Function render_changed_slice 

pub fn render_changed_slice(cursor: &SourceCursor) -> String

Render the ## Source changes since the last sync preface — the changed slice to steer at first, any no-signal sources, plus the projection advance “record your dispositions LAST” section. Extends the plugin’s changedSliceBlock with the no-signal notes. Returns the empty string when nothing changed, nothing needs reseeding, and every source is genuinely unchanged (no no-signal notes) — making the brief byte-identical to a plain roam.