Explicitly allow writeVersion to be non-decreasing

Instead of strictly increasing.

Internal.h

@@ -523,7 +523,7 @@ template <class ConflictSetImpl> struct TestDriver {
   explicit TestDriver(const uint8_t *data, size_t size)
       : arbitrary({data, size}) {}
 
-  int64_t writeVersion = 0;
+  int64_t writeVersion = 1000;
   int64_t oldestVersion = 0;
   ConflictSetImpl cs{oldestVersion};
   ReferenceImpl refImpl{oldestVersion};
@@ -545,7 +545,7 @@ template <class ConflictSetImpl> struct TestDriver {
     {
       int numPointWrites = arbitrary.bounded(100);
       int numRangeWrites = arbitrary.bounded(100);
-      int64_t v = ++writeVersion;
+      int64_t v = (writeVersion += arbitrary.bounded(10));
       auto *writes =
           new (arena) ConflictSet::WriteRange[numPointWrites + numRangeWrites];
       auto keys = set<std::string_view>(arena);
@@ -605,8 +605,8 @@ template <class ConflictSetImpl> struct TestDriver {
 
       refImpl.addWrites(writes, numPointWrites + numRangeWrites, v);
 
-      oldestVersion = std::max<int64_t>(writeVersion - arbitrary.bounded(10),
-                                        oldestVersion);
+      oldestVersion =
+          std::min(writeVersion - 10, oldestVersion + arbitrary.bounded(10));
       cs.setOldestVersion(oldestVersion);
       refImpl.setOldestVersion(oldestVersion);
     }

include/ConflictSet.h

@@ -71,12 +71,12 @@ struct __attribute__((__visibility__("default"))) ConflictSet {
   /** `writes` must be sorted ascending, and must not have adjacent or
    * overlapping ranges. Reads intersecting writes where readVersion <
    * `writeVersion` will result in `Conflict` (or `TooOld`, eventually).
-   * `writeVersion` must be greater than every write version in all previous
-   * calls to `addWrites` */
+   * `writeVersion` must be greater than or equal to all previous write
+   * versions. */
   void addWrites(const WriteRange *writes, int count, int64_t writeVersion);
 
   /** Reads where readVersion < oldestVersion will result in `TooOld`. Must be
-   * greater than any previous oldestVersion */
+   * greater than or equal to all previous oldest versions. */
   void setOldestVersion(int64_t oldestVersion);
 
   /** Reads where readVersion < oldestVersion will result in `TooOld`. There are
@@ -160,14 +160,14 @@ void ConflictSet_check(const ConflictSet *cs,
 /** `writes` must be sorted ascending, and must not have adjacent or
  * overlapping ranges. Reads intersecting writes where readVersion <
  * `writeVersion` will result in `Conflict` (or `TooOld`, eventually).
- * `writeVersion` must be greater than all write versions in all previous
- * calls to `addWrites` */
+ * `writeVersion` must be greater than or equal to all previous write versions.
+ */
 void ConflictSet_addWrites(ConflictSet *cs,
                            const ConflictSet_WriteRange *writes, int count,
                            int64_t writeVersion);
 
 /** Reads where readVersion < oldestVersion will result in `TooOld`. Must be
- * greater than any previous oldestVersion */
+ * greater than or equal to all previous oldest versions. */
 void ConflictSet_setOldestVersion(ConflictSet *cs, int64_t oldestVersion);
 
 /** Reads where readVersion < oldestVersion will result in `TooOld`. There are