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 as staged D-M, coupled to D-C, in the charter's registry. The vector stage can ripen independently after the n0 compiler-read inventory and vector-input/mixed-composition spike recorded in the Web renderer adoption patrol, but only if that spike proves one private orchestration seam can interleave admitted vector facts with fact kinds whose join remains open. The text stage is not yet ripe because its second producer does not exist. If mixed-fact composition cannot meet that condition without a source-specific or opaque escape hatch, text blocks the join rather than being wished away by staging.

The crux

The amendment leaves one question to a later spike: does n0 emit the common resolved contract (one compiler, one private drawlist, one executor, and shared frame/damage/cache behavior), or does it join below its private drawlist (n0 and Web each retain a resolved form, compiler, private drawlist, and private executor while sharing only the leaf-paint vocabulary and realization utilities plus the raster backend)? The latter is called the low join here. It does not mean that one executor consumes two unrelated private drawlist types.

The prototype showed that a 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. It did not show that n0's real compiler can stop reading authored/effective model state. 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 a source-neutral candidate (eligible for a high join after equivalence evidence) or n0-coupled (would leak an n0/authoring concept into the contract, or is bound to n0's environment and therefore pushes the join lower). The join point is then the lowest fact that must stay coupled — and it need not be uniform across kinds. Eligibility is not proof: the current compiler also reads document topology, payload kinds, and effective values, as the adoption patrol records.

The deciding factor

Everything except text is eligible to converge high or is blocked on the leaf-vocabulary seat decision, but eligibility still needs the vector-stage compiler equivalence evidence. Shaped text is a separate later question where "emit the common contract" and "join below the private 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 — each engine's private compiler and executor retain its own text artifact, font registry, glyph replay policy, and text item. Sharing then stops at backend glyph/raster utilities that require no common font key or shaped-text representation. Both remain D-M candidates; (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, by stage)

• Do not take a uniform A-vs-B decision. The honest shape is a per-fact boundary: glyphless visual primitives are high-join candidates subject to the vector equivalence spike, while shaped text is separately open.
• 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.
• Prove mixed-fact composition before treating the stages as independent. The vector spike must preserve order, scopes, identity, damage, and cache behavior for a frame that mixes admitted vector facts with still-private text. Failure collapses the stages into one later decision; it is not permission for a second compositor.

The registered stages

D-M is registered in the charter's decision registry with independent stages. The vector stage, coupled with D-C and the leaf-vocabulary seat, chooses the glyphless join and proving-shell disposition after the compiler-read inventory, paint/stroke gap report, and normalized-input equivalence spike, including its mixed-fact composition condition. The text stage later chooses high or low for shaped text after the two-producer font-key spike. D-C does not, by itself, choose either stage. Until its applicable stage is taken, the n0 canary stays a deliberately tiny invariant probe, not a widening integration.