diff --git a/background.js b/background.js
index 9243ed3..ee14af5 100644
--- a/background.js
+++ b/background.js
@@ -6,6 +6,7 @@
 const DEFAULT_TARGETS = ['instagram.com', 'reddit.com', 'youtube.com'];
 const processingTabs = new Set(); // Tracks tabs currently being processed (short-lived lock)
 const pendingPromptTabs = new Set(); // Tracks tabs redirected to prompt.html, waiting for session start
+const tabsCurrentlyAtPrompt = new Set(); // Tracks tabs that have committed to prompt.html
 
 // --- Time Range Helpers ---
 
@@ -119,17 +120,23 @@ chrome.tabs.onUpdated.addListener(async (tabId, changeInfo, tab) => {
     // when status events fire after a redirect has already been issued.
     const currentUrl = changeInfo.url || tab.url;
 
-    // If the tab is heading to or already at the prompt, leave pendingPromptTabs intact and stop.
-    if (currentUrl.startsWith(chrome.runtime.getURL('prompt.html'))) return;
+    // If the tab has committed to the prompt page, mark it and clear the debounce lock
+    // (the redirect is complete; the lock is no longer needed).
+    if (currentUrl.startsWith(chrome.runtime.getURL('prompt.html'))) {
+        tabsCurrentlyAtPrompt.add(tabId);
+        processingTabs.delete(tabId);
+        return;
+    }
 
-    if (pendingPromptTabs.has(tabId)) {
-        if (changeInfo.url) {
-            // A fresh URL navigation away from the prompt — clear pending state and process normally.
-            pendingPromptTabs.delete(tabId);
-        } else {
-            // Stale status (loading/complete) event for a tab still waiting at the prompt — skip.
-            return;
-        }
+    // If the tab was genuinely at prompt.html and is now navigating away (e.g. after starting a session):
+    if (tabsCurrentlyAtPrompt.has(tabId)) {
+        tabsCurrentlyAtPrompt.delete(tabId);
+        pendingPromptTabs.delete(tabId);
+        // Fall through — process this navigation normally
+    } else if (pendingPromptTabs.has(tabId)) {
+        // Tab was redirected to prompt but hasn't committed there yet — this is a redirect-chain
+        // event (e.g. youtube.com → www.youtube.com) arriving before the tab reaches prompt.html.
+        return;
     }
 
     if (processingTabs.has(tabId)) return;
@@ -455,6 +462,7 @@ chrome.alarms.onAlarm.addListener(async (alarm) => {
 // Handle Messages from Prompt or Content Script
 chrome.tabs.onRemoved.addListener((tabId) => {
     pendingPromptTabs.delete(tabId);
+    tabsCurrentlyAtPrompt.delete(tabId);
     processingTabs.delete(tabId);
 });
 
diff --git a/tests/flows.test.js b/tests/flows.test.js
index ce8a645..88a5c46 100644
--- a/tests/flows.test.js
+++ b/tests/flows.test.js
@@ -1,6 +1,6 @@
 // Cross-site and shared flows: time ranges, pendingPromptTabs, alarms, startSession message.
 const {
-    loadBackground, fireUpdated, fireRemoved, fireAlarm, setStorage,
+    loadBackground, fireUpdated, fireRemoved, fireCommitted, fireAlarm, setStorage,
     expectPromptRedirect, expectNoRedirect, flushPromises, NOW,
 } = require('./helpers');
 
@@ -125,12 +125,15 @@ test('pendingPromptTabs: stale status:complete after redirect does not double-pr
 });
 
 test('pendingPromptTabs: fresh URL navigation away from prompt clears pending state', async () => {
-    // Redirect to prompt
+    // Step 1: navigate to YT — no session → redirect to prompt
     await nav(TAB, YT_HOME);
     expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1);
 
