diff --git a/packages/base/card-api.gts b/packages/base/card-api.gts
index 9a8696c74c4..a9878d7d903 100644
--- a/packages/base/card-api.gts
+++ b/packages/base/card-api.gts
@@ -3007,6 +3007,10 @@ function trackRuntimeRelationshipModuleDependencies(
     return;
   }
 
+  // getKnownConsumedModules is fast now: the Loader caches the dependency
+  // graph traversal result in collectKnownModuleDependencies, and
+  // trimModuleIdentifier uses string ops + a cache instead of URL
+  // construction. No need for a caller-side skip cache here.
   for (let dep of loader.getKnownConsumedModules(identity.module)) {
     trackRuntimeModuleDependency(dep, dependencyTrackingContext);
   }
diff --git a/packages/runtime-common/dependency-tracker.ts b/packages/runtime-common/dependency-tracker.ts
index 7c2abfe5dfa..6ab15061eec 100644
--- a/packages/runtime-common/dependency-tracker.ts
+++ b/packages/runtime-common/dependency-tracker.ts
@@ -1,5 +1,5 @@
 import { logger } from './log';
-import { trimExecutableExtension } from './index';
+import { executableExtensions } from './index';
 
 export type RuntimeDependencyNodeKind = 'module' | 'instance' | 'file';
 export type RuntimeDependencyContextMode = 'query' | 'non-query';
@@ -47,23 +47,30 @@ interface ContextStackEntry {
   context: RuntimeDependencyTrackingContext;
 }
 
+// String-based URL normalization to avoid expensive URL constructor calls.
+// These are called on every dependency tracking operation (field getter access)
+// so performance is critical.
+
 function canonicalURL(url: string): string | undefined {
-  try {
-    let parsed = new URL(url);
-    parsed.search = '';
-    parsed.hash = '';
-    return parsed.href;
-  } catch (_err) {
+  if (!url || (!url.startsWith('http://') && !url.startsWith('https://'))) {
     return undefined;
   }
+  // Strip query string and hash using string ops instead of new URL()
+  let hashIdx = url.indexOf('#');
+  if (hashIdx !== -1) {
+    url = url.slice(0, hashIdx);
+  }
+  let searchIdx = url.indexOf('?');
+  if (searchIdx !== -1) {
+    url = url.slice(0, searchIdx);
+  }
+  return url;
 }
 
-function hasPathExtension(pathname: string): boolean {
-  let segment = pathname.split('/').pop() ?? '';
-  if (segment.length === 0) {
-    return false;
-  }
-  return segment.includes('.');
+function hasPathExtension(url: string): boolean {
+  let lastSlash = url.lastIndexOf('/');
+  let segment = lastSlash !== -1 ? url.slice(lastSlash + 1) : url;
+  return segment.length > 0 && segment.includes('.');
 }
 
 function normalizeModuleURL(url: string): string | undefined {
@@ -71,7 +78,12 @@ function normalizeModuleURL(url: string): string | undefined {
   if (!canonical) {
     return undefined;
   }
-  return trimExecutableExtension(new URL(canonical)).href;
+  for (let ext of executableExtensions) {
+    if (canonical.endsWith(ext)) {
+      return canonical.slice(0, -ext.length);
+    }
+  }
+  return canonical;
 }
 
 function normalizeInstanceURL(url: string): string | undefined {
@@ -79,11 +91,10 @@ function normalizeInstanceURL(url: string): string | undefined {
   if (!canonical) {
     return undefined;
   }
-  let parsed = new URL(canonical);
-  if (!hasPathExtension(parsed.pathname)) {
-    parsed.pathname = `${parsed.pathname}.json`;
+  if (!hasPathExtension(canonical)) {
+    return `${canonical}.json`;
   }
-  return parsed.href;
+  return canonical;
 }
 
