diff --git a/packages/dashboard/app/components/__tests__/workflow-flow-mapping.test.ts b/packages/dashboard/app/components/__tests__/workflow-flow-mapping.test.ts
index 18dd5b39b3..19d46d461c 100644
--- a/packages/dashboard/app/components/__tests__/workflow-flow-mapping.test.ts
+++ b/packages/dashboard/app/components/__tests__/workflow-flow-mapping.test.ts
@@ -9,6 +9,7 @@ import {
   fragmentSeamConflicts,
   copyIrWithFreshIds,
   columnsOf,
+  optionalStepsOf,
   columnForY,
   bandTop,
   columnsToBandNodes,
@@ -1503,3 +1504,84 @@ describe("copyIrWithFreshIds", () => {
     expect(t1NewId).toEqual({ x: 10, y: 20 });
   });
 });
+
+describe("optionalSteps round-trip (U2)", () => {
+  const v2WithOptional = (optionalSteps?: { templateId: string; defaultOn?: boolean }[]) =>
+    makeDef(
+      parseWorkflowIr({
+        version: "v2",
+        name: "wf-opt",
+        columns: [
+          { id: "triage", name: "Triage", traits: [] },
+          { id: "done", name: "Done", traits: [{ trait: "complete" }] },
+        ],
+        nodes: [
+          { id: "start", kind: "start", column: "triage" },
+          { id: "end", kind: "end", column: "done" },
+        ],
+        edges: [{ from: "start", to: "end" }],
+        ...(optionalSteps ? { optionalSteps } : {}),
+      }),
+    );
+
+  it("optionalStepsOf reads declarations from a v2 IR and returns a copy", () => {
+    const def = v2WithOptional([{ templateId: "browser-verification", defaultOn: true }]);
+    const read = optionalStepsOf(def);
+    expect(read).toEqual([{ templateId: "browser-verification", defaultOn: true }]);
+    // mutating the result does not mutate the source IR
+    read[0].defaultOn = false;
+    expect(optionalStepsOf(def)).toEqual([{ templateId: "browser-verification", defaultOn: true }]);
+  });
+
+  it("optionalStepsOf returns [] for v1 and for v2 without optionalSteps", () => {
+    const v1 = makeDef({
+      version: "v1",
+      name: "legacy",
+      nodes: [
+        { id: "start", kind: "start" },
+        { id: "end", kind: "end" },
+      ],
+      edges: [{ from: "start", to: "end" }],
+    });
+    expect(optionalStepsOf(v1)).toEqual([]);
+    expect(optionalStepsOf(v2WithOptional())).toEqual([]);
+  });
+
+  it("flowToIr preserves optionalSteps across a full irToFlow round-trip", () => {
+    const def = v2WithOptional([{ templateId: "browser-verification", defaultOn: true }]);
+    const { nodes, edges } = irToFlow(def);
+    const { ir: out } = flowToIr("wf-opt", nodes, edges, columnsOf(def), [], [], optionalStepsOf(def));
+    expect((out as { optionalSteps?: unknown }).optionalSteps).toEqual([
+      { templateId: "browser-verification", defaultOn: true },
+    ]);
+  });
+
+  it("serializes as v2 when optionalSteps present but no custom columns/fields/settings", () => {
+    const { ir: out } = flowToIr(
+      "opt-only",
+      [
+        { id: "start", type: "workflowNode", position: { x: 0, y: 0 }, data: { kind: "start" } },
+        { id: "end", type: "workflowNode", position: { x: 0, y: 200 }, data: { kind: "end" } },
+      ] as unknown as FlowNode<WorkflowFlowNodeData>[],
+      [{ id: "e1", source: "start", target: "end" }],
+      [],
+      [],
+      [],
+      [{ templateId: "browser-verification" }],
+    );
+    expect(out.version).toBe("v2");
+    expect((out as { optionalSteps?: unknown }).optionalSteps).toEqual([
+      { templateId: "browser-verification" },
+    ]);
+  });
+
+  it("omits the optionalSteps key entirely when empty (R6 byte-identity)", () => {
+    const def = v2WithOptional();
+    const { nodes, edges } = irToFlow(def);
+    const { ir: out } = flowToIr("wf-opt", nodes, edges, columnsOf(def), [], [], []);
+    expect("optionalSteps" in out).toBe(false);
+    // and with the arg omitted entirely
+    const { ir: out2 } = flowToIr("wf-opt", nodes, edges, columnsOf(def));
+    expect("optionalSteps" in out2).toBe(false);
+  });
+});
diff --git a/packages/dashboard/app/components/workflow-flow-mapping.ts b/packages/dashboard/app/components/workflow-flow-mapping.ts
index 4cf2f9ee10..4881e01514 100644
--- a/packages/dashboard/app/components/workflow-flow-mapping.ts
+++ b/packages/dashboard/app/components/workflow-flow-mapping.ts
@@ -9,6 +9,7 @@ import type {
   WorkflowDefinition,
   WorkflowFieldDefinition,
   WorkflowSettingDefinition,
+  WorkflowOptionalStep,
 } from "@fusion/core";
 import type { WorkflowFlowNodeData, WorkflowEditorNodeKind } from "./nodes/WorkflowNodeTypes";
 
@@ -434,6 +435,7 @@ export function flowToIr(
   columns?: WorkflowIrColumn[],
   fields?: WorkflowFieldDefinition[],
   settings?: WorkflowSettingDefinition[],
+  optionalSteps?: WorkflowOptionalStep[],
 ): { ir: WorkflowIr; layout: Record<string, { x: number; y: number }> } {
   const realNodes = nodes.filter((n) => !isColumnBandNode(n.id));
   // Partition by parentId: foreach group children reassemble into that group's
@@ -453,9 +455,12 @@ export function flowToIr(
   );
   const hasFields = Array.isArray(fields) && fields.length > 0;
   const hasSettings = Array.isArray(settings) && settings.length > 0;
-  // Fields and settings are v2-only declarations: a workflow with either but no
-  // custom columns still serializes as v2 (with the synthesized default columns).
-  const v2 = (Array.isArray(columns) && columns.length > 0) || hasFields || hasSettings;
+  const hasOptionalSteps = Array.isArray(optionalSteps) && optionalSteps.length > 0;
+  // Fields, settings, and optional steps are v2-only declarations: a workflow with
+  // any of them but no custom columns still serializes as v2 (with the synthesized
+  // default columns). Empty/absent → not a v2 signal (R6 byte-identity).
+  const v2 =
+    (Array.isArray(columns) && columns.length > 0) || hasFields || hasSettings || hasOptionalSteps;
   const layout: Record<string, { x: number; y: number }> = {};
 
   /** Project one flow node (top-level or template child) into an IR node. */
@@ -556,6 +561,12 @@ export function flowToIr(
         render: s.render ? { ...s.render } : undefined,
       }));
     }
+    if (hasOptionalSteps) {
+      // Optional-step DECLARATIONS round-trip through the editor opaquely (they are
+      // not graph nodes; the resolver + server validator are the source of truth).
+      // Omitted entirely when empty so legacy graphs stay byte-identical (R6).
+      (ir as { optionalSteps?: unknown }).optionalSteps = optionalSteps!.map((o) => ({ ...o }));
+    }
     return { ir, layout };
   }
 
@@ -967,6 +978,16 @@ export function settingsOf(def: WorkflowDefinition): WorkflowSettingDefinition[]
   }));
 }
 
+/** Extract the editor's working optional-step declaration list from a definition.
+ *  v2 with `optionalSteps` → a shallow copy; v1 or none → empty. Display metadata
+ *  (name/icon/phase) is NOT carried here — it is resolved from the step-template
+ *  catalog at render time so the resolver stays the single source of truth. */
+export function optionalStepsOf(def: WorkflowDefinition): WorkflowOptionalStep[] {
+  const ir = def.ir as { optionalSteps?: WorkflowOptionalStep[] };
+  if (!isV2(def.ir) || !Array.isArray(ir.optionalSteps)) return [];
+  return ir.optionalSteps.map((o) => ({ ...o }));
+}
+
 /** Seed graph for a brand-new workflow: start → end with room to insert steps. */
 export function emptyWorkflowIr(name: string): WorkflowIr {
   return {