Backport Xcode 27 support to TCA 1.23

[igorcamilo]

Description

Unfortunately my team still needs to support iOS 15, so we've been stuck on TCA 1.23 for months.

It was fine until Xcode 27 beta 1. I was hoping that it could be an Xcode regression but we're at beta 3 now and the error persists.

I checked on my machine and cherry-picking #3931 fixes the compilation error. Could that be backported to 1.23?

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Being able to compile a version of the project that supports iOS 15 using Xcode 27.

Actual behavior

The compiler fails with this error:

Sources/ComposableArchitecture/Observation/NavigationStack+Observation.swift:167:17 Cannot form key path to main actor-isolated subscript 'subscript(fileID:filePath:line:column:)'

Reproducing project

No extra project necessary, simply try to compile TCA tag 1.23.2 on Xcode 27.

The Composable Architecture version information

1.23.2

Destination operating system

iOS 15

Xcode version information

Version 27.0 beta 3 (27A5218g)

Swift Compiler version information

swift-driver version: 1.168.4 Apple Swift version 6.4 (swiftlang-6.4.0.25.4 clang-2100.3.25.1)
Target: arm64-apple-macosx26.0