feat(server): grant-scope org attachment write paths in pre-receive hook

crates/relicario-server/src/lib.rs

@@ -6,7 +6,8 @@
 pub enum PathClass {
     /// `members.json`, `collections.json`, `org.json` — only Owner/Admin may write.
     Protected,
-    /// `items/<slug>/<id>.enc` — writer must hold a grant for `<slug>`.
+    /// `items/<slug>/<id>.enc` and `attachments/<slug>/<item-id>/<att-id>.enc` —
+    /// writer must hold a grant for `<slug>`.
     Item { collection: String },
     /// `keys/<id>.enc`, `manifest.enc`, `.gitignore`, etc. — gated only by the
     /// per-commit signature check (signer must be a current member).
@@ -42,6 +43,23 @@ pub fn classify_path(path: &str) -> PathClass {
         return PathClass::Item { collection: slug.to_string() };
     }
 
+    if let Some(rest) = path.strip_prefix("attachments/") {
+        // Expect exactly: <slug>/<item-id>/<att-id>.enc → three segments.
+        let segments: Vec<&str> = rest.split('/').collect();
+        if segments.len() != 3 {
+            return PathClass::Rejected(
+                "attachments path must be attachments/<slug>/<item-id>/<att-id>.enc".to_string());
+        }
+        let slug = segments[0];
+        if slug.is_empty() {
+            return PathClass::Rejected("empty collection slug in attachments path".to_string());
+        }
+        if slug.contains('.') {
+            return PathClass::Rejected(format!("invalid collection slug: {:?}", slug));
+        }
+        return PathClass::Item { collection: slug.to_string() };
+    }
+
     PathClass::Unrestricted
 }