feat: AspectRatioOverride enum — Phase 2 of Screen Scaling standardization

- Add AspectRatioOverride enum to PVPrimitives (auto/4:3/16:9/1:1/8:7/stretch)
  with displayName, subtitle, symbolName, aspectRatioValue, and isWidescreen metadata
- Extend CoreOptional protocol with supportedAspectRatioOverrides and
  preferredAspectRatioOverride; default impls return .auto (no-op for all existing cores)
- Enable scalingModeRenderer feature flag by default (was: disabled, gated behind flag)
- Add AspectRatioOverrideTests covering raw values, CaseIterable, Codable, and display metadata
- Update reviewer-context.md with ScalingMode + AspectRatioOverride review rules

Part of #2673

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: github-actions[bot]

.changelog/3619.md

@@ -0,0 +1,6 @@
+### Added
+- **AspectRatioOverride enum** — New `AspectRatioOverride` enum in `PVPrimitives` defines per-core aspect ratio overrides (Auto, 4:3, 16:9, 1:1, 8:7, Stretch) with display metadata and aspect ratio values.
+- **CoreOptional aspect ratio protocol** — `CoreOptional` now declares `supportedAspectRatioOverrides` and `preferredAspectRatioOverride` static properties; default implementations return `.auto` so all existing cores are unaffected.
+
+### Changed
+- **ScalingMode renderer enabled by default** — The `scalingModeRenderer` feature flag is now enabled by default; the new `ScalingMode`-driven renderer paths (Stretch, Aspect Fill, Integer Scale, Native Resolution) are active for all users. Legacy boolean shims remain for backwards compatibility.

.github/prompts/reviewer-context.md

@@ -418,6 +418,16 @@ will fail Linux CI — flag as 🟡 MINOR if in a Tier 0–2 module, ⚪ NIT oth
 - **Flag 🟠 MAJOR** if new DSU code modifies `listener`/`browser` state outside the `self.queue` serial queue in the Discovery classes.
 - **Flag 🟠 MAJOR** if `DSUSocket.startListening()` is inlined into `init` — the two-step design is load-bearing.
 
+### Screen Scaling — ScalingMode + AspectRatioOverride (Phase 1 #3616 / Phase 2 #3617)
+- `ScalingMode` enum is in `PVSettings/Sources/PVSettings/Settings/Model/ScalingMode.swift` — replaces the legacy `nativeScaleEnabled` / `integerScaleEnabled` boolean pair. The old booleans are `@available(*, deprecated)` shims.
+- `AspectRatioOverride` enum is in `PVPrimitives/Sources/PVPrimitives/System/AspectRatioOverride.swift` — per-core display geometry override. Default `.auto` means no override.
+- `CoreOptional.supportedAspectRatioOverrides` — static var declaring which `AspectRatioOverride` cases the core supports. Default: `[.auto]`.
+- `CoreOptional.preferredAspectRatioOverride` — static var returning the currently selected override. Default: `.auto`.
+- The `scalingModeRenderer` feature flag in `PVFeatureFlags` is **enabled by default** as of Phase 2. The renderer uses `ScalingMode` for layout; **do not** re-introduce the old boolean code paths.
+- **Flag 🔴 CRITICAL** if new code compares against `nativeScaleEnabled`/`integerScaleEnabled` directly instead of reading `scalingMode`.
+- **Flag 🟠 MAJOR** if a new core overrides `preferredAspectRatioOverride` without also declaring the case in `supportedAspectRatioOverrides`.
+- **Flag 🟡 MINOR** if a core's `supportedAspectRatioOverrides` includes `.ratio_16_9` but no widescreen option key is wired in the core options.
+
 ## GitHub Workflow Awareness
 
 Reviewers should be aware of — but NOT flag as code issues — the following:

