fix(runtime): harden application service boundaries

ios/Runner/MpvPlayer/MpvPlayerCore.swift

@@ -12,7 +12,6 @@ class MpvPlayerCore: MpvPlayerCoreBase {
   private weak var window: UIWindow?
   private var mainBlankView: UIView?
   private var isVisible = false
-  private var isDisposed = false
   private static var activeDisplayCriteriaKey: String?
   private var lastDisplayCriteriaMutation: DisplayCriteriaMutation = .skipped
   #if os(tvOS)
@@ -777,11 +776,7 @@ class MpvPlayerCore: MpvPlayerCoreBase {
   #endif
 
   func dispose(preserveDisplayCriteria: Bool = false) {
-    // Guard double-dispose: the plugin calls dispose() then drops the
-    // strong ref, which fires deinit → dispose() again. The second call
-    // would re-enter and crash on weak-ref formation during dealloc.
-    guard !isDisposed else { return }
-    isDisposed = true
+    guard beginDisposal() else { return }
 
     #if os(tvOS)
       if preserveDisplayCriteria {
@@ -867,7 +862,7 @@ class MpvPlayerCore: MpvPlayerCoreBase {
   }
 
   @objc private func enterBackground() {
-    isBackgrounded = true
+    setBackgrounded(true)
     if isPipActive || isPipStarting {
       print("[MpvPlayerCore] Entering background - PiP active/starting, keeping video")
       return
@@ -878,7 +873,7 @@ class MpvPlayerCore: MpvPlayerCoreBase {
   }
 
   @objc private func enterForeground() {
-    isBackgrounded = false
+    setBackgrounded(false)
     if isPipActive {
       print("[MpvPlayerCore] Entering foreground - PiP active, skipping vid restore")
       return
@@ -890,7 +885,7 @@ class MpvPlayerCore: MpvPlayerCoreBase {
 
   #if os(iOS)
     @objc private func sceneDidActivate() {
-      isBackgrounded = false
+      setBackgrounded(false)
       if isPipActive {
         return
       }

ios/Runner/MpvPlayer/MpvPlayerPlugin.swift

@@ -239,7 +239,8 @@ class MpvPlayerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler, MpvPluginS
     isManualPipRequest = false
     stopPipTimebaseSync()
     if pause {
-      playerCore?.setPropertyAsync("pause", value: "yes") { [weak self] _ in
+      playerCore?.setPropertyAsync("pause", value: "yes") { [weak self] propertyResult in
+        guard case .success = propertyResult else { return }
         self?.pipController?.invalidatePlaybackState()
         self?.syncPipTimebase()
       }
@@ -485,7 +486,8 @@ extension MpvPlayerPlugin: MpvPipDelegate {
   }
 
   func pipSetPlaying(_ playing: Bool) {
-    playerCore?.setPropertyAsync("pause", value: playing ? "no" : "yes") { [weak self] _ in
+    playerCore?.setPropertyAsync("pause", value: playing ? "no" : "yes") { [weak self] propertyResult in
+      guard case .success = propertyResult else { return }
       self?.pipController?.invalidatePlaybackState()
       self?.syncPipTimebase()
     }

