Open the Design tab's sketches only once their plane is picked

Sketch on a picked flat face or reference plane opens the sketch on it at once. With nothing
picked it no longer enters sketch mode: the reference planes and axes come up, and the plane or
flat face clicked next opens the sketch and puts them away. Esc or Cancel leaves without one.
A picked plane is used up by the sketch on it and dropped by Esc or a click on nothing, the plane
prompt is no longer replaced by a stale tool hint, and clicking the face a sketch was just
cancelled on picks that face again rather than the whole body.

scripts/CAD/check-gui-click-edit.py

@@ -480,13 +480,14 @@ def type_into_open_field(value, mark):
 def enter_sketch(timeout=180):
     """Open a real sketch on a real plane, and PROVE it with the socket before drawing anything.
 
-    THE SEQUENCE MATTERS AND IT IS NOT OBVIOUS. The reference planes are hidden until Shift+S
-    enters sketch MODE, so the plane is clicked AFTER it. Entering with a plane an earlier rung
-    chose pops the plane offer at once, and a click outside a popup menu only closes it, so the
-    plane is clicked twice, apart: the second click always lands on the plane. No Escape — with
-    no offer up, Escape in an empty sketch leaves it. Then a tool letter starts the session.
-    check-gui-sketching.py does the same steps. This ladder once did two of them — Design tab,
-    then Shift+S — and went straight to the tool letters.
+    THE SEQUENCE MATTERS AND IT IS NOT OBVIOUS. The reference planes are hidden until Shift+S,
+    with nothing picked, brings them up to choose from, so the plane is clicked AFTER it. That
+    click opens the session on the plane and pops the tool offer, and a click outside a popup
+    menu only closes it, so the spot is clicked twice, apart: the second click closes the offer,
+    and inside the session it is empty canvas. No Escape — with no offer up, Escape in an empty
+    sketch leaves it. Then a tool letter arms the tool. check-gui-sketching.py does the same
+    steps. This ladder once did two of them — Design tab, then Shift+S — and went straight to
+    the tool letters.
 
     That intermediate state is the trap. `is_sketching` reads 1, every tool key is accepted and
     traced, and not one click draws anything, because there is no plane under them. The ladder
@@ -502,10 +503,10 @@ def enter_sketch(timeout=180):
         click(132, 53)                   # Design tab
         time.sleep(2.0)
         dismiss_modals()
-        key("shift+s", 1.0)              # sketch mode brings the reference planes up
-        click(*PLANE_PX, pause=0.8)      # closes the offer if an earlier rung's plane popped it...
-        click(*PLANE_PX)                 # ...so this is the click that picks the plane IN THE VIEWPORT
-        key("p", 0.6)                    # any sketch tool starts the session on that plane
+        key("shift+s", 1.0)              # nothing picked: the reference planes come up
+        click(*PLANE_PX, pause=0.8)      # picks the plane IN THE VIEWPORT: session open, offer up...
+        click(*PLANE_PX)                 # ...and this closes the offer
+        key("p", 0.6)                    # arms Point in the session
         if try_call("sketch_describe") is not None:
             # NO Escape here. Every rung already opens with one to drop whatever tool the last
             # one left armed, and Escape in the Design tab walks a LIFO: first press drops the
@@ -520,7 +521,7 @@ def enter_sketch(timeout=180):
 
 # tool key, the clicks that draw it, and one distinct value per queued field. The values are
 # deliberately nothing like the as-drawn size, so a committed prefill cannot coincide with them.
-# Where the plane label sits in the viewport once sketch mode has brought the planes up. Same
+# Where the plane label sits in the viewport once Shift+S has brought the planes up. Same
 # constant the gesture ladder uses; it is a label on the 3D view, not a widget, so it moves only
 # if the camera does.
 PLANE_PX = (913, 359)

scripts/CAD/check-gui-sketching.py

@@ -268,16 +268,17 @@ def reset_document():
 def enter_sketch(tool_key, plane_px=(913, 359)):
     """Enter a sketch the way the design law says: pick the plane in the viewport, then the tool.
 
-    Shift+S enters sketch MODE, which brings the reference planes up; the click picks one; the
-    tool letter then starts the session on it. Entering with a plane an earlier rung chose pops
-    the offer at once, and a click outside a popup menu only closes it, so the plane is clicked
-    twice, apart. No Escape: with no offer up, Escape in an empty sketch leaves it. All of it is
-    real input — nothing here goes through the socket.
+    leave_sketch()'s Escapes let go of every pick, so Shift+S finds nothing to sketch on and only
+    brings the reference planes up; the click on one opens the session on it and pops the tool
+    offer. A click outside a popup menu only closes it, so the same spot is clicked again, apart:
+    inside the session it is empty canvas, so it selects nothing if the offer is slow to appear.
+    No Escape: with no offer up, Escape in an empty sketch leaves it. The tool letter then arms
+    the tool. All of it is real input — nothing here goes through the socket.
     """
     leave_sketch()
     key("shift+s", 0.8)
-    click(*plane_px, pause=0.8)   # closes the offer if an earlier rung's plane popped it...
-    click(*plane_px)              # ...so this is the click that picks the plane
+    click(*plane_px, pause=0.8)   # picks the plane: the session opens and the offer pops...
+    click(*plane_px)              # ...and this closes the offer
     key("p", 0.6)
     if try_call("sketch_describe") is None:
         shot("/shots/gl-enter-failed.png")

scripts/CAD/tool_atlas.json

@@ -229,11 +229,11 @@
         "none"
       ],
       "needs": {},
-      "refusal": "Click a face or a reference plane in the viewport, then a sketch tool",
+      "refusal": "Select a flat face or a reference plane to sketch on",
       "gui": true,
       "action": "key:S+S",
       "icon": "design_sketch",
-      "hint": "Click a face or a reference plane, then pick a drawing tool"
+      "hint": "Sketch on the selected flat face or plane, or click one next"
     },
     {
       "id": "extrude",