diff --git a/README.md b/README.md
index d83389b..f8064e4 100644
--- a/README.md
+++ b/README.md
@@ -97,6 +97,8 @@ The picker works offline with 1,870 emoji from [gemoji v4.1.0](https://github.co
 
 Search for **Conjure Translate** and open it. Enter English in the search bar, choose a provider, then press Return or click **Translate**. Typing alone never sends text. Copy selected Japanese output with Command-C; the copy hint appears beside the Translate action at the bottom. The Back chevron beside the input or Escape returns to the launcher and restores your search.
 
+Editing the input, switching providers, forgetting the key, or leaving Translate cancels the active request; cancelled results are not shown. After a request fails, submit again to retry.
+
 - **MyMemory:** No account or key required. Limits are 500 UTF-8 bytes per request and [5,000 characters per day](https://mymemory.translated.net/doc/usagelimits.php) for anonymous use.
 - **OpenAI:** Requires an API key, access to `gpt-6-luna`, and sufficient API billing. Choose **Save Key** to store it in macOS Keychain; **Forget Key** removes it. Requests disable API response storage, but OpenAI's retention policies still apply.
 
diff --git a/Sources/Conjure/TranslationController.swift b/Sources/Conjure/TranslationController.swift
index 9cfddab..dfeb534 100644
--- a/Sources/Conjure/TranslationController.swift
+++ b/Sources/Conjure/TranslationController.swift
@@ -15,11 +15,25 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
     private var task: Task<Void, Never>?
     var input: (() -> String)?
     var closed: (() -> Void)?
-    private static let credential: [String: Any] = [
-        kSecClass as String: kSecClassGenericPassword,
-        kSecAttrService as String: "Conjure.OpenAI",
-        kSecAttrAccount as String: "translation",
-    ]
+    private let defaults: UserDefaults
+    private let credentialsStore: Credentials
+    private let myMemory: @MainActor (String) async throws -> String
+    private let openAI: @MainActor (String, String) async throws -> String
+
+    init(
+        defaults: UserDefaults = .standard,
+        credentials: Credentials = .keychain,
+        myMemory: @escaping @MainActor (String) async throws -> String = { try await MyMemoryAPI.translate($0) },
+        openAI: @escaping @MainActor (String, String) async throws -> String = { try await TranslationAPI.translate($0, apiKey: $1) }
+    ) {
+        self.defaults = defaults
+        self.credentialsStore = credentials
+        self.myMemory = myMemory
+        self.openAI = openAI
+        super.init(nibName: nil, bundle: nil)
+    }
+
+    required init?(coder: NSCoder) { fatalError("Conjure creates Translate programmatically") }
 
     override func loadView() {
         view = NSView()
@@ -27,7 +41,7 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
         title.font = .systemFont(ofSize: 13, weight: .semibold)
         title.textColor = SunsetPalette.text
         provider.addItems(withTitles: ["MyMemory (no key)", "OpenAI · gpt-6-luna"])
-        provider.selectItem(at: UserDefaults.standard.string(forKey: "translationProvider") == "openai" ? 1 : 0)
+        provider.selectItem(at: defaults.string(forKey: "translationProvider") == "openai" ? 1 : 0)
         provider.setAccessibilityLabel("Translation provider")
         provider.target = self
         provider.action = #selector(providerChanged)
@@ -132,21 +146,18 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
     func controlTextDidChange(_ notification: Notification) { inputChanged() }
 
     @objc func goBack() {
-        task?.cancel()
-        task = nil
+        cancelRequest()
         closed?()
     }
 
     func inputChanged() {
-        task?.cancel()
-        task = nil
-        translateButton.isEnabled = true
+        cancelRequest()
         output.string = ""
         setStatus("Press Return to translate.")
     }
 
     @objc private func providerChanged() {
-        UserDefaults.standard.set(usesMyMemory ? "mymemory" : "openai", forKey: "translationProvider")
+        defaults.set(usesMyMemory ? "mymemory" : "openai", forKey: "translationProvider")
         keyField.stringValue = ""
         updateProvider()
     }
@@ -165,33 +176,26 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
             setStatus("Enter a valid API key before saving.", isError: true)
             return
         }
-        let data = Data(key.utf8)
-        var result = SecItemUpdate(Self.credential as CFDictionary, [kSecValueData as String: data] as CFDictionary)
-        if result == errSecItemNotFound {
-            var item = Self.credential
-            item[kSecValueData as String] = data
-            item[kSecAttrAccessible as String] = kSecAttrAccessibleWhenUnlockedThisDeviceOnly
-            result = SecItemAdd(item as CFDictionary, nil)
-        }
-        if result == errSecSuccess {
+        do {
+            try credentialsStore.save(key)
             keyField.stringValue = ""
             setStatus("API key saved in Keychain. Press Return to translate.")
-        } else { showKeychainError(result) }
+        } catch { setStatus(error.localizedDescription, isError: true) }
     }
 
