re: the game never draws ptlogo_back2eff3 -- reproduced, with three explanations

ruled out

Last iteration I recorded eff3's absence as unexplained after withdrawing a bad
explanation for it. The previous capture survived on disk with 6907 frames, and
the attract loop returns to the title, so it contains a SECOND build-in at
frames 5942..7025. eff3 is absent there too.

Three alternative explanations tested and failed:

  * sampling phase -- eff3 is non-zero for t in (58,64), SIX units, against a
    2.23-unit step. A window wider than the step cannot be missed; frames 133
    (t=60.1) and 134 (t=62.3) sit inside it and draw eff2 and eff4 instead.
  * a draw the log cannot see -- exactly 2 draws per frame carry no geometry,
    on all 932 settled title frames, always the same full-screen-triangle
    shader, and present on frames where no wipe element is active.
  * a bad position guess -- dropping position entirely, ZERO quads anywhere on
    screen in either build-in window have a width within +-30 of 408. The width
    spectrum jumps straight from 262 to 748.

Draw counts across both entries: eff1 4, eff2 3, eff3 0, eff4 6, against ~5
expected each. The four are a right-aligned wipe (938+258, 788+408, 447+749,
64+1133, all ending at x~1196) -- a left-growing reveal in four widths, of
which the game draws three.

Why is NOT established: nothing in eff3's element record differs from its
neighbours. Classified measured, not decoded, and the port is told that
dropping eff3 means authoring a behaviour I cannot derive from the file.

Two further corrections, both to my own earlier claims:

  * "frame 107 is the title composited once" was an over-read. It binds NO
    texture and only 4 of its 27 draws log geometry. The second title entry
    has no such frame.
  * the two build-ins are NOT frame-identical. I had that from a coincidentally
    aligned pair of rows; aligned properly only 4 of 46 frames match. They are
    the same animation at different sampling phases -- which is precisely what
    makes the eff3 result robust.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd

docs/port/HANDOFF.md

@@ -2026,3 +2026,51 @@ generalise. Read the same way, `eff4` gives 255 / 127 / 254 on frames 133 / 134
 135 — non-monotonic. The glow's exact agreement is evidence about the glow, not a
 decoded rule about vertex colour.
 
+## 2026-08-29 — `ptlogo_back2eff3` is declared on the disc and never drawn by the game
+
+✅ **measured**, and this one is actionable: **you draw `eff3` at t=60–62 and the
+console does not.**
+
+Last time I called `eff3`'s absence unexplained and withdrew a bad explanation for
+it. Re-examined against the **second** title build-in in the same capture — the
+attract loop returns, so one run contains two — it is absent there too, and three
+alternative explanations now fail:
+
+* **Sampling phase.** `eff3` is non-zero for t ∈ (58, 64) — **six units** — against
+  a step of **2.23 units per presented frame**. A window wider than the step cannot
+  be missed. Frames 133 (t = 60.1) and 134 (t = 62.3) sit inside it and draw `eff2`
+  and `eff4`, not `eff3`.
+* **A draw the log cannot see.** Exactly **2** draws per frame carry no geometry,
+  on all 932 settled title frames, always the same full-screen-triangle shader, and
+  present on frames where no wipe element is active. `eff3` is not among them.
+* **A bad position guess on my side.** Dropping position entirely: across both
+  build-in windows, **zero** quads anywhere on screen have a width within ±30 of
+  408. The width spectrum jumps straight from 262 to 748.
+
+Draw counts across both entries — `eff1` **4**, `eff2` **3**, **`eff3` 0**, `eff4`
+**6**, against ~5 expected each.
+
+The four are a right-aligned wipe (`eff2` 938+258, `eff3` 788+408, `eff4` 447+749,
+`eff5` 64+1133, all ending at x≈1196) — a left-growing reveal in four widths, of
+which the game draws three.
+
+❔ **Why is not established.** Nothing in `eff3`'s element record distinguishes it
+from its neighbours: same kind `0x0`, same keyframe shape, same `u4`/`u8`, same
+scale. So this is *measured*, not decoded — if you drop `eff3` you are authoring a
+behaviour I cannot derive from the file, and you should know that.
+
+⚠️ **Two corrections to what I sent you before**, both mine and both found by
+following up my own claims:
+
+* **"Frame 107 is the title composited once" was an over-read.** It is a 27-draw
+  spike between the movie's last frame and the title's first, it binds **no
+  texture**, and only 4 of its 27 draws log geometry. I do not know what it is. The
+  second title entry has no such frame at all.
+* **The two build-ins are NOT frame-identical.** I had that impression from a
+  coincidentally aligned pair of rows. Aligned properly, only **4 of 46** frames
+  match. They are the same animation sampled at different phases — which is the
+  reason the `eff3` result is robust rather than a coincidence.
+
+Detail and the ruled-out explanations:
+[`docs/re/structures/ui-title-buildin-measured.md`](../re/structures/ui-title-buildin-measured.md).
+