docs(directions): scope the distance rounding threshold precisely

docs/CURRENT-STATE.md

@@ -4081,9 +4081,9 @@ routing it shows `Routing…`, and a router miss reads
 The layer holds continuous render only while a route is drawn (the dashes
 animate). Disable clears all state.
 
-Route distance labels round to the nearest ten metres before selecting the
-unit, switching to kilometres at 995 metres; a 996-metre leg displays as
-`1.0 km` rather than `1000 m`.
+At the metre/kilometre boundary, route distance labels use the rounded
+ten-metre value to select the unit, switching to kilometres at 995 metres;
+a 996-metre leg displays as `1.0 km` rather than `1000 m`.
 
 **Keys needed: none.** Directions works on a keyless boot, and the layer is off
 until the operator turns it on.