FORGE-1549-Fixes for Swift 6.3

[Bryan Malumphy (bmalumphy)]

Fix Swift 6.3 strict concurrency errors in Concurrency.swift

Problem

Under Xcode 26.4 / Swift 6.3 with strict concurrency checking enabled, the asyncMap Publisher extension produced two errors:

1. "Sending Main actor-isolated value to nonisolated callee risks causing data races" — asyncMap was marked @MainActor, making value (of type Output) main-actor-isolated. Future's attemptToFulfill closure is a plain escaping, nonisolated closure, so Swift 6.3 flagged the capture of value as an unsafe send across actor boundaries.

2. "Passing closure as a 'sending' parameter risks causing data races" — After removing @MainActor, Future.Promise ((Result<T, Failure>) -> Void) is not Sendable. Swift 6.3's Task initializer requires a sending closure, so capturing promise inside Task { } was rejected.

Solution

• Removed @MainActor from both asyncMap overloads. The functions only build a Combine chain and have no reason to be main-actor-isolated.
• Added where Output: Sendable on the extension. Values crossing task boundaries must be Sendable — this is the correct Swift 6 constraint.
• Added @Sendable and T: Sendable to the transform closures, required because they escape into Task.
• Introduced SendableBox<T>: @unchecked Sendable — a minimal wrapper that allows Future.Promise (a non-Sendable closure) to be captured by Task's sending closure. This is safe because each box is created once per Future, the promise is called exactly once from a single task, and there is no concurrent mutation.

Files Changed

• sdks/swift/Sources/DittoChatCore/Utilities/Concurrency.swift

[github-actions]

🟢 Test Coverage Report - @dittolive/ditto-chat-core

Overall Coverage: 87.93%

Metric	Coverage	Status
🟢 Lines	86.6%	green
🟢 Statements	86.6%	green
🟢 Functions	92.45%	green
🟢 Branches	86.08%	green

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📊 View Detailed Coverage Report

ℹ️ Coverage Thresholds

• 🟢 Excellent (≥ 80%)
• 🟡 Good (60-79%)
• 🟠 Fair (40-59%)
• 🔴 Poor (< 40%)

[github-actions]

🟢 Test Coverage Report - @dittolive/ditto-chat-ui

Overall Coverage: 89.67%

Metric	Coverage	Status
🟢 Lines	91.94%	green
🟢 Statements	91.94%	green
🟢 Functions	86.11%	green
🟢 Branches	88.67%	green

---

📊 View Detailed Coverage Report

ℹ️ Coverage Thresholds

• 🟢 Excellent (≥ 80%)
• 🟡 Good (60-79%)
• 🟠 Fair (40-59%)
• 🔴 Poor (< 40%)