ios/RunnerTests/RunnerTests.swift

@@ -0,0 +1,206 @@
+import Flutter
+import XCTest
+
+@testable import Runner
+
+final class ControllablePropertyCore: MpvPlayerCoreBase {
+  var nextResult: Result<Void, Error>?
+  private(set) var propertyCalls: [(String, String)] = []
+  private var pendingCompletion: ((Result<Void, Error>) -> Void)?
+
+  override func setPropertyAsync(
+    _ name: String,
+    value: String,
+    completion: @escaping (Result<Void, Error>) -> Void
+  ) {
+    propertyCalls.append((name, value))
+    if let nextResult {
+      self.nextResult = nil
+      completion(nextResult)
+    } else {
+      pendingCompletion = completion
+    }
+  }
+
+  func finish(_ result: Result<Void, Error>) {
+    let completion = pendingCompletion
+    pendingCompletion = nil
+    completion?(result)
+  }
+}
+
+final class RecordingMpvPlugin: MpvPluginShared {
+  var coreBase: MpvPlayerCoreBase?
+  var eventSink: FlutterEventSink?
+  var nameToId: [String: Int] = [:]
+  private(set) var pauseHookValues: [String] = []
+
+  init(core: MpvPlayerCoreBase?) {
+    coreBase = core
+  }
+
+  func setPlayerVisible(_ visible: Bool, restoreOnWindowVisible: Bool) {}
+  func updatePlayerFrame() {}
+
+  func didSetPauseProperty(value: String) {
+    pauseHookValues.append(value)
+  }
+}
+
+final class MpvPlayerContractTests: XCTestCase {
+  private let failure = NSError(
+    domain: "MpvPlayerContractTests",
+    code: 1,
+    userInfo: [NSLocalizedDescriptionKey: "controlled failure"]
+  )
+
+  func testSharedSetPropertyMapsSuccessFailureMissingCoreAndInvalidArguments() {
+    let core = ControllablePropertyCore()
+    let plugin = RecordingMpvPlugin(core: core)
+
+    core.nextResult = .success(())
+    let success = invokeSetProperty(plugin, name: "pause", value: "no")
+    XCTAssertEqual(success.count, 1)
+    XCTAssertNil(success[0])
+    XCTAssertEqual(plugin.pauseHookValues, ["no"])
+
+    core.nextResult = .failure(failure)
+    let rejected = invokeSetProperty(plugin, name: "pause", value: "yes")
+    XCTAssertEqual(rejected.count, 1)
+    XCTAssertEqual((rejected[0] as? FlutterError)?.code, "SET_PROPERTY_FAILED")
+    XCTAssertEqual(plugin.pauseHookValues, ["no"])
+
+    plugin.coreBase = nil
+    let missing = invokeSetProperty(plugin, name: "volume", value: "50")
+    XCTAssertEqual(missing.count, 1)
+    XCTAssertEqual((missing[0] as? FlutterError)?.code, "NOT_INITIALIZED")
+
+    var invalidResults: [Any?] = []
+    plugin.handleSetProperty(
+      call: FlutterMethodCall(methodName: "setProperty", arguments: ["name": "pause"])
+    ) {
+      invalidResults.append($0)
+    }
+    XCTAssertEqual(invalidResults.count, 1)
+    XCTAssertEqual((invalidResults[0] as? FlutterError)?.code, "INVALID_ARGS")
+  }
+
+  func testRealSetPropertyValidInvalidNonexistentAndPauseCache() {
+    let core = MpvAudioPlayerCore()
+    XCTAssertTrue(core.initialize())
+    defer {
+      core.dispose()
+      core.queue.sync {}
+    }
+
+    XCTAssertSuccess(awaitProperty(core, name: "volume", value: "50"))
+    XCTAssertTrue(core.isPaused)
+
+    XCTAssertFailure(awaitProperty(core, name: "pause", value: "not-a-flag"))
+    XCTAssertTrue(core.isPaused, "A rejected raw pause write must not change the cache")
+
+    XCTAssertFailure(
+      awaitProperty(core, name: "plezy-property-does-not-exist", value: "ignored")
+    )
+    XCTAssertTrue(core.isPaused)
+
+    XCTAssertSuccess(awaitProperty(core, name: "pause", value: "no"))
+    XCTAssertFalse(core.isPaused, "The accepted pause write must commit before completion")
+  }
+
+  func testPendingSetPropertyIsCancelledExactlyOnceOnDispose() {
+    let core = MpvAudioPlayerCore()
+    XCTAssertTrue(core.initialize())
+
+    let queueEntered = expectation(description: "mpv queue blocked")
+    let releaseQueue = DispatchSemaphore(value: 0)
+    core.queue.async {
+      queueEntered.fulfill()
+      releaseQueue.wait()
+    }
+    wait(for: [queueEntered], timeout: 2)
+
+    let completion = expectation(description: "cancelled property completion")
+    completion.assertForOverFulfill = true
+    var completionCount = 0
+    core.setPropertyAsync("volume", value: "51") { result in
+      completionCount += 1
+      if case .success = result {
+        XCTFail("Disposal must fail an accepted-but-pending property request")
+      }
+      completion.fulfill()
+    }
+
+    core.dispose()
+    releaseQueue.signal()
+    wait(for: [completion], timeout: 2)
+    core.queue.sync {}
+    XCTAssertEqual(completionCount, 1)
+    XCTAssertFailure(awaitProperty(core, name: "volume", value: "52"))
+  }
+
+  func testRapidAudioCoreReplacementOwnsLifecycleOnce() {
+    for _ in 0..<5 {
+      autoreleasepool {
+        let core = MpvAudioPlayerCore()
+        XCTAssertTrue(core.initialize())
+        core.dispose()
+        core.dispose()
+        core.queue.sync {}
+        XCTAssertFalse(core.hasActiveMpv)
+      }
+    }
+  }
+
+  private func invokeSetProperty(
+    _ plugin: RecordingMpvPlugin,
+    name: String,
+    value: String
+  ) -> [Any?] {
+    var results: [Any?] = []
+    plugin.handleSetProperty(
+      call: FlutterMethodCall(
+        methodName: "setProperty",
+        arguments: ["name": name, "value": value]
+      )
+    ) {
+      results.append($0)
+    }
+    return results
+  }
+
+  private func awaitProperty(
+    _ core: MpvPlayerCoreBase,
+    name: String,
+    value: String
+  ) -> Result<Void, Error> {
+    let completion = expectation(description: "set \(name)")
+    var propertyResult: Result<Void, Error>?
+    core.setPropertyAsync(name, value: value) {
+      propertyResult = $0
+      completion.fulfill()
+    }
+    wait(for: [completion], timeout: 2)
+    return propertyResult ?? .failure(failure)
+  }
+
+  private func XCTAssertSuccess(
+    _ result: Result<Void, Error>,
+    file: StaticString = #filePath,
+    line: UInt = #line
+  ) {
+    if case .failure(let error) = result {
+      XCTFail("Expected success, received \(error)", file: file, line: line)
+    }
+  }
+
+  private func XCTAssertFailure(
+    _ result: Result<Void, Error>,
+    file: StaticString = #filePath,
+    line: UInt = #line
+  ) {
+    if case .success = result {
+      XCTFail("Expected failure", file: file, line: line)
+    }
+  }
+}