Finding: where n0 joins the shared downstream

Genre: finding — grounded evidence for an open owner decision. Not a spec and not a plan. It reframes a question the Web-First Amendment defers, using n0's actual downstream types, so the decision can be taken on evidence when it is ripe.

Status: open, and not yet ripe — the deciding evidence needs a second producer for the hard fact (shaped text), which does not exist yet. This finding says what the decision hinges on and names the smallest spike that would ripen it.

The crux

The amendment leaves one question to a later spike: does n0 emit the common resolved contract (its resolver output lowers into rframe::Frame, and the whole downstream — drawlist, painter, bounds, damage, caches — is shared), or does it join only at the drawlist boundary (n0 keeps its own resolved form and its own drawlist; only the painter and raster tiers are shared)?

The prototype already showed the high join is possible for the trivial case: the n0 canary lowers a resolved rectangle into rframe::Frame and paints it through the shared downstream. But a rectangle proves nothing about the facts that actually differ between producers. The amendment already supplies the resolving principle — sharing begins only where the inputs genuinely match — so the real question is per fact kind, not one global switch.

The reframing

n0's downstream is an ordered primitive stream. Each primitive kind carries a set of facts. Classify each as source-neutral (belongs in the common contract → n0 can join high for it) or n0-coupled (would leak an n0/authoring concept into the contract, or is bound to n0's environment → n0 should join lower for it). The join point is then the lowest fact that must stay coupled — and it need not be uniform across kinds.

The deciding factor

Everything except text either converges high already or converges high behind the leaf-vocabulary seat decision (the two are coupled — resolve them together). Shaped text is where "emit the common contract" and "join at the drawlist" genuinely diverge:

• The amendment's MAY list does admit "shaped-text artifacts" and "declared font/image/resource environments" — so a neutral shaped-text contract is not forbidden. The blocker is that n0's shaped text is implemented coupled to a private font registry and its own oracle; there is no neutral font-key boundary.
• So the choice is: (a) define that neutral shaped-text + font-key boundary and push text into the high join too, or (b) let text join low — n0 emits its own text drawlist item, and only the painter/backend is shared for glyphs. Both honor the amendment; (a) is more work and more sharing, (b) is less of both. The evidence that should decide it does not exist yet, because there is only one shaped-text producer today.

Recommendation (for the owner to decide, when ripe)

• Do not take a uniform A-vs-B decision. The honest shape is a per-fact boundary: visual primitives converge high, shaped text is open. Record it that way.
• Couple this decision with the leaf-vocabulary seat. n0 cannot emit the common contract for paint/stroke facts until the neutral leaf vocabulary exists; deciding one without the other is deciding on air.
• Name the smallest deciding spike, and gate it on a second text producer. When the Web family gains a real shaped-text producer, push a text run from both it and n0 toward a candidate neutral shaped-text + font-key contract, and observe whether a neutral font-key boundary holds (→ text joins high) or forces the boundary down (→ text joins low). Until that second producer exists, per the amendment's "two real producers first," the text join stays deliberately undecided.

The decision to file

File in the charter's decision registry, coupled with the leaf-vocabulary seat: n0's join point per fact kind — high (emit the common contract) for the visual primitives once the neutral vocabulary exists, and high-or-low for shaped text pending the font-key spike above. Its evidence bar is this gap analysis plus the two-producer text spike. Until then the n0 canary stays a deliberately tiny invariant probe, not a widening integration.