diff --git a/src/agents/provider-attribution.ts b/src/agents/provider-attribution.ts
index 228be76fa15..6763181b07a 100644
--- a/src/agents/provider-attribution.ts
+++ b/src/agents/provider-attribution.ts
@@ -573,6 +573,23 @@ export function resolveProviderRequestCapabilities(
     compatibilityFamily = "moonshot";
   }
 
+  const isResponsesApi = api !== undefined && OPENAI_RESPONSES_APIS.has(api);
+  const promptCacheKeySupport = input.compat?.supportsPromptCacheKey;
+  // Default strip behavior (proxy-like endpoints with responses APIs) is
+  // preserved as a safety net for providers that reject prompt_cache_key,
+  // see #48155 (Volcano Engine DeepSeek). Operators running their payload
+  // through an OpenAI-compatible proxy known to forward the field
+  // (CLIProxy, LiteLLM, etc.) can opt out via compat.supportsPromptCacheKey
+  // to recover prompt caching; providers known to reject the field can
+  // force the strip with compat.supportsPromptCacheKey = false even on
+  // native endpoints.
+  const shouldStripResponsesPromptCache =
+    promptCacheKeySupport === true
+      ? false
+      : promptCacheKeySupport === false
+        ? isResponsesApi
+        : isResponsesApi && policy.usesExplicitProxyLikeEndpoint;
+
   return {
     ...policy,
     isKnownNativeEndpoint,
@@ -599,29 +616,14 @@ export function resolveProviderRequestCapabilities(
       (endpointClass === "default" || endpointClass === "anthropic-public"),
     // This is intentionally the gate for emitting `store: false` on Responses
     // transports, not just a statement about vendor support in the abstract.
-    supportsResponsesStoreField:
-      input.compat?.supportsStore !== false && api !== undefined && OPENAI_RESPONSES_APIS.has(api),
+    supportsResponsesStoreField: input.compat?.supportsStore !== false && isResponsesApi,
     allowsResponsesStore:
       input.compat?.supportsStore !== false &&
       provider !== undefined &&
-      api !== undefined &&
-      OPENAI_RESPONSES_APIS.has(api) &&
+      isResponsesApi &&
       OPENAI_RESPONSES_PROVIDERS.has(provider) &&
       policy.usesKnownNativeOpenAIEndpoint,
-    // Default strip behavior (proxy-like endpoints with responses APIs) is
-    // preserved as a safety net for providers that reject prompt_cache_key —
-    // see #48155 (Volcano Engine DeepSeek). Operators running their payload
-    // through an OpenAI-compatible proxy known to forward the field
-    // (CLIProxy, LiteLLM, etc.) can opt out via compat.supportsPromptCacheKey
-    // to recover prompt caching; providers known to reject the field can
-    // force the strip with compat.supportsPromptCacheKey = false even on
-    // native endpoints.
-    shouldStripResponsesPromptCache:
-      input.compat?.supportsPromptCacheKey === true
-        ? false
-        : input.compat?.supportsPromptCacheKey === false
-          ? api !== undefined && OPENAI_RESPONSES_APIS.has(api)
-          : api !== undefined && OPENAI_RESPONSES_APIS.has(api) && policy.usesExplicitProxyLikeEndpoint,
+    shouldStripResponsesPromptCache,
     // Native endpoint class is the real signal here. Users can point a generic
     // provider key at Moonshot or DashScope and still need streaming usage.
     supportsNativeStreamingUsageCompat:
diff --git a/test/scripts/bundle-a2ui.test.ts b/test/scripts/bundle-a2ui.test.ts
index 8611625a317..6abfa705e8c 100644
--- a/test/scripts/bundle-a2ui.test.ts
+++ b/test/scripts/bundle-a2ui.test.ts
@@ -65,16 +65,16 @@ describe("scripts/bundle-a2ui.mjs", () => {
     const repoRoot = process.cwd();
     const dependencyPaths = getResolvedBundleDependencyPackageJsonPaths(repoRoot);
     const relativeDependencyPaths = dependencyPaths.map((dependencyPath) =>
-      path.relative(repoRoot, dependencyPath),
+      path.relative(repoRoot, dependencyPath).replaceAll(path.sep, "/"),
     );
 
     expect(
       relativeDependencyPaths.map((relativePath) => relativePath.replace(/^ui\//u, "")),
     ).toEqual([
-      path.join("node_modules", "lit", "package.json"),
-      path.join("node_modules", "@lit/context", "package.json"),
-      path.join("node_modules", "@lit-labs/signals", "package.json"),
-      path.join("node_modules", "signal-utils", "package.json"),
+      path.posix.join("node_modules", "lit", "package.json"),
+      path.posix.join("node_modules", "@lit/context", "package.json"),
+      path.posix.join("node_modules", "@lit-labs/signals", "package.json"),
+      path.posix.join("node_modules", "signal-utils", "package.json"),
     ]);
     expect(
       relativeDependencyPaths.every((relativePath) => /^(ui\/)?node_modules\//u.test(relativePath)),