this kind of works but I'm abandoning this branch

Basically it seems that the sqlite extension pattern of 'allocate
a struct and stick it in the context pointer' is not going to work
for us here. I wonder if using the id of the pointer returned by
sqlite3_aggregate_context would be enough? Since no two functions
could use the same pointer, per https://www.sqlite.org/c3ref/aggregate_context.html ?

src/api.js

@@ -69,6 +69,7 @@ Module["onRuntimeInitialized"] = function onRuntimeInitialized() {
     var SQLITE_FLOAT = 2;
     var SQLITE_TEXT = 3;
     var SQLITE_BLOB = 4;
+    var SQLITE_NULL = 5;
     // var - Encodings, used for registering functions.
     var SQLITE_UTF8 = 1;
     // var - cwrap function
@@ -225,6 +226,14 @@ Module["onRuntimeInitialized"] = function onRuntimeInitialized() {
         "",
         ["number", "string", "number"]
     );
+
+    // https://www.sqlite.org/c3ref/aggregate_context.html
+    // void *sqlite3_aggregate_context(sqlite3_context*, int nBytes)
+    var sqlite3_aggregate_context = cwrap(
+        "sqlite3_aggregate_context",
+        "number",
+        ["number", "number"]
+    );
     var registerExtensionFunctions = cwrap(
         "RegisterExtensionFunctions",
         "number",
@@ -1265,6 +1274,7 @@ Module["onRuntimeInitialized"] = function onRuntimeInitialized() {
 
         var state;
         function wrapped_step(cx, argc, argv) {
+            var p = sqlite3_aggregate_context(cx, 999);
             if (!state) {
                 state = aggregateFunctions["init"].apply(null);
             }

src/exported_functions.json

@@ -41,5 +41,6 @@
 "_sqlite3_result_int",
 "_sqlite3_result_int64",
 "_sqlite3_result_error",
+"_sqlite3_aggregate_context",
 "_RegisterExtensionFunctions"
 ]