15. Allocation-Free Action Plumbing in All Backends

• With change 14 the VMs' remaining allocations were mostly in code shared with the closure engine, around actions rather than in the actions' own values:

  • an action whose body is not a sequence got its element list ($1) as a fresh one-element slice (finish, lineResult); on JSON this was over a third of all allocations;
  • field lists of struct nodes (newStruct) and of captures (attachCaptures) were separate make calls;
  • function.apply(args ...any) is an interface call, so the variadic argument slice escaped on every lambda call;
  • list, map and concat built their element slices with make/append and newList then copied them;
  • an Operators Rule operator action allocated a local for each of $op, $lhs, $rhs.

• Now: the one-element list is a buffer in the parser (parser.one; the list is only read during the action, and $0 copies it); field lists come from chunks like nodes (parser.fields, with capacity limited to the list so an append past it reallocates instead of overwriting a neighbour); apply takes two arguments; the list built-ins gather elements on kidStack and hand the copied-out slice to the list node; the operator locals live in the parser (parser.oplocals), like the evaluation context.

• Effect (min of 6 interleaved runs, codepoints, Apple M3 Max; allocs/op before → after, time in parentheses):

  Workload	closure	bytecode	iterative
  JSON	153k → 38k (22.7 → 22.0 ms)	147k → 32k (27.2 → 26.5 ms)	147k → 32k (38.3 → 38.1 ms)
  CSV	131k → 56k (11.3 → 10.8 ms)	116k → 41k (12.9 → 12.3 ms)	116k → 41k (15.7 → 15.2 ms)
  XML	64k → 39k (19.0 → 19.2 ms)	72k → 47k (24.8 → 24.0 ms)	72k → 47k (34.4 → 34.0 ms)
  Arith_OperatorsRule	134k → 41k (14.1 → 12.9 ms)	94k → 0.7k (17.8 → 17.0 ms)	95k → 0.8k (27.0 → 26.4 ms)
  Minilang	75k → 21k (19.0 → 18.2 ms)	68k → 14k (24.6 → 23.9 ms)	68k → 14k (32.3 → 31.6 ms)

  Bytes per parse drop by 2–13% (XML +0.3%: partly used field chunks).