fix(npf): port DS halo-under-rim cross-fade AA to kill the sphere seam ring

The node-graph glow-halo pass started exactly at the sphere edge (discard
r<1.0) while the body's antialiased rim feathers to alpha 0 by r=1 — leaving
the ~1px feather band lit by neither, so the dark page showed through as a
1-2px seam ring around every sphere (glaring when the halo flared red). This
is the antialiasing defect vs the GRCE Design System canvas.

Surgical port of the DS fix: only the SPHERE_FS halo pass changes — it now
ramps the halo up from inner = 1 - 2*vFeather (the body feather start), so
body-fade and halo-rise are exact complements and cross-fade into continuous
light. Expressed in this page's own vFeather varying so the complement is
exact against its crisper ~1.2px body feather, preserving the page's superior
frustum-fill/AA tuning (FILL 1.08, rim-bias, 280 cap, DPR budget) untouched.

Mirror (grce-design-system) already carried the canvas fix (commit 8d08367).

Author: p4gs

docs/projects/nthpartyfinder/ds/PROVENANCE.txt

@@ -26,6 +26,27 @@ catch-up (FILL=0.85, no rim-bias, 220-node cap, no DPR area budget, no
 pulse-edge AA). Re-vendoring from the canvas at this point would be a
 regression. See the audit ISA above for the full line-by-line comparison.
 
+Halo-under-rim cross-fade AA ported 2026-07-15 (owner reported a dark seam
+ring around every sphere on the live page vs the DS canvas): the DS canvas
+NodeGraphBackground has since gained a genuine antialiasing improvement this
+page lacked — the glow-halo pass used to start exactly at the sphere edge
+(discard r<1.0) while the body's rim feather fades to alpha 0 by r=1, leaving
+the ~1px feather band lit by NEITHER body nor halo → the dark page shows
+through as a 1-2px seam ring (glaring when the halo flares red). Ported the
+fix SURGICALLY: only the SPHERE_FS halo pass changed — it now ramps the halo
+up from `inner = 1 - 2*vFeather` (the body feather start) so body-fade and
+halo-rise are exact complements and cross-fade into continuous light. Expressed
+in THIS page's own vFeather varying (not the canvas's vPixelRadius/featherR
+scheme) so the complement is exact against this page's crisper ~1.2px body
+feather, and so the page's superior frustum-fill/AA tuning documented above is
+preserved untouched — the ONLY change is the halo annulus inner edge. The
+grce-design-system mirror already carried the canvas fix (synced earlier this
+session, commit 8d08367), so no mirror update was needed. Verified: node
+--check clean; halo inner edge now r>=inner not r>=1.0. Rendered-pixel
+confirmation deferred to the live site — browser automation was unreachable
+this background session (and WebGL scenes don't composite into plain
+screenshots regardless).
+
 SiteHeader adopted 2026-07-15: the nav (previously a page-local `.np-nav`,
 position:sticky bar) is now `ds/site-header.js` — a vanilla auto-mount port
 of the DS `SiteHeader.jsx` (grce-design-system re-synced from the Claude

docs/projects/nthpartyfinder/ds/node-graph.js

@@ -187,10 +187,23 @@ void main(){
     gl_FragColor = vec4(col, aa);
   } else {
     // ---- halo pass (annulus around the body) ----
-    if (r < 1.0 || r > uGlowMax) discard;
+    // Ramp the halo up UNDER the body's rim feather — its exact complement — so the
+    // body fade and halo rise cross-fade into continuous light at the edge. A halo
+    // that starts at r=1 leaves the body's ~1px feather band (which fades to alpha 0
+    // by r=1) unlit, showing the dark page through as a seam ring around every sphere
+    // (glaring when it flares red). Matches the GRCE Design System NodeGraphBackground
+    // antialiasing fix (halo ramps up under the rim feather).
+    float f = max(vFeather, 8.0e-4);
+    float inner = 1.0 - 2.0 * f;                                 // == body feather start ([inner,1])
+    if (r < inner || r > uGlowMax) discard;
     float pulse = 0.5 + 0.5 * sin(uTime * 0.0020944 + vPhase);   // per-sphere phase
-    float halo = 1.0 - smoothstep(1.0, uGlowMax, r);             // strong at rim → 0 at edge
-    halo = pow(halo, 2.2);
+    float halo;
+    if (r < 1.0) {
+      halo = smoothstep(inner, 1.0, r);                          // rises under the rim feather (complements body fade)
+    } else {
+      halo = 1.0 - smoothstep(1.0, uGlowMax, r);                 // strong at rim → 0 at edge
+      halo = pow(halo, 2.2);
+    }
     float ch = clamp(vCharge, 0.0, 1.0);
     if (uHaloMode < 0.5) {
       // dark theme: additive glow; flares RED when an energy pulse arrives