Semantic Fractal Topology

Purpose

D25 is the public reference implementation of Semantic Fractal Topology: a language-addressable spatial intermediate representation that keeps semantic identity, recursive spatial address, metric evidence, deterministic calculation, revision history, and human authority separate.

Version 2 replaces the primary embedded teaching animation with a native React workbench backed by reusable TypeScript modules. The earlier standalone Spatial Intent Deck remains downloadable as a compact compatibility artifact, but it is no longer the authoritative implementation surface.

The runtime is browser-local. It makes no paid API call and requires no network after the page has loaded. Every visible result is derived from authored fixture state and deterministic code in the repository.

Implemented runtime

Typed semantic scene graph

The authoritative fixture object is sft.scene.v1. It contains:

• persistent entity IDs;
• typed entity kinds such as building, level, space, opening, object, assembly, service, access zone, robot, path node, obstacle, and game actor;
• typed relations such as contains, connected-to, opens-into, supported-by, attached-to, requires-before, blocks, reachable-from, services, joint-to, and occupies;
• local metric frames;
• exact or bounded volumes;
• source pointers and adapter lineage;
• and explicit evidence state.

The validator rejects duplicate IDs, missing relation endpoints, unknown frame references, inverted bounds, frame cycles, containment cycles, and assembly-order cycles. Semantic-only entities remain legal but produce warnings when a metric query requires dimensions.

Adaptive recursive spatial index

Entities with metric bounds are transformed into a world frame and inserted into an adaptive octree. Only occupied branches subdivide. Objects spanning multiple children remain at the nearest containing parent rather than being duplicated into every child.

The public inspector exposes:

• recursive spatial key;
• node and leaf counts;
• maximum depth reached;
• indexed entity count;
• entities retained at a parent because they cross child boundaries;
• point queries;
• bounded-range queries;
• and the complete deterministic index snapshot.

The octree is a broad-phase locality structure. Its address does not replace exact geometry.

Exact and bounded local metric frames

Every metric object identifies its local frame, unit, precision, and tolerance. Frame transforms support translation, basis orientation, scale, parent-frame composition, unit conversion, world-space bounds, interval arithmetic, signed clearance, and bounded fit predicates.

A conclusion is:

• EXACT when all required authored facts are exact under the selected kernel;
• BOUNDED when tolerance or bounded primitives are involved;
• UNKNOWN when the available interval crosses the decision boundary;
• or refused when the required metric facts do not exist.

Immutable content-addressed revisions

Canonical JSON serialization and an in-browser SHA-256 implementation produce stable content identities. Scene revisions are immutable objects containing:

• scene content ID;
• one or more parent revisions;
• deterministic logical time;
• actor;
• typed command where applicable;
• event note;
• and the exact canonical graph.

Branch names are mutable pointers. MAIN is never silently rewritten. Two agents may fork the same accepted head, propose disjoint changes, receive a conflict assessment, and materialize a two-parent MERGE_CANDIDATE. That candidate remains non-accepted until a separate authority gate acts.

Solver dispatch

The typed dispatcher currently exposes eight commands and bounded kernels:

1. QUERY_FIT — axis-aligned bounded object projections through an authored opening;
2. QUERY_COLLISION — adaptive-octree candidate reduction plus bounded AABB overlap;
3. VALIDATE_CONSTRAINTS — graph, frame, endpoint, and directed-cycle validation;
4. QUERY_REACHABILITY — deterministic breadth-first path search with blocked and minimum-clearance edges;
5. AUDIT_ASSEMBLY — topological ordering of requires_before relations;
6. AUDIT_ARCHITECTURAL_CLEARANCE — authored project-policy checks for openings, routes, headroom, and service depth;
7. AUDIT_SERVICE_ACCESS — obstruction checks against authored service-access zones;
8. MOVE_ENTITY — a typed containment-change proposal that may be committed to a non-main branch by an explicit user action.

