Constant NODE_COST_GROWTH 

pub const NODE_COST_GROWTH: f64 = 2.5;

Per-lot exponential growth rate. Each step further from the origin multiplies the node’s cost by this factor (manhattan distance). The shape of the late-game wall lives here — bump it to make deep nodes balloon faster, lower it for a gentler ramp.

Reference: fingerers grow at 1.15^count (classic Cookie Clicker 15%-per-buy). The tree grows much steeper because each “lot step” gives only ONE upgrade, vs many buys per fingerer.

Bumped 1.75 → 2.5 along with the 1000× shrink in roll_magnitude. Per-node power is now tiny, so the player wants to buy many nodes; a steeper cost ramp keeps the player from sweeping the entire frontier in a single session and lets the alphabetic-suffix number range (10^36+ and beyond) become a real late-game milestone instead of a transient overflow.