port: close their XPR lead, and find their class in the lane I called clean

They flagged five XPR_* texture toggles as relevant since I consume textures, and
my off-edge splash residual -- non-tonal, ~0.5 RMSE above quantisation, no
candidate -- has the shape a subtle decode difference would produce.

Closed: the toggles live in texture.rs::decode_surface, shared by from_xpr2 and
cube_faces_from_xpr2, and my exporter calls neither -- sprites come from
t8ad::parse. t8ad.rs reads no environment variables in its 202 lines, so the
sprite path has no hidden freedom either. The candidate is eliminated with no
replacement.

Enumerating what my exporter reaches turned up SYLPHEED_KF_TIME_SHIFT, which they
reported as absent from crates/. True on their branch, false on mine: my
ui_layout.rs is the stale era and the knob is live at line 497. The pinned tag has
0 occurrences (2 of LEGACY) so export/ cannot be perturbed, but verify-screen
builds its reference from the workspace, which can.

Tested both directions: with the knob the reference reports rest t=12, the
corrected reading, and the era guard passes; without it, t=70 and the guard
refuses. So the knob is the working remedy that makes a workspace-built reference
usable, and it appeared in no tool, help text or instruction in my tree -- their
exact class, in the lane I had just told them was clean. The refusal message now
carries the remedy.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF

tools/port/verify-screen

@@ -172,6 +172,13 @@ if [ -n "$ref_rest" ] && [ "$ref_rest" != "$exp_rest" ]; then
   echo "   reference $CLI says pteff00 rest t=$ref_rest" >&2
   echo "   export/   (built by the pinned exporter) says rest t=$exp_rest" >&2
   echo "   Every row below would compare two decoder eras. Refusing." >&2
+  echo "" >&2
+  echo "   REMEDY, verified both directions 2026-08-30: this workspace's" >&2
+  echo "   ui_layout.rs is the STALE era and still carries the retired" >&2
+  echo "   SYLPHEED_KF_TIME_SHIFT knob, which converts it to the corrected" >&2
+  echo "   reading. Re-run with SYLPHEED_KF_TIME_SHIFT=1 and the reference" >&2
+  echo "   reports rest t=12, matching the pinned exporter; without it, t=70." >&2
+  echo "   The knob is absent from the pinned tag, so it cannot affect export/." >&2
   exit 2
 fi
 mkdir -p "$OUT"