CLI: `--no-validate` cannot bypass validation — `IfcxLayerStack` always validates during `Build()`

## TL;DR

`ifcx-cli compose --no-validate` still throws `SchemaValidationError` on any input that
fails schema validation, because `IfcxLayerStack`'s constructor eagerly composes with
validation hardcoded on — inside `IfcxLayerStackBuilder.Build()`, before the CLI's
`validate` flag is ever consulted. The flag only skips a *second* validation of a layer
stack that already survived the first, so it is a no-op for the exact case it exists for.

## Environment

- Commit: `02b0b21aaa4ab10354cdf931a6ec0d704d6e8d22` (current `main`)
- Node v25.9.0, CLI built per the repository's own instructions:
`cd src && npm install && npx esbuild ifcx-cli/ifcx-cli.ts --bundle --outfile=ifcx-cli.js --external:three --platform=node`

## Reproduction

Any layer stack that fails schema validation triggers it. The fixtures below set a
String-typed attribute in one layer and `null` it in a later one (found while
investigating the companion issue #132, which this bug has been masking).

base.ifcx + override-null.ifcx

`base.ifcx`:
```json
{
"header": {
"id": "repro/minimal/base.ifcx",
"ifcxVersion": "ifcx_alpha",
"dataVersion": "1.0.0",
"author": "repro",
"timestamp": "2026-07-22"
},
"imports": [],
"schemas": {
"test::rating": {
"uri": "https://example.com/repro/test-rating",
"value": { "dataType": "String" }
}
},
"data": [
{ "path": "wall-0001", "attributes": { "test::rating": "A" } }
]
}
```

`override-null.ifcx`:
```json
{
"header": {
"id": "repro/minimal/override-null.ifcx",
"ifcxVersion": "ifcx_alpha",
"dataVersion": "1.0.0",
"author": "repro",
"timestamp": "2026-07-22"
},
"imports": [],
"schemas": {},
"data": [
{ "path": "wall-0001", "attributes": { "test::rating": null } }
]
}
```

```
$ node ifcx-cli.js compose --no-fetch --no-validate base.ifcx override-null.ifcx out.json
SchemaValidationError: Error validating ["wall-0001"].attributes["test::rating"]: Expected "null" to be of type string
at ValidateAttributeValue (.../ifcx-core/schema/schema-validation.ts:40)
at Validate (.../ifcx-core/schema/schema-validation.ts:134)
at LoadIfcxFile (.../ifcx-core/workflows.ts:32)
at IfcxLayerStack.Compose (.../ifcx-core/layers/layer-stack.ts:31)
at new IfcxLayerStack (.../ifcx-core/layers/layer-stack.ts:18)
at IfcxLayerStackBuilder.Build (.../ifcx-core/layers/layer-stack.ts:80)
exit: 1
```
(Stack trace re-annotated with source locations for readability; the raw run against the
esbuild bundle shows the same frames as `ifcx-cli.js` line numbers. `out.json` is never
written.)

## Root cause

`IfcxLayerStack`'s constructor eagerly calls `Compose()`, which calls
`LoadIfcxFile(this.federated)` with no second argument — so `checkSchemas` takes its
default `true` (`LoadIfcxFile(file: IfcxFile, checkSchemas: boolean = true, ...)`,
`workflows.ts` L24):

https://github.com/buildingSMART/IFC5-development/blob/02b0b21aaa4ab10354cdf931a6ec0d704d6e8d22/src/ifcx-core/layers/layer-stack.ts#L14-L31

```ts
constructor(layers: IfcxFile[])
{
this.layers = layers;
this.Compose();
}
...
private Compose()
{
this.federated = Federate(this.layers);
// TODO: schema files
this.schemas = this.federated.schemas;
this.tree = LoadIfcxFile(this.federated);
}
```

`Build()` catches the resulting exception and returns it as an `Error`, which the CLI
rethrows — all before reaching the CLI's own, correctly wired second call
`LoadIfcxFile(federated, validate, true)`:

https://github.com/buildingSMART/IFC5-development/blob/02b0b21aaa4ab10354cdf931a6ec0d704d6e8d22/src/ifcx-cli/ifcx-cli.ts#L102-L109

```ts
let layerStack = await (new IfcxLayerStackBuilder(provider).FromId(userDefinedOrder.header.id)).Build();
if (layerStack instanceof Error)
{
throw layerStack;
}

let federated = layerStack.GetFederatedLayer();
let composed = LoadIfcxFile(federated, validate, true);
```

## Impact

- `--no-validate` cannot be used for its stated purpose: inspecting composition output of
files that fail validation. This has been masking the companion `attributes: null`
composition bug, since a nulled schema-declared attribute always dies in validation
before flatten's output can be observed.
- Library consumers going through `IfcxLayerStackBuilder` have no way to opt out of
validation at all.

## Suggested fix

Thread `checkSchemas` through `IfcxLayerStack`'s constructor and `Build()`, and have the
CLI pass its existing `validate` flag into `Build(validate)`:

fix-no-validate.patch

```diff
diff --git a/src/ifcx-core/layers/layer-stack.ts b/src/ifcx-core/layers/layer-stack.ts
index 7a2b78c..d31945a 100644
--- a/src/ifcx-core/layers/layer-stack.ts
+++ b/src/ifcx-core/layers/layer-stack.ts
@@ -11,10 +11,12 @@ export class IfcxLayerStack
private tree: PostCompositionNode;
private schemas: {[key:string]:IfcxSchema};
private federated: IfcxFile;
+ private checkSchemas: boolean;

- constructor(layers: IfcxFile[])
+ constructor(layers: IfcxFile[], checkSchemas: boolean = true)
{
this.layers = layers;
+ this.checkSchemas = checkSchemas;
this.Compose();
}

@@ -28,7 +30,7 @@ export class IfcxLayerStack
this.federated = Federate(this.layers);
// TODO: schema files
this.schemas = this.federated.schemas;
- this.tree = LoadIfcxFile(this.federated);
+ this.tree = LoadIfcxFile(this.federated, this.checkSchemas);
}

public GetFullTree()
@@ -64,7 +66,7 @@ export class IfcxLayerStack
return this;
}

- async Build(): Promise
+ async Build(checkSchemas: boolean = true): Promise
{
if (!this.mainLayerId) throw new Error(`no main layer ID specified`);

@@ -77,7 +79,7 @@ export class IfcxLayerStack

try
{
- return new IfcxLayerStack(layers);
+ return new IfcxLayerStack(layers, checkSchemas);
}
catch (e)
{
```
(plus a one-line call-site change in `ifcx-cli.ts`, `.Build()` -> `.Build(validate)`)

Happy to send this as a PR — either standalone or as a preceding step to the companion
issue's fix, since this bug is what has kept that one unobservable through the CLI.

Start with src/ifcx-core/layers/layer-stack.ts, especially IfcxLayerStack.Compose() and IfcxLayerStackBuilder.Build(), then inspect the compose call in src/ifcx-cli/ifcx-cli.ts and LoadIfcxFile in src/ifcx-core/workflows.ts. Reproduce with the documented `compose --no-fetch --no-validate` command and the supplied fixtures. Done means invalid input can be composed and written with `--no-validate`, while validation remains enabled by default.

Written by the indexing model from the issue text.