feat(chat): #155 paste image depuis presse-papier dans le composer custom (QA verte)

- frontend: onPaste sur CustomAgentChatView, détection MIME image, chip/preview d'attachment, envoi via le contrat #154 (adapters/agent, ports)

- backend: import d'image par bytes dans le store attachments (commands, chat_attachments app+infra, dto, ports) + tests

crates/infrastructure/tests/chat_attachments.rs

@@ -72,6 +72,57 @@ async fn fs_chat_attachment_store_imports_outside_file_to_project_managed_path()
     let _ = tokio::fs::remove_dir_all(outside_root).await;
 }
 
+#[tokio::test]
+async fn fs_chat_attachment_store_imports_bytes_to_project_managed_path() {
+    let project_root = temp_dir("project-bytes");
+    tokio::fs::create_dir_all(&project_root).await.unwrap();
+
+    let store = FsChatAttachmentStore::new();
+    let project_path = ProjectPath::new(project_root.to_string_lossy().into_owned()).unwrap();
+    let project_id = ProjectId::new_random();
+    let agent_id = AgentId::new_random();
+    let session_id = SessionId::new_random();
+    let attachment_id = ChatAttachmentId::new("attach-bytes").unwrap();
+
+    let attachment = store
+        .import_from_bytes(
+            &project_path,
+            project_id,
+            agent_id,
+            session_id,
+            b"clipboard png bytes",
+            ChatAttachmentImport {
+                id: attachment_id,
+                filename: "clipboard.png".to_owned(),
+                mime: "image/png".to_owned(),
+                source_kind: ChatAttachmentSourceKind::Clipboard,
+                created_at: 43,
+            },
+        )
+        .await
+        .unwrap();
+
+    assert_eq!(attachment.project_id, project_id);
+    assert_eq!(attachment.agent_id, agent_id);
+    assert_eq!(attachment.session_id, session_id);
+    assert_eq!(attachment.filename, "clipboard.png");
+    assert_eq!(attachment.size_bytes, 19);
+    assert_eq!(attachment.source_kind, ChatAttachmentSourceKind::Clipboard);
+    assert!(attachment
+        .readable_path
+        .starts_with(&format!("{}/.ideai/attachments/", project_root.display())));
+    let stored_bytes = tokio::fs::read(&attachment.readable_path).await.unwrap();
+    assert_eq!(stored_bytes, b"clipboard png bytes");
+
+    let listed = store
+        .list_for_session(&project_path, session_id)
+        .await
+        .unwrap();
+    assert_eq!(listed, vec![attachment]);
+
+    let _ = tokio::fs::remove_dir_all(project_root).await;
+}
+
 #[tokio::test]
 async fn fs_chat_attachment_store_rejects_directories() {
     let project_root = temp_dir("project-dir");
@@ -103,3 +154,32 @@ async fn fs_chat_attachment_store_rejects_directories() {
     let _ = tokio::fs::remove_dir_all(project_root).await;
     let _ = tokio::fs::remove_dir_all(outside_root).await;
 }
+
+#[tokio::test]
+async fn fs_chat_attachment_store_rejects_empty_bytes() {
+    let project_root = temp_dir("project-empty-bytes");
+    tokio::fs::create_dir_all(&project_root).await.unwrap();
+
+    let store = FsChatAttachmentStore::new();
+    let err = store
+        .import_from_bytes(
+            &ProjectPath::new(project_root.to_string_lossy().into_owned()).unwrap(),
+            ProjectId::new_random(),
+            AgentId::new_random(),
+            SessionId::new_random(),
+            &[],
+            ChatAttachmentImport {
+                id: ChatAttachmentId::new("attach-empty").unwrap(),
+                filename: "empty.png".to_owned(),
+                mime: "image/png".to_owned(),
+                source_kind: ChatAttachmentSourceKind::Clipboard,
+                created_at: 42,
+            },
+        )
+        .await
+        .unwrap_err();
+
+    assert!(matches!(err, ChatAttachmentStoreError::Invalid(_)));
+
+    let _ = tokio::fs::remove_dir_all(project_root).await;
+}