[ECO-5702] Fix Xcode 26.4 compilation error

[lawrence-forooghian]

Resolves ably/ably-cocoa#2202. See commit message for more details.

Summary by CodeRabbit

Release Notes

• Chores
  • Updated CI/CD pipeline runner configuration to macOS 26 across all build jobs for improved compatibility and stability
  • Updated Xcode build tooling to version 26.4
  • Enhanced thread safety in asynchronous request handling

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 86eb9cbd-92c5-4500-a05e-5be9022057da

📥 Commits

Reviewing files that changed from the base of the PR and between 571f2a0 and b8c7443.

📒 Files selected for processing (3)

• .github/workflows/check.yaml
• Sources/AblyChat/TypingOperationQueue.swift
• Sources/BuildTool/BuildTool.swift

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Walkthrough

This PR updates CI infrastructure to support Xcode 26.4/Swift 6.2 by upgrading macOS runner versions, fixes a Swift 6.2 actor-isolation compilation error in TypingOperationQueue by adding @MainActor annotation, and updates the build matrix tooling to reference Xcode 26.4.

Changes

Cohort / File(s)	Summary
CI Runner Configuration .github/workflows/check.yaml	Updated macOS runner from macos-15 to macos-26 across all CI jobs (lint, spec-coverage, generate-matrices, build-and-test-spm, build-release-configuration-spm, build-and-test-xcode, build-release-configuration-xcode, check-example-app, check-documentation) and commented-out code-coverage job.
Actor Isolation Fix Sources/AblyChat/TypingOperationQueue.swift	Added @MainActor annotation to the nested Request.performOperation() method to satisfy Swift 6.2 stricter actor-isolation requirements.
Build Tooling Version Sources/BuildTool/BuildTool.swift	Updated generated build matrix Xcode version from 26.2 to 26.4.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 Swift and steady, we hop to the beat,
With actors aligned, our fix is complete!
From twenty-six-two to twenty-six-four,
The tools and the runners, now ready for more! 🚀

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR contains out-of-scope changes: updating macOS runner versions from 15 to 26 in CI workflows and updating Xcode version in build matrices are unrelated to fixing the Xcode 26.4 compilation error.	Remove CI workflow runner version updates and Xcode version updates in BuildTool.swift as they are separate from the compilation fix and should be addressed in separate PRs.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main fix addressing the Xcode 26.4 compilation error in TypingOperationQueue, which is the primary change in the changeset.
Linked Issues check	✅ Passed	The PR fully addresses the compilation error by annotating TypingOperationQueue.Request.performOperation() with @MainActor as required by issue #2202, resolving the actor-isolation sendability checking failure.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch typing-queue-fix

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[ttypic]

LGTM, just a thought: maybe it's worth to run on macos-latest? Can it help us find future bugs with new version of Xcode faster?

[lawrence-forooghian]

Unfortunately macos-latest isn't actually the latest; it's still on macOS 15! https://github.com/actions/runner-images?tab=readme-ov-file#available-images

and likewise the default version of xcode that the runners use is not the latest either; e.g. it's currently 26.2: https://github.com/actions/runner-images/blob/main/images/macos/macos-26-Readme.md

We could have a CI job that also tests against whatever the default version of Xcode is too, so that we will eventually catch issues introduced by new versions of Xcode (once they become the default)

[lawrence-forooghian]

I think another problem is the fact that we only run our CI jobs when we actually make a change, so in periods where there isn't much change on a given SDK it can take a while to find out; maybe we should consider nightly builds of everything too