Audit Markdown document type ownership, Open Recent, and Finder interop metadata

[clintecker]

Problem

Quoin declares Markdown/plain-text document support, but the current metadata and app shell do not yet fully express Quoin as a native editor in Finder, Open With, Open Recent, and document-management surfaces.

Why it matters for target users

Privacy-conscious local-first users expect .md files to behave like real files everywhere: Finder, Open With, recent documents, document icons, drag/drop, and system document pickers. Engineers and writers also need Quoin to coexist politely with other Markdown tools.

Evidence / code or doc references

• App/macOS/Info.plist and App/macOS/project.yml declare net.daringfireball.markdown with CFBundleTypeRole = Viewer and LSHandlerRank = Alternate.
• The app imports the Markdown UTI and also declares public.plain-text as a viewer.
• App/macOS/Sources/AppDelegate handles Finder open URLs manually, while MainWindow keeps library tabs separately.
• Existing issues Add Core Spotlight indexing for documents, headings, and snippets #14-Add Quick Look thumbnail/preview support for Markdown documents #16 cover Spotlight/App Intents/Quick Look; this issue focuses on document type and Finder/Open Recent semantics.
• Apple's Uniform Type Identifier documentation recommends declaring the data types an app supports so the system can route files correctly.

Suggested direction

• Decide whether Quoin should register as Viewer or Editor for Markdown at v1, and whether plain text support should remain alternate viewer-only.
• Add document icons/metadata if the release target needs Finder polish.
• Make Finder-opened files integrate with library/tabs/session restoration instead of becoming detached one-off state.
• Add or restore Open Recent behavior, either through a document-based app shell or explicit recent-document management.
• Document coexistence rules with other Markdown apps.

Acceptance or test ideas

• Finder Open With, double-click where selected, drag-to-Dock, and Open Recent all route to the expected document/session.
• File type metadata is intentional and documented in docs/architecture.md or release notes.
• Quoin does not unexpectedly claim ownership of .txt or .md beyond the chosen product stance.
• Manual release checklist includes Finder/Open With/Open Recent verification.