Side quest 2: give three churning scenes something to develop

Curl Flow, Signal Decay and Circuit Bloom had no parameter that changed their
structure. Each was one process at one scale, statistically identical
everywhere and at every moment — which is the technical statement of "it
looks the same for five minutes". Every pixel moving, the image never
changing.

Each got the large-scale structure it was missing, and the slow axis now has
something real to walk:

- Curl Flow gains a CURRENT: one broad band carries the filaments and the
  rest runs bare. The axis is the band's strength rather than its position,
  and that choice was measured — moving the band preserves the frame's total
  energy, so a ten-second average of it is nearly the same image wherever it
  sits (0.0028 across a full sweep). Opening and closing it changes how much
  of the frame is lit at all. The current gates the final image rather than
  only the vein term, because the feedback trail and the flow tint each fill
  the frame on their own.
- Signal Decay gains a DAMAGE FRONT: lock falls away on one side of a moving
  boundary, so the stack has a shape instead of every lane being an
  independent coin flip. Hiss had to be gated by it too — hiss rises as lock
  falls, so without that a damaged lane simply traded signal for noise and
  carried the same energy, and the front cancelled itself out.
- Circuit Bloom now actually BLOOMS. `reach` was a fixed vignette, so the
  packets ran, the pads blinked and the board never changed. Its range stops
  at 1.6 because the frame's far corner is ~1.4 units out and travel spent
  past that changes nothing — the first attempt wasted most of the axis up
  there.

The gate itself was wrong, and this is the more important half of the commit.
It compared the scene at thirty seconds against the scene at two and a half
minutes and divided by what it did between those points with frozen
parameters. Those are two different places in the song, so the denominator
was full of audio reactivity: it was really asking "does the axis move this
scene MORE than the music does", which no scene should have to pass. Circuit
Bloom failed at 0.92x while its mean luminance moved 5.6x across the axis — a
large structural change scored as nothing.

The experiment now holds time constant and varies only the axis, against a
control that is the same parameters over the next window — the residual churn
the ten-second average failed to cancel, which is the noise floor it has to
beat. With the axis disabled the two parameter sets are identical and the
ratio is 0.00 by construction, so the companion check is a real discriminator
rather than a formality. It reads 0.00x on all six scenes.

Moiré Grid 28.7x · Gate Corridor 14.3x · Truchet Fold 3.3x · Signal Decay
1.9x · Curl Flow 1.7x · Circuit Bloom 1.4x, against a 1.25x bar.

104/104 checks pass including the slow set. Closes SIDE-QUESTS.md §2 and the
open half of EPIC-2.md §3.4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

flow-state/src/checks/phase11.js

@@ -556,7 +556,29 @@ function meanAbs(a, b) {
     return sum / a.length / 255;
 }
 
-/** How much the declared axis moves a scene, against how much it moves anyway. */
+/**
+ * How much the declared axis moves a scene, against the metric's own noise.
+ *
+ * The experiment holds TIME constant and varies only the axis, which the first
+ * version of this check did not — and getting that wrong made it measure
+ * something else entirely.
+ *
+ * That version compared the scene at thirty seconds against the scene at two
+ * and a half minutes, and divided by what the scene did between those points
+ * with its parameters frozen. But those are two different places in the song,
+ * so the denominator was full of audio reactivity: the check was really asking
+ * "does the slow axis move this scene MORE than the music does", which is a
+ * different and much harder question, and one no scene should have to pass.
+ * Circuit Bloom failed it at 0.92x while its mean luminance was moving 5.6x
+ * across the axis — a large structural change, scored as nothing.
+ *
+ * So: one frame window, two parameter sets, and a control that is the same
+ * parameters over the next window — the residual churn the ten-second average
+ * failed to cancel, which is exactly the noise floor this measurement has to
+ * beat. With the axis disabled the two parameter sets are identical and the
+ * ratio is 0.00 by construction, which is what makes the companion check below
+ * a real discriminator rather than a formality.
+ */
 function axisRatio(engine, arc, look, track, module, { withAxis }) {
     const paramsAt = (seconds) => {
         const out = sampleValues(module, new Rng(77), look.sections[0].bias,
@@ -570,18 +592,16 @@ function axisRatio(engine, arc, look, track, module, { withAxis }) {
         }
         return out;
     };
-    // The control is the same scene with its parameters held: whatever it does
-    // on its own between these two points in the track.
-    const frozenA = averagedFrame(engine, look, module,
-        sampleValues(module, new Rng(77), look.sections[0].bias, look.personality.temperament), 1800);
-    const frozenB = averagedFrame(engine, look, module,
-        sampleValues(module, new Rng(77), look.sections[0].bias, look.personality.temperament), 9000);
-    const movedA = averagedFrame(engine, look, module, paramsAt(30), 1800);
-    const movedB = averagedFrame(engine, look, module, paramsAt(150), 9000);
 
-    const own = meanAbs(frozenA, frozenB);
-    const moved = meanAbs(movedA, movedB);
-    return { own, moved, ratio: moved / Math.max(1e-6, own) };
+    const FRAME = 1800;
+    const WINDOW = 90 * 7;
+    const early = averagedFrame(engine, look, module, paramsAt(0), FRAME);
+    const late = averagedFrame(engine, look, module, paramsAt(track.duration), FRAME);
+    const control = averagedFrame(engine, look, module, paramsAt(0), FRAME + WINDOW);
+
+    const moved = meanAbs(early, late);
+    const noise = meanAbs(early, control);
+    return { moved, noise, ratio: moved / Math.max(1e-6, noise) };
 }
 
 check(11, 'a declared slow axis actually changes the scene', () => {
@@ -604,8 +624,8 @@ check(11, 'a declared slow axis actually changes the scene', () => {
             const r = axisRatio(engine, arc, look, t, module, { withAxis: true });
             detail.push(`${module.name} ${r.ratio.toFixed(2)}x`);
             if (r.ratio < 1.25) {
-                problems.push(`${module.name}: axis moved ${r.moved.toFixed(4)} against ` +
-                    `${r.own.toFixed(4)} on its own — only ${r.ratio.toFixed(2)}x`);
+                problems.push(`${module.name}: axis moved ${r.moved.toFixed(4)} against a ` +
+                    `${r.noise.toFixed(4)} noise floor — only ${r.ratio.toFixed(2)}x`);
             }
         }
         if (!declared.length) problems.push('no scene declares a slow axis');