A press that only brings the window to the front draws nothing

From the development repository at 62e0967.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/guest.md

@@ -81,7 +81,9 @@ from the palette joins the row and stays there in this browser.  White
 is for painting over.  The four lines to the right of the colours are
 the line widths: 0.4, 0.7, 1.2 and 2.4 mm at ordinary pressure.
 
-If a pen is in use, a hand resting on a touch screen is ignored.
+If a pen is in use, a hand resting on a touch screen is ignored.  A
+click on the page that only brings the browser window to the front, when
+you come back to it from another window, makes no mark.
 
 ### Text
 

docs/implementation.md

@@ -283,7 +283,7 @@ the zoom step of the wheel and the zoom per 100 pixels of a pen drag
 (`renderer.js`), the dead zone of that drag (`pen_input.js`), the margin
 by which the page grows (`page_model.js`), the tooltip delay (1 s,
 `DELAY_MS` in `tooltip.js`) and how long after one tooltip the next
-button's comes at once (1 s, `WARM_MS` there), the hold that moves an image (600 ms, with 6 pixels of
+button's comes at once (1 s, `WARM_MS` there), the time within which a press after the window comes to the front is taken for the click that raised it and draws nothing (250 ms, `FOCUS_SETTLE_MS` in `pen_input.js`), the hold that moves an image (600 ms, with 6 pixels of
 slack, `pen_input.js`), the reach of an image's corner (24 pixels,
 `renderer.js`), the smallest an image can be scaled to (1 cm,
 `page_model.js`), how often a dragged image's place is sent (40 ms,