Attempt at test fix

internal/datastore/postgres/postgres_shared_test.go

@@ -1465,7 +1465,10 @@ func StrictReadModeTest(t *testing.T, ds datastore.Datastore) {
 	// Perform a read at a manually constructed revision beyond head, which should fail.
 	badRev := postgresRevision{
 		snapshot: pgSnapshot{
-			xmax: 9999999999999999999,
+			// NOTE: the struct defines this value as uint64, but the underlying
+			// revision is defined as an int64, so we run into an overflow issue
+			// if we try and use a big uint64.
+			xmax: math.MaxInt64,
 		},
 	}
 

internal/datastore/postgres/revisions.go

@@ -157,14 +157,19 @@ func parseRevisionProto(revisionStr string) (datastore.Revision, error) {
 
 	xminInt, err := safecast.ToInt64(decoded.Xmin)
 	if err != nil {
-		return datastore.NoRevision, spiceerrors.MustBugf("Could not cast xmin to int64")
+		return datastore.NoRevision, spiceerrors.MustBugf("could not cast xmin to int64")
 	}
 
 	var xips []uint64
 	if len(decoded.RelativeXips) > 0 {
 		xips = make([]uint64, len(decoded.RelativeXips))
 		for i, relativeXip := range decoded.RelativeXips {
-			xips[i] = uint64(xminInt + relativeXip)
+			xip := xminInt + relativeXip
+			uintXip, err := safecast.ToUint64(xip)
+			if err != nil {
+				return datastore.NoRevision, spiceerrors.MustBugf("could not cast xip to int64")
+			}
+			xips[i] = uintXip
 		}
 	}