refactor(connectivity): remove DispatchQueue from observer notifications

[leogdion]

Summary

Removes forced main queue dispatch from ConnectivityObserverManaging notification methods. Observers are now responsible for their own thread management.

Problem

Intermittent test failures on watchOS simulators (particularly Xcode 16.3) where observer notification tests would timeout at 16-18 seconds:

Failed CI Run: https://github.com/brightdigit/SundialKit/actions/runs/19305857262/job/55213040666

Root Cause:

• ConnectivityManager (actor) → DispatchQueue.main.async → TestObserver (actor)
• This queue hopping created a race condition/deadlock under load
• TestObserver used unstructured Task {} which compounded the timing issue
• watchOS simulators exposed this fragility more than other platforms

Solution

Removed DispatchQueue.main.async from 6 notification methods:

1. notifyActivationStateChanged(_:)
2. notifyReachabilityChanged(_:)
3. notifyCompanionAppInstalledChanged(_:)
4. notifyPairedStatusChanged(_:) (iOS only)
5. notifyMessageReceived(_:)
6. notifyApplicationContextReceived(_:)

Now: Direct actor-to-actor communication without queue hopping

Changes

Files Modified

• Sources/SundialKitConnectivity/ConnectivityObserverManaging.swift - Removed DispatchQueue wrappers
• Sources/SundialKitConnectivity/ConnectivityStateObserver.swift - Updated documentation

Breaking Change

Before (automatic main thread):

class MyObserver: ConnectivityStateObserver {
  func connectivityManager(_ manager: ConnectivityManager, 
                          didChangeActivationState state: ActivationState) {
    // Already on main thread
    self.updateUI()
  }
}

After (explicit threading):

@MainActor
class MyObserver: ConnectivityStateObserver {
  func connectivityManager(_ manager: ConnectivityManager,
                          didChangeActivationState state: ActivationState) {
    // @MainActor ensures main thread
    self.updateUI()
  }
}

Benefits

✅ Fixes intermittent watchOS test failures
✅ More flexible threading model - observers choose their execution context
✅ Better Swift 6 concurrency compliance - no forced GCD usage
✅ Faster notifications - no queue hopping overhead
✅ Cleaner code - removed weak self capture and guard unwrapping

Migration

This is acceptable as a breaking change because:

1. SundialKit v2.0.0 is already a major version bump
2. Modern Swift encourages explicit concurrency annotations
3. More flexible for non-UI use cases
4. Aligns with Swift 6 strict concurrency best practices

Testing

• ✅ Build successful: swift build
• ⏳ CI tests running - should fix watchOS observer test timeouts

Related Issues

Addresses intermittent CI failures:

• https://github.com/brightdigit/SundialKit/actions/runs/19303981481 (watchOS timeout)
• https://github.com/brightdigit/SundialKit/actions/runs/19305857262 (watchOS timeout)

Previous attempt to fix with timeout increase was insufficient - this addresses the root architectural issue.

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✨ Finishing touches

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• Create PR with unit tests
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• Commit unit tests in branch fix/remove-dispatchqueue-observer-notifications

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.33%. Comparing base (e9a9a43) to head (5c7e607).
⚠️ Report is 5 commits behind head on 48-demo-applications-part-3.

Additional details and impacted files

@@                     Coverage Diff                      @@
##           48-demo-applications-part-3      #60   +/-   ##
============================================================
  Coverage                        45.33%   45.33%           
============================================================
  Files                               30       30           
  Lines                              514      514           
============================================================
  Hits                               233      233           
  Misses                             281      281           

Flag	Coverage Δ
spm	45.33% <ø> (ø)
swift-6.1-jammy	41.07% <ø> (ø)
swift-6.1-jammy-nightly	41.07% <ø> (ø)
swift-6.1-noble	41.07% <ø> (ø)
swift-6.1-noble-nightly	41.07% <ø> (ø)
swift-6.2-jammy	41.07% <ø> (ø)
swift-6.2-jammy-nightly	41.07% <ø> (ø)
swift-6.2-noble	41.07% <ø> (ø)
swift-6.2-noble-nightly	41.07% <ø> (ø)

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[claude]

PR Review: Remove DispatchQueue from Observer Notifications

This PR removes forced DispatchQueue.main.async dispatch from 6 notification methods, transferring thread management responsibility to observers. This is a breaking change appropriate for v2.0.0 that aligns with Swift 6 concurrency best practices.