PVCoreBridge/Sources/PVCoreBridge/CoreOptions/Protocols/CoreOptional.swift

@@ -7,6 +7,7 @@
 //
 
 import Foundation
+import PVPrimitives
 
 
 public protocol CoreOptional {//where Self: EmulatorCoreIOInterface {
@@ -20,6 +21,24 @@ public protocol CoreOptional {//where Self: EmulatorCoreIOInterface {
     /// Set this when a game is loaded and clear it on unload.
     static var currentGameMD5: String? { get }
 
+    /// The set of aspect ratio overrides this core supports.
+    ///
+    /// Cores that support widescreen hacks, aspect ratio selection, or other
+    /// display geometry modifications should return the relevant cases here.
+    /// The UI uses this list to show only the options the core actually supports.
+    ///
+    /// The default implementation returns `[.auto]` (no overrides available).
+    static var supportedAspectRatioOverrides: [AspectRatioOverride] { get }
+
+    /// The aspect ratio override currently selected for this core.
+    ///
+    /// The renderer reads this property when compositing the frame. Returning
+    /// `.auto` (the default) means the core's native reported aspect ratio is used.
+    ///
+    /// Cores that store this preference in their own `CoreOption` key should
+    /// override this property to read from `UserDefaults` via `string(forOption:)`.
+    static var preferredAspectRatioOverride: AspectRatioOverride { get }
+
 //    static func bool(forOption option: String) -> Bool
 //    static func int(forOption option: String) -> Int
 //    static func float(forOption option: String) -> Float
@@ -40,6 +59,12 @@ public extension CoreOptional {
     /// Default implementation: no per-game MD5 override.
     static var currentGameMD5: String? { nil }
 
+    /// Default: only `.auto` is available (no override supported).
+    static var supportedAspectRatioOverrides: [AspectRatioOverride] { [.auto] }
+
+    /// Default: use the core's natural aspect ratio.
+    static var preferredAspectRatioOverride: AspectRatioOverride { .auto }
+
     /// Reset a specific set of options to their default values
     /// - Parameter options: The options to reset
     static func resetOptions(_ options: [CoreOption]) {

PVFeatureFlags/Sources/PVFeatureFlags/PVFeatureFlags.swift

@@ -305,8 +305,8 @@ public struct FeatureFlag: Codable, Sendable {
     )
 
     public static let scalingModeRenderer = FeatureFlag(
-        enabled: false,
-        description: "Activates the ScalingMode-enum renderer paths (Stretch, Aspect Fill, Integer Scale, Native Resolution). When disabled the legacy nativeScaleEnabled/integerScaleEnabled boolean code paths are used — existing scaling is unchanged. Enable in Settings > Advanced > Feature Flags to test new modes (Phase 2 of screen-scaling standardisation)."
+        enabled: true,
+        description: "Activates the ScalingMode-enum renderer paths (Stretch, Aspect Fill, Integer Scale, Native Resolution). Enabled by default as of Phase 2. The legacy nativeScaleEnabled/integerScaleEnabled boolean shims remain for backwards compatibility."
     )
 }
 

