re: additive blending refuted, the swoosh is not displaced, and the

residual is smaller than I said

Testing the candidate I raised last iteration rather than carrying it.
Blending bit-0x02 sprites additively moves every measure the wrong way --
whole-frame mean diff +0.55 to +1.04, swoosh-band mean +1.83 to +3.98,
band edge-correlation 0.6971 down to 0.5578. So the bit is real and
independent but does not select an additive blend. I reverted the
experiment and kept the word as T8adImage::flags, documented and not
acted on; the render is byte-identical to before.

Second refutation: the swoosh is not displaced. Shifting the band over
plus or minus 80 by 8 pixels peaks sharply at zero, 0.7342, falling to
0.22 at 24 px. So the pivot story is dead twice over -- inert at scale
100, and no displacement to explain anyway.

And I have restated the residual, because earlier sections overstated it.
The +16 to +34 band tiles I quoted were measured WITHOUT --primitives.
With the dim drawn the band's average is nearly right at +1.83; what is
wrong is its structure, tiles running -38.6 then +33.8 and cancelling.
Six candidates eliminated now and none confirmed.

One caveat I owe the port agent about the capture I gave them: it is at
t=4.0s, roughly 174 keyframe units into a screen whose elements have
keyframes out to t=600. I judged "settled" from mean luminance, which
cannot see a thin sprite still moving. It is settled for the bulk of the
screen and not proven settled for every element -- which is a live
alternative explanation for a structural difference in exactly the band
the sweeps cross.

METHOD: cargo build passing does not mean cargo test compiles. Adding the
field built the library in 1.48s and broke two test-only struct literals;
cargo test failed with exit 101.

docs/re/METHOD.md

@@ -294,3 +294,8 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   first one in the file. It failed its own control instantly: different sprites
   reported identical dimensions. Match on something the header itself carries
   (here width × height against the decoded PNGs) rather than on proximity.
+* **`cargo build` passing does not mean `cargo test` compiles.** Adding a field to
+  `T8adImage` built the library fine in 1.48 s — and broke two *test-only* struct
+  literals, so `cargo test` failed to compile with exit 101. A green build on the
+  binary is not a gate for a struct change; run the tests before believing a
+  data-structure edit is safe.