Module modifier 

Per-fingerer modifier system.

A Modifier is a composable buff or debuff attached to a single fingerer’s crate::game::state::FingererState. Each modifier carries a stable ModifierSource id, zero or more ModifierEffects, and an optional duration in ticks. Modifiers stack freely — multiple of the same source on the same fingerer is fine and additive.

Stacking semantics

• ModifierEffect::FlatFps values across modifiers sum, applied before any percent.
• ModifierEffect::AddPercent values across modifiers sum (two +10% Green Coins = +20%, not +21%).
• ModifierEffect::MulFactor values across modifiers multiply (two x2 buffs = x4).

Final fingerer output:

((base * count + flat_fps) * (1 + add_percent) * mul_factor) * upgrades_mult

Aggregate cache

Hot-path reads (FPS calc, sidebar render) MUST go through FingererAggregate, never iterate the Vec<Modifier> directly. The aggregate is rebuilt in three situations only:

1. A modifier is added or removed via the public API.
2. The per-tick walk drops an expired ModifierDuration::Ticks entry whose count just hit zero.
3. The save loader reconstructs it (the field is #[serde(skip)]).

Adding a new buff/debuff source

Add a variant to ModifierSource and map it in ModifierSource::id. No tick-loop changes needed — the existing per-tick walk already decrements timed modifiers and rebuilds aggregates on expiry. The id string is load-bearing forever; treat it like a fingerer or upgrade id.

Structs

FingererAggregate

Pre-computed sum/product of every effect across every modifier on a fingerer. Read on every FPS calc — the tick path rebuilds this when modifiers are added, removed, or expire, so reads are O(1).

Modifier

A single buff or debuff attached to a fingerer. Composable: a fingerer may carry an unbounded number of these. See module docs for the stacking rules and aggregate-cache contract.

Enums

ModifierDuration

Lifetime of a modifier. Permanent modifiers stick for the rest of the run (cleared only by prestige_reset). Timed modifiers decrement once per state.tick() and drop when they hit zero.

ModifierEffect

One contribution from a modifier. A single Modifier may carry multiple effects — e.g. a future debuff could combine [FlatFps(-10.0), MulFactor(0.5)].

ModifierSource

Stable identifier for the kind of buff or debuff a modifier represents. Used for de-duping in the UI (“3× Green Coin” instead of three identical chips), for save serialization, and for future per-source rules.