[Roxas2712]

Adds API-3 portable show_object(mapId, ref), hide_object(mapId, ref) and replace_block(bx, by, blockId) on Gen1–3.

Extracts pure validation plans from the public edit adapter so a script can preflight every row without mutating the map or relaxing public idle-world guards. Dispatch repeats validation against live stores. The owned script survives Gen1's native seamless map/default-runner replacement and restores the replacement idle runner afterward. Foreign overlays pause execution; unloading and changed saves/maps/runners cancel later effects.

Dependency: merge #111 and its prerequisites first. Stacked branch; focused change 7671788…25af724.

Validation at clean feature head 25af724d2ae554ec206ec4715ac10fc63b679aaa:

• 117 targeted script checks; 238 existing public object/block checks and 5,268 existing portable script checks pass.
• 104 cross-engine comparisons / 208 isolated loader runs against Gen1 79ea62f45fb2ea8f65d081a109431e4eb1bbdb36.
• Full headless: 86/96 engine suites, SDK 3/3, B30 pass.
• All-PR integration e1e60ec2f9c043408676c4a0edcea5a683567ccc: 91/101 engine suites, SDK 3/3, B30 and 104/208 cross-engine checks.
• Both full commands exit 1 with exactly the same 27 FAIL lines as the fresh prerequisite baseline. No additional failures.
• StyLua and git diff --check pass.

ROM-free tests exercise real loaders, native maps and native edit commands with fixture rendering/world seams. ROM-content tier is skipped; no ROM gameplay/pixel equivalence claim. Gen2/3 object scripts require the active map; the complete list is validated before its first effect.

Hosted Actions: API 3 contracts and ci are action_required (fork workflow approval). Hosted tests have not run; the results above are local.