Context

A landing pad belongs to a rotating body. An absolute position captured when a scene starts leaves the terrain as soon as Mars moves. Putting the pad inside the cinematic renderer also leaves ordinary flight with no facility to visit, save, or land on.

Ships already have entity records, but those records participate in thrust, rails, and contact integration. A structure needs an address and an anchor; giving it a flight state would introduce motion it cannot make.

Decision

World owns durable surface placements; every mode derives their poses from the body's rotating frame at the presentation instant.

A placement contains an ID, asset ID, body address, latitude, longitude, height above terrain, and heading. World verbs validate and replace whole records. The read view is immutable and ordered by ID. Every stored field participates in the state hash.

The portable asset registry defines dimensions and a support radius. The browser maps its IDs to glTF files. Blender authors metric geometry with +Y up and the asset's deck at y=0; the loader preserves that datum instead of recentering the mesh as it does for a ship.

Snapshots resolve anchors at their own renderTime. Drawing samples drawn terrain; physical support samples canonical terrain. Nearby structures share the camera's render origin. Distant structures are culled before planetary compression can separate a full-size building from its body.

The initial Mars pad is an ordinary placement seeded in a new Milky Way session, whichever system it starts in; initialStructures(galaxy) is the one list a new session and a migrating save both read. Loading a save restores its records without seeding the pad again. Save schema 2 carries a typed structures array; schema 1 predates structures, so a Milky Way save migrates to the seeded pad and any other galaxy to an empty array, and a removal made after that migration is what the next save carries. Asset geometry, terrain samples, and derived positions are not saved.

Cinema borrows a placement and the same pose resolver. Its script may hold a presentation instant for the body, terrain, and lighting while the director advances its playhead from simulation render time. A missing authored facility can be staged for the scene without inserting it into the saved world.

Alternatives considered

A pad local to the Cinema scene cannot support ordinary flight or persistence.
A static ship entity carries unnecessary dynamics and gives every integration path a new exception.
Absolute saved transforms drift from rotating terrain and duplicate values already determined by the anchor.
An opaque placed mutation payload defers validation until restoration. Typed records make invalid coordinates and unsupported assets a load error.

Consequences

Structures survive save/load and system unloading without retaining generated bodies. Future assets use the same record, loader, and pose path. Adding a new asset requires a portable definition and a browser model mapping.

Support is a tangent disk, suitable for a flat landing deck. It is not a triangle collision mesh, and does not model walls, ramps, or destruction. Placement tools use the harness and World verbs; there is no construction editor in the HUD.