diff --git a/src/app.cpp b/src/app.cpp
index 5f5adcf..646994d 100644
--- a/src/app.cpp
+++ b/src/app.cpp
@@ -868,14 +868,17 @@ void App::update()
     // If a wallet switch's daemon failed to start, revert to the previous wallet (main-thread-safe).
     processWalletSwitchRevert();
 
-    // Track user interaction for auto-lock. Not in the background: a minimized window runs update() without
-    // new frames, so the IO state is the last frame's, and a stale mouse delta kept auto-lock from ever firing.
+    // Real input arrives through App::noteUserInput() (main.cpp event ingest). What stays here covers input
+    // that produces no new SDL event this frame: a held mouse button (a drag or scrollbar grab without
+    // motion). NOT in the background: a minimized window runs update() with the last frame's IO, and a stale
+    // mouse delta once kept auto-lock from ever firing. Deliberately NOT IsAnyItemActive(): a focused text
+    // field stays active indefinitely (C21).
     if (!window_background_ &&
         (io.MouseDelta.x != 0 || io.MouseDelta.y != 0 ||
          io.MouseClicked[0] || io.MouseClicked[1] ||
          io.InputQueueCharacters.Size > 0 ||
-         ImGui::IsAnyItemActive())) {
-        last_interaction_ = std::chrono::steady_clock::now();
+         ImGui::IsAnyMouseDown())) {
+        idle_.noteActivity();
     }
 
     // Advance the refresh timers by the real time since the last update BEFORE the RPC results are
diff --git a/src/app.h b/src/app.h
index 4307950..b089714 100644
--- a/src/app.h
+++ b/src/app.h
@@ -43,6 +43,7 @@
 #include "util/background_sampler.h"
 #include "util/coalescing_writer.h"
 #include "util/fetch_backoff.h"
+#include "util/idle_tracker.h"
 #include "util/pool_stats_service.h"
 #include "wallet/wallet_capabilities.h"
 #include "chat/chat_service.h"
@@ -559,6 +560,9 @@ public:
     // output parser skips while the wallet is locked), so a background witness rebuild that started and
     // finished meanwhile isn't parsed in one batch and mistaken for a completed rescan (spurious toast).
     void skipDaemonOutputBacklog();
+    // A real user input event (key, text, mouse, touch, pen, gamepad button) was ingested. Main thread only.
+    // Called from main.cpp's noteEvent; do NOT call from an SDL event watch/filter (resizeWatcher).
+    void noteUserInput() { idle_.noteActivity(); }
     void refreshMiningInfo();
     void refreshPeerInfo();
     void refreshMarketData();
@@ -1935,8 +1939,9 @@ private:
     char wizard_pin_confirm_buf_[16] = {};
     std::string wizard_pin_status_;
 
-    // Auto-lock on idle
-    std::chrono::steady_clock::time_point last_interaction_ = std::chrono::steady_clock::now();
+    // Auto-lock on idle. Fed by real input events (noteUserInput, from main.cpp's event ingest), NOT by
+    // widget state: a focused-but-untouched text field must not keep the wallet unlocked (C21).
+    util::IdleTracker idle_;
 
     // Wall-clock delta for logic timers (see logicDeltaTime()).
     std::chrono::steady_clock::time_point last_update_time_{};
diff --git a/src/app_security.cpp b/src/app_security.cpp
index 0ea28a7..896be28 100644
--- a/src/app_security.cpp
+++ b/src/app_security.cpp
@@ -479,7 +479,7 @@ void App::applyUnlockSuccess(const std::string& passphrase, int timeout) {
     lock_error_msg_.clear();
     lock_attempts_ = 0;
     memset(lock_passphrase_buf_, 0, sizeof(lock_passphrase_buf_));
-    last_interaction_ = std::chrono::steady_clock::now();
+    idle_.noteActivity();
     state_.encrypted = true;
     state_.locked = false;
     state_.unlocked_until = std::time(nullptr) + timeout;
@@ -726,17 +726,16 @@ void App::checkAutoLock() {
                         || (xmrig_manager_ && xmrig_manager_->isRunning());
     if (miningActive) {
         // Keep resetting the idle timer so we don't lock the instant mining stops
-        last_interaction_ = std::chrono::steady_clock::now();
+        idle_.noteActivity();
         return;
     }
 
     int timeout = settings_ ? settings_->getAutoLockTimeout() : 300;
     if (timeout <= 0) return; // disabled
 
-    auto now = std::chrono::steady_clock::now();
-    float elapsed = std::chrono::duration<float>(now - last_interaction_).count();
+    const double elapsed = idle_.idleSeconds();
 
