re: the forced-backdrop span -- 256 vs 211 is a bundle mismatch, and the hold

decides 55% of verdicts

The port implemented the forced-backdrop rule and reported a discrepancy:
palogo_eff0.prm at 256 opaque instants against this corpus's 211.

There is no discrepancy. palogo_eff0.prm appears on BOTH splashes -- the
publisher (entries 10, 13) runs to t=255, giving 256 instants; the developer
(11, 14) runs to t=210, giving 211. Same definition, different bundle. The page
now names the entries so it cannot recur.

The definition, stated: the span is 0..=max keyframe time over every element in
the build, and an element HOLDS its final pose past its own last keyframe --
which is what pose_at does, and which is decoded rather than assumed (a group
holds at its last keyframe rather than looping; the declared +0x08 never falls
short of the last keyframe, the slack being that hold).

The port's instinct that the hold was load-bearing was right. Over the 130
keyless full-screen primitives with an opaque interval:

  * span = the header's declared +0x08          ->  0 verdicts change
  * span = the primitive's own last keyframe    -> 72 change
  * elements GONE after their last keyframe     -> 72 change

So the hold decides 55% of verdicts -- and dropping it is REFUTED by a measured
order. palogo_eff0.prm is a single keyframe at t=0: without the hold it is
opaque for one instant, no other element is up yet, and the rule calls it free,
against a game measured painting it first. Pinned by a new test that spells out
the counterfactual rather than importing it.

The verdicts that matter are convention-independent: pgloading_eff00.prm is
FIRST under all four conventions and pteff00.prm FREE under all four. And the
header length is interchangeable with the elements' maximum -- zero
disagreements disc-wide.

