docs(ledger): record the World's inferential-honesty gap as an open thread

Family-selection across a sweep has no false-discovery control (no
trials-deflation, plateau-over-peak, or cross-instrument generalization);
recorded as the World's third unbuilt half. refs #144 #145 #146 #139

docs/design/INDEX.md

@@ -1405,6 +1405,24 @@ load-bearing in the flat graph.
   the CLI itself* (a deliberate amendment to C17's no-DSL, C22's no-UI-topology, and
   C9's no-by-name-node-registry). Deferred by the user (2026-06-22); #109 is its
   durable home until promoted to a milestone seeded by that brainstorm.
+- **Inferential honesty of the World — family-selection without false-discovery
+  control (tracked: milestone "Inferential validation (defend against false
+  discovery at sweep scale)", #144 / #145 / #146; adjacent #139).** The World's
+  massively-parallel sweep (C12 axes 1–2, C21) is aura's differentiator *and* its
+  most direct route to false discovery: `optimize` / `rank_by` select the single
+  best family member by a bare argmax, with no penalty for the number of
+  configurations tried, no preference for a robust parameter neighbourhood over a
+  sharp in-sample peak, and no cross-instrument generalization read; `mc` is a
+  descriptive seed-sweep, not an inferential significance test. The hygiene
+  invariants keep one backtest honest (C1 determinism, C2 no look-ahead); they do
+  **not** make a *selection across a family* honest. Recognized direction: the
+  selection/aggregation layer must deflate a winner for the family size (#144),
+  prefer a plateau over a peak (#145), and score cross-instrument generalization
+  (#146), with a per-candidate out-of-sample bootstrap as the adjacent
+  significance read (#139). Distinct from the two threads above — neither
+  orchestration *composability* (#109) nor a search *policy* (Bayesian/genetic),
+  but the statistical *validity* of the selection itself. Not a C-invariant until
+  built (the engine today violates it); recorded as the World's third unbuilt half.
 - **`aura-std` contents** — the crate exists (doc-only); which universal blocks
   land first follows the walking-skeleton's needs.
 - **`strategies/` split** — a later split, *inside a project*, of top-level