factory=list)
@@ -154,6 +157,14 @@ class WorkflowBuilder:
             suffix += 1
         return f"{base}_{suffix}"
 
+    def set_entry_point(self, step: StepRef) -> None:
+        """Set the workflow start node explicitly."""
+        self.start = _step_id(step)
+
+    def registry(self) -> dict[str, SyncRegistryHandler]:
+        """Export handlers for all node specs used by this builder."""
+        return build_registry(*self.node_specs.values())
+
     def condition(self, *, id: str, check: CoreCondition | Expr) -> ConditionNode:
         node = ConditionNode(
             id=id,
@@ -213,6 +224,11 @@ class WorkflowBuilder:
         )
 
     def compile(self) -> Workflow:
+        if self.start is None:
+            raise WorkflowExecutionError(
+                "workflow builder requires an explicit start; call set_entry_point(...) "
+                "or pass start=..."
+            )
         node_defs = [spec.to_node_def() for spec in self.node_specs.values()]
         return Workflow(
             name=self.name,

tests/test_authoring_schemas.py

@@ -4,8 +4,10 @@ from typing import Annotated, TypedDict
 
 from pydantic import BaseModel, Field
 
-from wf_authoring import WorkflowBuilder, build_registry, node, state_field
-from wf_core import RunStatus, execute_workflow
+import pytest
+
+from wf_authoring import WorkflowBuilder, node, state_field
+from wf_core import RunStatus, WorkflowExecutionError, execute_workflow
 
 
 class WorkflowInput(BaseModel):
@@ -138,7 +140,7 @@ def test_builder_auto_binds_matching_node_inputs_and_outputs_to_state() -> None:
     run = execute_workflow(
         workflow,
         {"text": "hello", "count": 1},
-        build_registry(auto_bind_node),
+        builder.registry(),
     )
 
     assert step.in_map == {
@@ -168,3 +170,43 @@ def test_builder_can_auto_id_node_uses_from_spec_name() -> None:
 
     assert first.id == "test_auto_bind"
     assert second.id == "test_auto_bind_2"
+
+
+def test_builder_can_compile_with_explicit_start_set_later() -> None:
+    builder = WorkflowBuilder(
+        name="optional_start_demo",
+        input_schema=AutoBindInput,
+        state_schema=AutoBindState,
+        output_schema=AutoBindOutput,
+    )
+    step = builder.use(auto_bind_node)
+    builder.set_entry_point(step)
+
+    workflow = builder.compile()
+
+    assert workflow.start == "test_auto_bind"
+
+
+def test_builder_requires_explicit_start_before_compile() -> None:
+    builder = WorkflowBuilder(
+        name="missing_start_demo",
+        input_schema=AutoBindInput,
+        state_schema=AutoBindState,
+        output_schema=AutoBindOutput,
+    )
+
+    with pytest.raises(WorkflowExecutionError, match="start"):
+        builder.compile()
+
+
+def test_builder_registry_exports_used_node_specs() -> None:
+    builder = WorkflowBuilder(
+        name="registry_demo",
+        input_schema=AutoBindInput,
+        state_schema=AutoBindState,
+        output_schema=AutoBindOutput,
+        start="test_auto_bind",
+    )
+    builder.use(auto_bind_node)
+
+    assert set(builder.registry()) == {"test.auto_bind"}