PVPrimitives/Sources/PVPrimitives/System/AspectRatioOverride.swift

@@ -0,0 +1,113 @@
+//
+//  AspectRatioOverride.swift
+//  PVPrimitives
+//
+//  Created by Provenance Emu on 2026-04-03.
+//  Copyright © 2026 Provenance Emu. All rights reserved.
+//
+
+import Foundation
+
+/// A per-core aspect ratio override that can be applied on top of the global `ScalingMode`.
+///
+/// Each emulator core may support a subset of these overrides depending on the capabilities
+/// of the underlying emulator. Cores declare which overrides they support via the
+/// `CoreOptional.supportedAspectRatioOverrides` property.
+///
+/// When a core returns a non-`.auto` value from `CoreOptional.preferredAspectRatioOverride`,
+/// the renderer applies that override instead of (or in combination with) the global
+/// `ScalingMode` setting.
+///
+/// ## Override vs ScalingMode
+/// | `ScalingMode` | `AspectRatioOverride` | Result |
+/// |---|---|---|
+/// | `.aspectFit` | `.ratio_16_9` | Widescreen content letterboxed to fit |
+/// | `.aspectFill` | `.ratio_4_3` | 4:3 content zoomed to fill screen |
+/// | `.stretch` | `.auto` | Core's native ratio stretched to fill |
+/// | Any | `.ratio_1_1` | Square-pixel / pixel-perfect mapping |
+public enum AspectRatioOverride: String, Codable, Equatable, Hashable,
+    CaseIterable, Sendable, CustomStringConvertible {
+
+    /// Let the core report its natural aspect ratio — no override applied.
+    /// This is the default for all cores.
+    case auto = "auto"
+
+    /// Force a 4:3 display ratio (classic TV / arcade).
+    case ratio_4_3 = "4:3"
+
+    /// Force a 16:9 widescreen display ratio.
+    case ratio_16_9 = "16:9"
+
+    /// Force a 1:1 square-pixel ratio (equal horizontal and vertical scaling).
+    case ratio_1_1 = "1:1"
+
+    /// Force a 8:7 ratio used by the SNES / Super Famicom (non-square pixels).
+    case ratio_8_7 = "8:7"
+
+    /// Stretch to fill the display, ignoring all aspect ratio constraints.
+    /// Equivalent to `ScalingMode.stretch` but applied at the per-core level.
+    case stretch = "stretch"
+
+    // MARK: - Display Metadata
+
+    public var displayName: String {
+        switch self {
+        case .auto:       return "Auto"
+        case .ratio_4_3:  return "4:3"
+        case .ratio_16_9: return "16:9"
+        case .ratio_1_1:  return "1:1"
+        case .ratio_8_7:  return "8:7"
+        case .stretch:    return "Stretch"
+        }
+    }
+
+    public var subtitle: String {
+        switch self {
+        case .auto:
+            return "Use the aspect ratio reported by the core"
+        case .ratio_4_3:
+            return "Classic TV / arcade (4 wide, 3 tall)"
+        case .ratio_16_9:
+            return "Widescreen — enables widescreen hack if supported"
+        case .ratio_1_1:
+            return "Square pixels — 1:1 horizontal/vertical mapping"
+        case .ratio_8_7:
+            return "SNES native — non-square pixel correction"
+        case .stretch:
+            return "Stretch to fill — ignores aspect ratio"
+        }
+    }
+
+    public var symbolName: String {
+        switch self {
+        case .auto:       return "aspectratio"
+        case .ratio_4_3:  return "tv"
+        case .ratio_16_9: return "tv.fill"
+        case .ratio_1_1:  return "square"
+        case .ratio_8_7:  return "rectangle"
+        case .stretch:    return "arrow.left.and.right.righttriangle.left.righttriangle.right"
+        }
+    }
+
+    /// The floating-point aspect ratio value, or `nil` for `.auto` and `.stretch`.
+    public var aspectRatioValue: Float? {
+        switch self {
+        case .auto:       return nil
+        case .ratio_4_3:  return 4.0 / 3.0
+        case .ratio_16_9: return 16.0 / 9.0
+        case .ratio_1_1:  return 1.0
+        case .ratio_8_7:  return 8.0 / 7.0
+        case .stretch:    return nil
+        }
+    }
+
+    /// Whether this override requests widescreen rendering (16:9 or wider).
+    public var isWidescreen: Bool {
+        switch self {
+        case .ratio_16_9: return true
+        default: return false
+        }
+    }
+
+    public var description: String { displayName }
+}

