Mind vNext: neutral challenge contract and exact verifier adapters

[Kitahl]

Scope

Implements the first skill slice from EGR-FOIL-INT-001 on the pinned baseline 4f088d688fa9e25b4608f44000a5d9812efa45f9:

• WO-000 contract/authority freeze and import boundary
• WO-001 additive egrt.challenge.v1 types, store, events, configuration, discriminator selection, and challenge gate
• WO-002 generic candidate binding and distinct structural/semantic verification, with foil_authority.py compatibility wrappers
• WO-003 Mind vNext native proof challenges and claim-native verifier receipts

Mind vNext behavior

• candidate-bound alternate formalizations, negation, edge-case, and counterexample challenges
• ordinal minimum-discriminator selection, capped at two load-bearing plans
• exact symbolic-equivalence adapter with explicit assumptions and fail-closed availability
• bounded exact enumeration/DP receipts
• counterexample receipts
• separate natural-language-to-formal scope status
• explicit proof-bundle finalization

Boundaries

• SHADOW remains the default challenge mode; OFF preserves baseline behavior
• challenge resolutions never replace domain receipts
• FOIL remains proposal-only and cannot clear proof obligations, execute repairs, or authorize writes
• no non-FOIL module imports foil_*
• no Soul, Space, Reality, Power, Time, Gauntlet-monitor, Meditate, Council, or FOIL-bridge upgrade is included
• this implementation makes no behavioral-efficacy claim

Validation

All required pull-request workflows pass on clean squashed commit af8dc2621099dd4993272cbc9e623190ef23ca9c:

• Research software validation: passed, including lint, runtime/layout tests, typed-runtime validation, showcase validation, syntax, and repository metadata
• Security gates: passed, including full-history secret scan, dependency audits, deterministic hash-lock verification, and exact locked installation
• Runtime portability: passed
• CodeQL: passed
• focused challenge/Mind implementation suite: 24 tests passed
• complete repository unit run during implementation audit: 493 tests passed

The branch contains one implementation commit and no temporary payload or diagnostics workflow files.