Index Funds

Index funds are investment vehicles that passively track a market segment. Rather than picking individual stocks, a player subscribes to a fund that holds a basket of underlying assets, and the fund's net asset value (NAV) moves with that basket. Income from the underlying holdings is distributed to subscribers through a dividend pass-through.

Feature Flag

Index funds are gated behind a three-state feature flag:

getIndexFundsMode() → "off" | "partial" | "full"
``

| Mode | Behaviour |
| --- | --- |
| `off` | No index funds exist in the game |
| `partial` | Funds are visible but players cannot transact (view-only) |
| `full` | Full subscribe / redeem functionality is enabled |

Check the mode before building any UI that assumes the player can trade funds — in `partial` mode the data is read-only.

## How a Fund Works

Each fund holds a fixed basket of underlying holdings (corporate shares, sovereign instruments, or other market positions). The fund computes a **net asset value (NAV)** from the current market value of those holdings:

NAV = sum(holding.quantity × holding.marketPrice)


When a player **subscribes** (buys in), cash is converted into fund units at the current NAV. When a player **redeems** (withdraws), units are converted back to cash at NAV. There is no active management — the fund simply tracks its basket.

## Dividend Pass-Through

When underlying holdings pay dividends, the income is split between the fund and its subscribers:

dividendIncome = sum(holding.dividendPerUnit × holding.quantity)

reinvested = dividendIncome × 0.75 // → fund cash, grows NAV passThrough = dividendIncome × 0.25 // → paid to current unit holders ``

Portion	Destination	Effect
75%	Fund cash (reinvested)	Increases underlying positions / NAV over time
25%	Unit holders (pass-through)	Direct income to subscribers each turn

This means a fund compounds 75% of its income internally while still giving holders a steady 25% cash yield — a hybrid between a growth ETF and an income fund.

Subscribing and Redeeming

Action	Requirement	Result
Subscribe	Cash ≥ subscription amount	New units credited at current NAV
Redeem	Fund units ≥ redeem amount	Units destroyed, cash credited at NAV

Transactions settle at the NAV computed on the turn the order is processed. There is no intraday pricing — NAV updates once per turn with the market cycle.

NAV Example

Suppose a fund holds 1,000 units of Stock A at ¥120 and 500 units of Stock B at ¥80:

NAV = (1,000 × 120) + (500 × 80) = 120,000 + 40,000 = ¥160,000

If the fund has 2,000 outstanding subscriber units, each unit is worth ¥80. A player subscribing ¥4,000 receives 50 units; the fund's cash grows and NAV is recomputed next turn.

Strategic Notes

Passive exposure: Index funds are the cheapest way to gain broad exposure to a market segment without managing individual positions.
Compounding: Because 75% of dividends reinvest, funds with strong underlying holdings grow NAV over time — ideal for long-term holds.
Liquidity: Redeem at any time at NAV. Unlike individual bonds, there is no maturity lock-up.
No active management fee: The pass-through split (75/25) is the only cost — there is no separate management fee deducted.