Port step 4: measure the anchor and the mouth, condition on its own

`stabilize` is three things wearing one name, and it is now three functions in two
stages: `flow/measure/anchor` fits the rigid transform, `flow/condition` smooths
its parameters, `flow/measure/mouth` measures the lip rings through the result.
Parity is on the COMPOSITION and not on the pieces -- a split that agreed
function by function and not end to end would be a split rather than a port.

The oracle now drives `stabilize` at three configurations and the port agrees to
1e-9 on ref, rigid, transforms, outer, inner and aperture, plus `smoothContours`
at three radii. Two of the three configurations are at aspect 0.5625, a 1080x1920
phone clip, because at aspect 1 `pick` is the identity: a port that dropped the
anisotropy correction outright would pass every other assertion in the suite.
148 tests, up from 134.

Three decisions worth the reading time.

`makeXform` is not ported, and its absence takes the face oval with it. It
centres on the oval's bounding box and zooms until the face is 80% of the raster
height, so every vertex it touched carried a cropping decision made once, at
analysis time, from one frame's landmarks. Geometry belongs in the node's own
local space with the framing as a transform on a node, so this is a deletion. The
oval's only other consumer was the placeholder plate outline, which is painting.

The residual is taken against the RAW fit, and the prototype took it against the
smoothed one. That is the only deliberate numeric divergence here, and parity is
kept by asserting `anchor/residuals` on exactly what the prototype handed it. The
number's job is to say whether a section is stabilisable at all; folding the
smoothing error into it makes a slider look like a property of the footage, and
docs/architecture.md lists the residual under stage 3, which requires it to be
knob-free. `condition/anchor` therefore replaces `:transforms` and leaves
`:residual` alone.

The stage order is not the strict chain the table in docs/architecture.md looks
like, and that document now says so. The fit is knob-free, conditioning smooths
it, and the rings are measured *through* the conditioned transform -- so
`anchor avg` does re-run the ring mapping, which is a few hundred frames of twenty
points. The guarantee was only ever about the part that reads a source pixel, and
that part never sees a transform.

Two things fall out and are asserted rather than assumed. Smoothing and
subsampling commute, because both are per-slot, which is what lets `vertices`
stay a stage-5 knob downstream of a stage-4 one -- and it is also why the port can
smooth the full twenty slots where the prototype smooths eight and still match.
And `condition/contours` is `geom/moving-average` per vertex per axis rather than
its own clamped window, so "radius 2" cannot come to mean two different things at
the two knobs.

One dead end recorded so nobody walks it twice: the synth's head is perfectly
rigid -- its jitter is a whole-head translation, which a similarity absorbs
exactly -- so every frame's rigid configuration is congruent with frame zero's and
the Procrustes mean IS frame zero to 1e-15, jitter or none. "The reference is the
mean and not frame zero" cannot be asserted on this track and is asserted in
geom-test, where the two can differ.

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

frontend/README.md

@@ -72,7 +72,12 @@ From step 9 Django serves the page and `:dev-http` goes away.
 
 `js/` is the numeric oracle, not dead weight. `test/parity/` runs both
 implementations on the same synthetic track and diffs them: `fit-similarity` and
-`procrustes-mean` agree to 1e-9, the raster pixel-for-pixel.
+`procrustes-mean` agree to 1e-9, the raster pixel-for-pixel, and `stabilize`'s
+whole output agrees across the three namespaces it was split into.
+
+The oracle drives `stabilize` at aspect 0.5625 as well as at 1. Aspect 1 makes the
+anisotropy correction the identity, so a port that dropped it entirely would pass
+— which is the one thing a parity suite on normalised landmarks can be blind to.
 
 Both sides get the identical track because `js/synth.js` reads `Math.random` at
 call time, so `oracle.mjs` stubs it to a constant and the CLJS side passes
@@ -86,6 +91,7 @@ the prototype's mistakes into the rewrite and make them permanent.
 
 ```
 src/arthur/domain/      pure. No re-frame, no DOM, no flow/.
+src/arthur/flow/        the stages. `(f params inputs) -> output`, no state.
 src/arthur/demo.cljs    the hand-written scene, read from demo/scene.edn
 src/arthur/ui/canvas.cljs  the one imperative sink — the only DOM canvas call
 test/arthur/synth.cljs  the synthetic track — test infrastructure, not src