Update InternalVersionT::zero in addWrite call

There can be other conflict sets in the same thread

ConflictSet.cpp

@@ -3177,6 +3177,11 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   }
 
   void addWrites(const WriteRange *writes, int count, int64_t writeVersion) {
+    // There could be other conflict sets in the same thread. We need
+    // InternalVersionT::zero to be correct for this conflict set for the
+    // lifetime of the current call frame.
+    InternalVersionT::zero = oldestVersion;
+
     assert(writeVersion >= newestVersionFullPrecision);
 
     if (writeVersion > newestVersionFullPrecision + kNominalVersionWindow) {

test_conflict_set.py

@@ -56,6 +56,20 @@ def test_conflict_set():
         assert cs.check(read(0, key), read(1, key)) == [Result.TOO_OLD, Result.COMMIT]
 
 
+def test_update_zero():
+    with DebugConflictSet() as cs1:
+        with DebugConflictSet() as cs2:
+            cs1.addWrites(2, write(b""))
+            cs1.setOldestVersion(2)
+            # "zero" is now 2
+
+            # make a Node48
+            for i in range(256 - 17, 256):
+                cs2.addWrites(int(1), write(bytes([i])))
+            # Scan until first point write
+            cs2.check(read(0, b"\x00", bytes([256 - 17])))
+
+
 def test_inner_full_words():
     with DebugConflictSet() as cs:
         cs.addWrites(1, write(b"\x3f\x61"), write(b"\x81\x61"))