Explicit tensor planes in RiXCel

RiXCel materializes a tensor only when explicitly requested. A finite Shaped, Matrix, Vector, Covector or Tensor supplies its components. Select one complete plane with two distinct, 1-based viewAxes and a rank-matching slice: visible axes are null, hidden axes are fixed positive indices. Defaults select axes 1 and 2 with hidden indices 1. A rank-one value becomes a single column.

The shared JavaScript helpers live in src/runtime/rixcel-tensor.js:

const options = { viewAxes: [3, 1], slice: [null, 2, null] };
const plane = rixCelTensorPlane(tensor, options);
// plane: { shape: [rows, columns], values, indices, viewAxes, slice }
const readonlySheet = createRixCelTensorSheet(tensor, options);
const candidate = materializeRixCelTensorPlane(document, tensor, {
  ...options,
  targetAxes: [1, 2],
  targetStart: [1, 1],
});
// candidate: { document, event, shape }; event is one slot:batch.

targetStart contains one canonical numeric index for every destination axis. targetAxes selects its row and column axes; other destination coordinates stay fixed. The complete plane must fit. A rank-one destination accepts only a single column. The operation does not grow the document or introduce spill behavior.

Each selected value becomes a literal formula source: exact integers, rationals, intervals, strings, null and undecided values are supported. Fractions and large integers retain their exact values, and strings remain inert. Unsupported scalar kinds fail explicitly; there is no fallback through rounded display text. Finite sparse Rational coordinates are read directly without allocating the full ambient tensor. Countable coordinates require an explicit bounded projection before this operation. Unsupported coordinate storage is rejected.

Only a slot whose source is _ and whose view.blank is true is vacant. A nonblank formula that evaluates to null still collides. Drafts also collide. Collision, invalid axis/slice, unsupported scalar, bounds and shape failures leave the input document unchanged. The helper constructs a complete candidate with one batch event; hosts validate and publish that candidate atomically through the workbook transaction API. Subsequent source changes never alter the snapshot.

A linked view uses createRixCelTensorSheet after each observed source update. The returned Sheet is read-only and holds no editable binding. Hosts retain the expression or named export, subscribe to its workbook, rebuild the complete selected plane after a committed update, and dispose the subscription with the session. Plane changes likewise rebuild a complete candidate before replacing the visible output. A failed refresh must preserve the last valid output and report its diagnostic. Linked views are session-local; explicit materialization is the route to persistent formula slots.

All helpers cap a selected plane at 4,096 cells before reading its values; sparse support is additionally bounded at 2,048 canonical terms. maxCells can lower this ceiling. They do not enumerate the other planes of a rank-N tensor. Empty, infinite, malformed or oversized planes fail before output allocation. Formatting and named regions do not change these canonical addresses or exact values.

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