Capture checking and SAM

[nrinaudo]

Compiler version

3.8.0-RC3 and 3.8.1-RC1-bin-20260105-f08de70-NIGHTLY

Minimized code

//> using scala 3.nightly
//> using option -language:experimental.captureChecking

import caps.*

trait Rand extends SharedCapability

trait Plan:
  def execute(test: Rand ?=> Unit): Boolean

object Plan:
  def execute(test: Rand ?=> Unit): Boolean =
    true

  val standard: Plan =
    test =>
      execute(test)

Output

[error] Capability cap outlives its scope: it leaks into outer capture set 's1 of parameter test.
[error] The leakage occurred when trying to match the following types:
[error] 
[error] Found:    (contextual$1: rep$_.this.Rand^'s2) ?->{test} Unit
[error] Required: (rep$_.this.Rand^) ?=> Unit
[error] 
[error] where:    ?=> refers to a fresh root capability created in anonymous function of type (test²: (rep$_.this.Rand) ?=> Unit): Boolean when checking argument to parameter test of method execute
[error]           ^   refers to the universal root capability
[error]           cap is a fresh root capability classified as SharedCapability created in anonymous function of type (using contextual$1: rep$_.this.Rand^'s2): Unit of parameter parameter contextual$1² of method $anonfun
[error]       execute(test)

Expectation

I was (perhaps naively) expecting this to compile.

Context

More context can be found in the original scala users discussion.