anchor — the v2 node model

[softmarshmallow]

Status — 2026-07-11

Tracking issue for the anchor v2 node model and its authored, file-first projection: n0 XML Draft 0 (.n0.xml).

The current proof lives on model-v2-anchor, with the language RFD under docs/wg/format. This branch changes no production runtime under crates/grida and does not change the packed .grida archive schema. It proves the model, source language, resolver, display list, and raster materialization before promotion.

Current thesis

A node is an anchored box with typed content. The file stores authored intent; resolution derives boxes, transforms, layout, text lines, paint geometry, and visual bounds.

The model decisions that remain locked are:

• declared, measured, and derived box sources stay distinct;
• the box is the sole layout negotiation surface;
• rotation and flips are visual-only post-layout intent;
• no stored general matrix exists outside the quarantined lens operation list;
• primitives are parametric and may own ordinary children in their local box, so <rect><text>…</text></rect> needs no combined shape-with-text node;
• free positioning and flex layout preserve authored bindings instead of baking one viewport's coordinates;
• reads materialize resolved geometry while writes retarget or reject typed intent;
• derivable state is not serialized.

n0 XML Draft 0

.n0.xml is the inspectable, diffable authored source. .grida remains the packed archive; conversion between them is explicit.

The root contract is:

<grida version="0">
  <container width="960" height="540">
    <!-- one authored scene tree -->
  </container>
</grida>

Draft 0 uses direct semantic elements:

• container, rect, ellipse, line, text, group, and lens;
• no separate circle; equal ellipse extents express a circle;
• no render-node kind; <shape> is reserved for a future custom-shape design;
• long, stable property names such as width, min-width, and aspect-ratio;
• strict applicability and typed errors for unknown, contradictory, or out-of-context syntax.

Every property marked Draft 0 in the property registry is implemented by the proof reader/writer. Placeholder and Design rows remain deliberately invalid syntax.

Ordered paint, projected from Paint / Paints

The existing Grida paint variants and ordered Paints semantics are the source of truth. XML does not introduce a parallel style abstraction.

<rect width="320" height="180">
  <fill>
    <solid color="#101828"/>
    <gradient kind="linear" from="0 0" to="1 1" opacity="0.8">
      <stop offset="0" color="#7C3AED"/>
      <stop offset="1" color="#2563EB"/>
    </gradient>
    <image src="./noise.png" fit="cover" opacity="0.15"/>
  </fill>
  <text>Example</text>
</rect>

• <fill> owns an ordered paint channel; first paint is bottommost, last is topmost.
• Typed values are solid, gradient kind="linear|radial|sweep|diamond", and contextual image paint.
• visible, opacity, and blend-mode belong to each typed paint.
• Stops remain structured and ordered.
• fill="#RRGGBB" is not legacy syntax: it is the canonical compact form for the common one-solid case and is mutually exclusive with <fill>.
• <fill/> explicitly suppresses a primitive/text default.
• Inline paint definitions are canonical; reusable definitions/references are future work.

The accepted syntax alternatives are recorded in the RFD: direct typed children are accepted; a generic paint envelope is deferred; CSS-like functional paint attributes are rejected as canonical.

Native multiple strokes

stroke is repeatable. Each occurrence is an independent geometry with its own ordered Paints:

<rect width="320" height="180" fill="#101828">
  <stroke width="12" align="outside" join="round">
    <solid color="#111827"/>
  </stroke>
  <stroke width="3" align="inside">
    <solid color="#2563EB"/>
    <gradient kind="linear">
      <stop offset="0" color="#A78BFA"/>
      <stop offset="1" color="#60A5FA"/>
    </gradient>
  </stroke>
</rect>

This directly represents road casings, double borders, keylines, focus rings, and decorative outlines without duplicated scene geometry, nested wrappers, pseudo-elements, or shadow approximations. Strokes paint in source order after the node's children; each stroke's paints independently paint bottom to top.

This is the one intentional model extension: the proof owns Vec<Stroke>, while the current production scene/archive contract owns one stroke geometry plus one Paints. Production must adopt ordered stroke applications before claiming lossless Draft 0 support.

