re(ui): premultiplied alpha refuted for bit 0x02; parking the field

A per-sprite premultiplied-vs-straight-alpha flag would matter a lot to a
port and has a sharp static signature: premultiplied means RGB <= A
everywhere. Over the 170 decoded GP_TITLE textures that pair to a flag
word:

  bit SET    n= 61   mean %(RGB>A) 55.52   median 52.52
  bit clear  n=109   mean %(RGB>A) 33.66   median 30.17

Premultiplied requires ~0% for the flagged group. Both groups are far
from it and the flagged group violates MORE -- the opposite of the
hypothesis. Refuted.

What remains is a weak association: flagged sprites carry more
bright-RGB/low-alpha pixels, which is what glow art looks like. But the
best single threshold classifies 76.5% against a 64.1% base rate -- a
12-point lift with badly overlapping distributions. A tendency, not a
rule, and reported with its base rate so it cannot read as more.

Noted for whoever returns: "0x02 selects an additive blend" was refuted
by blending those sprites additively and finding every measure worse
against the capture -- but that ran through a title render since fixed
twice (rest_plateau, and the 8AX background the composer drops). The
refutation may well stand; it was measured through a renderer with known
other errors, so it is worth one re-run if blit ever gains additive
blending.

Parking the field. Four candidate meanings are dead -- additive blend,
eff name in both directions, transient element, premultiplied alpha --
none produced a positive account, and the bit blocks nothing: the port's
screens composite at 0.947 correlation against a capture without it. The
negative space and the sound attribution method (child order, not size)
are written down so a later attempt starts here.

METHOD: report a classifier's lift over its base rate; and park a field
after N failed hypotheses, saying what was eliminated.

docs/port/HANDOFF.md

@@ -120,7 +120,7 @@ authored version can be deleted.
   ⚠️ **Correlation only — untested.** Nothing yet shows it *means* additive; the
   test is to blend bit-`0x02` sprites additively and re-correlate the title
   against the capture. Note `ptlogo_back2eff` is `0x8830` despite its name, so
-  this is a field and not a naming pattern. ❔ Not diagnosed — but two candidate meanings are now dead: **not** "the name contains `eff`" — and not even the one-way "bit ⇒ `eff` name", which held 10/10 on the title but fails on **2 657 of 4 995** bit-set sprites disc-wide (`P(eff|set) = 0.468`). What survives is a 3.3× association, and the counterexamples are rings, glows and lights — effect-like art without the naming convention and **not** "the element is transient" (`pteff03`/`pteff03a` carry the bit and persist to `t=250`). ⚠️ Practical note for an asset pipeline: `T8aD` headers appear in **RATC child order** (18/18 verified on build 4 against decoded dimensions), which is the only sound way to attribute a header to a name when two sprites share a size — and two here do.
+  this is a field and not a naming pattern. ❔ Not diagnosed — but two candidate meanings are now dead: **not** "the name contains `eff`" — and not even the one-way "bit ⇒ `eff` name", which held 10/10 on the title but fails on **2 657 of 4 995** bit-set sprites disc-wide (`P(eff|set) = 0.468`). What survives is a 3.3× association, and the counterexamples are rings, glows and lights — effect-like art without the naming convention and **not** "the element is transient" (`pteff03`/`pteff03a` carry the bit and persist to `t=250`). 🛑 **Parked** — four candidate meanings are now dead (additive blend; `eff` name, both directions; transient element; **premultiplied alpha**, refuted because flagged sprites violate `RGB ≤ A` *more* than unflagged, 55.5 % vs 33.7 %) and none produced a positive account. It blocks nothing — your screens composite at 0.947 correlation against a capture without it. ⚠️ Practical note for an asset pipeline: `T8aD` headers appear in **RATC child order** (18/18 verified on build 4 against decoded dimensions), which is the only sound way to attribute a header to a name when two sprites share a size — and two here do.
   ⚠️ **The rotated draw is NOT the swoosh.** It was identified as the swoosh by
   elimination; that is **refuted** — its quads span y −209…925 in screen space,
   the swoosh is a band at y 126…360. ✅ **It is the two `ptloop` sweeps**