diff --git a/crates/idfoto-core/src/attachment.rs b/crates/idfoto-core/src/attachment.rs
new file mode 100644
index 0000000..8af857c
--- /dev/null
+++ b/crates/idfoto-core/src/attachment.rs
@@ -0,0 +1,75 @@
+//! Attachment refs (carried on Item) and summaries (carried in Manifest).
+//!
+//! Encryption helpers (`encrypt_attachment`, `decrypt_attachment`) are added
+//! later in Task 22 once the crypto module is settled.
+
+use serde::{Deserialize, Serialize};
+
+use crate::ids::AttachmentId;
+
+/// Reference to an attachment, carried on the Item record.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AttachmentRef {
+    pub id: AttachmentId,
+    pub filename: String,
+    pub mime_type: String,
+    /// Plaintext size in bytes.
+    pub size: u64,
+    /// Unix-seconds when this attachment was added.
+    pub created: i64,
+}
+
+/// Compact summary of an attachment, carried in the Manifest so the popup
+/// can show attachment indicators without decrypting the item file.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AttachmentSummary {
+    pub id: AttachmentId,
+    pub filename: String,
+    pub mime_type: String,
+    pub size: u64,
+}
+
+impl From<&AttachmentRef> for AttachmentSummary {
+    fn from(r: &AttachmentRef) -> Self {
+        Self {
+            id: r.id.clone(),
+            filename: r.filename.clone(),
+            mime_type: r.mime_type.clone(),
+            size: r.size,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn attachment_ref_round_trip() {
+        let r = AttachmentRef {
+            id: AttachmentId("0123456789abcdef".into()),
+            filename: "doc.pdf".into(),
+            mime_type: "application/pdf".into(),
+            size: 12345,
+            created: 1_700_000_000,
+        };
+        let json = serde_json::to_string(&r).unwrap();
+        let parsed: AttachmentRef = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.filename, "doc.pdf");
+        assert_eq!(parsed.size, 12345);
+    }
+
+    #[test]
+    fn attachment_summary_from_ref() {
+        let r = AttachmentRef {
+            id: AttachmentId("aabb".into()),
+            filename: "x.txt".into(),
+            mime_type: "text/plain".into(),
+            size: 5,
+            created: 0,
+        };
+        let s: AttachmentSummary = (&r).into();
+        assert_eq!(s.filename, "x.txt");
+        assert_eq!(s.id, r.id);
+    }
+}
diff --git a/crates/idfoto-core/src/lib.rs b/crates/idfoto-core/src/lib.rs
index 49f50ad..bfed8db 100644
--- a/crates/idfoto-core/src/lib.rs
+++ b/crates/idfoto-core/src/lib.rs
@@ -47,6 +47,9 @@ pub use item_types::{ItemCore, ItemType};
 pub mod item;
 pub use item::{Field, FieldKind, FieldValue, Section};
 
+pub mod attachment;
+pub use attachment::{AttachmentRef, AttachmentSummary};
+
 pub mod crypto;
 pub use crypto::{decrypt, derive_master_key, encrypt, KdfParams};