fix(tests): align browser fixture backend origins

examples/personal-workspace-browser/automation-cadence.mjs

@@ -7,7 +7,7 @@ import { promisify } from "node:util";
 
 import { resolveTestPython } from "../../scripts/test-python.mjs";
 import { outputDir, repoRoot } from "./fixture.mjs";
-import { openWorkspacePage } from "./scenario-context.mjs";
+import { fetchWorkspaceBackend, openWorkspacePage } from "./scenario-context.mjs";
 
 const execFileAsync = promisify(execFile);
 
@@ -114,6 +114,15 @@ export const automationCadenceScenario = {
     }
     let context;
     try {
+      // Forwarding must not make an unrelated browser origin trusted.
+      const refused = await fetchWorkspaceBackend({
+        request: () => ({
+          url: () => new URL(`${path}/preview`, url).href,
+          headers: () => ({ origin: "https://untrusted.example", "content-type": "application/json" }),
+        }),
+        fetch: ({ url: targetUrl, headers }) => fetch(targetUrl, { method: "POST", headers, body: "{}" }),
+      }, authority.url);
+      if (refused.status !== 403) throw new Error("Forwarding admitted a foreign origin");
       context = await openWorkspacePage(browser, url, {
         collectCoverage,
         beforeGoto: async (_api, page) => {
@@ -123,7 +132,7 @@ export const automationCadenceScenario = {
               concurrentChange = false;
               await interleaveGoalChange();
             }
-            const response = await route.fetch({ url: authority.url + parsed.pathname + parsed.search });
+            const response = await fetchWorkspaceBackend(route, authority.url);
             if (parsed.pathname.endsWith("/apply") && response.ok()) {
               applyCount += 1;
               changes.push(route.request().postDataJSON());

examples/personal-workspace-browser/configuration-backup.mjs

@@ -4,7 +4,7 @@ import {mkdtemp, readFile, realpath, rm} from "node:fs/promises";
 import {tmpdir} from "node:os";
 import {join, resolve} from "node:path";
 import {repoRoot, outputDir} from "./fixture.mjs";
-import {openWorkspacePage} from "./scenario-context.mjs";
+import {fetchWorkspaceBackend, openWorkspacePage} from "./scenario-context.mjs";
 import {resolveTestPython} from "../../scripts/test-python.mjs";
 
 // Only the backup routes use a real disposable server. Other workspace state
@@ -66,8 +66,7 @@ export const configurationBackupScenario = {
       const {port} = backend;
       context = await openWorkspacePage(browser, url, {beforeGoto: async (_api, page) => {
         await page.route("**/api/chat/configuration-backup/**", async route => {
-          const path = new URL(route.request().url()).pathname;
-          const response = await route.fetch({url: `http://127.0.0.1:${port}${path}`});
+          const response = await fetchWorkspaceBackend(route, `http://127.0.0.1:${port}`);
           await route.fulfill({response});
         });
       }});

examples/personal-workspace-browser/explore-composition-owner.mjs

@@ -6,7 +6,7 @@ import { resolve } from "node:path";
 import { createInterface } from "node:readline";
 import { resolveTestPython } from "../../scripts/test-python.mjs";
 import { outputDir, repoRoot } from "./fixture.mjs";
-import { openWorkspacePage } from "./scenario-context.mjs";
+import { fetchWorkspaceBackend, openWorkspacePage } from "./scenario-context.mjs";
 
 const GOAL = "research-monitor";
 const AGENT = "research-agent";
@@ -133,7 +133,7 @@ export const exploreCompositionOwnerScenario = {
           await page.route("**/api/chat/goal-configuration**", async (route) => {
             const target = new URL(route.request().url());
             if (!target.pathname.startsWith("/api/chat/goal-configuration")) { await route.fallback(); return; }
-            const response = await route.fetch({ url: `${owner.url}${target.pathname}${target.search}` });
+            const response = await fetchWorkspaceBackend(route, owner.url);
             ownerResponses.push({ method: route.request().method(), path: target.pathname, status: response.status() });
             await route.fulfill({ response });
           });

examples/personal-workspace-browser/scenario-context.mjs

@@ -1,5 +1,18 @@
 import { installApi } from "./fixture.mjs";
 
+// A disposable backend has a different port from the browser fixture. Rebase
+// same-origin requests with it; foreign origins must still reach the real guard.
+export function fetchWorkspaceBackend(route, backendUrl) {
+  const request = route.request();
+  const source = new URL(request.url());
+  const target = new URL(backendUrl);
+  target.pathname = source.pathname;
+  target.search = source.search;
+  const headers = { ...request.headers(), host: target.host };
+  if (headers.origin === source.origin) headers.origin = target.origin;
+  return route.fetch({ url: target.href, headers });
+}
+
 export async function openWorkspacePage(
   browser,
   url,