From 55a0dd60191a172569a17a9c58d2b1f8f0246da9 Mon Sep 17 00:00:00 2001
From: majiayu000 <1835304752@qq.com>
Date: Tue, 31 Mar 2026 12:54:50 +0800
Subject: [PATCH] fix: clear thought_signature in DropReasoningDetails
 transformer

DropReasoningDetails only cleared reasoning_details but left
thought_signature intact. When switching from a provider like MiniMax
back to Claude, the leftover signature caused a 400 error because
Claude rejects unknown thinking block signatures.

ReasoningNormalizer already clears both fields on model change, but
DropReasoningDetails (used when the target model does not support
reasoning at all) missed the thought_signature field.

Signed-off-by: majiayu000 <1835304752@qq.com>
---
 .../src/transformer/drop_reasoning_details.rs | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/crates/forge_domain/src/transformer/drop_reasoning_details.rs b/crates/forge_domain/src/transformer/drop_reasoning_details.rs
index e6a016feb7..6e02006b27 100644
--- a/crates/forge_domain/src/transformer/drop_reasoning_details.rs
+++ b/crates/forge_domain/src/transformer/drop_reasoning_details.rs
@@ -9,6 +9,7 @@ impl Transformer for DropReasoningDetails {
         context.messages.iter_mut().for_each(|message| {
             if let crate::ContextMessage::Text(text) = &mut **message {
                 text.reasoning_details = None;
+                text.thought_signature = None;
             }
         });
 
@@ -181,4 +182,30 @@ mod tests {
             TransformationSnapshot::new("DropReasoningDetails_preserve_non_text", fixture, actual);
         assert_yaml_snapshot!(snapshot);
     }
+
+    #[test]
+    fn test_drop_reasoning_clears_thought_signature() {
+        let reasoning_details = vec![ReasoningFull {
+            text: Some("thinking".to_string()),
+            signature: Some("sig_minimax".to_string()),
+            ..Default::default()
+        }];
+
+        let fixture = Context::default().add_message(ContextMessage::Text(
+            TextMessage::new(Role::Assistant, "response")
+                .model(crate::ModelId::new("MiniMax-M2.7"))
+                .reasoning_details(reasoning_details)
+                .thought_signature("minimax_thought_sig".to_string()),
+        ));
+
+        let mut transformer = DropReasoningDetails;
+        let actual = transformer.transform(fixture);
+
+        if let crate::ContextMessage::Text(text) = &*actual.messages[0] {
+            assert_eq!(text.reasoning_details, None);
+            assert_eq!(text.thought_signature, None);
+        } else {
+            panic!("expected TextMessage");
+        }
+    }
 }