test(diagnostics): lock the start-point clamp rapid warning

D10 (user decision 2026-10-13, keep the warning): a clamp footprint covering
the modeled program start (0,0) makes the first rapid of every posting attempt
cross it, and that warning has no exemption and no persisted bypass. Lock the
behavior in all four quadrants with a physical-footprint oracle and a mutation
red (skipping rapids that start inside a zone reddens exactly the four
origin-covering rows). Document the design in docs/post-verification.md.

docs/post-verification.md

@@ -73,6 +73,9 @@ shows all three check categories, even when there are no findings:
   an obstacle yet. Actual uncut gaps are respected; enabling tabs in settings alone
   is not evidence that a gap exists. Clamp-rapid warnings are conservative: head
   height/retracts are not modeled, so inspect the emitted route and machine setup.
+  A clamp whose footprint covers the program start point warns on every posting
+  attempt by design; there is no exemption for the first rapid and no persisted
+  bypass (settled decision D10).
 
 Findings identify the plate and part's position in the cutting sequence. Read the
 scrollable report, cancel to fix the nest, then post again to rerun verification.