# `Labs.geometry.write`

> Contract 2.0.0 · package sha256 `a857eca95b35921109faf997094bb4192f12527d9d0fcd4be7e97f06425bad6e` · generated from `configurator-runtime.d.ts` by `services/onsite-scripter/scripts/build-contract-docs.mjs`; edit the source, not this file.

Method of [`Labs.geometry`](Labs.geometry.md) · labs · since 2.0.0 · called as `session.labs.geometry.write`

```ts
write(query: Query, data: GeometryWrite | null, options?: C & SignalOption): Promise<Report>;
```

Copy-on-write per part, local space. Joins a transaction when written through a `tx`. Stays
until written again, reset with null, or the part's model is replaced. Look-only. Data equal
to what the part shows from an earlier write (by content hash) is an equal write: no copy,
upload, bounds or BVH work, and the commit stays equal.
Errors: rejects HoloInputError on invalid input; no match records 'target-unmatched'.

**Default:** options.signal undefined

## Options

Through [`Session`](Session.md):

| Option | Type | Default | What it does |
| --- | --- | --- | --- |
| `actor` | `Actor` | the `expectGroup`'s actor when one is given, else 'app' | Who made the write. |
| `dryRun` | `boolean` | false | Runs and reports, then rolls back by design ('dry-run'). |
| `expectGroup` | `HistoryGroup` | undefined | A guard, checked at the call: this write belongs to the undo group you are running. |
| `expectRevision` | `number` | undefined (no check) | If-match on [`session.revision`](Session.revision.md). |
| `origin` | `string` | null | Your tag, echoed unchanged in [`Report.origin`](ReportFields.origin.md) and `cause.origin`. |
| `signal` | `AbortSignal` | undefined | Cancels this call; the member's JSDoc says what an abort does. |
| `supersede` | `boolean` | false (the write is queued behind the transaction and applies after it closes) | While a transaction is open: roll it back (it resolves 'superseded'); the writes queued behind it apply in call order, then this one, which supersedes an… |
| `undo` | `'rebase' \| (string & {})` | a recorded-state change gets one step labelled 'Change'; a look-only write gets none; the session's first model (cause 'load') gets none, whatever the label: it is the floor of history | An undo label makes this write one undo step. |

Through [`Tx`](Tx.md):

| Option | Type | Default | What it does |
| --- | --- | --- | --- |
| `signal` | `AbortSignal` | undefined | Cancels this call; the member's JSDoc says what an abort does. |

Refused here (typed `never`, so passing one fails to compile): `actor`, `checkpoint`, `dryRun`, `expectGroup`, `expectRevision`, `origin`, `supersede`, `undo`.

## Abort (`signal`)

This call is a write (`SignalOption.signal`, [the kinds of call](../read-this-first.md#conventions)).

> A write: before the commit point it rolls back and rejects AbortError; after it, no effect, except that a running camera move stops where the last frame drew it (`CameraMoveOptions`).
>
> Through a `tx` the commit point is the transaction's: aborting a write still loading rejects AbortError and stages nothing (catch it: unobserved, it rolls the transaction back, spec section 6.1, O6); aborting one already staged unstages it, its paths keeping the latest other write to them as after a failed savepoint (O7), and its Promise stays resolved 'staged'.

## Example

Imports: values (`has`, `validate`, the `Holo*Error` classes, the pure helpers) from `@holostep-configurators/runtime-client`, types from `@holostep-configurators/runtime-client/contract`, `/math` and `/testing` names from those entries; `boot` from the runtime module the root's `loadRuntimeAtFloor` resolves to. A type your page defines is your app's: declare it there, never import it from the package.

Compiled under the contract's strict settings (`examples/declaration/20-Labs.geometry.write.ts`):

```ts
import type { Session } from '@holostep-configurators/runtime-client/contract';
declare const session: Session;
declare const signal: AbortSignal;
declare const bedId: string;
const legs = await session.labs.geometry.read({ node: bedId, tag: 'leg' }, ['position'], { from: 'authored' });
for (const leg of legs) {                                  // every leg 1.5 × as tall, in its own space
  if (!leg.position) continue;
  const tall = leg.position.map((v, i) => (i % 3 === 1 ? v * 1.5 : v));
  await session.labs.geometry.write(leg.part, { position: tall });
}
await session.labs.geometry.write({ node: bedId, tag: 'leg' }, null);   // the legs as loaded again
```

## Generic-API test (spec 3.1)

| Rule | Result |
| --- | --- |
| 1. Neutral name | pass: `write` names no product |
| 2. A precedent | pass (through its owner [`Labs.geometry`](Labs.geometry.md)): [Unity Mesh.vertices](https://docs.unity3d.com/ScriptReference/Mesh-vertices.html) (row `G9`); [Unity Mesh.GetIndices](https://docs.unity3d.com/ScriptReference/Mesh.GetIndices.html) (row `G9`); [Unity Mesh.SetVertices](https://docs.unity3d.com/ScriptReference/Mesh.SetVertices.html) (row `K54`) |
| 3. Two apps, or labs | labs: it graduates when a second app uses it; apps today: app-b362a81c85, app-bcb7ef21da, app-f9a32142f1 |
| 4. The cheaper fix first | decided per need in Appendix B: rows `G9`, `K54` (through its owner [`Labs.geometry`](Labs.geometry.md)) at tier asset, labs (a member only where no rule, data, asset or app code serves the need) |