It uses the Yarn Spinner assemblies that ship inside NightclubArcadia/Packages/dev.yarnspinner.unity/Runtime/DLLs, so it always compiles against the exact compiler and virtual machine the game runs — not a NuGet copy that could drift.

Why

The EditMode suite lints Yarn source with regexes (CandidateYarnLintTests). This runs the compiled program instead, which catches a different class of bug: a branch that can never be reached because a flag was written earlier in the same node, a detour chain that never returns, a menu that recurses instead of looping. Those are invisible to a source lint and expensive to find by playtesting.

Usage

cd tools/YarnCheck

# compile everything; exit code 1 and diagnostics on failure
dotnet run -- ../../NightclubArcadia/Assets/Dialogue

# compile, then play a node, choosing option 0, then 0, then 3
dotnet run -- ../../NightclubArcadia/Assets/Dialogue Chair_Interaction 0 0 3

Picks are consumed as the run needs them. Leftover picks start the node again — that models the player walking away and coming back, which is how these scenes are actually played:

# ask the bartender questions, leave, return, and order a drink
dotnet run -- ../../NightclubArcadia/Assets/Dialogue Bartender_Talk 2 2 0 0

Output is the line / command / node-enter / node-exit trace, the options at each choice, and every declared variable's final value.

What it does not model

Unity commands are printed, not executed. <<check>>, <<enter_environment>> and <<skill_mod>> are stepped over, so $check_result stays false and any check-gated branch shows its failure side. Read traces with that in mind.
Yarn functions are stubbed in ProjectLibrary(): top_skill mirrors the real tie behaviour (first argument wins), alias_name returns an obvious placeholder, skill_rank returns 0. If a shipping function's behaviour changes in a way that steers dialogue, update the stub to match.
Variables start from their <<declare>> defaults every run. There is no save state.

Requirements

.NET 9 SDK. Bump <TargetFramework> in YarnCheck.csproj if you move to another version.