     @objc private func forgetKey() {
+        cancelRequest()
+        do {
+            try credentialsStore.forget()
+            keyField.stringValue = ""
+            setStatus("API key removed.")
+        } catch { setStatus(error.localizedDescription, isError: true) }
+    }
+
+    private func cancelRequest() {
         task?.cancel()
         task = nil
         translateButton.isEnabled = true
-        let result = SecItemDelete(Self.credential as CFDictionary)
-        if result == errSecSuccess || result == errSecItemNotFound {
-            keyField.stringValue = ""
-            setStatus("API key removed.")
-        } else { showKeychainError(result) }
-    }
-
-    private func showKeychainError(_ code: OSStatus) {
-        setStatus("Keychain error: \(SecCopyErrorMessageString(code, nil) as String? ?? String(code))", isError: true)
     }
 
     private func setStatus(_ message: String, isError: Bool = false) {
@@ -210,25 +214,27 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
         var key = ""
         if !myMemory {
             if !keyField.stringValue.isEmpty { saveKey(); guard keyField.stringValue.isEmpty else { return } }
-            var query = Self.credential
-            query[kSecReturnData as String] = true
-            var item: CFTypeRef?
-            let result = SecItemCopyMatching(query as CFDictionary, &item)
-            guard result == errSecSuccess, let data = item as? Data, let savedKey = String(data: data, encoding: .utf8) else {
-                if result == errSecItemNotFound { setStatus("Enter and save your OpenAI API key first.", isError: true) }
-                else { showKeychainError(result) }
+            do {
+                guard let savedKey = try credentialsStore.load() else {
+                    setStatus("Enter and save your OpenAI API key first.", isError: true)
+                    return
+                }
+                key = savedKey
+            } catch {
+                setStatus(error.localizedDescription, isError: true)
                 return
             }
-            key = savedKey
         }
         output.string = ""
         setStatus("Translating…")
         translateButton.isEnabled = false
+        let myMemoryTranslate = self.myMemory
+        let openAITranslate = self.openAI
         task = Task { [weak self] in
             do {
                 let translation = try await myMemory
-                    ? MyMemoryAPI.translate(text)
-                    : TranslationAPI.translate(text, apiKey: key)
+                    ? myMemoryTranslate(text)
+                    : openAITranslate(text, key)
                 guard !Task.isCancelled, let self else { return }
                 self.output.string = translation
                 self.setStatus("Japanese · Select text to copy (⌘C).")
@@ -241,4 +247,52 @@ final class TranslationController: NSViewController, NSTextFieldDelegate, NSText
             self.translateButton.isEnabled = true
         }
     }
+
+    @MainActor
+    struct Credentials {
+        var save: (String) throws -> Void
+        var load: () throws -> String?
+        var forget: () throws -> Void
+
+        private static var query: [String: Any] {
+            [kSecClass as String: kSecClassGenericPassword,
+             kSecAttrService as String: "Conjure.OpenAI",
+             kSecAttrAccount as String: "translation"]
+        }
+
+        static let keychain = Credentials(
+            save: { key in
+                let data = Data(key.utf8)
+                var result = SecItemUpdate(query as CFDictionary, [kSecValueData as String: data] as CFDictionary)
+                if result == errSecItemNotFound {
+                    var item = query
+                    item[kSecValueData as String] = data
+                    item[kSecAttrAccessible as String] = kSecAttrAccessibleWhenUnlockedThisDeviceOnly
+                    result = SecItemAdd(item as CFDictionary, nil)
+                }
+                guard result == errSecSuccess else { throw KeychainError(code: result) }
+            },
+            load: {
+                var query = Self.query
+                query[kSecReturnData as String] = true
+                var item: CFTypeRef?
+                let result = SecItemCopyMatching(query as CFDictionary, &item)
+                if result == errSecItemNotFound { return nil }
+                guard result == errSecSuccess, let data = item as? Data,
+                      let key = String(data: data, encoding: .utf8) else { throw KeychainError(code: result) }
+                return key
