diff --git a/packages/realm-server/tests/card-source-endpoints-test.ts b/packages/realm-server/tests/card-source-endpoints-test.ts
index 5add92a9509..6b1fd802be4 100644
--- a/packages/realm-server/tests/card-source-endpoints-test.ts
+++ b/packages/realm-server/tests/card-source-endpoints-test.ts
@@ -78,9 +78,14 @@ module(basename(import.meta.filename), function () {
 
     module('card source GET request', function (_hooks) {
       module('public readable realm', function (hooks) {
+        // Read-only module: every test either reads fixture files that no
+        // test mutates or writes to a path unique to that test, so the boot
+        // is safe to share across tests. `mode: 'before'` boots the realm
+        // once for the module instead of once per test.
         setupPermissionedRealmCached(hooks, {
           fixture: 'realistic',
           realmURL,
+          mode: 'before',
           permissions: {
             '*': ['read'],
             '@node-test_realm:localhost': ['read', 'realm-owner'],
@@ -498,9 +503,12 @@ module(basename(import.meta.filename), function () {
       });
 
       module('permissioned realm', function (hooks) {
+        // Read-only module (auth checks on GET /person.gts): shared boot is
+        // safe since no test mutates realm state.
         setupPermissionedRealmCached(hooks, {
           fixture: 'simple',
           realmURL,
+          mode: 'before',
           permissions: {
             john: ['read'],
             '@node-test_realm:localhost': ['read', 'realm-owner'],
@@ -550,9 +558,12 @@ module(basename(import.meta.filename), function () {
 
     module('card source HEAD request', function (_hooks) {
       module('public readable realm', function (hooks) {
+        // Read-only module: HEAD requests plus one write to a unique path
+        // (notes.md), so the boot is safe to share across tests.
         setupPermissionedRealmCached(hooks, {
           fixture: 'simple',
           realmURL,
+          mode: 'before',
           permissions: {
             '*': ['read'],
             '@node-test_realm:localhost': ['read', 'realm-owner'],
@@ -1149,6 +1160,10 @@ module(basename(import.meta.filename), function () {
       });
 
       module('public writable realm with size limit', function (hooks) {
+        // Carry the same file/audio/video limits as the binary size-limit
+        // module below so both share one cached template (the template cache
+        // key includes the limits). The audio/video limits are inert for this
+        // module's single .gts test but let it dedupe the template build.
         setupPermissionedRealmCached(hooks, {
           fixture: 'simple',
           realmURL,
@@ -1157,6 +1172,8 @@ module(basename(import.meta.filename), function () {
             '@node-test_realm:localhost': ['read', 'realm-owner'],
           },
           fileSizeLimitBytes: 512,
+          audioSizeLimitBytes: 2048,
+          videoSizeLimitBytes: 8192,
           onRealmSetup,
         });