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

docs/re/INDEX.md

@@ -174,3 +174,4 @@ files, which is how the same ground got covered twice.
 | [`structures/ui-title-buildin-measured.md`](structures/ui-title-buildin-measured.md) | The title's build-in and the plate glow, read out of the guest's own draw stream | ✅ **measured** (Canary, `ARM=early` draw capture): the decoded *mechanism* is observed, not just its end state. **The five flashes fire in a six-frame window and are absent from all 155 other sampled frames**; `ptlogo_back2eff1` is drawn in exactly 2 frames at **t = 54.0** against a decoded peak of **t54–56**, and `ptlogo1` first appears at **t = 42.2** against a decoded **t42** — with units/frame taken from the **glow's period alone**, a different element. The two holders (`ptlogo_back2eff`, `ptlogo_back2`) are continuous from frame 134. ✅ The glow's per-vertex colour alpha IS its fade alpha: **observed range 0…80 against a decoded peak of 80**, exact and unfitted; **period 51.158 presented frames** over 20 cycle starts; fitting the decoded ramp gives RMS **13.16** against **38.18 reversed** (2.9×), so the asymmetry is real and correctly directed. Structure: the settled title is 10–11 draws naming no sprite — which is why arming at the title sees nothing. ⚠️ Frame **107** is a 27-draw spike between the movie's last frame and the title's first; calling it "the composite" 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 entries are the same animation at **different sampling phases** (only 4 of 46 aligned frames match), which is what makes the `eff3` result robust. 🔴🔴 **RETRACTED — the game DOES draw `ptlogo_back2eff3`, and all five flashes fire in both entries in the declared stagger** (`eff3` at frames 133–134 / 5957–5958, i.e. t=60.1 and 62.3, inside its declared t∈(58,64)). The absence was an **instrument artefact**: a draw batches several quads (`indices=8` is two) and the log dumps only the first 8 vertices, so min/max over a line **merges** them — and because the wipe is right-aligned, `eff3` (788…1196) lies entirely inside `eff4` (447…1196), making the union *exactly* `eff4`'s extent. The merged box matched `eff4` to 1 px. 🔴 Three explanations had been "ruled out" and all three were aimed at the wrong failure — notably the invisible-draw check counted draws with **no** geometry, where the hiding place was **partial** geometry. Superseded text follows: ~~three alternative explanations tested and failed: *phase* (its window is **6 units** against a **2.23-unit** step, so it cannot be missed — frames 133/134 sit at t=60.1/62.3 inside it and draw `eff2` and `eff4` instead), *an unlogged draw* (exactly 2 blind draws/frame, always the same full-screen-triangle shader, present when no wipe is active), and *a bad position guess* (dropping position entirely, **zero** quads anywhere have a width within ±30 of 408; the spectrum jumps 262 → 748). Draw counts across both entries: eff1 **4**, eff2 **3**, eff3 **0**, eff4 **6**.~~ (all from the merged-box parse, and wrong) 🔴 **The port draws `eff3` at t=60–62 and the console does not.** ❔ Why is not established — nothing in its element record differs from its neighbours. ⚠️ An earlier "sub-frame phase" explanation and the advice that drawing all five "shows more sweep than the console" are both **withdrawn**. ⚠️ What a frame-by-frame build-in comparison *will* show is disagreement about which flash lands in which frame — 2 units/submitted frame against this run's 2.231 units/presented frame — and neither side is wrong. 🔴 **Trap:** matching a bound texture's dimensions to a sprite fails both ways — it missed every flash *and* read the intro movie's 640×360 YUV planes as `ptbase2`. ✅ A regression of five events' observed frames against their declared times (residuals ≤0.9 frames) recovers the intercept at frame **106.1** when the composite spike, not in the fit, is frame **107**. ⚠️ Per-vertex alpha = fade alpha holds for the **glow** and does not generalise — `eff4` reads 255/127/254 on consecutive frames. ❔ Frame rate not recorded, so nothing is in seconds; the glow's period implies a **114**-unit cycle against a declared 120, unexplained; `eff5` vs `ptlogo_back2eff` not separated |
 | [`structures/boot-splash-gap-measured.md`](structures/boot-splash-gap-measured.md) | The black gap between the two boot splashes | ✅ **measured** in the guest's **draw stream**, which separates true black from a fade tail where luminance cannot: the publisher's last sprite is frame 125 (alpha 7), then **frames 126–129 submit NO sprite quad at all**, then the developer fades in at alpha 34. **The gap is 4 presented frames.** Converted with the disc as its own clock — `palogo_sqex` declares alpha≥1 for **239.8 units** and is drawn in **105** frames → **2.284 units/frame** (the title capture independently gave 2.231) — that is **~9.1 units ≈ 0.152 s**, against the **12** the port authored; ⚠️ and the true black is *shorter*, since both boundary frames still carry picture. 🔴 **RETRACTED**: "the developer splash is ONE composited 525×259 quad" — the same batching artefact. It draws three logos and three glows as separate quads in one `indices=24` call; the 525×259 was `gamearts_eff` merged with `seta_eff`. The port refuted it with arithmetic (a 259-tall box cannot hold logos spanning y 164…585) before I checked. ⚠️ The gap measurement is unaffected — those glows are the developer splash's first draw. ❌ Not declared on the disc: `palogo_eff0.prm` is a single static keyframe, and the top-level `+0x08` is a **family constant** (300 / 60) whose slack ranges 12–226 units. ❔ The executable is **not** looked at — named, not claimed. 🔴 The instrument was perturbing the measurement: the capture script taps Ⓐ on "screen changed a lot", which is also true of a fading splash — it tapped through the publisher and the developer never appeared. `GRACE=1` and `NOTAP=1` knobs added |
 | [`structures/ui-forced-backdrop.md`](structures/ui-forced-backdrop.md) | Where a keyless primitive paints, when the file forces it | ✅ **decoded**, partly closing `ui-prm-primitives.md`'s standing blocker: **an element covering the screen and fully opaque at some instant cannot paint above anything visible then**, and where that set is *every* other element its position is **forced first**. Disc-wide **80** instances forced, 50 constrained but not forced, 0 unconstrained. ✅ **Two controls, both measured orders from the running game**: it reproduces `palogo_eff0.prm` = FIRST (opaque 211 instants, below 6/6) — which a **name**-based rule gets wrong, since it is named like an overlay — and permits `pteff00.prm` on top (opaque 2 instants, below 3/23), which is where it is measured. ✅ Answers the port's `build_12`/`build_15` blank-screen contradiction: `pgloading_eff00.prm` is forced first, 4/4. ✅ Explains 36 builds the corpus recorded as "one colour" with no cause — `pzeff00.prm` forced first 32/32, so **our own sort wiped them**. 🔴 The rule's limit was found by its own test failing: applied to `.t32` sprites it claimed 22 must sort first against their own keys (`pneff01` 0xd850 at #8/13, `pbfriendly` 0x9230 at #17/49) — a sprite's *element* alpha says nothing about its *texture*'s coverage, so it is now restricted to untextured primitives. ⚠️ Assumes straight alpha-over; blend mode is still ❔. ⚠️ A lower bound, not an ordering. ⚠️ No new oracle run — the controls are prior measurements |
+| [`structures/ui-forced-backdrop.md`](structures/ui-forced-backdrop.md) *(span sensitivity)* | How much of the forced-backdrop rule rests on the timeline convention | ✅ **decoded**: the span is `0..=max keyframe time over every element`, and an element **holds** its final pose — decoded, not assumed ([`ui-keyframe-time-unit.md`](ui-keyframe-time-unit.md), [`ui-record-loop-length.md`](structures/ui-record-loop-length.md)). Sensitivity over the 130 keyless full-screen primitives with an opaque interval: using the header's declared **`+0x08`** instead changes **0** verdicts (interchangeable); using the primitive's **own** last keyframe changes **72**; counting elements **gone** after their last keyframe changes **72**. 🔴 So the hold decides **55 %** of verdicts — and dropping it is **refuted by a measured order**: `palogo_eff0.prm` is a single keyframe at t=0, so without the hold it is opaque for one instant, nothing else is up, and the rule calls it *free* against a game measured painting it first. ✅ The verdicts that matter are convention-independent — `pgloading_eff00.prm` is FIRST under all four, `pteff00.prm` FREE under all four. ⚠️ The port's **256 vs 211** was a **bundle mismatch, not a definitional one**: `palogo_eff0.prm` runs to t=255 on the publisher splash (entries 10/13) and t=210 on the developer (11/14) |

