diff --git a/src/client/index.ts b/src/client/index.ts
index 874b5648..885c0a6e 100644
--- a/src/client/index.ts
+++ b/src/client/index.ts
@@ -99,9 +99,10 @@ import type {
   Output,
 } from "./types.js";
 import { streamText } from "./streamText.js";
-import { errorToString, willContinue } from "./utils.js";
+import { errorToString, hasSuccessfulToolCall, willContinue } from "./utils.js";
 
 export { stepCountIs } from "ai";
+export { hasSuccessfulToolCall };
 export {
   docsToModelMessages,
   toModelMessage,
diff --git a/src/client/utils.ts b/src/client/utils.ts
index abda1e16..d5c3b454 100644
--- a/src/client/utils.ts
+++ b/src/client/utils.ts
@@ -1,5 +1,19 @@
 import type { StepResult, StopCondition } from "ai";
 
+/**
+ * A stop condition that only matches tool calls which completed
+ * successfully (i.e. produced a `tool-result`, not a `tool-error`).
+ *
+ * Use this instead of the AI SDK's `hasToolCall` when you want the
+ * agent to retry on argument validation failures rather than stopping.
+ */
+export function hasSuccessfulToolCall(toolName: string): StopCondition<any> {
+  return ({ steps }) =>
+    steps[steps.length - 1]?.toolResults?.some(
+      (result) => result.toolName === toolName,
+    ) ?? false;
+}
+
 export async function willContinue(
   steps: StepResult<any>[],
 
@@ -9,8 +23,15 @@ export async function willContinue(
   // we aren't doing another round after a tool result
   // TODO: whether to handle continuing after too much context used..
   if (step.finishReason !== "tool-calls") return false;
+  // Count both successful results and errors as completed outputs.
+  // In AI SDK v6, failed tool calls produce tool-error content parts
+  // instead of tool-result, so only checking toolResults misses them.
+  const completedOutputs =
+    step.content?.filter(
+      (p) => p.type === "tool-result" || p.type === "tool-error",
+    ).length ?? step.toolResults.length;
   // we don't have a tool result, so we'll wait for more
-  if (step.toolCalls.length > step.toolResults.length) return false;
+  if (step.toolCalls.length > completedOutputs) return false;
   if (Array.isArray(stopWhen)) {
     return (await Promise.all(stopWhen.map(async (s) => s({ steps })))).every(
       (stop) => !stop,