diff --git a/test/imf.test.ts b/test/imf.test.ts
index fafa915..f8efb7b 100644
--- a/test/imf.test.ts
+++ b/test/imf.test.ts
@@ -195,15 +195,18 @@ describe("registry", () => {
     const indexUrl = `http://127.0.0.1:${port}/index.yaml`
     indexBody = `version: 1\nmodels:\n  tiny-1.0:\n    filename: tiny.zip\n    url: http://127.0.0.1:${port}/tiny.zip\n    sha256: ${sha}\n`
 
-    const store = new Map<string, Response>()
+    // store raw bytes: Response.clone() stream semantics differ across
+    // undici versions (node 20 vs 24) and are irrelevant to the contract
+    const store = new Map<string, Uint8Array>()
     const fakeCache = {
       async match(req: RequestInfo) {
         const key = String(req instanceof Request ? req.url : req)
-        return store.get(key)?.clone()
+        const bytes = store.get(key)
+        return bytes === undefined ? undefined : new Response(bytes)
       },
       async put(req: RequestInfo, res: Response) {
         const key = String(req instanceof Request ? req.url : req)
-        store.set(key, res.clone())
+        store.set(key, new Uint8Array(await res.arrayBuffer()))
       },
       async delete(req: RequestInfo) {
         const key = String(req instanceof Request ? req.url : req)
@@ -212,29 +215,38 @@ describe("registry", () => {
     }
     const g = globalThis as Record<string, unknown>
     g["caches"] = { open: async () => fakeCache }
-    // simulate a browser host: no Node fs, so the Cache API path runs
-    const versions = process.versions as { node?: string }
-    const realNode = versions.node
-    delete versions.node
+    // Simulate a browser host by swapping the globalThis.process
+    // reference (the registry detects Node via globalThis). Deleting
+    // process.versions.node instead breaks node 20's bundled undici,
+    // which splits it inside fetch().
+    const realProcess = globalThis.process
+    const withBrowserHost = async <T>(fn: () => Promise<T>): Promise<T> => {
+      const gg = globalThis as { process?: unknown }
+      gg.process = { env: {}, versions: {} }
+      try {
+        return await fn()
+      } finally {
+        gg.process = realProcess
+      }
+    }
     try {
       process.env["SECRYST_CACHE"] = undefined
-      const first = await resolve("tiny-1.0", indexUrl)
+      const first = await withBrowserHost(() => resolve("tiny-1.0", indexUrl))
       expect([...first.bytes]).toEqual([...fixtureZip])
       expect(store.size).toBe(1)
 
       // channel dies; the cached copy serves, still sha-verified
       channelUp = false
-      const second = await resolve("tiny-1.0", indexUrl)
+      const second = await withBrowserHost(() => resolve("tiny-1.0", indexUrl))
       expect([...second.bytes]).toEqual([...fixtureZip])
 
       // a corrupted cache entry falls through to a fresh download
       channelUp = true
       const key = store.keys().next().value as string
-      store.set(key, new Response(new Uint8Array([1, 2, 3])))
-      const third = await resolve("tiny-1.0", indexUrl)
+      store.set(key, new Uint8Array([1, 2, 3]))
+      const third = await withBrowserHost(() => resolve("tiny-1.0", indexUrl))
       expect([...third.bytes]).toEqual([...fixtureZip])
     } finally {
-      if (realNode !== undefined) versions.node = realNode
       delete g["caches"]
       delete process.env["SECRYST_CACHE"]
       await new Promise<void>((r) => server.close(() => r()))