Velocity limits and review queues

The velocity check: sum debits over a moving window.

-- Has this user moved more than NGN200,000 in the last hour?
-- Source of truth is the ledger; no separate "totals" table to drift.
SELECT COALESCE(SUM(jl.debit), 0) AS debited_last_hour
  FROM journal_line jl
  JOIN journal_entry je ON je.id = jl.entry_id
 WHERE jl.account_code = $1                       -- the user's wallet
   AND je.posted_at >= now() - interval '1 hour';

-- Index for the lookup:
CREATE INDEX journal_line_velocity
  ON journal_line (account_code, entry_id)
  INCLUDE (debit);

Gate the route: either post normally or send to the review queue.

import { Client } from "pg";

const VELOCITY_LIMIT_HOURLY = 20_000_000n;  // NGN200,000 in minor units

export async function transfer(
  client: Client,
  args: { fromCode: string; toCode: string; amount: bigint },
): Promise<{ status: "posted" | "held" }> {
  try {
    await client.query("BEGIN");

    const { rows: [row] } = await client.query<{ debited_last_hour: string }>(
      `SELECT COALESCE(SUM(jl.debit), 0)::text AS debited_last_hour
         FROM journal_line jl
         JOIN journal_entry je ON je.id = jl.entry_id
        WHERE jl.account_code = $1
          AND je.posted_at >= now() - interval '1 hour'`,
      [args.fromCode],
    );

    const recent = BigInt(row.debited_last_hour);
    const wouldExceed = recent + args.amount > VELOCITY_LIMIT_HOURLY;

    const destination = wouldExceed ? "2200" : args.toCode;
    const description = wouldExceed
      ? `Hold NGN${args.amount} for manual review`
      : `Transfer NGN${args.amount}`;

    const { rows } = await client.query<{ id: string }>(
      `INSERT INTO journal_entry (description) VALUES ($1) RETURNING id`,
      [description],
    );
    const entryId = rows[0].id;

    await client.query(
      `INSERT INTO journal_line (entry_id, account_code, debit, credit) VALUES
         ($1, $2, $3, 0),
         ($1, $4, 0, $3)`,
      [entryId, args.fromCode, args.amount, destination],
    );

    await client.query("COMMIT");
    return { status: wouldExceed ? "held" : "posted" };
  } catch (err) {
    await client.query("ROLLBACK");
    throw err;
  }
}