Improve GC for deactivated client's nodes (#926)

This change enhances garbage collection logic to handle nodes created by deactivated
clients by introducing a minLamport comparison method. When actor information
is missing from the min version vector, the minimum value is used to determine
node removal.

---------

Co-authored-by: Youngteac Hong <[email protected]>

packages/sdk/src/document/time/version_vector.ts

@@ -58,6 +58,26 @@ export class VersionVector {
     return max;
   }
 
+  /**
+   * `minLamport` returns min lamport value from vector
+   */
+  public minLamport(): bigint {
+    // TODO(hackerwins): If the version vector is empty, minLamport could be the
+    // max value of int64. This is because if the last client leaves the
+    // document, the min version vector becomes empty.
+    // This is a temporary solution and needs to be fixed later.
+
+    // 2^63-1 (int64 max)
+    let min = 9223372036854775807n;
+
+    for (const [, lamport] of this) {
+      if (lamport < min) {
+        min = lamport;
+      }
+    }
+    return min;
+  }
+
   /**
    * `max` returns new version vector which consists of max value of each vector
    */
@@ -96,7 +116,7 @@ export class VersionVector {
     const lamport = this.vector.get(other.getActorID());
 
     if (lamport === undefined) {
-      return false;
+      return this.minLamport() > other.getLamport();
     }
 
     return lamport >= other.getLamport();