+            },
+            forget: {
+                let result = SecItemDelete(query as CFDictionary)
+                guard result == errSecSuccess || result == errSecItemNotFound else { throw KeychainError(code: result) }
+            }
+        )
+    }
+
+    private struct KeychainError: LocalizedError {
+        let code: OSStatus
+        var errorDescription: String? {
+            "Keychain error: \(SecCopyErrorMessageString(code, nil) as String? ?? String(code))"
+        }
+    }
 }
diff --git a/Tests/ConjureKitTests/TranslationExecutionTests.swift b/Tests/ConjureKitTests/TranslationExecutionTests.swift
new file mode 100644
index 0000000..b417668
--- /dev/null
+++ b/Tests/ConjureKitTests/TranslationExecutionTests.swift
@@ -0,0 +1,201 @@
+import AppKit
+import Foundation
+import Testing
+@testable import Conjure
+
+@MainActor
+private final class TranslationRequests {
+    var inputs: [(text: String, key: String?)] = []
+    var pending: [CheckedContinuation<String, any Error>] = []
+    var returned = 0
+
+    // Deliberately ignore cancellation: the controller must reject late completions itself.
+    func translate(_ text: String, key: String? = nil) async throws -> String {
+        inputs.append((text, key))
+        defer { returned += 1 }
+        return try await withCheckedThrowingContinuation { pending.append($0) }
+    }
+}
+
+private struct CredentialFailure: LocalizedError {
+    var errorDescription: String? { "Credential access denied" }
+}
+
+@MainActor
+private final class TranslationKeys {
+    var value: String?
+    var accesses = 0
+    var denied = false
+    var store: TranslationController.Credentials {
+        .init(save: { [self] key in
+            accesses += 1
+            if denied { throw CredentialFailure() }
+            value = key
+        }, load: { [self] in
+            accesses += 1
+            if denied { throw CredentialFailure() }
+            return value
+        }, forget: { [self] in
+            accesses += 1
+            if denied { throw CredentialFailure() }
+            value = nil
+        })
+    }
+}
+
+@MainActor
+private func waitForTranslation(_ condition: () -> Bool) async throws {
+    // This is a scheduling deadline, not a clock used by the behavior under test.
+    for _ in 0..<1_000 {
+        if condition() { return }
+        try await Task.sleep(for: .milliseconds(1))
+    }
+    try #require(condition(), "Translate did not reach the expected observable state")
+}
+
+@MainActor
+private func descendants(_ view: NSView) -> [NSView] { [view] + view.subviews.flatMap(descendants) }
+
+@Test @MainActor
+func translationExecutionIsExplicitAndMyMemoryNeverTouchesCredentials() async throws {
+    _ = NSApplication.shared
+    let suite = "TranslateExecution.\(UUID().uuidString)"
+    let defaults = UserDefaults(suiteName: suite)!
+    defer { defaults.removePersistentDomain(forName: suite) }
+    let keys = TranslationKeys()
+    keys.value = "private-key"
+    let requests = TranslationRequests()
+    let tool = TranslationController(defaults: defaults, credentials: keys.store,
+        myMemory: { try await requests.translate($0) },
+        openAI: { try await requests.translate($0, key: $1) })
+    tool.input = { "Hello" }
+    let views = descendants(tool.view)
+    let output = try #require(views.compactMap { $0 as? NSTextView }.first)
+    tool.inputChanged()
+    #expect(requests.inputs.isEmpty)
+    tool.translate()
+    tool.translate() // A second submission while busy must not send another request.
+    try await waitForTranslation { requests.pending.count == 1 }
+    requests.pending[0].resume(returning: "こんにちは")
+    try await waitForTranslation { output.string == "こんにちは" }
+    #expect(requests.inputs.count == 1)
+    #expect(requests.inputs[0].text == "Hello")
+    #expect(requests.inputs[0].key == nil)
+    #expect(keys.accesses == 0)
+}
+
+@Test @MainActor
+func translationExecutionRejectsOldCompletionsWithoutClearingNewRequests() async throws {
+    _ = NSApplication.shared
+    let suite = "TranslateLifetime.\(UUID().uuidString)"
+    let defaults = UserDefaults(suiteName: suite)!
+    defer { defaults.removePersistentDomain(forName: suite) }
+    let keys = TranslationKeys()
+    keys.value = "saved-key"
+    let requests = TranslationRequests()
+    let tool = TranslationController(defaults: defaults, credentials: keys.store,
+        myMemory: { try await requests.translate($0) },
+        openAI: { try await requests.translate($0, key: $1) })
+    var input = "first"
