Fix ExtendedContextTests crash: nonisolated deinit on SuggestionSettingsModel

[FuJacob]

Summary

ExtendedContextTests was crashing the test host with malloc: pointer being freed was not allocated on every test that creates and destroys a SuggestionSettingsModel. All 5 settings-model tests failed as a result (the first crash killed the runner; the restart ran 0 tests).

The crash happens in SuggestionSettingsModel.__deallocating_deinit via swift_task_deinitOnExecutorMainActorBackDeploy. Because SuggestionSettingsModel is @MainActor, Swift schedules the deinit to hop to the main actor executor through the macOS 14 back-deployment shim. That shim has a bug on macOS 26 where swift::TaskLocal::StopLookupScope::~StopLookupScope() attempts to free stack memory through malloc, triggering abort().

Fix: add nonisolated deinit {} (SE-0371 / Swift 5.9). This instructs the compiler that the deinit is not actor-isolated and requires no executor hop, bypassing the buggy back-deployment path entirely. All stored state (@Published property wrappers and the UserDefaults reference) is thread-safe to release from any thread.

Validation

xcodebuild test \
  -project Cotabby.xcodeproj \
  -scheme Cotabby \
  -destination 'platform=macOS' \
  -only-testing:CotabbyTests/ExtendedContextTests \
  CODE_SIGNING_ALLOWED=NO
# Executed 12 tests, with 0 failures (0 unexpected)
# ** TEST SUCCEEDED **

swiftlint lint --quiet
# exit 0

Before this change: 5 failures (test_setExtendedContext_*), test host crash.
After: all 12 ExtendedContextTests pass.

Linked issues

Risk / rollout notes

nonisolated deinit is a Swift 5.9 language feature (available in Xcode 15+). The project already builds with Xcode 26. It has no runtime component — it only suppresses compiler-generated executor-hopping in the deinit, which is safe because @Published subjects and UserDefaults have no main-actor deallocation requirement.

Greptile Summary

This PR adds a single nonisolated deinit {} to SuggestionSettingsModel to fix a test-host crash on macOS 26 caused by a Swift back-deployment shim bug in the main-actor teardown path.

• The empty nonisolated deinit prevents the compiler from generating an executor-hop to the main actor during deallocation, bypassing the StopLookupScope double-free in swift_task_deinitOnExecutorMainActorBackDeploy.
• The stored state (@Published value-type properties and a UserDefaults reference) has no main-thread deallocation requirement, so the thread-safety claim in the comment is sound.

Confidence Score: 5/5

Safe to merge — the change is a single-line, well-scoped fix with no side effects on production behaviour.

The model holds only value-type @published properties and a UserDefaults reference, none of which require main-thread deallocation. No AnyCancellable sets, NotificationCenter observers, or other cleanup work exists in the deinit, so moving teardown off the main-actor executor cannot introduce new problems. In production the model is effectively a singleton and is rarely deallocated, so the change primarily affects test teardown.

No files require special attention.

Important Files Changed

Filename	Overview
Cotabby/Models/SuggestionSettingsModel.swift	Adds nonisolated deinit {} to suppress main-actor executor hop during teardown; all stored properties are value types or thread-safe reference types with no main-thread deallocation requirement.

Sequence Diagram

sequenceDiagram
    participant T as Test / ARC
    participant S as SuggestionSettingsModel
    participant MA as MainActor Executor
    participant Shim as Back-Deploy Shim (macOS 26)

    Note over T,Shim: Before fix
    T->>S: last strong reference released
    S->>MA: schedule deinit hop (compiler-generated)
    MA->>Shim: swift_task_deinitOnExecutorMainActorBackDeploy
    Shim-->>T: 💥 malloc: pointer being freed was not allocated

    Note over T,S: After fix (nonisolated deinit)
    T->>S: last strong reference released
    S->>S: deinit runs on current thread (no hop)
    S-->>T: ✅ stored properties released safely

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_{Reviews (1): Last reviewed commit: "Add nonisolated deinit to SuggestionSett..." | Re-trigger Greptile}