SwarmWriter::open refuses a store holding a record it does not read

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/mind-body/src/control.rs

@@ -506,6 +506,10 @@ impl SwarmWriter {
         let mut cache = swarm_cache()?;
         cache.add_generic_backing_store(SingleFileMessagePackBackingStore::new(&path))?;
         cache.pull_all_backing_stores()?;
+        // A pull carries a record no registered type claims instead of refusing it; the writer still must not write beside one.
+        if !cache.foreign_records().is_empty() {
+            bail!("{} holds a record this swarm store does not read: archive it, nothing migrates it", path.display());
+        }
         Ok(Self { cache, path })
     }
 

crates/mind-body/src/control/tests.rs

@@ -271,3 +271,18 @@ fn a_writer_refuses_to_open_over_a_store_holding_a_record_it_does_not_read() {
     assert!(refusal.contains("does not read"), "{refusal}");
     assert_eq!(std::fs::read(&path).unwrap(), before, "the refused open leaves the store bytes alone");
 }
+
+#[test]
+fn a_swarm_writer_refuses_to_open_over_a_store_holding_a_record_it_does_not_read() {
+    let dir = tempfile::tempdir().unwrap();
+    let path = swarm_path(dir.path());
+    let mut cache = CultCache::new();
+    cache.register_entry_type::<OldDial>().unwrap();
+    cache.add_generic_backing_store(SingleFileMessagePackBackingStore::new(&path)).unwrap();
+    cache.pull_all_backing_stores().unwrap();
+    cache.put("dial", &OldDial { heat: "1".into() }).unwrap();
+    let before = std::fs::read(&path).unwrap();
+    let refusal = SwarmWriter::open(&path).err().expect("a foreign record refuses the open").to_string();
+    assert!(refusal.contains("does not read"), "{refusal}");
+    assert_eq!(std::fs::read(&path).unwrap(), before, "the refused open leaves the store bytes alone");
+}