Measure where visual difference comes from, and correct the epic's framing

Two cheap measurements settled a question three expensive ones had not, and both
of them contradicted the diagnosis offered for it.

The stated diagnosis was that the identity's expressive range had become the
bottleneck. It has not. A census of the identities themselves — no GPU, seconds
to run — puts mean distance between twelve songs at 0.43 with no near-identical
pairs and full coverage of every decision space: six of six fills, five of five
lattices, six of six protagonist forms, three of three element scales. The songs
are handed genuinely different designs.

The decomposition then asked whether those designs reach the picture, by holding
the container fixed and varying only the identity, then the reverse:

    identity only    0.0299
    container only   0.0557
    both             0.1101
    neither          0.0000

Identity is worth 54% of what the container is worth, against an instrument
noise floor of exactly zero, and the two compose to more than their sum. The
inversion works at the frame level. What it does not do is replace the container.

That corrects EPIC-3 §5, which proposed a song picking two to five stages on the
theory that shared content would substitute for container variety. Container
variety is the larger of the two effects and identity adds to it. Four stages
with a rich identity throws away the 0.056 the library was already providing —
which is exactly the shape of every measurement in this epic: stages have the
lowest floor of any arm and no advantage in spread.

The direction is therefore not a small set of stages. It is the whole library
consuming the cast: keep the sixty-one containers and make them draw the song's
content rather than their own. The migration was filed as a cost; it is the
payoff.

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

flow-state/EPIC-3.md

@@ -339,6 +339,41 @@ as if they differed in one. And this metric's noise floor at seven songs is
 large enough to invent findings — anything under about 0.01 of spread needs
 repeats before it is believed.
 
+## 9b. Where the difference comes from — and the correction to §5
+
+Two cheap measurements settled what three expensive ones could not.
+
+**The identity is not the bottleneck.** `tools/identity-census.js` over twelve
+songs: mean identity distance 0.43, no near-identical pairs, and full coverage
+of every decision space — six of six fills, five of five lattices, six of six
+protagonist forms, three of three element scales. The songs are handed genuinely
+different designs.
+
+**The identity does reach the frame.** `checks.html?decompose=1` holds the stage
+fixed and varies only the identity, then holds the identity fixed and varies
+only the stage:
+
+    identity only    0.0299     one stage, each song's cast, ink and lattice
+    container only   0.0557     one identity, four different stages
+    both             0.1101     what the generator actually does
+    neither          0.0000     the same thing twice — the noise floor
+
+Identity is worth 54% of what the container is worth, on a noise floor of
+exactly zero, and the two compose to more than their sum.
+
+That is the mechanism working, and it corrects the framing in §5. The proposal
+there was that a song picks two to five stages — that the identity would
+*replace* container variety. It does not. Container variety is still the larger
+of the two effects, and identity adds to it rather than substituting for it. A
+generator with four stages and a rich identity throws away the 0.056 it could
+have had from the library.
+
+So the direction is not "a small set of stages". It is **the whole library
+consuming the cast**: keep the sixty-one containers, and make them draw the
+song's content instead of their own. The migration in §8 stops being a nice-to-
+have and becomes the entire point — and the payoff is additive with everything
+the library already provides.
+
 ## 10. The smallest experiment worth running first
 
 One artifact, three stages, one measurement. Do not build the whole identity layer on a