Implement VS Code Source-First View Preview

Goal

Provide a useful editor-native preview for Markdown-backed list, table, and kanban views without hiding or mutating source.

Sources

• design/editor-extension-mvp-design
• architecture/editor-extension-adapter-contract
• tasks/extend-view-render-for-editor-preview

In Scope

• Keep .forma/views/*.md and other configured view files in the normal Markdown text editor by default.
• Add Open View Preview, Open View Preview to the Side, source-opening toolbar behavior, and a focused CodeLens near the content mount.
• Compose Markdown before the mount, the structured projection, and Markdown after the mount.
• Add save-driven refresh with cancellation and stale-result suppression.
• Map VS Code WebView color, contrast, focus, selection, chart, and editor font variables into host-neutral --forma-* tokens.
• Render accessible, keyboard-navigable list, table, and kanban modes with source links, configured labels, columns, cards, badges, empty states, and diagnostics.
• Use a strict Content Security Policy and narrow local resource roots.
• Show an intentional deferred state for graph views with source access and diagnostics; do not port or redesign Graph.

Out Of Scope

• Custom editor as the default source handler.
• Writable kanban, inline metadata editing, or graph interaction.
• Unsaved transient View rendering.
• Graph renderer selection or implementation.

Acceptance Criteria

• Source remains directly editable and Preview to the Side works from configured view files.
• Markdown content before and after the mount is preserved in preview.
• List, table, and kanban fixtures render useful output and open entry source files.
• Light, dark, high-contrast, custom theme-token, editor-font, and reduced-motion behavior is verified.
• Narrow editor groups handle table and kanban overflow without breaking the workbench.
• Invalid and empty views have distinct, actionable states.
• Graph views clearly state the deferral and keep source accessible.
• WebView tests and Extension Host integration tests cover refresh, navigation, and theme messages.