From 3040758128a46b325e84e4696557c4bc0031ffc6 Mon Sep 17 00:00:00 2001
From: Buck Doyle <buck.doyle@cardstack.com>
Date: Tue, 4 Aug 2026 17:45:58 -0500
Subject: [PATCH] host: Answer test-realm fetches in-page instead of via the
 service worker
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Host tests serve http://test-realm/* URLs through a service worker that
relays them to the in-browser mock realm. The worker only intercepts
once it controls the page and its per-module activation has been acked,
so a fetch issued before that window closes escapes to the real network
and fails — test-realm is not a real host. When the fetch is
fire-and-forget (a card component loading a realm's _types summary as
it renders), the rejection surfaces as a QUnit global error and fails
the whole shard rather than a single test.

The test fetch wrapper now answers requests whose URL falls under a
registered test realm via realm.maybeHandle. The registry is populated
at realm construction, before any component can render, so this path
has no startup window. A request the realm declines still falls through
to the network, and non-fetch resources (images, workers) continue to
rely on the service worker.

Module-loading latency normally hides the race: base card modules are
fetched and transpiled before their components can render, which takes
long enough that the worker is ready. Anything that shortens that path
re-exposes it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 packages/host/tests/helpers/setup.ts | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/packages/host/tests/helpers/setup.ts b/packages/host/tests/helpers/setup.ts
index 0a4e48f354c..c1eace22d6e 100644
--- a/packages/host/tests/helpers/setup.ts
+++ b/packages/host/tests/helpers/setup.ts
@@ -20,6 +20,8 @@ import { clearHtmlComponentCache } from '@cardstack/host/lib/html-component';
 import type SessionService from '@cardstack/host/services/session';
 import { AiAssistantOpen } from '@cardstack/host/utils/local-storage-keys';
 
+import { getTestRealmRegistry } from './test-realm-registry';
+
 import { cleanupMonacoEditorModels } from './index';
 
 // Pin `yaml` into the eager test bundle. `markdown-file-def` parses frontmatter
@@ -268,6 +270,25 @@ function setupFetchDebugging(hooks: NestedHooks) {
         startedAt: Date.now(),
       });
       try {
+        // Requests to a registered test realm are answered in-page rather
+        // than dispatched to the network. The service-worker relay that
+        // otherwise serves these URLs only intercepts once the worker
+        // controls the page and its per-module activation has been acked;
+        // a card component that renders (and fetches) before that window
+        // closes would otherwise hit the real network and fail, since the
+        // test-realm host doesn't exist outside the harness. The registry
+        // is populated at realm construction, so this path has no such
+        // window. Non-fetch resources (images, workers) still rely on the
+        // service worker.
+        for (let [realmUrl, { realm }] of getTestRealmRegistry()) {
+          if (url.startsWith(realmUrl)) {
+            let response = await realm.maybeHandle(new Request(input, init));
+            if (response) {
+              return response;
+            }
+            break;
+          }
+        }
         return await boundFetch(input, init);
       } catch (error) {
         let reason = formatErrorForLog(error);