DXサポーター・経済産業省「DX認定制度（デジタルガバナンス・コード3.0）」実践ガイド：
ベンダーロックインを防ぎ、現場が今日から楽になる段階的業務改革

-- Target: db01.ok.st (PostgreSQL 19 + OpenZFS recordsize=8K)
CREATE TABLE corporate_dx_ledger (
    entry_id        uuid PRIMARY KEY DEFAULT uuidv7(),
    tenant_id       uuid NOT NULL,
    idempotency_key text NOT NULL,
    tx_date         date NOT NULL,
    counterparty    text NOT NULL,
    amount_yen      bigint NOT NULL CHECK (amount_yen >= 0),
    prev_hash       bytea NOT NULL,
    entry_hash      bytea NOT NULL,
    UNIQUE (tenant_id, idempotency_key)
);

ALTER TABLE corporate_dx_ledger ENABLE ROW LEVEL SECURITY;
ALTER TABLE corporate_dx_ledger FORCE ROW LEVEL SECURITY;

-- InitPlan scalar subquery evaluation (O(1) per query, zero leak)
CREATE POLICY tenant_isolation_policy ON corporate_dx_ledger
    AS RESTRICTIVE
    USING (tenant_id = (SELECT sovereign_auth.current_tenant_id()))
    WITH CHECK (tenant_id = (SELECT sovereign_auth.current_tenant_id()));

-- PostgreSQL 19: Zero-WAL idempotent read-or-insert in 1 round-trip
INSERT INTO corporate_dx_ledger (
    tenant_id, idempotency_key, tx_date, counterparty, amount_yen, prev_hash, entry_hash
) VALUES ($1, $2, $3, $4, $5, $6, $7)
ON CONFLICT (tenant_id, idempotency_key) DO SELECT
RETURNING entry_id, entry_hash;

#![forbid(unsafe_code)]

/// Verifies a sequence of hash-chained electronic ledger entries (Electronic Books Preservation Act).
/// Each entry commits to `prev_hash` and `expected_hash` computed over canonical fields.
#[inline]
pub fn verify_hash_chain_continuity(chain: &[([u8; 32], [u8; 32])]) -> Result<usize, usize> {
    // chain[i] = (prev_hash, current_hash)
    let mut i = 1;
    while i < chain.len() {
        let expected_prev = &chain[i - 1].1;
        let observed_prev = &chain[i].0;
        let mut diff: u8 = 0;
        let mut b = 0;
        while b < 32 {
            diff |= expected_prev[b] ^ observed_prev[b];
            b += 1;
        }
        if diff != 0 {
            return Err(i); — Tampering or missing record detected at index i
        }
        i += 1;
    }
    Ok(chain.len())
}