diff --git a/Sources/LockIME/AppState.swift b/Sources/LockIME/AppState.swift
index 1ccac44..66a97fa 100644
--- a/Sources/LockIME/AppState.swift
+++ b/Sources/LockIME/AppState.swift
@@ -179,6 +179,10 @@ final class AppState {
     /// Build and start the engine. Called once at launch from the app delegate.
     func start() {
         guard engine == nil else { return }
+        // Capture this *before* loading (and before the save below writes one):
+        // it tells a genuine first run apart from a returning user who set the
+        // global default to "None". Both load as `defaultSourceID == nil`.
+        let isFirstRun = !store.hasPersistedConfiguration
         config = store.load()
         activationCount = activationStore.count
 
@@ -210,8 +214,11 @@ final class AppState {
         engine.start()
 
         availableSources = engine.selectableSources()
-        // First run: default the global lock to the currently active source.
-        if config.defaultSourceID == nil, let current = engine.currentSourceID() {
+        // First run only: seed the global lock from the currently active source.
+        // Gated on `isFirstRun` — a returning user who set the default to "None"
+        // persists `nil`, and re-seeding that would silently turn "None" back
+        // into whatever source was active at launch (e.g. ABC) on every relaunch.
+        if isFirstRun, config.defaultSourceID == nil, let current = engine.currentSourceID() {
             config.defaultSourceID = current
         }
         engine.apply(config, reason: .startupApplied)
diff --git a/Sources/LockIMEKit/Rules/RuleStore.swift b/Sources/LockIMEKit/Rules/RuleStore.swift
index ccdaaa6..589a734 100644
--- a/Sources/LockIMEKit/Rules/RuleStore.swift
+++ b/Sources/LockIMEKit/Rules/RuleStore.swift
@@ -23,6 +23,17 @@ public final class RuleStore: @unchecked Sendable {
         return config
     }
 
+    /// Whether a configuration has ever been written to `defaults`. This is the
+    /// only way to tell a genuine **first run** — where the app seeds the global
+    /// default from the currently active input source — apart from a returning
+    /// user who deliberately set that default to **None**. Both surface as a
+    /// loaded config with `defaultSourceID == nil`, so gating the first-run seed
+    /// on `defaultSourceID == nil` alone would silently overwrite a chosen "None"
+    /// with whatever source happened to be active at launch, on *every* relaunch.
+    public var hasPersistedConfiguration: Bool {
+        defaults.data(forKey: key) != nil
+    }
+
     public func save(_ config: LockConfiguration) {
         guard let data = try? JSONEncoder().encode(config) else { return }
         defaults.set(data, forKey: key)
diff --git a/Tests/LockIMEKitTests/RuleStoreTests.swift b/Tests/LockIMEKitTests/RuleStoreTests.swift
index 11279a6..e266950 100644
--- a/Tests/LockIMEKitTests/RuleStoreTests.swift
+++ b/Tests/LockIMEKitTests/RuleStoreTests.swift
@@ -62,6 +62,27 @@ struct RuleStoreTests {
         #expect(loaded.urlRules.first?.action == .lock)
     }
 
+    @Test("hasPersistedConfiguration is false until a save happens")
+    func hasPersistedConfigurationStartsFalse() {
+        let store = RuleStore(defaults: freshDefaults())
+        #expect(store.hasPersistedConfiguration == false)
+        store.save(.default)
+        #expect(store.hasPersistedConfiguration == true)
+    }
+
+    // Regression: a returning user who set the global default to "None" persists
+    // `defaultSourceID == nil`, yet the config *is* on disk — so the first-run
+    // seed (which turns a nil default into the live source) must NOT fire for
+    // them. `hasPersistedConfiguration` is what tells the two apart; assert it
+    // reports `true` even though the saved default is nil.
+    @Test("a saved config with a nil default still counts as persisted")
+    func nilDefaultStillCountsAsPersisted() {
+        let store = RuleStore(defaults: freshDefaults())
+        store.save(LockConfiguration(isEnabled: true, defaultSourceID: nil))
+        #expect(store.hasPersistedConfiguration == true)
+        #expect(store.load().defaultSourceID == nil)
+    }
+
     @Test("a later save overwrites an earlier one")
     func overwrite() {
         let defaults = freshDefaults()