feat: set unused digest outputs to null based on method

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/meta_plugin/digest.rs

@@ -166,6 +166,7 @@ impl MetaPlugin for DigestMetaPlugin {
             let hash_value = hasher.finalize();
             let output_name = hasher.output_name();
             
+            // Add the selected hash output
             if let Some(meta_data) = crate::meta_plugin::process_metadata_outputs(
                 output_name, 
                 hash_value, 
@@ -173,6 +174,23 @@ impl MetaPlugin for DigestMetaPlugin {
             ) {
                 metadata.push(meta_data);
             }
+            
+            // Set unused outputs to None
+            let unused_outputs: Vec<&str> = match hasher {
+                Hasher::Md5(_) => vec!["digest_sha256", "digest_sha512"],
+                Hasher::Sha256(_) => vec!["digest_md5", "digest_sha512"],
+                Hasher::Sha512(_) => vec!["digest_md5", "digest_sha256"],
+            };
+            
+            for output_name in unused_outputs {
+                if let Some(meta_data) = crate::meta_plugin::process_metadata_outputs(
+                    output_name, 
+                    serde_yaml::Value::Null, 
+                    &self.outputs
+                ) {
+                    metadata.push(meta_data);
+                }
+            }
         }
         
         self.is_finalized = true;