SIL verifier abort on `~Copyable` `Optional` `var` captured into async task group

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Description

A recent main toolchain aborts the SIL verifier while compiling swift-subprocess in the debug configuration. The failing check is:

SIL verification failed: debug_value type chain should hold: inst->isExprTypeValid()
Verifying instruction:
   undef<${ var Optional<IODescriptor> }>
->   debug_value [moveable_value_debuginfo] undef : ${ var Optional<IODescriptor> }, var, name "diskIO", type $Optional<IODescriptor> // id: %247
In function:
// closure #1 in closure #1 in run<A, B, C, D>(_:input:output:error:body:)
// Isolation: @concurrent

Observed on swiftlang/swift-subprocess#261, where the offending function is Subprocess.run(_:input:output:error:body:) in Sources/Subprocess/API.swift.

Reproduction

Reproduces identically on unrelated PRs against the same base (same failing SIL instruction, same source range), so this is a toolchain regression rather than anything specific to the changes under test. Examples:

swiftlang/swift-subprocess#261
swiftlang/swift-subprocess#314

Stack dump

https://github.com/swiftlang/swift-subprocess/actions/runs/27469889276/job/81198764398?pr=261
https://github.com/swiftlang/swift-subprocess/actions/runs/27441717856/job/81117121105?pr=314

Expected behavior

The package compiles, or at minimum the compiler emits a diagnostic rather than aborting in the SIL verifier.

Environment

• Swift version: 6.5-dev (LLVM 0ada7abaeee4c8c, Swift d1ce3ae)
• Platform: x86_64 Linux (Ubuntu 22.04.5 LTS)
• Configuration: -Onone, -swift-version 6, -enable-testing, with StrictConcurrency, Lifetimes, NonisolatedNonsendingByDefault, ExistentialAny, MemberImportVisibility, InternalImportsByDefault

Additional information

No response