Describe picking an object of the same scene (#258)

Behaviors.md

@@ -59,11 +59,25 @@ playing use the same two words.
   reads the same object back: `Expand` gives the field back as the object, `Item at` the item.
   `Raycast all` (#157) hands out a list of objects, and written into a list variable it stays one.
   An object lives for the run only. At rest (in the file, a snapshot, the inspector) its place
-  always holds the empty object, stored as `{"$object": ""}` wherever it sits, and the inspector and
-  its inline lists show `(null)` and offer nothing to pick. During a run the object sits right in the
-  value, and every way out of the run empties it again (`core/graph/liveObjects.ts`,
-  `withoutObjects`): the values the editor run writes back into the scene as overrides, the save of
-  a persistent Variables asset, the live values the inspector shows and the test hooks. A struct
+  holds the empty object, stored as `{"$object": ""}` wherever it sits, or **an object of the same
+  scene picked on the placed behavior** (#258).
+  - **Picking one:** on a placed object the row of an object variable, an object field or an
+    object item is a dropdown with `None` and every object of the scene in hierarchy order, the
+    object itself included. The pick is stored as the object's id, `{"$object": "<id>"}`, and a run
+    reads the object itself. On the behavior asset there is no scene, so the row says `(null)` and
+    offers nothing; the default is always no object.
+  - **Inside a container** an object only gets the objects of the same container to choose from,
+    named by their template id. Every placement of the container then reaches its own copy.
+  - **The reference follows the object:** removing it empties the reference in the same undo step,
+    copying and pasting several objects points a reference among them at the copy (one out of them
+    stays), *Create container* and *Unpack* carry it along.
+  - An object that is gone reads as `(null)`, and the row shows `(missing)`.
+
+  During a run the object sits right in the value, and every way out of the run empties what a
+  graph wrote there again (`core/graph/liveObjects.ts`, `withoutObjects`): the values the editor run
+  writes back into the scene as overrides, the save of a persistent Variables asset, the live values
+  the inspector shows and the test hooks. A picked reference is left alone: a graph that writes
+  another object into the place keeps it for the run, and the scene keeps its pick. A struct
   whose only change is an object therefore writes no override. A list that grew by an object does:
   the scene learns the new item, as the empty object. A **destroyed** object reads as `(null)`,
   alone as well as out of a list or a struct, as does one from a scene that was restarted or left.

Development.md

@@ -15,7 +15,7 @@ npm run build        # writes dist/ and regenerates index.html
 php tools/make-user.php <name> <password> [admin|user]        # an account; every tool signs in (see Accounts)
 php tests/php/accounts.test.php                               # the API's account rules, no server needed (CI's gate job)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1527 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1532 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result