fix(agents): preserve thinking/redacted_thinking blocks in stripThoughtSignatures

iamhitarth · claude · iamhitarth · commit 004e91311b55 · 2026-02-28T22:05:42.000+13:00
stripThoughtSignatures removes thought_signature fields from content
blocks for cross-provider compatibility. However, it also modifies
thinking and redacted_thinking blocks, which Anthropic's API requires
to be identical to the original response. When these modified blocks
appear in the latest assistant message on a subsequent turn, the API
rejects the request with:

  "thinking or redacted_thinking blocks in the latest assistant message
   cannot be modified"

Skip thinking/redacted_thinking block types in stripThoughtSignatures
to preserve them unchanged.

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/src/agents/pi-embedded-helpers/bootstrap.ts b/src/agents/pi-embedded-helpers/bootstrap.ts
@@ -65,6 +65,12 @@ export function stripThoughtSignatures<T>(
     if (!block || typeof block !== "object") {
       return block;
     }
+    // Never modify thinking/redacted_thinking blocks — Anthropic requires these
+    // to be identical to the original API response.
+    const blockType = (block as { type?: unknown }).type;
+    if (blockType === "thinking" || blockType === "redacted_thinking") {
+      return block;
+    }
     const rec = block as ContentBlockWithSignature;
     const stripSnake = shouldStripSignature(rec.thought_signature);
     const stripCamel = includeCamelCase ? shouldStripSignature(rec.thoughtSignature) : false;
