create-file: emit RRI prefix only for base-realm imports

The generated-import canonicalization was rewriting every registered
realm's module ref to its RRI prefix form, including cross-realm
references (e.g. a card in workspace A extending one in workspace B
became `@test-realm/test2/animal`). Generated user source should
address the base realm by its stable alias (`@cardstack/base/X`,
matching the emitted Component import) but keep cross-realm references
as their absolute URL, which is how they resolve. Narrow the
canonicalization to the base realm; other realms keep the absolute URL.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: backspace

packages/host/app/components/operator-mode/create-file-modal.gts

@@ -35,6 +35,7 @@ import {
   specRef,
   chooseCard,
   baseRealm,
+  baseRealmRRI,
   RealmPaths,
   Deferred,
   SupportedMimeType,
@@ -844,15 +845,22 @@ export default class CreateFileModal extends Component<Signature> {
         this.network.virtualNetwork,
       ) as ResolvedCodeRef
     ).module;
+    // Address the base realm by its stable RRI prefix (`@cardstack/base/X`),
+    // matching the `Component` import emitted below — base modules are
+    // referenced by alias, not by a deployment-specific real URL.
     // `codeRefWithAbsoluteIdentifier` returns the resolved real URL for
-    // RRI-prefix inputs (`@cardstack/base/X` → `https://localhost:4201/base/X`).
-    // Canonicalize to the registered RRI prefix form when one matches so
-    // generated import lines use the stable identifier (`@cardstack/base/X`)
-    // instead of a deployment-specific real URL.
+    // RRI-prefix inputs, so map it back to the prefix form for base only.
+    // Cross-realm references keep their absolute URL: a generated import
+    // pointing at another workspace resolves by real URL and is not
+    // rewritten to a realm-prefix form here.
     const canonicalModule =
       this.network.virtualNetwork.unresolveURL(absoluteModuleHref);
+    const moduleForImport: RealmResourceIdentifier | URL =
+      canonicalModule.startsWith(`${baseRealmRRI}`)
+        ? (canonicalModule as RealmResourceIdentifier)
+        : new URL(absoluteModuleHref);
     let moduleURL = maybeRelativeReference(
-      canonicalModule,
+      moduleForImport,
       url,
       new URL(this.selectedRealmURL),
     );