v0.56.0

Two passes ship together: the markdown editor's folding gets a proper home, and the engine's gates, tooling, and docs harden.

Editor folding moves into a gutter

The editor folds directive containers (:::name blocks), and the fold control now lives in a real gutter column to the left of the text rather than a chevron hidden in the line. At rest the gutter is empty; the chevron reveals when you hover the gutter cell, stays while a block is folded, and shows while the caret is inside a block. The control is a real button now, so folding is reachable by keyboard and screen reader, where before only unfolding was. The folded-row tint and the "N lines" pill carry over unchanged, and the fold scope is the same: directive containers only.

Gates, tooling, and DX

For consumers, two additive surface touches. A concept can set an optional singular label, so the create affordances read "New post" instead of "New Posts" (it defaults to the concept's label). And AuthEnv is now exported from @glw907/cairn-cms/sveltekit as well as the root, so the app.d.ts Platform block can import it from the subpath the auth helpers live on.

The rest hardens the engine's own gates and docs: a check:reference:signatures gate, a plain-Node dist-spawn test for the /delivery/data node-safety guarantee, an admin-shell DOM check, a cairn-manifest bin root fix, and a docs sweep.

No consumer action: every change is additive, the singular field is optional, and the folding redesign is internal to the admin editor.