Strengths

1. Root Cause Fix

• Correctly identifies the race condition: Actor → DispatchQueue.main.async → Actor
• Direct actor-to-actor communication eliminates queue hopping overhead
• Right long-term solution vs. increasing timeouts

2. Swift 6 Concurrency Alignment

• Removes forced GCD usage in favor of structured concurrency
• Observers choose their isolation domain (@mainactor, actor, or none)
• Maintains zero @unchecked Sendable

3. Improved Architecture

• Before: All observers forced to main thread
• After: Observers control execution context
• Better separation of concerns

4. Documentation Quality

• Clear inline docs explain thread management responsibility
• Guides users to use @mainactor for UI updates

Concerns & Recommendations

1. Unstructured Task Usage in TestObserver (Medium)

TestObserver still uses unstructured Task in notification handlers (TestObserver.swift:32-34, 41-43). The PR description states this compounded timing issues, but the fix only removes DispatchQueue hop, not the unstructured Task pattern.

Recommendation: Consider making protocol methods async or using Task(priority: .high) to ensure deterministic completion for tests.

2. ObserverRegistry.notify() Fire-and-Forget (Low)

ObserverRegistry.notify() spawns unstructured Task with no await (ObserverRegistry.swift:95-98). Consider adding notifyAndWait() variant for testing scenarios where completion matters.

3. Coverage Regression (Investigate)

Coverage dropped from 85.25% to 45.13%. Appears related to dropping Swift 5.9/5.10/6.0 test jobs. Verify this is a reporting artifact.

Files Reviewed

Core Changes:

• ConnectivityObserverManaging.swift:89-145 - Removed DispatchQueue wrappers
• ConnectivityStateObserver.swift:39-41 - Updated docs

Test Changes:

• TestObserver.swift - Actor-based with Task wrappers
• ConnectivityManagerObserverTests.swift - Verifies new behavior

Recommendation

APPROVE with minor suggestions

This fixes the root cause of watchOS test failures and aligns with Swift 6 best practices.

Before merge:

1. Verify CI passes consistently (5-10 runs)
2. Consider async protocol methods or structured tasks
3. Investigate coverage regression

Great work! The shift to observer-controlled execution is the right direction for modern Swift concurrency.

[claude]

Code Review: Remove DispatchQueue from Observer Notifications

This PR removes forced DispatchQueue.main.async from observer notifications, making observers responsible for their own thread management. Well-justified architectural improvement that fixes watchOS test failures and aligns with Swift 6.

✅ Strengths

1. Clear Problem ID: Documented CI failures, root cause (actor-queue-actor race), watchOS-specific
2. Correct Direction: Swift 6 concurrency, flexibility, clarity, performance gains
3. Clean Code: Direct actor-to-actor via ObserverRegistry.notify()
4. Good Tests: TestObserver actor + waitUntil with Task.yield()
5. Documentation: All 6 methods document threading responsibility

Code Quality

• ObserverRegistry actor pattern: thread-safe, clean
• Concurrency: nonisolated methods, actor isolation, no @unchecked Sendable
• Test coverage: activation, reachability, messages, removal, multi-observer

Improvements

1. Breaking change docs: Add to CHANGELOG (v2.0.0 acceptable)
2. ObserverRegistry: Fire-and-forget Task - consider error logging (not blocker)
3. Test timeout: Document why 10s (CI simulators)
4. Platform code: Comment on iOS-only isPaired

Issues: None

No bugs, leaks, security concerns. Follows Swift concurrency correctly.

Performance

Positive: Eliminated queue hopping, reduced main thread contention
Neutral: Sequential iteration (could use TaskGroup)

Test Suggestions

• Concurrency stress test
• Observer error handling
• Performance with 10+ observers

✅ APPROVE

High quality PR: fixes watchOS timeouts, improves Swift 6 compliance, well-tested.

Before merge: CI passes all platforms, no new timeouts, CHANGELOG updated

Great work! Excellent diagnosis, clean solution, comprehensive testing.

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Reviewed: Claude Code (Sonnet 4.5) | Focus: quality, concurrency, tests, perf, security