KOS_OP_ITEM_INPLACE

• Style: OPCOUNT (operator selector, value count).

• Stack: [..., obj, key, v0 .. v_{n-1}] → [...]. Reduce obj[key] in place with the count values left to right and store it back with the object on the stack and the key on the stack.

• Cache: one KOS_CACHE_ITEM slot; the site elects a body for the container kind it first sees through the shared helper in eval/eval_item.c (see the items section of the VM reference).

• Compiler form: Emitted by compile/inplace-item; the compress pipeline folds the run of feeders (bare VAR and CONST loads) ahead of it into the rows that name them.

• Implementation: koskari/lib/opcode/ITEM_INPLACE.c