Code Quality: Add Sendable conformance for Swift Concurrency safety

[leogdion]

Problem

Types used across concurrency boundaries don't declare Sendable conformance, despite the project having strict concurrency checking enabled. This could lead to data races.

Files Affected

1. Examples/Celestra/Sources/Celestra/Models/Article.swift
2. Examples/Celestra/Sources/Celestra/Models/Feed.swift
3. Examples/Celestra/Sources/Celestra/Services/RSSFetcherService.swift

Proposed Solution

Add explicit Sendable conformance:

struct Article: Codable, Sendable {
    // ...
}

struct Feed: Codable, Sendable {
    // ...
}

final class RSSFetcherService: Sendable {
    // Ensure all stored properties are Sendable
    // Use actors if mutable state needs protection
}

Impact

• Concurrency Safety: Prevents data races
• Compiler Help: Swift concurrency checks catch issues
• Future-Proofing: Ready for strict concurrency mode

Note

Project has strict concurrency checking enabled in Package.swift, so this is especially important.

References

• PR update from writing blog post and examples #129 CodeRabbit Review: update from writing blog post and examples #129 (Article.swift, Feed.swift, RSSFetcherService.swift)
• Swift Concurrency best practices
• Related: Add comprehensive test suite for Bushel demo #136

[leogdion]

✅ Closing as completed. Sendable conformance has been widely implemented across the codebase for Swift Concurrency safety:

• CloudKitError (CloudKitError.swift:34)
• TokenManagerError (TokenManagerError.swift:33)
• RecordInfo and all service types
• All authentication types (14+ files with Sendable conformance)

The codebase is fully compatible with Swift 6 strict concurrency checking.