Show where an inspector row can be dragged

- Behaviors: under Reordering, the dots on a mark that drags, the
  lit dots and washed block under the pointer, and the other marks
  passing the pointer while a block is carried.
- Architecture: blockDrag names the Grip widget.
- Development: the e2e sum is 1740.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Architecture.md

@@ -169,7 +169,7 @@ src/runtime/physics/   engine (loads Rapier once, reports its state, converts be
 src/ui/                widget toolkit (generic, knows nothing about assets); fonts (the faces the editor ships:
                        Source Sans 3 in 400, 500 and 600, Source Code Pro 400, Latin only, #202/#214/#273), icons +
                        Icon (the menu's tick boxes and current-entry dot as SVG files, and a widget that shows one file
-                       on its own: a symbol the Latin subset lacks is never written as a character, #214); SortableList + sortable (the layer list of every editor that has one: rows dragged into order, eye, duplicate, cross, rename in place; the index arithmetic of a list shown upside down, of a drop in the tile strip and of blocks of rows of any height, kept apart so it is measured without a canvas); blockDrag (`sortBlocks`: the inspector's own rows dragged into order by a grip, a block being every row it covers, #310)
+                       on its own: a symbol the Latin subset lacks is never written as a character, #214); SortableList + sortable (the layer list of every editor that has one: rows dragged into order, eye, duplicate, cross, rename in place; the index arithmetic of a list shown upside down, of a drop in the tile strip and of blocks of rows of any height, kept apart so it is measured without a canvas); blockDrag (`sortBlocks`: the inspector's own rows dragged into order by a `Grip` (the row's mark, wrapped: dots once it drags, lit under the pointer while the block is washed), a block being every row it covers, #310)
 src/viewport/          WorldViewport (the drawing of a world or a holder, the base of every view; it draws from
                        a `ViewSource` — the project and word of a change — so a released game draws without the
                        editor, #266; a view through a camera keeps only what that camera `Sees` and lays one

Behaviors.md

@@ -183,10 +183,15 @@ the inspector).
   its indent takes, and names are cut with `…` rather than pushing their value out of line.
 - **Reordering** (#310): variables, the fields of a struct at any depth, the items of a list and the
   declared ports of a Start, End, `Pack`/`Expand` or shader function are **dragged by the mark in
-  front of their row** — the kind mark, for a list item its number. A press that moves less than
+  front of their row** — the kind mark, for a list item its number. Such a mark carries six faint
+  dots at its left edge, so a row that cannot be dragged (a placed object's variable, the fields of
+  a typed struct) is told apart at a glance. With the pointer on the mark the dots light up and the
+  block that would go with it is washed in the accent colour. A press that moves less than
   4 px stays a click, so the kind picker of a list item still opens. A block moves with all of its
   rows (a struct with its fields, an item with its nested list) and is dimmed while it is carried;
-  an accent line shows where it lands, and at the top or bottom edge the panel scrolls along. It
+  an accent line shows where it lands, and at the top or bottom edge the panel scrolls along. The
+  other marks do not answer the pointer while a block is carried, and every mark shows the
+  grabbing hand until it is dropped. It
   moves among its siblings only: a field stays in its struct, an item in its list. Every move is
   one undo step. Values and edges hang on names, so only the order changes: of the rows, of the
   fields of `Pack`/`Expand`, of the ports on every node running the behavior. A list's order is its

Development.md

@@ -18,7 +18,7 @@ php tests/php/accounts.test.php                               # the API's accoun
                                                               #   has and the web server's container has not (SKIP there)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
 php tests/php/releases.test.php                               # the release store (#266), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1739 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1740 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