re: F6 unit 1 -- 238..250 on the sweep is an EXIT, not a start

One unit, per the new PROTOCOL section. Question, look-at, and
not-covered written before the work.

pteff03 and pteff03a -- the sweep parents behind ptloop01/ptloop02 --
declare 0:a=0 70:a=0 100:a=255 238:a=255 250:a=0. So they rise 70->100 and
fall 238->250. The brief's own warning was right: 238..250 is a fade-out,
the same shape ptcopyright uses, and ptcopyright starts nothing.

The sweep is declared visible from t=100, which is 136 units BEFORE the
plate reaches full alpha at 236, and is fading out by 238.

That contradicts the human's report that the sweep only starts when the
plate appears -- and the reason both can be true is the next unit.
ptloop01/ptloop02 are .rat leaves whose own timeline is a TRANSLATION:
ptloop01 runs x = -639 -> 1521 over a 600-unit loop, so at its own t=0 the
sweep sits off the left edge of a 1280-wide screen. The parent's alpha says
"drawn"; the leaf's position says "where". A quad can be fully opaque and
entirely off-screen.

Explicitly not actionable alone: this says 238 is not a start. It does not
say the port should show the sweep from t=100, because if the leaf is
off-screen there then both renderers can be correct on alpha and differ
entirely in what is visible.

Refutation of the brief's own lead that "236-238 is a synchronisation point
and a human reported a behaviour change there": the synchronisation is
real -- pteff02 at 236, ptlogo_back2eff and ptcopyright at 238 -- but the
reading is refuted. For the sweep it is where things END. A cluster of
keyframes marks a moment; it does not say which direction anything moves
through it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jc4pciRArGHfxGGhEbwp5t

docs/re/f6-unit1-238-is-an-exit.md

@@ -0,0 +1,62 @@
+# F6 unit 1 — `238…250` on the sweep is an **EXIT**, not a start
+
+**Status: ✅ decoded ⟨disc⟩.** 2026-09-02. One unit, per `PROTOCOL.md` §"Work in
+units a human can check in a minute".
+
+**Question:** on the sweep elements, is `238…250` a start or an exit?
+**Look at:** their declared alpha. Rising 0→255 = start; falling 255→0 = exit.
+**Not covered:** what the game does at runtime; the plate's timing; F5.
+
+---
+
+## The answer
+
+`sylpheed-cli screen info --build 4 --geometry`, GP_TITLE:
+
+```
+pteff03.t32    0:a=0   70:a=0   100:a=255   238:a=255   250:a=0
+pteff03a.t32   0:a=0   70:a=0   100:a=255   238:a=255   250:a=0
+ptcopyright    0:a=0  138:a=0   160:a=255   238:a=255   244:a=0
+```
+
+**The sweep's parents rise `70→100` and fall `238→250`.** So `238…250` is a
+**fade-out**, and the brief's own warning was right: it is the same shape
+`ptcopyright` uses, and `ptcopyright` starts nothing.
+
+> **The sweep is declared visible from `t = 100` — 136 units BEFORE the plate
+> reaches full alpha at 236 — and it is fading out by 238.**
+
+## 🔴 So the declared data contradicts the report, and that is the finding
+
+The human reports the sweep *"only starts when the plate appears"*. On the parents'
+alpha alone it should already be on screen for the whole build-in. **Both can be
+true**, and the reason is the next unit:
+
+`ptloop01`/`ptloop02` are `.rat` **leaves with their own timeline**, and that
+timeline is a **translation**: `ptloop01` runs `x = −639 → 1521` over a **600-unit**
+loop ([`data/sweep-leaf-ramp.txt`](data/sweep-leaf-ramp.txt)). At its own `t = 0`
+the sweep sits at `x = −639` — **off the left edge of a 1280-wide screen.**
+
+**The parent's alpha says "drawn". The leaf's position says "where".** A quad can
+be fully opaque and entirely off-screen, and this one starts that way.
+
+## Next unit (not done)
+
+**When does the leaf's clock start, and where is the sweep at the moment the plate
+appears?** That decides whether the human is watching an alpha gate (answered: no)
+or a quad travelling on screen. It needs the leaf's clock origin, which is the
+same open question as the title's own — so it may need the capture, not the disc.
+
+⚠️ **Do not act on this unit alone.** It says `238` is not a start. It does **not**
+say the port should show the sweep from `t=100` — if the leaf is off-screen there,
+both renderers can be "correct on alpha" and differ entirely in what is visible.
+
+## Refutation attempt
+
+**Target:** the brief's lead that *"236–238 is a synchronisation point in the
+declared data and a human just reported a behaviour change there."*
+
+**Result: the synchronisation is real, the reading of it is REFUTED.** `pteff02` is
+keyed at 236 and `ptlogo_back2eff`/`ptcopyright` at 238 — so 236–238 *is* a shared
+instant. But for the sweep it is where things **end**, not begin. A cluster of
+keyframes marks a moment; it does not say which direction anything moves through it.