+    tool.input = { input }
+    let views = descendants(tool.view)
+    let output = try #require(views.compactMap { $0 as? NSTextView }.first)
+    let provider = try #require(views.compactMap { $0 as? NSPopUpButton }.first)
+    let button = try #require(views.compactMap { $0 as? NSButton }.first { $0.action == NSSelectorFromString("translate") })
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 1 }
+    input = "second"
+    tool.inputChanged()
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 2 }
+    requests.pending[0].resume(returning: "obsolete")
+    try await waitForTranslation { requests.returned == 1 }
+    #expect(output.string.isEmpty)
+    #expect(!button.isEnabled)
+    tool.translate()
+    #expect(requests.inputs.count == 2)
+
+    provider.selectItem(at: 1)
+    _ = tool.perform(provider.action, with: provider)
+    #expect(defaults.string(forKey: "translationProvider") == "openai")
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 3 }
+    #expect(requests.inputs[2].key == "saved-key")
+    requests.pending[1].resume(throwing: CredentialFailure())
+    try await waitForTranslation { requests.returned == 2 }
+    #expect(!button.isEnabled)
+    requests.pending[2].resume(returning: "最新")
+    try await waitForTranslation { output.string == "最新" }
+    #expect(button.isEnabled)
+
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 4 }
+    var closed = false
+    tool.closed = { closed = true }
+    tool.goBack()
+    requests.pending[3].resume(returning: "after close")
+    try await waitForTranslation { requests.returned == 4 }
+    #expect(closed)
+    #expect(output.string.isEmpty)
+}
+
+@Test @MainActor
+func translationExecutionRecoversFromCredentialAndRequestFailures() async throws {
+    _ = NSApplication.shared
+    let suite = "TranslateCredentials.\(UUID().uuidString)"
+    let defaults = UserDefaults(suiteName: suite)!
+    defaults.set("openai", forKey: "translationProvider")
+    defer { defaults.removePersistentDomain(forName: suite) }
+    let keys = TranslationKeys()
+    let requests = TranslationRequests()
+    let tool = TranslationController(defaults: defaults, credentials: keys.store,
+        myMemory: { try await requests.translate($0) },
+        openAI: { try await requests.translate($0, key: $1) })
+    tool.input = { "Hello" }
+    let views = descendants(tool.view)
+    let field = try #require(views.compactMap { $0 as? NSSecureTextField }.first)
+    let output = try #require(views.compactMap { $0 as? NSTextView }.first)
+    let status = try #require(views.compactMap { $0 as? NSTextField }.first { $0.accessibilityLabel() == "Translation status and errors" })
+    let button = try #require(views.compactMap { $0 as? NSButton }.first { $0.action == NSSelectorFromString("translate") })
+    let forget = try #require(views.compactMap { $0 as? NSButton }.first { $0.action == NSSelectorFromString("forgetKey") })
+
+    tool.translate() // No stored key.
+    #expect(requests.inputs.isEmpty)
+    #expect(button.isEnabled)
+    #expect(status.textColor == .systemRed)
+    field.stringValue = "typed-key"
+    keys.denied = true
+    tool.translate() // A failed save must not silently send the typed key.
+    #expect(requests.inputs.isEmpty)
+    #expect(field.stringValue == "typed-key")
+    #expect(keys.value == nil)
+    #expect(status.stringValue.contains("Credential access denied"))
+    field.stringValue = ""
+    tool.translate() // Failed reads are also recoverable without a request.
+    #expect(requests.inputs.isEmpty)
+    #expect(button.isEnabled)
+    keys.denied = false
+    field.stringValue = "typed-key"
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 1 }
+    #expect(keys.value == "typed-key")
+    #expect(field.stringValue.isEmpty)
+    #expect(requests.inputs[0].key == "typed-key")
+    requests.pending[0].resume(throwing: CredentialFailure())
+    try await waitForTranslation { button.isEnabled }
+    #expect(status.textColor == .systemRed)
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 2 }
+    forget.performClick(nil)
+    #expect(keys.value == nil)
+    #expect(button.isEnabled)
+    requests.pending[1].resume(returning: "forgotten request")
+    try await waitForTranslation { requests.returned == 2 }
+    #expect(output.string.isEmpty)
+    keys.value = "replacement"
+    tool.translate()
+    try await waitForTranslation { requests.pending.count == 3 }
+    requests.pending[2].resume(returning: "成功")
+    try await waitForTranslation { output.string == "成功" }
+    #expect(status.textColor != .systemRed)
+}