Design: a verb's address is data, so the toolbar widget can stop existing

snaporca-7ih's remaining half. Both flyout factories registered their verbs INSIDE the
widget-building loop, so the ~40 retired tool buttons had to be constructed and then
Hide()n: skipping construction would have deleted 42 offer verbs (26 fly:<family>#<row>
+ 16 Shift+keys) while their rows still rendered and did nothing when picked.

Register first, build second. The addresses are pure data; the widget is one door onto
them, not their owner. A family absent from kBarKeep now returns before any wxWindow is
made. The keep-list stays a one-line data decision, not a structural one.

And close the class of bug for good: the constructor now verifies, once, that every verb
the atlas marks wired resolves to a real registration, logging each break and asserting in
debug. Rows that render and do nothing have shipped three times (edit_feature and sk_move
with action:null, then this) and are invisible from either side alone.

Verified on the snaporca rig by walking the offer, not by reading the code — all four
at-risk address kinds run with no widget behind them: fly:design_rect#2 drew an OBLIQUE
rectangle (the third variant, not the family's first), key:S+E opened Extrude with its
10 mm gizmo, fly:material#4 opened Thicken. Hover hints, icons and nesting intact. This
fork is code-identical here bar the two permitted DropDown divergences; it still owes a
build of its own (snaporca-5pl).

Two hints were wrong and are fixed: Cut said "Split the body with a plane", colliding with
the Split verb one row away and pointing at a card for a value the canvas already offers as
a draggable arrow; Split never said its plane comes from a picked face.

Also, because it blocked the verification and will block the next one: gui-session.sh
killed by full path while its own app_pid() matched by basename, so a differently-pathed
instance survived, held the single-instance lock, and got reported as a healthy session —
a Jul-30 binary nearly passed as this build. It now kills by basename and prints which
binary is actually on screen. Traps 6 and 7 documented.

src/slic3r/GUI/DesignOffer.hpp

@@ -99,8 +99,8 @@ static const OfferVerb kOfferVerbs[] = {
     {"hole", "Hole", 2, "Shift+H", "key:S+H", "Pick a face or a plane to drill into", 0x00000402u, 1, 0, false, false, nullptr, "design_hole", "Drill a hole, centred on a picked face or placed on a plane"},
     {"thread", "Thread", 2, "Shift+T", "key:S+T", "Pick a cylindrical surface (bore / outer) or a circular edge for a thread", 0x00000024u, 1, 0, false, false, nullptr, "design_thread", "Thread a cylindrical surface (inner bore / outer) or a circular edge"},
     {"shell", "Shell", 2, "Shift+K", "key:S+K", "Shell needs a solid body", 0x00000082u, 1, 0, false, false, nullptr, "design_shell", "Hollow the body to a wall thickness, opening a picked face"},
-    {"cut", "Cut", 2, "Shift+X", "key:S+X", "Create a solid body to cut first", 0x00000480u, 1, 0, false, false, nullptr, "design_cut", "Split the body with a plane; set the offset in the card"},
-    {"split", "Split", 2, nullptr, nullptr, "Split needs a solid body", 0x00000080u, 1, 0, false, false, nullptr, nullptr, "Split the body into separate solids"},
+    {"cut", "Cut", 2, "Shift+X", "key:S+X", "Create a solid body to cut first", 0x00000480u, 1, 0, false, false, nullptr, "design_cut", "Trim the body with a plane — drag the offset arrow; keep one half or both"},
+    {"split", "Split", 2, nullptr, nullptr, "Split needs a solid body", 0x00000080u, 1, 0, false, false, nullptr, nullptr, "Split the body along a picked face into two solids"},
     {"fillet", "Fillet", 3, "Shift+F", "btn:dress#0", "Pick an edge to round", 0x000000b2u, 1, 0, false, false, nullptr, "design_filletedge", "Pick an edge, then drag the radius arrow or type it"},
     {"chamfer", "Chamfer", 3, nullptr, "btn:dress#1", "Pick an edge to bevel", 0x000000b2u, 1, 0, false, false, nullptr, "design_chamfer", "Pick an edge, then drag the distance arrow or type it"},
     {"draft", "Draft", 3, "Shift+D", "key:S+D", "Pick a face to taper", 0x0000000au, 1, 0, false, false, nullptr, "design_draft", "Tilt a picked face by a draft angle"},