Each result exposes the selected solver, status, precision, trace, warnings, and structured result object. An AABB overlap is labeled as a narrow-phase candidate, not proven mesh contact. An authored architectural policy is labeled as project policy, not building-code certification.

Natural-language compilation

The public compiler is deterministic and rule-based. It recognizes bounded forms for fit, reachability, service access, assembly order, architectural clearance, collision, constraint validation, and movement.

The compiler resolves references against scene IDs and names. It returns:

• COMPILED with a typed command;
• AMBIGUOUS with visible candidate entities;
• INVALID when a required reference is absent;
• or UNSUPPORTED when no approved pattern matches.

No model call occurs. The compiler refuses “make the building perfect” rather than inventing an executable interpretation.

Import adapters

Five public-safe normalization paths feed the same graph:

• glTF 2.0 JSON: node hierarchy, TRS transforms, semantic extras, and authored bounds;
• OpenUSD ASCII subset: bounded USDA parsing for Xform, Scope, Mesh, Cube, translation, extent, and cube size;
• CAD manifest v1: explicit assemblies, parts, frames, bounds, and dependency projection;
• BIM/IFC projection v1: explicit spaces, openings, services, containment, and connectivity projection;
• robot scene graph v1: explicit links, joints, path nodes, obstacles, and clearance edges.

The adapter boundary is deliberately honest. The browser runtime does not claim native STEP/IGES B-rep parsing, complete IFC semantics, binary USD crate support, glTF accessor geometry decoding, URDF/SDF XML parsing, mesh collision, IK, SLAM, or controller execution.

Application fixtures

The runtime includes twelve deterministic conformance cases:

1. a lobby sofa fitting through an authored front-door opening;
2. an architectural project-policy audit with intentionally failing clearances;
3. an intentionally obstructed air-handler service zone;
4. a six-step cabinet assembly sequence;
5. a robot route that avoids a blocked narrow aisle;
6. a deterministic game route refused while the exit door remains locked;
7. two-agent branch isolation and a non-accepted two-parent merge candidate;
8. glTF normalization;
9. OpenUSD subset normalization;
10. CAD manifest normalization;
11. BIM/IFC projection normalization;
12. robot scene normalization.

All twelve currently satisfy their authored deterministic expectations. This is DETERMINISTIC_FIXTURE_CONFORMANCE, not a performance, scaling, interoperability, geometric-accuracy, building-code, robot-safety, or production result.

Near-term product applications

The runtime now provides a concrete starting point for:

• auditable clearance checks: object/opening and project-policy predicates with signed intervals and proof traces;
• assembly sequencing: deterministic dependency order with cycle refusal;
• robot environment memory: stable entities, local frames, blocked edges, clearance edges, and addressed route state;
• service-access validation: authored maintenance envelopes checked against obstructions;
• deterministic game state: locked routes, movable items, immutable branches, and replayable world revisions;
• shared spatial state for multiple agents: separate proposals, conflict detection, multi-parent candidates, and preserved accepted state.

The most credible first product is not a universal world simulator. It is an audit layer that sits between heterogeneous scene sources, language requests, deterministic specialist kernels, and an authority-controlled revision ledger.

Downloadable artifacts

The public package includes:

• scene JSON Schema;
• typed-command JSON Schema;
• revision-ledger JSON Schema;
• authored architecture scene fixture and content ID;
• deterministic application fixture receipt;
• runtime manifest;
• downloadable active scene and browser-local operation receipt;
• and the compact standalone Spatial Intent Deck.

Evidence boundary

IMPLEMENTED applies to the versioned browser-local runtime, its schemas, deterministic algorithms, authored fixtures, and public interface.

It does not establish:

• native or complete CAD/BIM/USD/robot interchange;
• exact arbitrary-mesh fit or collision;
• continuous physics;
• structural analysis;
• code compliance;
• serviceability certification;
• robot safety;
• measured scaling advantage;
• language-model quality;
• or production digital-twin reliability.

Those claims remain governed by b18-semantic-fractal-topology. A fixture, schema, green build, or clean merge candidate cannot promote itself into accepted real-world evidence.