Make platform compilation branches explicit

.github/workflows/benchmarks.yml

@@ -14,13 +14,13 @@ jobs:
   benchmarks:
     runs-on: macos-26
     env:
-      DEVELOPER_DIR: /Applications/Xcode_26.6.app/Contents/Developer
+      DEVELOPER_DIR: /Applications/Xcode_26.3.app/Contents/Developer
     steps:
       - uses: actions/checkout@v6
-      - name: Verify Swift 6.3.3
+      - name: Verify Swift 6.2.4
         run: |
           swift --version
-          swift --version | grep -Eq 'Swift version 6\.3\.3([[:space:]]|$)'
+          swift --version | grep -Eq 'Swift version 6\.2\.4([[:space:]]|$)'
       - name: Release benchmarks without instrumentation
         shell: bash
         run: |

.github/workflows/checks.yml

@@ -26,17 +26,22 @@ jobs:
         os: [macos-26, ubuntu-24.04]
         configuration: [debug, release]
         include:
+          - os: macos-26
+            swift-version: 6.2.4
           - os: ubuntu-24.04
-            container: swift:6.3.3
+            container: swift:6.2.3
+            swift-version: 6.2.3
     steps:
       - uses: actions/checkout@v6
-      - name: Select Xcode 26.6
+      - name: Select Xcode 26.3
         if: runner.os == 'macOS'
-        run: echo 'DEVELOPER_DIR=/Applications/Xcode_26.6.app/Contents/Developer' >> "$GITHUB_ENV"
-      - name: Verify Swift 6.3.3
+        run: echo 'DEVELOPER_DIR=/Applications/Xcode_26.3.app/Contents/Developer' >> "$GITHUB_ENV"
+      - name: Verify Swift ${{ matrix.swift-version }}
+        env:
+          EXPECTED_SWIFT_VERSION: ${{ matrix.swift-version }}
         run: |
           swift --version
-          swift --version | grep -Eq 'Swift version 6\.3\.3([[:space:]]|$)'
+          swift --version | grep -F "Swift version $EXPECTED_SWIFT_VERSION "
       - name: Functional tests
         run: swift test -c ${{ matrix.configuration }} --skip PerformanceTests
       - name: Coverage gate tests

AGENTS.md

@@ -1,8 +1,9 @@
 # Project guidance
 
 Enigmatic is a dependency-free SwiftPM library for Codable value trees and
-composable coding strategies. It requires Swift 6.3; CI uses 6.3.3 on macOS 26
-and Ubuntu 24.04.
+composable coding strategies. It requires Swift 6.2.3; Checks uses 6.2.4 on
+macOS 26 and 6.2.3 on Ubuntu 24.04. Release uses 6.3.3 to build the previous
+API baseline.
 
 Follow the existing two-space Swift style. Preserve typed throws, runtime
 availability guards, and visibility required by `@inlinable` code. Update the

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:6.3
+// swift-tools-version:6.2.3
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -9,25 +9,10 @@ let package = Package(
     .library(name: "Enigmatic", targets: ["Enigmatic"]),
   ],
   targets: [
-    .target(
-      name: "Enigmatic",
-      swiftSettings: SwiftSetting.allSettings
-    ),
+    .target(name: "Enigmatic"),
     .testTarget(
       name: "EnigmaticTests",
-      dependencies: ["Enigmatic"],
-      swiftSettings: SwiftSetting.allSettings
+      dependencies: ["Enigmatic"]
     ),
   ]
 )
-
-extension SwiftSetting {
-#if compiler(<6.4)
-  static let anyAppleOSAvailability: [Self] = [.enableExperimentalFeature("AnyAppleOSAvailability")]
-#else
-  static let anyAppleOSAvailability: [Self] = []
-#endif
-  static let allSettings: [Self] = [
-    anyAppleOSAvailability,
-  ].flatMap(\.self)
-}

