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engine: additive forward probability, behaviour-preserving

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Forwarding was a single global ForwardProb; make it a per-student
composite (Config.ForwardChance): baseline propensity raised by the
fake's Novelty, lowered by ambient HarmAwareness, and scaled down for an
educated student by ProgramEffect (1 = today's hard block). RunCascade
now takes a precomputed per-student []float64 chance and has no education
special case. Defaults are behaviour-neutral, so the 82/58/6 golden
tests are unchanged; the model is tuned in a later slice.
This commit is contained in:
Justin Visser 2026-06-18 20:03:04 +02:00
parent 4c58e8a0f5
commit a0635544d9
4 changed files with 148 additions and 21 deletions
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20
internal/engine/cascade.go
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@ -40,14 +40,12 @@ type CascadeResult struct {
// RunCascade spreads the fake from origin: in every round, each newly
// reached student forwards to each neighbour whose edge threshold falls
// below forwardProb. Educated students receive the fake but never forward
// it; that is the entire effect of the education lever.
func RunCascade(graph *Graph, origin int, forwardProb float64, educated []int, thresholds EdgeThresholds) CascadeResult {
isEducated := make([]bool, graph.NumNodes())
for _, student := range educated {
isEducated[student] = true
}
// below that student's forwarding chance. forwardChance[student] already
// encodes the education lever (an educated student's chance is scaled down,
// to zero under a full-strength program), so the cascade has no education
// special case; an educated student receives the fake like anyone else and
// simply forwards it with a lower chance.
func RunCascade(graph *Graph, origin int, forwardChance []float64, thresholds EdgeThresholds) CascadeResult {
reachedAtRound := make([]int, graph.NumNodes())
for node := range reachedAtRound {
reachedAtRound[node] = NeverReached
@ -60,12 +58,10 @@ func RunCascade(graph *Graph, origin int, forwardProb float64, educated []int, t
for round := 1; len(frontier) > 0; round++ {
var nextFrontier []int
for _, forwarder := range frontier {
if isEducated[forwarder] {
continue // received the fake, refuses to pass it on
}
chance := forwardChance[forwarder]
for _, receiver := range graph.Neighbors(forwarder) {
alreadyReached := reachedAtRound[receiver] != NeverReached
forwards := thresholds[[2]int{forwarder, receiver}] < forwardProb
forwards := thresholds[[2]int{forwarder, receiver}] < chance
if !alreadyReached && forwards {
reachedAtRound[receiver] = round
numReached++