geometry: disagreement belongs on the edge, not averaged into the region

co_registration is corr(hebb strength, semantic proximity) over a region's
internal edges. Whether use and meaning agree is a property of EACH EDGE;
the correlation averages it into one scalar per region, so a region holding
one violently disagreeing edge beside one violently agreeing edge reports
~0. The disagreements cancel and the summary destroys exactly what it was
built to reveal — the mean-versus-min error, in different clothes.

Measured: 375 live neighborhoods, 340 positive, 31 AT ZERO, 4 negative.
Read as a count that says 'four things to be curious about'. Read correctly
it says four were lopsided enough to survive averaging, and the 31 zeros
are where opposing sites cancelled.

The loop computing the aggregate already had both halves per edge — w and
cs — and threw them away. Now:
    discord = z(semantic proximity) - z(association strength)
standardized within the region from accumulators already gathered. No
second statistic, no constant, no threshold; |discord| IS the nucleation
strength. >0 near in meaning yet unlinked by use; <0 linked by use yet far
in meaning. Both surprising.

This also removes the reason curiosity looked like a search problem. With a
per-region number the only way to find sites is to enumerate regions — I
wrote exactly that sweep, and it is a supervisor walking the structure,
O(n) per call, fine at 375 and impossible at a million. Nothing in a mind
scans its neighborhoods to find what is surprising; the surprise captures
attention. That sweep is reverted here.

co_registration is deprecated, not deleted: it is embedded in the persisted
GEO1 blob and removing it is a format migration that must not ride along.
Nothing new may read it.

lang/runtime/engram_geometry.h

@@ -40,7 +40,11 @@ typedef struct {
 
 /* One skeleton edge (indices into members[]). eff_weight = weight*(1+0.5*hebb),
  * clamped to 1.0 — the effective propagation strength eg_edge_eff_weight uses. */
-typedef struct { uint32_t a, b; double eff_weight; double hebb; } GeoEdge;
+/* discord = z(semantic proximity) - z(association strength), standardized
+ * within the region. How much closer in meaning this edge is than its use
+ * predicts. >0 near in meaning yet unlinked by use; <0 linked by use yet far
+ * in meaning. Both surprising; |discord| is nucleation strength. No threshold. */
+typedef struct { uint32_t a, b; double eff_weight; double hebb; double discord; } GeoEdge;
 
 /* A compact principal axis of the ellipsoid: unit direction in R^dim + extent
  * (sqrt of the covariance eigenvalue = the ellipsoid's half-width along it). */
@@ -76,6 +80,12 @@ typedef struct {
     GeoEdge*   edges;          /* strong internal hebb edges = the backbone      */
     int        k_core;         /* the maximum core number present in the skeleton*/
     /* ── diagnostics ── */
+    /* DEPRECATED — see GeoEdge.discord. This aggregates a PER-EDGE property
+     * into one scalar per region, so opposing disagreements cancel and the
+     * summary hides the sites it was meant to expose. Retained only because
+     * it is embedded in the persisted GEO1 blob; removing it is a format
+     * migration and must not ride along with this change. Nothing new may
+     * read it. */
     double     co_registration;/* corr(hebb strength, semantic proximity) over   */
                                /* internal edges: >0 = geometries agree (reify);  */
                                /* <0 = disagree (surprising links / dream cands). */