Materialized proof

The model-v2 proof now includes:

• a strict parser and fallible, self-validating canonical writer;
• semantic round-trip independent of arena IDs, with dead/cyclic/mis-parented tree rejection;
• direct primitive composition, responsive bindings, size constraints, free/flex layout, padding, gap, grow, alignment, clipping, opacity, flips, rotation, and lens operations;
• all existing solid, linear, radial, sweep, diamond, and image paint variants where Draft 0 can spell their state;
• ordered fill paints and repeated stroke geometries with alignment, caps, joins, miter limits, and dashes;
• per-paint visibility, opacity, and blend execution in painter order;
• node-local unit paint coordinates with the defined one-pixel fallback for a degenerate axis;
• structured text-line topology shared by measurement, fill, and repeated text strokes;
• host-relative image RID loading with authored/resolved-path diagnostics;
• conservative stroke-aware visual bounds and descendant-only container clipping;
• a thin .n0.xml → PNG host using the same resolve → drawlist → paint pipeline.

The flagship source is source-becomes-surface.n0.xml. It exercises every Draft 0 element/property family, all four gradients, image paints, clipping, responsive bindings, nested text, lenses, and native multi-stroke composition.

cd model-v2/engine
cargo run -p n0 --bin n0_xml_render -- \
  fixtures/test-n0-xml/examples/source-becomes-surface.n0.xml \
  target/n0-xml-source-becomes-surface.png 1600 1000

Evidence

All reviewed proof suites are green:

(cd model-v2/a/lab && cargo test)             # 195 tests
(cd model-v2/engine && cargo test)            # 59 tests
(cd model-v2/a/spike-canvas && cargo test)    # 1 regression test

The example corpus is parsed, canonicalized, resource-resolved, resolved without ignored/error reports, and actually rendered in tests. XML well-formedness, Rust formatting, docs formatting, the repository pre-commit formatter, and root-workspace clippy also pass.

The legacy re-host screenshot oracle has not been silently re-blessed. Its old goldens encode implicit frame borders and the earlier parent-stroke order; reviewing/rebaselining those four screenshots is an explicit follow-up after the new semantics are accepted.

Compatibility boundary

Surface	Current status
Existing Grida Paint variants / ordered Paints	Projected directly; no parallel XML paint model
Model-v2 lab/engine	Parses, canonicalizes, resolves, and renders Draft 0
Multiple stroke geometry	Implemented in the proof; incompatible with the current production single-geometry shape
crates/grida production runtime	Not yet a .n0.xml consumer
Packed .grida archive	Not extended for Draft 0 or repeated strokes
Image resources	Strict file host preflights relative RIDs; the low-level paint executor expects an already-populated resource context
Text	Topology is deterministic, but the proof metric is still synthetic; production promotion needs one real shared shaper/font contract

No production model incompatibility was hidden by inventing XML-only state. Unrepresentable model values fail the writer; unsupported source syntax fails the reader.

Landed commits

1. 0cf5b29b8 — docs(format): specify n0 XML Draft 0
2. 6e3e7c4a8 — feat(model-v2): ingest and render n0 XML
3. eb22e7ec4 — test(model-v2): add canonical n0 XML showcase

Canonical reading order

1. n0 XML Draft 0 RFD
2. n0 XML property registry
3. Anchor model statement
4. Model-v2 engine guide
5. Lab parser/writer boundary

Remaining promotion work

• Lock the anchor model and visual-only transform framing.
• Specify .n0.xml Draft 0 and its property applicability.
• Prove strict parse/canonical write, resolution, ordered paint, repeated strokes, resources, and raster output.
• Add canonical examples and an all-properties showcase.
• Decide and migrate production nodes/archive to ordered stroke applications.
• Promote the parser/materializer out of the model-v2 proof without coupling the engine to XML I/O.
• Add .n0.xml loading/saving and file association to the product surface.
• Replace the synthetic text metric with the production shaping/font-resource contract.
• Define portable resource declarations/packaging and network policy.
• Reconcile scene/archive gaps before enabling additional registry placeholders.
• Review and intentionally rebaseline the legacy screenshot oracle.

The issue remains open through production and archive promotion. Effects, editable vector networks, attributed text, components/reuse, durable IDs, scene images, masks, and animation remain later, versioned design work—not implicit Draft 0 syntax.