inline proxy values appear in capture sets (inline methods retain references?)

[bishabosha]

blocker for Make -> sugar an inline method #24728

Compiler version

main branch @ ba45875

Minimized code

taken from an error in library/src/scala/collection/package.scala when trying to make Predef.ArrowAssoc inline

import language.experimental.{captureChecking, separationChecking}

import scala.collection.SeqOps

extension [A](self: A) inline def --> [B](y: B): (A, B) = (self, y)

object +: {
  def unapply[A, CC[_] <: Seq[?], C <: SeqOps[A, CC, C]](t: (C & SeqOps[A, CC, C])^): Option[(A, C^{t})] =
    if(t.isEmpty) None
    else Some(t.head --> t.tail)
}

Output

-- [E007] Type Mismatch Error: local/reproducer.scala:10:14 --------------------
10 |    else Some(t.head --> t.tail)
   |              ^^^^^^^^^^^^^^^^^
   |        Found:    (A^'s1, C^{y$proxy1})
   |        Required: (A, C)
   |
   |        Note that capability y$proxy1 is not included in capture set {}.
   |----------------------------------------------------------------------------
   |Inline stack trace
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |This location contains code that was inlined from reproducer.scala:5
 5 |extension [A](self: A) inline def --> [B](y: B): (A, B) = (self, y)
   |                                                          ^^^^^^^^^
    ----------------------------------------------------------------------------
   |
   | longer explanation available when compiling with `-explain`
1 error found

Expectation

i would not expect inline proxy values in capture sets

[bishabosha]

if i make everything inline, so no proxies, then also get an error:

import language.experimental.{captureChecking, separationChecking}

import scala.collection.SeqOps

extension [A](inline self: A) inline def --> [B](inline y: B): (A, B) = (self, y)

object +: {
  def unapply[A, CC[_] <: Seq[?], C <: SeqOps[A, CC, C]](t: (C & SeqOps[A, CC, C])^): Option[(A, C^{t})] =
    if(t.isEmpty) None
    else Some(t.head --> t.tail)
}

-- [E007] Type Mismatch Error: local/reproducer.scala:10:14 --------------------
10 |    else Some(t.head --> t.tail)
   |              ^^^^^^^^^^^^^^^^^
   |              Found:    (A^'s1, C^{t})
   |              Required: (A, C)
   |
   |              Note that capability t is not included in capture set {}.
   |----------------------------------------------------------------------------
   |Inline stack trace
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |This location contains code that was inlined from reproducer.scala:5
 5 |extension [A](inline self: A) inline def --> [B](inline y: B): (A, B) = (self, y)
   |                                                                        ^^^^^^^^^
    ----------------------------------------------------------------------------
   |
   | longer explanation available when compiling with `-explain`
1 error found