Implement VS Code Reference Navigation

Goal

Let users follow Forma-recognized relationships to canonical Markdown source from the normal editor.

Sources

• design/editor-extension-mvp-design
• architecture/editor-extension-adapter-contract
• tasks/implement-forma-reference-resolve-operation

In Scope

• Register focused document-link, definition, and hover behavior for ordinary Markdown links where Forma adds workspace semantics.
• Recognize the token under the cursor for wikilinks, aliases, fragments, and embeds, then delegate target resolution to reference.resolve.
• Support schema-declared frontmatter entryRef and named semantic reference values.
• Open resolved targets and heading fragments in the normal text editor.
• Show candidate selection for ambiguous results and diagnostics for unresolved or invalid results.
• Support navigation from an unsaved editor buffer when the raw target and source path are sufficient for reference.resolve.
• Avoid overriding useful built-in Markdown behavior when Forma adds no value.

Out Of Scope

• Rename, move, automatic fix, or batch reference rewriting.
• Backlinks or relationship explorer panels.
• Live whole-document schema diagnostics for unsaved content.

Acceptance Criteria

• Definition and click navigation work for all supported syntax forms in fixtures.
• Heading fragments land at the resolved location when available.
• Ambiguous and unresolved cases are explicit and never silently guessed.
• Untrusted, no-workspace, and incompatible-binary states do not execute resolution.
• Tests separate cursor-token recognition from Core resolution semantics.
• Navigation works with local workspace paths and remains extension-host-relative for remote workspaces.