build: dev does not compile on Xcode 27 — SwiftUI.Document now collides with InterlinedDomain.Document #98

dev does not build on Xcode 27. This blocks every open PR and every new one.

What happened

Xcode was updated on this machine at 12:23 on 2026-09-15, mid-session — builds from the same commit succeeded before it and fail after.

The macOS 27 SDK adds a Document protocol to SwiftUI:

SwiftUI.Document:4:17: note: found this candidate
  public protocol Document : ReadableDocument, WritableDocument {

InterlinedDomain has exported a Document struct since M4. Any file that imports both — which is every documents-feature view — now has an ambiguous Document in scope.

The errors

Nine sites, six files, all in App/Features/**:

App/Features/AI/AIDocumentSheet.swift:25:21
App/Features/Documents/ConflictBannerView.swift:18:27
App/Features/Documents/DocumentEditorView.swift:24:27
App/Features/Documents/DocumentsListView.swift:15:20
App/Features/Documents/DocumentsListView.swift:24:20
App/Features/Documents/DocumentsListView.swift:106:19
App/Features/Documents/DocumentsRootView.swift:436:21
App/Features/Documents/DocumentsRootView.swift:452:15
App/Features/Documents/DocumentTemplatePickerView.swift:39:21

Every one is import SwiftUI + import InterlinedDomain with a bare Document used as a type.

Note the view models are unaffected — they import Foundation, Observation and InterlinedDomain, not SwiftUI. It is exactly the SwiftUI-importing files, which is what makes the diagnosis unambiguous.

Fix

Qualify the domain type at the use sites: InterlinedDomain.Document.

Considered and rejected:

• Renaming the domain type. Document is the correct domain name and it is right across the Kit/Domain/Persistence layers and their tests. Renaming a core model to dodge a name collision in one consumer is the tail wagging the dog.
• A module-level typealias ILDocument = InterlinedDomain.Document. Shorter at the use sites, but it introduces a second name for one concept, and the next reader has to learn that ILDocument and Document are the same thing. Explicit qualification says exactly what it means.
• Dropping import SwiftUI. Not possible; these are SwiftUI views.

Worth knowing for the future

This is a standing hazard, not a one-off. Any domain type sharing a name with a SwiftUI symbol is one SDK update away from the same break. Current domain models at risk by name: Document, Message, List-adjacent names, Section-adjacent names. Nothing to do pre-emptively, but the diagnosis is worth writing down so the next occurrence takes minutes rather than an afternoon.

Acceptance

• xcodebuild build -scheme InterlinedList -destination 'platform=macOS' → ** BUILD SUCCEEDED ** on Xcode 27.
• No domain model is renamed.
• The full gate is green.