`noUncheckedIndexedAccess: false` override not working with `vue-tsc --build`

[Baejw0111]

Describe the bug

When using @vue/tsconfig@0.8.x with vue-tsc --build (project references mode), overriding noUncheckedIndexedAccess: false in tsconfig.app.json does not take effect. The type checker still behaves as if noUncheckedIndexedAccess: true.

Reproduction

tsconfig.json

{
	"files": [],
	"references": [
		{ "path": "./tsconfig.node.json" },
		{ "path": "./tsconfig.app.json" }
	]
}

tsconfig.app.json

{
	"extends": "@vue/tsconfig/tsconfig.dom.json",
	"include": ["src/**/*", "src/**/*.vue"],
	"compilerOptions": {
		"noUncheckedIndexedAccess": false,
		"paths": {
			"@/*": ["./src/*"]
		}
	}
}

package.json scripts

{
	"type-check": "vue-tsc --build",
	"build": "run-p type-check \"build-only {@}\" --",
}

Example code that errors

const vNodes = slots.default();
if (vNodes.length !== 1) {
    return vNodes;
}
// Error: vNodes[0] is VNode | undefined, even though we checked length
cloneVNode(vNodes[0], { ref: wrapperRef });

Expected behavior

noUncheckedIndexedAccess: false in tsconfig.app.json should override the true value from @vue/tsconfig/tsconfig.json, and array index access should not include undefined in the type.

Actual behavior

The override is ignored. vNodes[0] is still typed as VNode | undefined.

Workaround

Downgrade to @vue/tsconfig@0.7.0 which does not include noUncheckedIndexedAccess.

Environment

• @vue/tsconfig: 0.8.1
• vue-tsc: 3.2.1
• typescript: 5.8.3 / 5.9.3 (same issue on both)
• OS: Windows 10

Additional context

• Clearing build cache (node_modules/.tmp/*.tsbuildinfo) does not help