fix(broadcast): build on non-Apple platforms; require Swift 6.0

Boutique (Bodega/SQLite/swift-collections) imports CryptoKit, which is
unavailable off Apple platforms. Gate its target dependency to Apple via
`.when(platforms:)` so SwiftPM never compiles it on Linux, and wrap
`MultiSessionLogger` + its test in `#if canImport(Boutique)`. `Log.default`
drops the OSLog-only `ConsoleLogger` where OSLog is absent.

Bump swift-tools to 6.0 (with swiftLanguageModes [.v5]): the library uses
`Synchronization.Mutex` and `Foundation.FormatStyle`, both of which only exist
in the Swift 6.0 toolchain on Linux. The iOS 18 / macOS 15 floor already
requires Swift 6 on Apple, so 5.10 toolchains now get a clean tools-version
error instead of failing deep in the FormatStyle layer.

Verified: `swift build` is green on Linux (swift:6.3) and macOS (6.3.2);
5.10 fails fast with a clear "requires Swift tools 6.0" message.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: leogdion

Package.swift

@@ -1,8 +1,19 @@
-// swift-tools-version:5.10
+// swift-tools-version:6.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
 
+// Broadcast requires Swift 6.0+: it uses `Synchronization.Mutex` and, on non-Apple platforms,
+// `Foundation.FormatStyle` — both of which only exist in the Swift 6.0 toolchain on Linux.
+//
+// Boutique (and its Bodega/SQLite/swift-collections chain) imports `CryptoKit`, which is
+// unavailable on non-Apple platforms, so its *target* dependency is gated to Apple platforms
+// with `.when(platforms:)`. On Linux SwiftPM still resolves Boutique but never compiles it,
+// and `MultiSessionLogger` (guarded by `#if canImport(Boutique)`) compiles to nothing.
+// `ConsoleLogger` is likewise gated on `#if canImport(OSLog)`.
+//
+// `swiftLanguageModes: [.v5]` keeps Swift 5 language mode so existing `static var` globals do
+// not become hard concurrency errors under Swift 6 mode.
 let package = Package(
 	name: "Broadcast",
 	platforms: [
@@ -23,15 +34,24 @@ let package = Package(
 		.target(
 			name: "Broadcast",
 			dependencies: [
-				.product(name: "Boutique", package: "Boutique")
+				.product(
+					name: "Boutique",
+					package: "Boutique",
+					condition: .when(platforms: [.iOS, .macOS, .tvOS, .watchOS, .visionOS])
+				)
 			]
 		),
 		.testTarget(
 			name: "BroadcastTests",
 			dependencies: [
-				.product(name: "Boutique", package: "Boutique"),
-				"Broadcast"
+				"Broadcast",
+				.product(
+					name: "Boutique",
+					package: "Boutique",
+					condition: .when(platforms: [.iOS, .macOS, .tvOS, .watchOS, .visionOS])
+				)
 			]
 		)
-	]
+	],
+	swiftLanguageModes: [.v5]
 )

Sources/Broadcast/Log/Log.swift

@@ -88,22 +88,30 @@ public extension Log {
 	/// lifetime control, deterministic tests, or multiple independently exported buffers.
 	static let sessionLogger = SessionLogger()
 
+	#if canImport(OSLog)
 	/// Broadcast's shared console destination.
 	///
 	/// Prefer creating your own ``ConsoleLogger`` with your app's subsystem and category
 	/// for production integrations.
 	static let consoleLogger = ConsoleLogger(subsystem: "com.mergesort.broadcast", category: "logs")
+	#endif
 
 	/// A convenience log that writes to Broadcast's default console and session destinations.
 	///
 	/// This is useful for quick integration or examples. Apps that need support-log
 	/// export, privacy-specific routing, or dependency injection should construct
 	/// their own ``Log``.
+	///
+	/// ``ConsoleLogger`` is only included on Apple platforms where OSLog is available;
+	/// elsewhere the default log writes to the ``SessionLogger`` alone.
 	static let `default` = Log(
-		destinations: [
-			Log.consoleLogger,
-			Log.sessionLogger
-		]
+		destinations: {
+			#if canImport(OSLog)
+			return [Log.consoleLogger, Log.sessionLogger]
+			#else
+			return [Log.sessionLogger]
+			#endif
+		}()
 	)
 }
 

Sources/Broadcast/Loggers/MultiSessionLogger.swift

@@ -1,3 +1,4 @@
+#if canImport(Boutique)
 import Boutique
 import Foundation
 import Synchronization
@@ -137,3 +138,5 @@ private final class MultiSessionLogStorage {
 		try? await self.$records.removeAll()
 	}
 }
+
+#endif

Tests/BroadcastTests/MultiSessionLogger.Tests.swift

@@ -1,3 +1,4 @@
+#if canImport(Boutique)
 import Boutique
 @testable import Broadcast
 import Foundation
@@ -183,3 +184,5 @@ private final class SequentialDateProvider: Sendable {
 		}
 	}
 }
+
+#endif