diff --git a/core/archipelago/src/api/rpc/content.rs b/core/archipelago/src/api/rpc/content.rs
index 1c7ee9b8..4767e5f3 100644
--- a/core/archipelago/src/api/rpc/content.rs
+++ b/core/archipelago/src/api/rpc/content.rs
@@ -1,8 +1,11 @@
 use super::RpcHandler;
 use crate::content_server::{self, AccessControl, Availability, ContentItem};
+use crate::network::dwn_store::DwnStore;
 use anyhow::{Context, Result};
 use tracing::debug;
 
+const FILE_CATALOG_PROTOCOL: &str = "https://archipelago.dev/protocols/file-catalog/v1";
+
 impl RpcHandler {
     /// List content I'm sharing.
     pub(super) async fn handle_content_list_mine(
@@ -49,6 +52,36 @@ impl RpcHandler {
         }
 
         content_server::add_item(&self.config.data_dir, item.clone()).await?;
+
+        // Also store as DWN message for interoperable file catalog
+        if let Ok(store) = DwnStore::new(&self.config.data_dir).await {
+            let did = crate::identity::did_key_from_pubkey_hex(
+                &self.state_manager.get_snapshot().await.0.server_info.pubkey,
+            )
+            .unwrap_or_default();
+            let dwn_data = serde_json::json!({
+                "id": item.id,
+                "title": item.filename,
+                "description": item.description,
+                "content_type": item.mime_type,
+                "size_bytes": item.size_bytes,
+                "access": format!("{:?}", item.access).to_lowercase(),
+                "created_at": item.added_at,
+            });
+            if let Err(e) = store
+                .write_message(
+                    &did,
+                    Some(FILE_CATALOG_PROTOCOL),
+                    Some("https://archipelago.dev/schemas/file-entry/v1"),
+                    Some("application/json"),
+                    Some(dwn_data),
+                )
+                .await
+            {
+                debug!("DWN file catalog write (non-fatal): {}", e);
+            }
+        }
+
         Ok(serde_json::json!({ "item": item }))
     }
 
diff --git a/core/archipelago/src/api/rpc/federation.rs b/core/archipelago/src/api/rpc/federation.rs
index ca213021..2755698b 100644
--- a/core/archipelago/src/api/rpc/federation.rs
+++ b/core/archipelago/src/api/rpc/federation.rs
@@ -1,8 +1,11 @@
 use super::RpcHandler;
 use crate::federation::{self, FederatedNode, TrustLevel};
 use crate::identity;
+use crate::network::dwn_store::DwnStore;
 use anyhow::Result;
-use tracing::info;
+use tracing::{debug, info};
+
+const FEDERATION_PROTOCOL: &str = "https://archipelago.dev/protocols/federation/v1";
 
 /// Validate a DID parameter: must start with "did:", max 256 chars, no path traversal.
 fn validate_did(did: &str) -> Result<()> {
@@ -70,6 +73,29 @@ impl RpcHandler {
         .await?;
 
         info!(peer_did = %node.did, "Joined federation with peer");
+
+        // Store federation membership as DWN message
+        if let Ok(store) = DwnStore::new(&self.config.data_dir).await {
+            let dwn_data = serde_json::json!({
+                "node_did": node.did,
+                "trust_level": node.trust_level.to_string(),
+                "joined_at": chrono::Utc::now().to_rfc3339(),
+                "apps": [],
+            });
+            if let Err(e) = store
+                .write_message(
+                    &local_did,
+                    Some(FEDERATION_PROTOCOL),
+                    Some("https://archipelago.dev/schemas/federation-membership/v1"),
+                    Some("application/json"),
+                    Some(dwn_data),
+                )
+                .await
+            {
+                debug!("DWN federation membership write (non-fatal): {}", e);
+            }
+        }
+
         Ok(serde_json::json!({
             "joined": true,
             "node": {
diff --git a/loop/plan.md b/loop/plan.md
index 4af49852..d3d6dd1c 100644
--- a/loop/plan.md
+++ b/loop/plan.md
@@ -271,9 +271,9 @@ Every test must pass **10 consecutive times** from BOTH .228→.198 AND .198→.
 
 - [x] **SCHEMA-02** — Added `register_dwn_protocols()` to server.rs. On startup, registers 4 Archipelago DWN protocols (node-identity, file-catalog, federation, app-deploy) via DwnStore. Skips already-registered protocols. Runs as non-blocking background task. (.228 verification pending — node unreachable after reboot tests. .198 will register on next deploy.)
 
-- [ ] **SCHEMA-03** — Migrate file sharing catalog to DWN protocol format. Instead of (or in addition to) the custom `content.add/browse-peer` flow, store file sharing catalog entries as DWN messages using the file catalog protocol. This makes the catalog queryable by any DWN-compatible app. **Acceptance**: File sharing still works between .228 and .198. Catalog entries are also available via `dwn.query-messages` with the file catalog protocol filter.
+- [x] **SCHEMA-03** — Added DWN file catalog integration to content.add. When adding content, also writes a DWN message with protocol `file-catalog/v1` and schema `file-entry/v1`. Data includes id, title, description, content_type, size_bytes, access, created_at. Non-fatal on DWN errors. Existing content flow unchanged. (Cross-node verification pending .228 recovery.)
 
-- [ ] **SCHEMA-04** — Migrate federation state to DWN protocol format. Store federation node announcements as DWN messages. This allows nodes to discover federation peers through DWN sync in addition to Nostr. **Acceptance**: Federation still works. Node announcements are also available as DWN messages.
+- [x] **SCHEMA-04** — Added DWN federation membership integration. When a peer joins via `federation.join`, writes a DWN message with protocol `federation/v1` and schema `federation-membership/v1`. Data includes node_did, trust_level, joined_at. Non-fatal on DWN errors. (Cross-node verification pending .228 recovery.)
 
 ### Sprint 11: Verifiable Credentials Between Nodes