add "when" and "choose" as a draft step

src/wf_artifacts/drafts/__init__.py

@@ -6,18 +6,24 @@ from .api import (
     validate_workflow_draft,
 )
 from .models import (
+    DraftChooseClause,
+    DraftChooseStep,
     DraftForeachStep,
     DraftInterruptStep,
     DraftJoinStep,
+    DraftWhenStep,
     DraftUseStep,
     WorkflowDraft,
 )
 
 __all__ = [
     "DraftDiagnostic",
+    "DraftChooseClause",
+    "DraftChooseStep",
     "DraftForeachStep",
     "DraftInterruptStep",
     "DraftJoinStep",
+    "DraftWhenStep",
     "DraftUseStep",
     "WorkflowDraft",
     "build_workflow_from_draft",

src/wf_artifacts/drafts/adapter.py

@@ -9,6 +9,8 @@ from .models import (
     DraftJoinStep,
     DraftStep,
     DraftUseStep,
+    DraftWhenStep,
+    DraftChooseStep,
     WorkflowDraft,
 )
 
@@ -61,4 +63,20 @@ def _add_step(builder: WorkflowBuilder, step_id: str, step: DraftStep):
         node = JoinNode(id=step_id, type="join")
         builder.nodes.append(node)
         return node
+    if isinstance(step, DraftWhenStep):
+        return builder.when(
+            step.when.if_,
+            id=step_id,
+            then=step.when.then,
+            otherwise=step.when.otherwise,
+        ).entry
+    if isinstance(step, DraftChooseStep):
+        return builder.choose(
+            *[
+                (clause.if_, clause.then)
+                for clause in step.choose.clauses
+            ],
+            id=step_id,
+            default=step.choose.default,
+        ).entry
     raise TypeError(f"unsupported draft step {type(step)!r}")

src/wf_artifacts/drafts/models.py

@@ -4,8 +4,10 @@ from typing import Any, Literal
 
 from pydantic import BaseModel, Field, model_validator
 
+from wf_core.models.conditions import Condition
+
 JsonObject = dict[str, Any]
-STEP_KIND_KEYS = frozenset({"use", "foreach", "interrupt", "join"})
+STEP_KIND_KEYS = frozenset({"use", "foreach", "interrupt", "join", "when", "choose"})
 
 
 class DraftUseStep(BaseModel):
@@ -55,7 +57,48 @@ class DraftJoinStep(BaseModel):
     join: JsonObject = Field(default_factory=dict)
 
 
-DraftStep = DraftUseStep | DraftForeachStep | DraftInterruptStep | DraftJoinStep
+class DraftWhenPayload(BaseModel):
+    """Payload for one boolean draft decision."""
+
+    if_: Condition = Field(alias="if")
+    then: str
+    otherwise: str = "__end__"
+
+
+class DraftWhenStep(BaseModel):
+    """Draft step that delegates one boolean decision to `WorkflowBuilder.when`."""
+
+    when: DraftWhenPayload
+
+
+class DraftChooseClause(BaseModel):
+    """One ordered boolean clause in a draft choose decision."""
+
+    if_: Condition = Field(alias="if")
+    then: str
+
+
+class DraftChoosePayload(BaseModel):
+    """Payload for an ordered first-true draft decision."""
+
+    clauses: list[DraftChooseClause] = Field(min_length=1)
+    default: str = "__end__"
+
+
+class DraftChooseStep(BaseModel):
+    """Draft step that delegates ordered decisions to `WorkflowBuilder.choose`."""
+
+    choose: DraftChoosePayload
+
+
+DraftStep = (
+    DraftUseStep
+    | DraftForeachStep
+    | DraftInterruptStep
+    | DraftJoinStep
+    | DraftWhenStep
+    | DraftChooseStep
+)
 
 
 class WorkflowDraft(BaseModel):