Item 119: Hidden discord: a region-level convergence measure

*Re-filed 2026-10-21 by the rebuttal-and-end-to-end round from branch round/2026-09-17-convergence-measure, where it was item 95; content unchanged; the branch round is landed under projects/normativity/seed/rounds/2026-09-17-convergence-measure/.*

The convergence-measure round (projects/normativity/seed/rounds/2026-09-17-convergence-measure/) shows that the coordinate-wise profile (Hull, Ovl, Disc) on a declared fragment can report Disc = 0 while the merged bundle is infeasible — two humble reasoners holding y ≥ (9/10)x, x ≥ (9/10)y and x ≥ 4/5, y ≤ 3/10, and three reasoners pairwise compatible and jointly not (hidden_discord). Helly in dimension one makes coordinate discord pairwise (discord_iff_pair); nothing makes merged feasibility so. No declaration of fragment or weights blocks this. Define a region-level component of the profile — a merged-feasibility mass, or a relational discord over declared pairs of sentences, or the affine dimension of the merged region — that sees relational incompatibility, prove its monotonicity under nesting, and give its certificate.

Deliverable shape: the definition on IntervalData or on regions, the analogue of discord_persists, and the two hidden-discord fixtures scored positive by it. Acceptance check: python3 tests/run.py green; the Lean audits clean.

Context: MANY.md §2 and GAMEABILITY.md (what is not blocked) of the round. Consumed by: any use of Disc = 0 as "the reasoners could jointly hold their bundles". A solution ships: the component, its monotonicity theorem, and the fixtures.