fix(hermes): preserve artifact blocks when converting to native content

src/harness/hermes.rs

@@ -748,7 +748,8 @@ fn native_content(blocks: &[Block]) -> Value {
         let text = blocks
             .iter()
             .filter_map(|block| match block {
-                Block::Text { text } => Some(text.as_str()),
+                Block::Text { text } => Some(text.clone()),
+                Block::Artifact { artifact } => Some(artifact.display_text()),
                 _ => None,
             })
             .collect::<Vec<_>>()
@@ -764,6 +765,9 @@ fn native_content(blocks: &[Block]) -> Value {
             .iter()
             .filter_map(|block| match block {
                 Block::Text { text } => Some(json!({"type": "text", "text": text})),
+                Block::Artifact { artifact } => {
+                    Some(json!({"type": "text", "text": artifact.display_text()}))
+                }
                 Block::Image { source } => Some(json!({
                     "type": "image_url",
                     "image_url": {

tests/integration/hermes.rs

@@ -236,6 +236,59 @@ fn from_common_with_empty_id_is_deterministic() {
     assert!(!first.meta.id.is_empty());
 }
 
+#[test]
+fn from_common_preserves_artifacts() {
+    let mut common = sample_common();
+    common.body[0]
+        .content
+        .push(txcript::common::Block::Artifact {
+            artifact: txcript::common::Artifact {
+                id: "art-1".into(),
+                name: "report.pdf".into(),
+                source: txcript::common::ArtifactSource::Path {
+                    path: "/tmp/report.pdf".into(),
+                    media_type: Some("application/pdf".into()),
+                },
+            },
+        });
+    common.body[3]
+        .content
+        .push(txcript::common::Block::Artifact {
+            artifact: txcript::common::Artifact {
+                id: "art-2".into(),
+                name: "summary.txt".into(),
+                source: txcript::common::ArtifactSource::Text {
+                    text: "result data".into(),
+                    media_type: Some("text/plain".into()),
+                },
+            },
+        });
+
+    let native = hermes::Hermes::from_common(&common).unwrap();
+    let user_msg = native.body["messages"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .find(|m| m["role"] == "user")
+        .unwrap();
+    let assistant_msgs = native.body["messages"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .filter(|m| m["role"] == "assistant")
+        .collect::<Vec<_>>();
+
+    let user_text = user_msg["content"].as_str().unwrap();
+    assert!(user_text.contains("[artifact: report.pdf] /tmp/report.pdf"));
+
+    let has_artifact = assistant_msgs.iter().any(|m| {
+        m["content"]
+            .as_str()
+            .is_some_and(|t| t.contains("[artifact: summary.txt]\nresult data"))
+    });
+    assert!(has_artifact);
+}
+
 #[test]
 fn missing_or_invalid_started_at_uses_stable_epoch() {
     for text in [