Seams

Everything else a plugin declares adds. A seam replaces.

Exactly one plugin owns a seam, or nobody does. That exclusivity is the point: two plugins both rewriting the damage formula would have no defined result, so the engine does not allow it.

The seams

Seam	Replaces
variance	every damage spread in the game
armor	what a target subtracts
damageFormula	turning the parts of a blow into a number
damageTaken	what a blow costs the one taking it, after armour and guarding
weaponAttack	the whole swing
levelUpAward	what a level grants
enemyXpValue	what a kill is worth
simulateNpc	which NPCs the world bothers to think about while nobody is watching

They nest

Replacing damageFormula leaves variance and armor available — your formula can call them or ignore them. You are replacing one layer, not the whole stack.

That is why weaponAttack exists separately: a game whose attacks are not a roll against a defence at all replaces the whole swing rather than trying to express itself through a formula that assumes one.

Not every seam is about combat

simulateNpc is the one to look at if your world is large. Every NPC the background pass considers costs something, and the engine's own answer is "all of them" — which is right for a village and wrong for a continent. Narrow it and the rest of the world simply holds still until the party is nearer:

$.stat('hopsFromParty') <= 2

It reads how far each NPC is from the party on the map as it stands this turn, so a drawbridge your plugin opens changes what counts as near. -1 means there is no route at all, which fails every <= test on purpose.

The trap is writing a rule that is true forever. An NPC nobody ever simulates never finishes anything, so put a floor under it:

$.stat('hopsFromParty') <= 2 || $.stat('turnsSinceSimulated') > 10

You can also read your own plugin's fields with $.field(...), which is how a faction plugin keeps its own people alive while everyone else idles.

When to use one

Reach for a seam when the engine's calculation is wrong for your game, not when it needs tuning. A game that wants tougher characters edits the maxHp dial. A game where damage is decided by suit-matching cards replaces weaponAttack.

If a dial can express it, use the dial. Seams are the heavier tool and they take ownership away from everyone else.

Next

Cooperation — for everything that adds rather than replaces.