README.md

@@ -2,7 +2,7 @@
 
 [![Checks](https://github.com/SwiftUtility/Enigmatic/actions/workflows/checks.yml/badge.svg?branch=main&event=push)](https://github.com/SwiftUtility/Enigmatic/actions/workflows/checks.yml)
 [![Release](https://img.shields.io/github/v/release/SwiftUtility/Enigmatic)](https://github.com/SwiftUtility/Enigmatic/releases/latest)
-[![Swift](https://img.shields.io/badge/Swift-6.3%2B-orange?logo=swift)](Package.swift)
+[![Swift](https://img.shields.io/badge/Swift-6.2.3%2B-orange?logo=swift)](Package.swift)
 [![SwiftPM](https://img.shields.io/badge/Swift_Package_Manager-compatible-brightgreen)](#install)
 [![License](https://img.shields.io/github/license/SwiftUtility/Enigmatic)](LICENSE)
 [![Coverage](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftutility.github.io%2FEnigmatic%2Fcoverage-badge.json)](https://github.com/SwiftUtility/Enigmatic/actions/workflows/release.yml)
@@ -34,7 +34,7 @@ Foundation's `JSONDecoder`. With that same decoder, Enigma and PotentCodables'
 
 ## Install
 
-Requires Swift 6.3 or newer. Add
+Requires Swift 6.2.3 or newer. Add
 [SwiftUtility/Enigmatic](https://github.com/SwiftUtility/Enigmatic) in Xcode and
 link the **Enigmatic** product to your target. For SwiftPM targets, use
 `.product(name: "Enigmatic", package: "Enigmatic")`.

