Audit-ready and production-hard from commit one.

ALTER TABLE invoices ENABLE ROW LEVEL SECURITY;
ALTER TABLE invoices FORCE ROW LEVEL SECURITY;
CREATE POLICY invoices_tenant_isolation ON invoices
  USING (
    account_id = NULLIF(current_setting('app.current_account', true), '')
  );

export function hashChainLink(
  prevHash: string | null,
  payload: JsonValue,
): string {
  return createHash("sha256")
    .update(canonicalize([prevHash, payload]))
    .digest("hex");
}

  async verify(accountId: string): Promise<ChainVerification> {
    return withTenant(this.db, accountId, async (tx) => {
      const entries = await loadEntries(tx, accountId);

      // Truncation guard (TM-I): the WORM store is the trusted length oracle. An anchor for a length
      // past what the DB can now produce means the tail was dropped — invalid even if the surviving
      // prefix is internally consistent (which, being a true prefix, it always is).
      const beyond = await this.store.head(
        anchorKey(accountId, entries.length + 1),
      );
      if (beyond !== null) {
        return { valid: false, brokenAt: entries.length };
      }
      if (entries.length === 0) {
        return { valid: true, brokenAt: null };
      }

      const anchorObj = await this.store.get(
        anchorKey(accountId, entries.length),
      );
      const anchor = decodeAnchor(anchorObj.body);
      return verifyChain(entries, anchor);
    });
  }

  async decryptField(
    tenantId: string,
    stored: string,
    columnContext: string,
  ): Promise<string> {
    const env = parseEnvelope(stored);
    const key = await this.provider.keyFor(tenantId, env.keyVersion);
    const aad = buildAad(tenantId, env.keyVersion, columnContext);
    const cipher = cipherForAlg(env.algId);
    let plaintext: Buffer | undefined;
    try {
      plaintext = cipher.decrypt(
        key,
        { nonce: env.nonce, ciphertext: env.ciphertext, tag: env.tag },
        aad,
      );
      return plaintext.toString("utf8");
    } finally {
      plaintext?.fill(0);
      key.fill(0);
    }
  }