tools: never crop to a window too narrow to be a game frame

The app owns TWO windows of class xenia_canary -- measured in the tree right now
as 10x10+10+10 and 1280x745+1+20.  Largest-by-area picks the game window while
both are present, but during a load or mode switch the game window is briefly
absent from the tree, the 10x10 helper wins by default, and the crop produces a
10x710 SLIVER.  That is exactly the grab screen_id classified as `menu` on
2026-08-26, which let a nav guard pass on garbage and loaded the wrong stage.

Ignore candidates narrower than 640 so nothing is selected in that case and the
existing fall-through hands back the raw root grab -- itself a valid full frame.

Verified on the selection logic directly: with both windows listed the pick is
unchanged (1280x745+1+45); with only the helper listed the old logic returned
10x10+10+10 and the new one selects nothing.  Pairs with 30e53f5, which rejects
such a frame at the consumer.

tools/re-capture/bin/screenshot

@@ -42,7 +42,16 @@ geo=$(xwininfo -root -tree 2>/dev/null \
       | grep '"xenia_canary"' \
       | grep -oE '[0-9]+x[0-9]+\+-?[0-9]+\+-?[0-9]+[[:space:]]+\+-?[0-9]+\+-?[0-9]+' \
       | awk '{ split($1, g, /[x+]/); a = g[1] * g[2];
-               if (a > best) { best = a; split($2, p, /\+/);
+               # MIN_W: largest-by-area is not enough on its own. When the game
+               # window is momentarily absent from the tree (during a load or a
+               # mode switch) the only xenia_canary window left is the narrow
+               # helper, it wins by default, and the crop below produces a
+               # SLIVER. Measured 2026-08-26: a 10x710 grab that screen_id then
+               # classified as `menu`, so a nav guard passed on garbage and the
+               # run loaded the wrong stage. Ignore anything too narrow to be a
+               # game frame and fall through to the raw root grab instead.
+               if (g[1] >= 640 && a > best) {
+                                 best = a; split($2, p, /\+/);
                                  out = g[1] "x" g[2] "+" p[2] "+" p[3] } }
              END { if (best) print out }')
 if [ -z "$geo" ]; then           # no window found — hand back the raw grab