Sources/Enigmatic/Enigmatic.docc/Development.md

@@ -7,6 +7,19 @@ swift test --skip PerformanceTests
 swift test -c release --skip PerformanceTests
 ```
 
+To check Linux compatibility with the minimum compiler version from macOS, run
+the functional suite in the official Swift Docker image. The source mount is
+read-only; build artifacts stay in the container:
+
+```sh
+docker run --rm -v "$PWD:/package:ro" -w /package swift:6.2.3 \
+  swift test --scratch-path /tmp/enigmatic-build --skip PerformanceTests
+docker run --rm -v "$PWD:/package:ro" -w /package swift:6.2.3 \
+  swift test --scratch-path /tmp/enigmatic-build -c release --skip PerformanceTests
+```
+
+Apple-specific branches still require validation on macOS with Swift 6.2.3.
+
 On Windows, use Developer PowerShell for Visual Studio with the C++ tools and
 Windows SDK installed. Start a fresh shell after installing Swift so `PATH` and
 `SDKROOT` include the toolchain and its SDK.
@@ -32,9 +45,10 @@ These are toolchain workarounds, not package settings. The native build system i
 deprecated; recheck these workarounds when updating Swift. Windows validation
 does not replace the macOS and Linux CI jobs below.
 
-The macOS and Linux CI jobs use Swift 6.3.3 from Xcode 26.6 on macOS 26 and the
-`swift:6.3.3` container on Ubuntu 24.04. Each job verifies the compiler version
-before testing.
+The Checks workflow uses Swift 6.2.4 from Xcode 26.3 on macOS 26 and the
+`swift:6.2.3` container on Ubuntu 24.04 to test the minimum supported compiler.
+Benchmarks uses the same Xcode version as Checks.
+Each job verifies the compiler version before testing.
 The macOS Debug job also checks the coverage script, enforces 95% library line
 coverage, and builds DocC. It uploads the coverage report as `coverage.json` and
 the documentation as `Enigmatic.doccarchive.tar.gz`, preserving DocC filenames
@@ -44,6 +58,10 @@ Checks also runs separate Windows x64 Debug and Release jobs on `windows-2022`
 with Swift 6.4.1, Visual Studio's C++ environment, and the workarounds above.
 These jobs do not change the macOS/Linux checks or the Release workflow.
 
+Release validation uses Swift 6.3.3 from Xcode 26.6 and the `swift:6.3.3`
+container so the API gate can build previous releases requiring Swift 6.3.
+The Linux Checks jobs validate compatibility with the minimum supported compiler.
+
 The Release workflow publishes the DocC site to GitHub Pages after all release
 validation jobs pass and before creating the GitHub release. The site is at
 <https://swiftutility.github.io/Enigmatic/documentation/enigmatic/>. Enable

Sources/Enigmatic/Enigmatic.docc/Enigmatic.md

@@ -9,8 +9,8 @@ dates and data. Encode a model into a tree, modify selected paths, merge a secon
 model, then decode the result. ``Codec`` provides reusable coding strategies that
 compose through a property wrapper.
 
-The package requires Swift 6.3. Availability annotations on individual declarations
-specify Apple runtime requirements; Linux uses the toolchain runtime.
+The package requires Swift 6.2.3. Availability annotations on individual declarations
+specify Apple runtime requirements; Linux and Windows use the toolchain runtime.
 
 ## Serialization limitations
 
@@ -26,6 +26,9 @@ for date units, and a custom string strategy for non-finite numbers. See
 
 ## Compatibility
 
+The package supports macOS, iOS, tvOS, watchOS, visionOS, Linux, and Windows.
+Other platforms produce a compile-time error instead of using a fallback implementation.
+
 The manifest leaves deployment targets at SwiftPM's defaults. Some APIs have
 higher runtime requirements:
 
@@ -34,7 +37,7 @@ higher runtime requirements:
 - `Codec.UnixDate<scale>` and `Codec.UnixIntDate<scale>`: Apple OS 26.
   Use the named seconds/milliseconds strategies on older systems.
 
-Linux uses the toolchain runtime without Apple OS availability limits.
+Linux and Windows use the toolchain runtime without Apple OS availability limits.
 
 ## Topics
 

Sources/Enigmatic/Internal/Primitives/EnigmaConvertibleObject.swift

@@ -45,8 +45,10 @@ extension NSValue: EnigmaConvertibleObject {
   func extract<T: FixedWidthInteger>(seed: consuming T) -> T {
 #if os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
     withUnsafeMutablePointer(to: &seed) { getValue($0, size: MemoryLayout<T>.size) }
-#else
+#elseif os(Linux) || os(Windows)
     withUnsafeMutablePointer(to: &seed) { getValue($0) }
+#else
+#error("Unsupported platform: Enigmatic supports Apple platforms, Linux, and Windows.")
 #endif
