fix(loro.js): apply Text/List deletes imported while detached

.changeset/loro-js-detached-import-delete.md

@@ -0,0 +1,5 @@
+---
+"loro.js": patch
+---
+
+Fix `loro.js` losing Text/List deletions that were imported while the document was detached. After `checkout(...)`, importing an update that deleted characters or list items, and then calling `checkoutToLatest()` or `checkout(...)` to a version that includes the delete, kept the deleted content visible. It now matches `loro-crdt` and a fresh import of the same updates.

loro-js/src/runtime/document.ts

@@ -3824,6 +3824,17 @@ export class LoroDoc<T extends Record<string, Container> = Record<string, Contai
           if (!(container instanceof LoroList || container instanceof LoroText)) {
             return false;
           }
+          // A delete imported while detached is in the history but not in the
+          // sequence's deletion index yet; only a replay applies it.
+          let recorded = 0;
+          for (const run of container._sequence.idRunsDeletedBy(
+            change.id.peer,
+            operation.counter,
+            operation.counter + operation.length,
+          )) {
+            recorded += run.length;
+          }
+          if (recorded !== operation.length) return false;
         } else if (content.type === "map-insert" || content.type === "map-delete") {
           if (!(container instanceof LoroMap)) return false;
         } else if (

loro-js/tests/runtime.test.ts

@@ -361,6 +361,44 @@ describe("loro-wasm-compatible runtime", () => {
     expect(doc.getText("text").toString()).toBe("base latest");
   });
 
+  // A delete imported while detached was left out of the next transition:
+  // the transition looked it up in the sequence's deletion index, which only
+  // attached imports update. loro-crdt applies it.
+  test.each([
+    ["text", "latest"],
+    ["text", "checkout"],
+    ["list", "latest"],
+    ["list", "checkout"],
+  ] as const)("applies a %s delete imported while detached (%s)", (kind, target) => {
+    const read = (doc: LoroDoc): unknown =>
+      kind === "text" ? doc.getText("seq").toString() : doc.getList("seq").toArray();
+    const source = new LoroDoc();
+    source.setPeerId(2);
+    if (kind === "text") source.getText("seq").insert(0, "hello");
+    else for (const value of "hello") source.getList("seq").push(value);
+    source.commit();
+
+    const doc = new LoroDoc();
+    doc.setPeerId(1);
+    doc.import(source.export({ mode: "update" }));
+    if (kind === "text") source.getText("seq").delete(4, 1);
+    else source.getList("seq").delete(4, 1);
+    source.commit();
+    doc.getCounter("counter").increment(1);
+    doc.commit();
+
+    doc.checkout([{ peer: "2", counter: 1 }]);
+    expect(read(doc)).toEqual(kind === "text" ? "he" : ["h", "e"]);
+    doc.import(source.export({ mode: "update", from: doc.oplogVersion() }));
+    if (target === "latest") doc.checkoutToLatest();
+    else doc.checkout(doc.oplogFrontiers());
+
+    expect(read(doc)).toEqual(kind === "text" ? "hell" : ["h", "e", "l", "l"]);
+    const replay = new LoroDoc();
+    replay.import(doc.export({ mode: "update" }));
+    expect(read(replay)).toEqual(read(doc));
+  });
+
   test("holds causally incomplete updates pending until dependencies arrive", () => {
     const source = new LoroDoc();
     source.setPeerId(1);