The face owns its placement, not the take that holds it

The source-to-stage mapping moves off :main's :face group and onto each face's
own :place, above its head. `face-placement` computes exactly what it computed
before, over every subject together, so two faces filmed side by side keep
their filmed relation — it is written into each face instead of onto a group
above them all. Same transform, same subtree, one level lower, and the
composite is identical to the pixel: a digest over every op :main emits across
the whole take is unchanged either way.

THE OWNER IS THE POINT. A face carrying its own mapping is the right size
wherever it is put — dropped into another symbol, or opened in its own tab to
be drawn over — and the take that holds it needs to know nothing. On a group
above the instances the scale belonged to the take, so a face taken out of it
had no size at all and drew at a fraction of a pixel.

The pool's thumbnails drop the workaround that knew about this: a symbol is
rendered rooted at itself again, because a face now carries the placement that
makes that honest, so the pool needs to know nothing about where a symbol
happens to be used. `domain/node` and `arthur.export` leave its requires with it.

The tests here were reading the placement off :main. The photo registration
test changes shape rather than location: its premise was that face-1's head is
its own root, so a photo sitting where it was filmed was image pixels over
image height and nothing else. The head still cancels — that is what the test
is about — but it now cancels against the face's own placement, which is why
the photo comes with the face into its own tab instead of sitting at a
fraction of a pixel beside it.

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

docs/port-plan.md

@@ -333,11 +333,12 @@ per-frame header.
 numbers: it centres on the face oval's bbox and zooms until the face is 80% of
 the raster height, so every vertex carries a cropping decision made once from one
 frame's landmarks. Dropping it is a deletion. Placement becomes `[:xform :*]` on
-an authored `:face` node, the stage clips whatever hangs off, and project
+an authored `:place` node inside the face, the stage clips whatever hangs off,
+and project
 dimensions stop being tied to the footage. See "What space geometry is in" in
 `docs/animation-model.md`.
 
-The anchor transform freezes onto `:head`, one level under `:face`, and the
+The anchor transform freezes onto `:head`, one level under `:place`, and the
 normalise on/off/per-plate toggle is which of the three channel shapes that node
 carries. Always measure and always store factored, whatever the toggle says:
 smoothing and velocity-minimum key selection both require the split to exist in