     return consume seed
   }

Sources/Enigmatic/Public/Codec/Strategies/Codec+PathURL.swift

@@ -23,10 +23,12 @@ extension Codec {
       } else {
         return URL(fileURLWithPath: value, isDirectory: value.hasSuffix("/"))
       }
+#elseif os(Linux)
+      return URL(fileURLWithPath: value, isDirectory: value.hasSuffix("/"))
 #elseif os(Windows)
       return URL(fileURLWithPath: value, isDirectory: value.hasSuffix("/") || value.hasSuffix("\\"))
 #else
-      return URL(fileURLWithPath: value, isDirectory: value.hasSuffix("/"))
+#error("Unsupported platform: Enigmatic supports Apple platforms, Linux, and Windows.")
 #endif
     }
 
@@ -35,16 +37,20 @@ extension Codec {
     /// - Complexity: O(n) in the URL or path string length.
     @inlinable
     public static func encode(value: BoxedValue, encoder: some Encoder) throws {
-#if os(Windows)
-      var path = value.path
-      if value.hasDirectoryPath && !path.hasSuffix("/") { path += "/" }
-      try path.encode(to: encoder)
-#else
+#if os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
       if #available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *) {
         try value.path(percentEncoded: false).encode(to: encoder)
       } else {
         try value.path.encode(to: encoder)
       }
+#elseif os(Linux)
+      try value.path(percentEncoded: false).encode(to: encoder)
+#elseif os(Windows)
+      var path = value.path
+      if value.hasDirectoryPath && !path.hasSuffix("/") { path += "/" }
+      try path.encode(to: encoder)
+#else
+#error("Unsupported platform: Enigmatic supports Apple platforms, Linux, and Windows.")
 #endif
     }
 

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixDate.swift

@@ -4,7 +4,11 @@ extension Codec {
   /// Encodes seconds since 1970 multiplied by 10 to the given scale as Double.
   ///
   /// Rejects non-finite values, invalid scale factors and unrepresentable results.
+#if compiler(<6.4)
+  @available(macOS 26, iOS 26, tvOS 26, watchOS 26, visionOS 26, *)
+#else
   @available(anyAppleOS 26, *)
+#endif
   public enum UnixDate<let scale: Int>: Hashable, DecodeStrategy, EncodeStrategy {
     /// Decodes scaled seconds since 1970 into a `Date`.
     /// - Throws: `DecodingError.dataCorrupted` for non-finite input or an invalid scale.

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixIntDate.swift

@@ -4,7 +4,11 @@ extension Codec {
   /// Encodes seconds since 1970 multiplied by 10 to the given scale as Int, truncating toward zero.
   ///
   /// Rejects non-finite values, invalid scale factors and unrepresentable results.
+#if compiler(<6.4)
+  @available(macOS 26, iOS 26, tvOS 26, watchOS 26, visionOS 26, *)
+#else
   @available(anyAppleOS 26, *)
+#endif
   public enum UnixIntDate<let scale: Int>: Hashable, DecodeStrategy, EncodeStrategy, Error {
     /// Decodes an integer scaled timestamp into a date.
     /// - Throws: `DecodingError.dataCorrupted` when the scale is invalid or the result is non-finite.

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixIntMillisecondsDate.swift

@@ -3,7 +3,15 @@ import Foundation
 extension Codec {
   /// Encodes milliseconds since 1970 as a truncated integer.
   /// Prefer `UnixIntDate<3>` when the deployment target supports it.
+#if compiler(<6.4)
+  @available(macOS, deprecated: 26.0)
+  @available(iOS, deprecated: 26.0)
+  @available(tvOS, deprecated: 26.0)
+  @available(watchOS, deprecated: 26.0)
+  @available(visionOS, deprecated: 26.0)
+#else
   @available(anyAppleOS, deprecated: 26.0)
+#endif
   public enum UnixIntMillisecondsDate: Hashable, DecodeStrategy, EncodeStrategy {
     /// Decodes integer milliseconds since 1970 into a date.
     /// - Complexity: O(1); the operation performs a fixed number of numeric conversions and arithmetic operations.

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixIntSecondsDate.swift

@@ -3,7 +3,15 @@ import Foundation
 extension Codec {
   /// Encodes seconds since 1970 as a truncated integer.
   /// Prefer `UnixIntDate<0>` when the deployment target supports it.
+#if compiler(<6.4)
+  @available(macOS, deprecated: 26.0)
+  @available(iOS, deprecated: 26.0)
+  @available(tvOS, deprecated: 26.0)
+  @available(watchOS, deprecated: 26.0)
+  @available(visionOS, deprecated: 26.0)
+#else
   @available(anyAppleOS, deprecated: 26.0)
+#endif
   public enum UnixIntSecondsDate: Hashable, DecodeStrategy, EncodeStrategy, Error {
     /// Decodes integer seconds since 1970 into a date.
     /// - Complexity: O(1); the operation performs a fixed number of numeric conversions and arithmetic operations.

