Amend ADR-0051: the floor U-value gate landed; roof stays evidence-gated 🟪

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

docs/adr/0051-wall-insulation-offered-only-when-it-lowers-the-derived-wall-u-value.md

@@ -54,9 +54,14 @@ materiality threshold — economics stay with the Optimiser, ADR-0016/0024).
   precedent as the heating generator reading the calculator's PCDB/Table 4b.
 - **Deferred:** (a) a cert that lodges an explicit `wall_u_value` overrides the
   cascade in the calculator, making fabric measures score +0.00 regardless of
-  this gate — the measure overlay should adjust the lodged U; (b) roof/floor
-  generators have the same anti-pattern in principle (roof age-band eligibility
-  is partly covered by ADR-0047); both tracked as follow-ups.
+  this gate — the measure overlay should adjust the lodged U (probed on
+  portfolio 796: 0/300 sampled certs lodge one, so no live evidence yet);
+  (b) roof/floor generators have the same anti-pattern in principle (roof
+  age-band eligibility is partly covered by ADR-0047). **Amended:** the floor
+  arm landed as `floor_u_value_gate` (probed live: solid_floor_insulation at
+  £3-4k for +0.00 on age-band-L dwellings 709782/709790); a 40-dwelling
+  band-K/L probe found no roof no-ops, so the roof arm stays unimplemented
+  until evidence appears.
 
 ### Alternatives rejected