FN-6335: record zero-step built-in workflow defaults

Record stepless built-in workflow defaults so zero-step selections survive task creation.\n\n- Return an explicit workflow selection for built-in workflows that compile to zero steps.\n- Cover both normal and reserved-id task creation for coding and interpreter-deferred stepwise defaults.\n- Add a patch changeset for the published Fusion package.\n\nFiles changed:\n .changeset/FN-6335-zero-step-workflow-defaults.md     |  5 +++++\n packages/core/src/__tests__/builtin-workflows.test.ts | 14 ++++++++++++++\n packages/core/src/store.ts                            |  4 +++-\n 3 files changed, 22 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-6335

Fusion-Task-Lineage: 521ef05d-bef7-4d26-9f6a-592363f522d1

.changeset/FN-6335-zero-step-workflow-defaults.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Record explicit `builtin:coding` project-default workflow selections even when the compiled built-in has zero materialized steps, while preserving interpreter-deferred `builtin:stepwise-coding` fallback behavior.

packages/core/src/__tests__/builtin-workflows.test.ts

@@ -380,10 +380,24 @@ describe("built-in workflows", () => {
       expect((await store.getTask(codingTask.id)).enabledWorkflowSteps ?? []).toEqual([]);
       expect(store.getTaskWorkflowSelection(codingTask.id)).toEqual({ workflowId: "builtin:coding", stepIds: [] });
 
+      const reservedCodingTask = await store.createTaskWithReservedId(
+        { description: "reserved default builtin coding" },
+        { taskId: "reserved-default-builtin-coding" },
+      );
+      expect((await store.getTask(reservedCodingTask.id)).enabledWorkflowSteps ?? []).toEqual([]);
+      expect(store.getTaskWorkflowSelection(reservedCodingTask.id)).toEqual({ workflowId: "builtin:coding", stepIds: [] });
+
       await store.setDefaultWorkflowId("builtin:stepwise-coding");
       const stepwiseTask = await store.createTask({ description: "default builtin stepwise" });
       expect((await store.getTask(stepwiseTask.id)).enabledWorkflowSteps ?? []).toEqual([]);
       expect(store.getTaskWorkflowSelection(stepwiseTask.id)).toBeUndefined();
+
+      const reservedStepwiseTask = await store.createTaskWithReservedId(
+        { description: "reserved default builtin stepwise" },
+        { taskId: "reserved-default-builtin-stepwise" },
+      );
+      expect((await store.getTask(reservedStepwiseTask.id)).enabledWorkflowSteps ?? []).toEqual([]);
+      expect(store.getTaskWorkflowSelection(reservedStepwiseTask.id)).toBeUndefined();
     });
 
     it("rejects selecting the PR lifecycle fragment for a task", async () => {

packages/core/src/store.ts

@@ -14912,6 +14912,8 @@ ${stepsSection}`;
     // default falls back cleanly with nothing written. Interpreter-deferred
     // built-ins are valid selectable workflows but not lowerable to legacy
     // WorkflowStep rows, so default materialization falls back to legacy defaults.
+    // Built-ins that compile to zero steps still record a stepless selection,
+    // mirroring explicit workflow materialization.
     let inputs: import("./types.js").WorkflowStepInput[];
     try {
       inputs = compileWorkflowToSteps(def.ir);
@@ -14920,7 +14922,7 @@ ${stepsSection}`;
       throw err;
     }
     if (isBuiltinWorkflowId(workflowId) && inputs.length === 0) {
-      return undefined;
+      return { workflowId, stepIds: [] };
     }
     const stepIds = await this.materializeWorkflowSteps(workflowId, inputs);
     return { workflowId, stepIds };