Resolves the puzzle the previous commit left open: payload+28 is a 1-12 index, yet
the drain hands it to a spawner that wants a code offset. The cause is that built-in
25 is not the only thing that appends a trigger node.
Searching for functions that write a double at +16 AND a word at +28 of the same
register finds exactly two: sub_8226A0D8 (built-in 25, vtable slot 28) which fills the
payload inline, and sub_8226E160, a free-list recycling variant whose sole caller
sub_82269ED0 is vtable slot 68 = BUILT-IN 19.
Built-in 19 passes local[4] -> node+0 (the unit), local[12] -> +4, local[24] -> +16 as
a double, and local[32] -> +28. That last one is the field the drain spawns from, and
it is a genuine code offset:
over all 79 call sites disc-wide
land on the instruction stream 79 / 79 = 100.0%
control, random 4-aligned offsets 27.8%
values 12164 .. 111080, 73 distinct
Large, distinct, and every one resolves against a control that resolves barely a
quarter of the time. So built-in 19 registers a trigger whose handler is a routine,
and the drain's `base + payload+28` spawn is that handler. The two builders simply
put different things in the same slot.
Observed alongside: built-in 25 writes +24 = 1 and built-in 19 writes +24 = 0, which
is kind-tag shaped -- but the drain was not shown branching on it, so that is recorded
as an observation and not a reading.
All artefacts regenerate byte-identical; documentation only.
Still open: whether +24 selects between the node kinds, and this STILL does not
explain the unreached code -- 0 of the 79 handler offsets are unreached run-starts.
1c21a00f7c