Implement per-model reasoning fixups for Anthropic models (#3067)

Co-authored-by: Amit Singh <amitksingh1490@gmail.com>
Co-authored-by: ForgeCode <noreply@forgecode.dev>

Author: 3 people

crates/forge_app/src/dto/anthropic/request.rs

@@ -5,10 +5,10 @@ pub struct ReasoningTransform;
 impl Transformer for ReasoningTransform {
     type Value = Context;
     fn transform(&mut self, mut context: Self::Value) -> Self::Value {
-        if let Some(reasoning) = context.reasoning.as_ref()
-            && reasoning.enabled.unwrap_or(false)
-        {
-            // if reasoning is enabled then we've to drop top_k and top_p
+        // Must stay in lockstep with the Anthropic request builder, which gates
+        // on the same predicate — otherwise `thinking`/`output_config` ship
+        // alongside sampling params that Anthropic rejects.
+        if context.is_reasoning_supported() {
             context.top_k = None;
             context.top_p = None;
         }
@@ -85,4 +85,51 @@ mod tests {
 
         assert_eq!(actual, expected);
     }
+
+    #[test]
+    fn test_enabled_none_with_effort_still_strips_top_k_and_top_p() {
+        // `enabled: None` + effort is treated as reasoning-on (domain rule).
+        let fixture = create_context_fixture().reasoning(ReasoningConfig {
+            enabled: None,
+            max_tokens: None,
+            effort: Some(forge_domain::Effort::High),
+            exclude: None,
+        });
+        let mut transformer = ReasoningTransform;
+        let actual = transformer.transform(fixture);
+
+        assert_eq!(actual.top_k, None);
+        assert_eq!(actual.top_p, None);
+    }
+
+    #[test]
+    fn test_enabled_none_with_positive_max_tokens_still_strips_top_k_and_top_p() {
+        let fixture = create_context_fixture().reasoning(ReasoningConfig {
+            enabled: None,
+            max_tokens: Some(8000),
+            effort: None,
+            exclude: None,
+        });
+        let mut transformer = ReasoningTransform;
+        let actual = transformer.transform(fixture);
+
+        assert_eq!(actual.top_k, None);
+        assert_eq!(actual.top_p, None);
+    }
+
+    #[test]
+    fn test_enabled_none_with_zero_max_tokens_preserves_top_k_and_top_p() {
+        // Matches `is_reasoning_supported`: max_tokens == 0 is treated as off.
+        let fixture = create_context_fixture().reasoning(ReasoningConfig {
+            enabled: None,
+            max_tokens: Some(0),
+            effort: None,
+            exclude: None,
+        });
+        let mut transformer = ReasoningTransform;
+        let actual = transformer.transform(fixture.clone());
+
+        assert_eq!(actual.top_k, fixture.top_k);
+        assert_eq!(actual.top_p, fixture.top_p);
+    }
 }

crates/forge_app/src/dto/anthropic/transforms/reasoning_transform.rs

@@ -11,6 +11,7 @@ use tokio::sync::Notify;
 use tracing::warn;
 
 use crate::agent::AgentService;
+use crate::transformers::ModelSpecificReasoning;
 use crate::{EnvironmentInfra, TemplateEngine};
 
 #[derive(Clone, Setters)]
@@ -208,7 +209,12 @@ impl<S: AgentService + EnvironmentInfra<Config = forge_config::ForgeConfig>> Orc
             .pipe(DropReasoningDetails.when(|_| !reasoning_supported))
             // Strip all reasoning from messages when the model has changed (signatures are
             // model-specific and invalid across models). No-op when model is unchanged.
-            .pipe(ReasoningNormalizer::new(model_id.clone()));
+            .pipe(ReasoningNormalizer::new(model_id.clone()))
+            // Normalize Anthropic reasoning knobs per model family before provider conversion.
+            .pipe(
+                ModelSpecificReasoning::new(model_id.as_str())
+                    .when(|_| model_id.as_str().to_lowercase().contains("claude")),
+            );
         let response = self
             .services
             .chat_agent(

crates/forge_app/src/orch.rs

@@ -1,7 +1,9 @@
 mod compaction;
 mod dedupe_role;
 mod drop_role;
+mod model_specific_reasoning;
 mod strip_working_dir;
 mod trim_context_summary;
 
 pub use compaction::SummaryTransformer;
+pub(crate) use model_specific_reasoning::ModelSpecificReasoning;