 function normalizeFileURL(url: string): string | undefined {
diff --git a/packages/runtime-common/loader.ts b/packages/runtime-common/loader.ts
index 2f73200628c..da6c65e3bdf 100644
--- a/packages/runtime-common/loader.ts
+++ b/packages/runtime-common/loader.ts
@@ -2,7 +2,7 @@ import TransformModulesAmdPlugin from 'transform-modules-amd-plugin';
 import { transformAsync } from '@babel/core';
 import { Deferred } from './deferred';
 import { cachedFetch, type MaybeCachedResponse } from './cached-fetch';
-import { trimExecutableExtension, logger } from './index';
+import { executableExtensions, logger } from './index';
 
 import { CardError } from './error';
 import flatMap from 'lodash/flatMap';
@@ -103,6 +103,11 @@ export class Loader {
 
   private moduleShims = new Map<string, Record<string, any>>();
   private moduleCanonicalURLs = new Map<string, string>();
+  // Cache the flattened dependency sets for evaluated modules. Once a module is
+  // evaluated its consumedModules never change, so the result of
+  // collectKnownModuleDependencies is stable and can be reused across repeated
+  // loader.import() calls (e.g. when deserializing 22 cards of the same type).
+  private knownDepsCache = new Map<string, Set<string>>();
   private identities = new WeakMap<
     Function,
     { module: string; name: string }
@@ -253,8 +258,10 @@ export class Loader {
     let knownDependencies = this.collectKnownModuleDependencies(
       resolvedModuleIdentifier,
     );
-    knownDependencies.delete(resolvedModuleIdentifier);
-    return [...knownDependencies];
+    // Filter rather than delete to avoid mutating the cached Set
+    return [...knownDependencies].filter(
+      (dep) => dep !== resolvedModuleIdentifier,
+    );
   }
 
   private trackKnownModuleDependencies(
@@ -276,6 +283,11 @@ export class Loader {
   private collectKnownModuleDependencies(
     rootModuleIdentifier: string,
   ): Set<string> {
+    let cached = this.knownDepsCache.get(rootModuleIdentifier);
+    if (cached) {
+      return cached;
+    }
+
     let pending = [rootModuleIdentifier];
     let visited = new Set<string>();
 
@@ -286,6 +298,16 @@ export class Loader {
       }
       visited.add(moduleIdentifier);
 
+      // If we already computed the full dep set for this subtree, merge it
+      // in and skip traversing its children.
+      let cachedSubtree = this.knownDepsCache.get(moduleIdentifier);
+      if (cachedSubtree) {
+        for (let dep of cachedSubtree) {
+          visited.add(dep);
+        }
+        continue;
+      }
+
       let module = this.getModule(moduleIdentifier);
       if (!module) {
         continue;
@@ -321,6 +343,7 @@ export class Loader {
       }
     }
 
+    this.knownDepsCache.set(rootModuleIdentifier, visited);
     return visited;
   }
 
@@ -562,7 +585,7 @@ export class Loader {
     module: any,
     moduleIdentifier: string,
   ) {
-    let moduleId = trimExecutableExtension(new URL(moduleIdentifier)).href;
+    let moduleId = trimModuleIdentifier(moduleIdentifier);
     for (let propName of Object.keys(module)) {
       let exportedEntity = module[propName];
       if (
@@ -850,8 +873,24 @@ function assertNever(value: never) {
   throw new Error(`should never happen ${value}`);
 }
 
+// Cache and use string operations to avoid expensive URL construction on every
+// getModule/setModule call. Module identifiers are always full URL strings so
+// we only need to strip executable extensions from the end.
+const trimCache = new Map<string, string>();
 function trimModuleIdentifier(moduleIdentifier: string): string {
-  return trimExecutableExtension(new URL(moduleIdentifier)).href;
+  let cached = trimCache.get(moduleIdentifier);
+  if (cached !== undefined) {
+    return cached;
+  }
+  let result = moduleIdentifier;
+  for (let ext of executableExtensions) {
+    if (moduleIdentifier.endsWith(ext)) {
+      result = moduleIdentifier.slice(0, -ext.length);
+      break;
+    }
+  }
+  trimCache.set(moduleIdentifier, result);
+  return result;
 }
 
 type ModuleState = Module['state'];