Canvas · Tools: single handles, a wrapping palette, the pen ends with its tool

Handles resize one shape, so a selection of several shows its outline
and no handles; a press there no longer falls through to a marquee.
ToggleGroup wraps its faces when narrow, so the ToolPalette stays in a
280px box. A pen path left open ends when the tool changes: two points
or more go to the owner after the frame, a lone point is dropped, and
the open path paints only while the pen is the tool.

TASKS.md

@@ -375,3 +375,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T31d | 2 | PASS | |
 | T32a | 1 | FAIL | the plain wheel panned against every scroll box; the handlers panned from the render's viewport, so events within a frame overwrote each other; the fit's cap at one went untested |
 | T32a | 2 | PASS | |
+| T32b | 1 | FAIL | handles drawn for a multi-selection fell through to a marquee; the palette ran past a 280px box; an open pen path outlived the tool |