docs/re/structures/ui-forced-backdrop.md

@@ -37,7 +37,8 @@ instances.
 
 | primitive | measured in the game | opaque instants | forced below | rule says |
 |---|---|---|---|---|
-| `palogo_eff0.prm` | **paints FIRST** | 211 | **6 of 6** | ✅ forced first |
+| `palogo_eff0.prm` (entry 11, developer) | **paints FIRST** | 211 | **6 of 6** | ✅ forced first |
+| `palogo_eff0.prm` (entry 10/13, publisher) | **paints FIRST** | 256 | 2 of 2 | ✅ forced first |
 | `pteff00.prm` (title) | **paints LAST** | 2 | 3 of 23 | ✅ permitted on top |
 | `pteff00.prm` (menu) | **paints LAST** | 2 | 7 of 15 | ✅ permitted on top |
 
@@ -47,6 +48,50 @@ order. Occlusion gets it right. `pteff00.prm` is opaque only for two instants, a
 its screen's entry and exit, so the constraint never binds it: it is the fade
 cover, and it belongs on top.
 
+## The span, and what it costs to get wrong
+
+The rule quantifies over "every instant the primitive is opaque" and "every
+element visible then", so it depends on where a screen's timeline ends and on what
+an element does after its own last keyframe. The port asked, having got **256**
+opaque instants for `palogo_eff0.prm` where this page said 211.
+
+⚠️ **That pair was a bundle mismatch, not a definitional one** — `palogo_eff0.prm`
+appears on both splashes, and the publisher (entries 10, 13) runs to t=255 while
+the developer (11, 14) runs to t=210. 256 and 211 are both right, for their own
+screen. The definitions already agreed.
+
+**The definition:** the span is `0 ..= max keyframe time over every element in the
+build`, and an element **holds its final pose** past its own last keyframe — which
+is what `pose_at` does, and it is decoded rather than assumed: a group holds at its
+last keyframe rather than looping
+([`ui-keyframe-time-unit.md`](../ui-keyframe-time-unit.md)), and
+[`ui-record-loop-length.md`](ui-record-loop-length.md) shows the declared length
+never falls short of the last keyframe, the slack being exactly that hold.
+
+**How much rests on it — 130 keyless full-screen primitives with an opaque
+interval, and how many verdicts change:**
+
+| alternative convention | verdicts changed |
+|---|---|
+| span = the bundle header's declared `+0x08` | **0** |
+| span = the primitive's **own** last keyframe | 72 |
+| elements counted **gone** after their last keyframe (no hold) | **72** |
+
+🔴 **The hold decides 55 % of the verdicts, and dropping it is refuted by a
+measured order.** `palogo_eff0.prm` is a *single* keyframe at t=0. Without the
+hold it would be opaque for one instant, no other element would be up yet, and the
+rule would call it **free** — against the order measured in the running game,
+which paints it first. Pinned by
+`the_hold_after_a_final_keyframe_is_required_by_a_measured_order`.
+
+✅ **And the header length is interchangeable with the elements' maximum**: zero
+disagreements disc-wide. Either may be used.
+
+✅ **The verdicts that matter are convention-independent.**
+`pgloading_eff00.prm` comes out **first** under all four conventions;
+`pteff00.prm` comes out **free** under all four. Only `palogo_eff0.prm` moves, and
+only under the convention its own measured order rules out.
+
 ## Disc-wide
 
 Keyless **full-screen** primitives with an opaque interval: