diff --git a/src/index.ts b/src/index.ts
index 1bdb353..ab3a4c9 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -923,7 +923,7 @@ export default function mainSupervisor(pi: ExtensionAPI) {
 				// Stock open sends startup only to a newly created context; existing panes receive nothing.
 				const pane = await openProjectPane({ cwd: ctx.cwd, message: workerAssignment(plan, self[0].id, requestId, params.task, model), focus: false, signal });
 				// Stock v1 emits these codes only before pane split/run. Other errors may follow a partial open.
-				const unopened = !pane.ok && ["INVALID_PROJECT_ROOT", "INVALID_BINDING", "BINDING_READ_FAILED", "PANE_OWNERSHIP_UNVERIFIED"].includes(pane.error.code);
+				const unopened = !pane.ok && ["INVALID_PROJECT_ROOT", "HERDR_UNSUPPORTED_VERSION", "INVALID_BINDING", "BINDING_READ_FAILED", "PANE_OWNERSHIP_UNVERIFIED"].includes(pane.error.code);
 				if ((pane.ok || unopened) && state.plan === plan && state.worker?.requestId === requestId) {
 					if (unopened || pane.ok && pane.data.disposition === "already-open" && superseded) {
 						state.worker = superseded; state.workerStopped = previouslyStopped;
diff --git a/test/goals.test.ts b/test/goals.test.ts
index 68ebe0a..676f5a9 100644
--- a/test/goals.test.ts
+++ b/test/goals.test.ts
@@ -1355,6 +1355,9 @@ it("retains worker history and report routing after definite pre-open failure, n
 	const reply = await tool.execute("failed", { task: "Proposed replacement" }, undefined, undefined, f.ctx);
 	expect(reply.content[0].text).toContain("INVALID_PROJECT_ROOT");
 	expect(f.entries.at(-1).data.worker).toEqual(previous);
+	vi.mocked(openProjectPane).mockResolvedValueOnce({ ok: false, error: { code: "HERDR_UNSUPPORTED_VERSION", message: "Stock version preflight rejected" } });
+	await tool.execute("preflight", { task: "Proposed replacement" }, undefined, undefined, f.ctx);
+	expect(f.entries.at(-1).data.worker).toEqual(previous);
 	const view = await f.tools.get("worker_view").execute("view", {}, undefined, undefined, f.ctx);
 	expect(view.content[0].text).toContain("Existing approved work");
 	f.event({ type: "message", fromSessionId: "old-worker", payload: { type: "stopped", to: previous.parentId, requestId: previous.requestId, plan: f.path, entryId: "still-routed", kind: "blocker", text: "Original worker reports a failure" } });