perf(test): eliminate resetModules via injectable seams

src/agents/bash-tools.exec.pty-fallback.e2e.test.ts

@@ -1,14 +1,15 @@
 import { afterEach, expect, test, vi } from "vitest";
 import { resetProcessRegistryForTests } from "./bash-process-registry";
+import { createExecTool, setPtyModuleLoaderForTests } from "./bash-tools.exec";
 
 afterEach(() => {
   resetProcessRegistryForTests();
-  vi.resetModules();
+  setPtyModuleLoaderForTests();
   vi.clearAllMocks();
 });
 
 test("exec falls back when PTY spawn fails", async () => {
-  vi.doMock("@lydell/node-pty", () => ({
+  setPtyModuleLoaderForTests(async () => ({
     spawn: () => {
       const err = new Error("spawn EBADF");
       (err as NodeJS.ErrnoException).code = "EBADF";
@@ -16,7 +17,6 @@ test("exec falls back when PTY spawn fails", async () => {
     },
   }));
 
-  const { createExecTool } = await import("./bash-tools.exec");
   const tool = createExecTool({ allowBackground: false });
   const result = await tool.execute("toolcall", {
     command: "printf ok",