fix(cutting): check every lead against all other material again

The second delta review compared the filtered checks with the previous
implementation on 5,400 generated cases. Rapid checks matched in every
case, but 114 lead checks differed: a long lead passing a small circle
or arc well over 0.001 away was reported clear, while the native
line/circle query, through rounding in its squared terms, reports a
contact there. A coordinate limit and a fixed margin cannot bound that
cancellation.

Lead checks therefore examine every other part's material again,
exactly as before the filter; LeadMaterialSnapshot no longer keeps an
extent. Rapid checks, including the pre-post review's, keep skipping
completed contours more than 0.001 clear of the rapid. The 900000-long
lead beside a radius-0.0001 circle is a regression test.

Planning a dense 144-part grid now takes about 19 s again (lead checks
dominate); a new part order is still found where the old search gave
up.

docs/cutting-planner.md

@@ -101,10 +101,13 @@ motions, never the nominal entry point alone. Existing lead styles are not
 shortened, disabled or substituted as a search fallback.
 
 Every candidate rapid is checked against contours already completed, including
-earlier holes in the same part. Future contours are not yet obstacles. Rapid and
-lead checks skip contours and material whose extents are more than 0.001 clear
-of the motion, ten times the widest band any native contact query allows beyond an
-extent; anything closer, touching included, gets the full native check. An arc's
+earlier holes in the same part. Future contours are not yet obstacles. Rapid
+checks skip completed contours whose extents are more than 0.001 clear of the
+rapid, ten times the widest band any native contact query allows beyond an
+extent; anything closer, touching included, gets the full native check. Lead
+checks examine every other part's material: native line/circle queries can report
+rounding contacts for long leads far from small circles, and leads keep those
+results. An arc's
 extent is its whole supporting circle widened to the distance at which the native
 contact query still counts it as touched (for a very small arc up to 0.0001 beyond
 its radius). Nothing is skipped when either extent has a nonfinite bound or reaches