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixMillisecondsDate.swift

@@ -3,7 +3,15 @@ import Foundation
 extension Codec {
   /// Encodes seconds since 1970 multiplied by 1,000 as a floating-point value.
   /// Prefer `UnixDate<3>` when the deployment target supports it.
+#if compiler(<6.4)
+  @available(macOS, deprecated: 26.0)
+  @available(iOS, deprecated: 26.0)
+  @available(tvOS, deprecated: 26.0)
+  @available(watchOS, deprecated: 26.0)
+  @available(visionOS, deprecated: 26.0)
+#else
   @available(anyAppleOS, deprecated: 26.0)
+#endif
   public enum UnixMillisecondsDate: Hashable, DecodeStrategy, EncodeStrategy, Error {
     /// Decodes finite milliseconds since 1970 into a date.
     /// - Throws: `DecodingError.dataCorrupted` for non-finite input.

Sources/Enigmatic/Public/Codec/Strategies/Codec+UnixSecondsDate.swift

@@ -3,7 +3,15 @@ import Foundation
 extension Codec {
   /// Encodes seconds since 1970 as a floating-point value.
   /// Prefer `UnixDate<0>` when the deployment target supports it.
+#if compiler(<6.4)
+  @available(macOS, deprecated: 26.0)
+  @available(iOS, deprecated: 26.0)
+  @available(tvOS, deprecated: 26.0)
+  @available(watchOS, deprecated: 26.0)
+  @available(visionOS, deprecated: 26.0)
+#else
   @available(anyAppleOS, deprecated: 26.0)
+#endif
   public enum UnixSecondsDate: Hashable, DecodeStrategy, EncodeStrategy, Error {
     /// Decodes finite seconds since 1970 into a date.
     /// - Throws: `DecodingError.dataCorrupted` for non-finite input.

Tests/EnigmaticTests/CodableTests.swift

@@ -107,11 +107,13 @@ final class CodableTests: XCTestCase {
   func testAnyHashable() throws {
     let key1 = "café"
     let key2 = "cafe\u{301}"
-    #if os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
+#if os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
     XCTAssertNotEqual(key1 as NSString, key2 as NSString)
-    #else
+#elseif os(Linux) || os(Windows)
     XCTAssertEqual(key1 as NSString, key2 as NSString)
-    #endif
+#else
+#error("Unsupported platform: Enigmatic supports Apple platforms, Linux, and Windows.")
+#endif
     XCTAssertEqual(key1, key2)
     let enigma1 = try Enigma(cast: [key1: 1])
     let enigma2 = try Enigma(cast: [key2: 1])
@@ -174,7 +176,11 @@ final class CodableTests: XCTestCase {
     XCTAssertEqual(direct, indirect)
   }
 
+#if compiler(<6.4)
+  @available(macOS 26, iOS 26, tvOS 26, watchOS 26, visionOS 26, *)
+#else
   @available(anyAppleOS 26, *)
+#endif
   func testUnixTime() throws {
     struct CodecDates: Codable, Equatable {
       @Codec.Box<Codec.UnixDate<0>>

Tests/EnigmaticTests/SerializationContractTests.swift

@@ -388,10 +388,10 @@ final class SerializationContractTests: XCTestCase {
         withUnsafeBytes(of: value) { bytes in
 #if os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS)
           NSValue(bytes: bytes.baseAddress!, objCType: type)
-#else
-          // Corelibs Foundation cannot construct NSValue with t/T encodings.
-          // Supply the same encoding and bytes through NSValue's primitive API.
+#elseif os(Linux) || os(Windows)
           BitInt128Value(bytes: bytes.baseAddress!, objCType: type)
+#else
+#error("Unsupported platform: Enigmatic supports Apple platforms, Linux, and Windows.")
 #endif
         }
       }
@@ -589,7 +589,9 @@ final class SerializationContractTests: XCTestCase {
   }
 }
 
-#if !(os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS))
+#if os(Linux) || os(Windows)
+// Corelibs Foundation cannot construct NSValue with t/T encodings.
+// Expose the encoding and bytes through NSValue's primitive API instead.
 private final class BitInt128Value: NSValue, @unchecked Sendable {
   private let storage: Data
   private let encoding: UnsafeMutablePointer<CChar>

Tests/EnigmaticTests/StrategyContractTests.swift

@@ -741,7 +741,11 @@ final class StrategyContractTests: XCTestCase {
     }
   }
 
+#if compiler(<6.4)
+  @available(macOS 26, iOS 26, tvOS 26, watchOS 26, visionOS 26, *)
+#else
   @available(anyAppleOS 26, *)
+#endif
   func testScaledDatesAndTruncation() throws {
     let date = Date(timeIntervalSince1970: -123.25)
     try roundTrip(Codec.UnixDate<0>.self, date, expected: .double(-123.25))

Tests/EnigmaticTests/Utility/ObjectiveC.swift

@@ -1,4 +1,4 @@
-#if !(os(anyAppleOS) || os(macOS) || os(iOS) || os(tvOS) || os(watchOS) || os(visionOS))
+#if os(Linux) || os(Windows)
 @inline(__always)
 func autoreleasepool<T>(_ body: () throws -> T) rethrows -> T {
   return try body()