diff --git a/src/agents/pi-tool-definition-adapter.ts b/src/agents/pi-tool-definition-adapter.ts
index f8fb0ba9b9c..2d8a73502bf 100644
--- a/src/agents/pi-tool-definition-adapter.ts
+++ b/src/agents/pi-tool-definition-adapter.ts
@@ -159,6 +159,9 @@ export function findClientToolNameConflicts(params: {
     if (existingNormalized.has(normalizedName)) {
       conflicts.add(rawName);
     }
+    // Keep the first client-provided spelling for each normalized name so every
+    // later duplicate is reported against a stable original entry, even when
+    // the later name also collides with an existing built-in tool.
     const priorClientName = seenClientNames.get(normalizedName);
     if (priorClientName) {
       conflicts.add(priorClientName);
diff --git a/src/gateway/openresponses-http.ts b/src/gateway/openresponses-http.ts
index 7de65ab354b..467bb9d2755 100644
--- a/src/gateway/openresponses-http.ts
+++ b/src/gateway/openresponses-http.ts
@@ -840,24 +840,6 @@ export async function handleOpenResponsesHttpRequest(
 
       finalUsage = finalUsage ?? createEmptyUsage();
       startStream();
-      if (isClientToolNameConflictError(err)) {
-        const errorResponse = createResponseResource({
-          id: responseId,
-          model,
-          status: "failed",
-          output: [],
-          error: { code: "invalid_request_error", message: "invalid tool configuration" },
-          usage: finalUsage,
-        });
-
-        writeSseEvent(res, { type: "response.failed", response: errorResponse });
-        emitAgentEvent({
-          runId: responseId,
-          stream: "lifecycle",
-          data: { phase: "error" },
-        });
-        return;
-      }
       const errorResponse = createResponseResource({
         id: responseId,
         model,