diff --git a/src/agents/pi-embedded-runner/run.ts b/src/agents/pi-embedded-runner/run.ts
index cf57890acd2..0c350d72b16 100644
--- a/src/agents/pi-embedded-runner/run.ts
+++ b/src/agents/pi-embedded-runner/run.ts
@@ -109,8 +109,10 @@ const ANTHROPIC_MAGIC_STRING_REPLACEMENT = "ANTHROPIC MAGIC STRING TRIGGER REFUS
 
 // Detect model safety-filter rejections (stop_reason: sensitive).
 // This is NOT a timeout — it is a content policy block that requires a user-facing message.
+// Matches both bare text ("stop_reason: sensitive") and JSON-stringified variants
+// ('"stop_reason":"sensitive"') since describeUnknownError uses JSON.stringify.
 const SENSITIVE_STOP_REASON_RE =
-  /\bunhandled\s+stop[_ ]reason:\s*sensitive\b|\bstop[_ ]reason:\s*sensitive\b|\breason:\s*sensitive\b/i;
+  /\bunhandled\s+stop[_ ]reason:\s*"?sensitive"?\b|\bstop[_ ]reason"?:\s*"?sensitive"?\b|\breason"?:\s*"?sensitive"?\b/i;
 
 function scrubAnthropicRefusalMagic(prompt: string): string {
   if (!prompt.includes(ANTHROPIC_MAGIC_STRING_TRIGGER_REFUSAL)) {