PVPrimitives/Tests/PVPrimitivesTests/AspectRatioOverrideTests.swift

@@ -0,0 +1,116 @@
+// AspectRatioOverrideTests.swift
+// PVPrimitivesTests
+//
+// Created by Provenance Emu on 2026-04-03.
+// Copyright © 2026 Provenance Emu. All rights reserved.
+//
+
+import XCTest
+@testable import PVPrimitives
+
+final class AspectRatioOverrideTests: XCTestCase {
+
+    // MARK: - Raw values
+
+    func testAutoRawValue() {
+        XCTAssertEqual(AspectRatioOverride.auto.rawValue, "auto")
+    }
+
+    func testRatio4_3RawValue() {
+        XCTAssertEqual(AspectRatioOverride.ratio_4_3.rawValue, "4:3")
+    }
+
+    func testRatio16_9RawValue() {
+        XCTAssertEqual(AspectRatioOverride.ratio_16_9.rawValue, "16:9")
+    }
+
+    func testRatio1_1RawValue() {
+        XCTAssertEqual(AspectRatioOverride.ratio_1_1.rawValue, "1:1")
+    }
+
+    func testRatio8_7RawValue() {
+        XCTAssertEqual(AspectRatioOverride.ratio_8_7.rawValue, "8:7")
+    }
+
+    func testStretchRawValue() {
+        XCTAssertEqual(AspectRatioOverride.stretch.rawValue, "stretch")
+    }
+
+    // MARK: - CaseIterable
+
+    func testAllCasesCount() {
+        XCTAssertEqual(AspectRatioOverride.allCases.count, 6)
+    }
+
+    func testAllCasesContainsAuto() {
+        XCTAssertTrue(AspectRatioOverride.allCases.contains(.auto))
+    }
+
+    // MARK: - aspectRatioValue
+
+    func testAutoAspectRatioValueIsNil() {
+        XCTAssertNil(AspectRatioOverride.auto.aspectRatioValue)
+    }
+
+    func testStretchAspectRatioValueIsNil() {
+        XCTAssertNil(AspectRatioOverride.stretch.aspectRatioValue)
+    }
+
+    func testRatio4_3Value() {
+        XCTAssertEqual(AspectRatioOverride.ratio_4_3.aspectRatioValue, 4.0 / 3.0, accuracy: 0.0001)
+    }
+
+    func testRatio16_9Value() {
+        XCTAssertEqual(AspectRatioOverride.ratio_16_9.aspectRatioValue, 16.0 / 9.0, accuracy: 0.0001)
+    }
+
+    func testRatio1_1Value() {
+        XCTAssertEqual(AspectRatioOverride.ratio_1_1.aspectRatioValue, 1.0, accuracy: 0.0001)
+    }
+
+    func testRatio8_7Value() {
+        XCTAssertEqual(AspectRatioOverride.ratio_8_7.aspectRatioValue, 8.0 / 7.0, accuracy: 0.0001)
+    }
+
+    // MARK: - isWidescreen
+
+    func testOnly16_9IsWidescreen() {
+        for override in AspectRatioOverride.allCases {
+            if override == .ratio_16_9 {
+                XCTAssertTrue(override.isWidescreen, "\(override) should be widescreen")
+            } else {
+                XCTAssertFalse(override.isWidescreen, "\(override) should not be widescreen")
+            }
+        }
+    }
+
+    // MARK: - Codable round-trip
+
+    func testCodableRoundTrip() throws {
+        let encoder = JSONEncoder()
+        let decoder = JSONDecoder()
+        for override in AspectRatioOverride.allCases {
+            let data = try encoder.encode(override)
+            let decoded = try decoder.decode(AspectRatioOverride.self, from: data)
+            XCTAssertEqual(decoded, override, "Codable round-trip failed for \(override)")
+        }
+    }
+
+    // MARK: - displayName
+
+    func testAutoDisplayName() {
+        XCTAssertEqual(AspectRatioOverride.auto.displayName, "Auto")
+    }
+
+    func testStretchDisplayName() {
+        XCTAssertEqual(AspectRatioOverride.stretch.displayName, "Stretch")
+    }
+
+    // MARK: - description
+
+    func testDescriptionMatchesDisplayName() {
+        for override in AspectRatioOverride.allCases {
+            XCTAssertEqual(override.description, override.displayName)
+        }
+    }
+}