-    if (elapsed >= (float)timeout) {
+    if (elapsed >= (double)timeout) {
         // Lite has no daemon `walletlock` — App::lockWallet() early-returns without rpc_, so route
         // lite through lockLiteWallet() (locks the backend + tears down the chat session so no
         // decrypted store / unlocked DB key survives the idle lock). In full-node builds
diff --git a/src/main.cpp b/src/main.cpp
index 8b28465..ff66bc2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1605,7 +1605,10 @@ int main(int argc, char* argv[])
     Uint64 lastFrameStartNs = 0;     // software frame cap bookkeeping (SDL_GetTicksNS)
     int settleFrames = kSettleFrames;
     auto noteEvent = [&](const SDL_Event& e) {
-        if (isInputEvent(e.type)) lastInputMs = SDL_GetTicks();
+        if (isInputEvent(e.type)) {
+            lastInputMs = SDL_GetTicks();
+            app.noteUserInput();   // auto-lock idle clock (C21): real input only, never widget state
+        }
         else if (isWindowStateEvent(e.type)) settleFrames = kSettleFrames;
     };
 
diff --git a/src/util/idle_tracker.h b/src/util/idle_tracker.h
new file mode 100644
index 0000000..c417873
--- /dev/null
+++ b/src/util/idle_tracker.h
@@ -0,0 +1,22 @@
+// Idle tracking for the auto-lock: pure, header-only, main-thread only.
+#pragma once
+#include <chrono>
+
+namespace dragonx {
+namespace util {
+
+class IdleTracker {
+public:
+    using Clock = std::chrono::steady_clock;
+    explicit IdleTracker(Clock::time_point start = Clock::now()) : last_(start) {}
+    // Never moves backwards (an event stamped before the last one must not shorten the idle time).
+    void noteActivity(Clock::time_point t = Clock::now()) { if (t > last_) last_ = t; }
+    double idleSeconds(Clock::time_point now = Clock::now()) const {
+        return now <= last_ ? 0.0 : std::chrono::duration<double>(now - last_).count();
+    }
+private:
+    Clock::time_point last_;
+};
+
+}  // namespace util
+}  // namespace dragonx
diff --git a/tests/test_phase4.cpp b/tests/test_phase4.cpp
index 3c78242..615111d 100644
--- a/tests/test_phase4.cpp
+++ b/tests/test_phase4.cpp
@@ -75,6 +75,7 @@
 #include "util/seed_phrase.h"
 #include "util/local_time.h"
 #include "util/text_fit.h"
+#include "util/idle_tracker.h"
 #include "util/image_decode_core.h"
 #include "daemon/daemon_startup_diagnosis.h"
 #include "util/amount_format.h"
@@ -1132,6 +1133,26 @@ void testSpendableFiltering()
 }
 
 // S8: deferFor() is an absolute hold, independent of the page interval (the retry-storm fix).
+void testIdleTracker()
+{
+    using dragonx::util::IdleTracker;
+    using Clock = IdleTracker::Clock;
+    const auto t0 = Clock::now();
+    IdleTracker idle(t0);
+    EXPECT_NEAR(idle.idleSeconds(t0), 0.0, 1e-9);
+    // No events: idle time keeps growing, however long a (conceptual) field stays focused.
+    EXPECT_NEAR(idle.idleSeconds(t0 + std::chrono::seconds(900)), 900.0, 1e-6);
+    EXPECT_TRUE(idle.idleSeconds(t0 + std::chrono::seconds(901)) >= 900.0);   // would trip a 900 s auto-lock
+    // Activity resets it.
+    idle.noteActivity(t0 + std::chrono::seconds(600));
+    EXPECT_NEAR(idle.idleSeconds(t0 + std::chrono::seconds(900)), 300.0, 1e-6);
+    // Never moves backwards.
+    idle.noteActivity(t0 + std::chrono::seconds(100));
+    EXPECT_NEAR(idle.idleSeconds(t0 + std::chrono::seconds(900)), 300.0, 1e-6);
+    // A query before the last activity is 0, not negative.
+    EXPECT_NEAR(idle.idleSeconds(t0 + std::chrono::seconds(10)), 0.0, 1e-9);
+}
+
 void testRefreshSchedulerDeferFor()
 {
     using dragonx::services::RefreshScheduler;
@@ -17475,6 +17496,7 @@ int main()
     testAmountFormatting();
     testSpendableFiltering();
     testRefreshScheduler();
+    testIdleTracker();
     testRefreshSchedulerDeferFor();
     testRpcBusyGate();
     testIsLongWalletMethod();