B2c: execute anchored-row qualification boundary

[yingyue2030699]

Scope

Implements the proof-only B2c anchored_difference_rows_v1 qualification boundary frozen by merged PR 200.

• validates the exact 294-artifact B2 corpus and frozen checkpoint binding
• executes all 20 oracle-independent candidate criteria exhaustively
• materializes all scientific and D12 applicability ledgers
• adds exact dyadic/544-bit MPFR boundary checks and strict binary64 evaluator semantics
• records the missing primary Stam eigenanalysis, uniform cross-check, and qualified-host D12 execution honestly

Exact-head development evidence

Exact head: 9820e95

The exact-head replay completed with 294/294 artifacts. All 20 oracle-independent candidate criteria passed. The report verdict is INCOMPLETE, with no candidate failures, because the frozen independently certified Stam/uniform oracle and qualified-host D12 execution are unavailable.

Non-authorization

This PR does not qualify the candidate, reopen D9a, unblock B3, select Far, or authorize production. Exact-SHA technical, scientific, and gatekeeper review remains required, followed by a later explicit user decision.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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