haku2: make server use haku2 (and make it work!)

crates/haku2/src/vm.zig

@@ -17,13 +17,12 @@ stack_top: u32 = 0,
 call_stack: []CallFrame,
 call_stack_top: u32 = 0,
 defs: []Value,
-fuel: u32,
+fuel: u32 = 0, // NOTE: VM must be refueled via reset() before running code
 exception: ?Exception = null,
 
 pub const Limits = struct {
     stack_capacity: usize = 256,
     call_stack_capacity: usize = 256,
-    fuel: u32 = 63336,
 };
 
 pub const CallFrame = struct {
@@ -50,10 +49,16 @@ pub fn init(a: mem.Allocator, defs: *const bytecode.Defs, limits: *const Limits)
         .stack = try a.alloc(Value, limits.stack_capacity),
         .call_stack = try a.alloc(CallFrame, limits.call_stack_capacity),
         .defs = try a.alloc(Value, defs.num_defs),
-        .fuel = limits.fuel,
     };
 }
 
+pub fn reset(vm: *Vm, fuel: u32) void {
+    vm.stack_top = 0;
+    vm.call_stack_top = 0;
+    vm.fuel = fuel;
+    vm.exception = null;
+}
+
 pub fn throw(vm: *Vm, comptime fmt: []const u8, args: anytype) Error {
     log.debug("throw: fmt={s}", .{fmt});