-    // User starts a session — simulate what prompt.js does: sends startSession message,
-    // then calls window.location.replace(intendedUrl) which fires a changeInfo.url event
+    // Step 2: tab commits to prompt.html — this is required before any away-navigation is processed
+    const promptUrl = `chrome-extension://fakeid/prompt.html?url=${encodeURIComponent(YT_HOME)}`;
+    await fireUpdated(TAB, { url: promptUrl }, { url: promptUrl, status: 'loading' });
+
+    // Step 3: user starts a session via the prompt UI
     setStorage({
         activeSessions: {
             'youtube.com': {
@@ -142,13 +145,38 @@ test('pendingPromptTabs: fresh URL navigation away from prompt clears pending st
         },
     });
 
-    // The replace fires a new URL navigation event — should clear pendingPromptTabs
-    // and then isTargetSite check should find an active session → no redirect
+    // Step 4: prompt.js calls window.location.replace(intendedUrl) → tab navigates back to YT
+    // Should clear pending state, find an active session, and allow access (no new redirect)
     await fireUpdated(TAB, { url: YT_HOME }, { url: YT_HOME });
-    // Active session exists → should be allowed (no new redirect)
     expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1);
 });
 
+test('pendingPromptTabs: www-redirect chain does not double-prompt', async () => {
+    // Step 1: navigate to bare domain (no www) — triggers redirect to prompt
+    await nav(TAB, 'https://youtube.com/');
+    expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1);
+
+    // Step 2: browser fires www-redirect BEFORE tab commits to prompt.html
+    // This must be suppressed — tab hasn't reached the prompt page yet
+    await nav(TAB, 'https://www.youtube.com/');
+    expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1); // still only 1
+});
+
+test('pendingPromptTabs: back button without session re-shows prompt', async () => {
+    // Step 1: navigate to YT — no session → redirect to prompt
+    await nav(TAB, YT_HOME);
+    expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1);
+
+    // Step 2: tab commits to prompt.html
+    const promptUrl = `chrome-extension://fakeid/prompt.html?url=${encodeURIComponent(YT_HOME)}`;
+    await fireUpdated(TAB, { url: promptUrl }, { url: promptUrl, status: 'loading' });
+
+    // Step 3: user presses back button without starting a session — tab returns to YT
+    await nav(TAB, YT_HOME);
+    // Should show prompt again — no valid session was started
+    expect(__mockFns__['tabs.update'].mock.calls.length).toBe(2);
+});
+
 test('pendingPromptTabs: tab removed cleans up state', async () => {
     await nav(TAB, YT_HOME);
     expect(__mockFns__['tabs.update'].mock.calls.length).toBe(1);
diff --git a/tests/helpers.js b/tests/helpers.js
index b9f71ce..2e06136 100644
--- a/tests/helpers.js
+++ b/tests/helpers.js
@@ -34,6 +34,12 @@ function fireMessage(message, sender = {}) {
     });
 }
 
+// Fire a webNavigation.onCommitted event.
+async function fireCommitted({ tabId, url, frameId = 0 }) {
+    const handlers = global.__listeners__.onCommitted;
+    await Promise.all(handlers.map(fn => fn({ tabId, url, frameId })));
+}
+
 // Fire an alarm event.
 async function fireAlarm(alarm) {
     const handlers = global.__listeners__.onAlarm;
@@ -85,6 +91,7 @@ module.exports = {
     loadBackground,
     fireUpdated,
     fireRemoved,
+    fireCommitted,
     fireMessage,
     fireAlarm,
     setStorage,
diff --git a/tests/setup.js b/tests/setup.js
index 965854c..ce78d0a 100644
--- a/tests/setup.js
+++ b/tests/setup.js
@@ -2,7 +2,7 @@
 // Test files access storage via global.__store__ and listeners via global.__listeners__.
 
 const store = {};
-const listeners = { onUpdated: [], onAlarm: [], onMessage: [], onRemoved: [] };
+const listeners = { onUpdated: [], onAlarm: [], onMessage: [], onRemoved: [], onCommitted: [] };
 const mockFns = {};
 
 function makeMockFn(key) {
@@ -74,4 +74,7 @@ global.chrome = {
         onAlarm: { addListener: (fn) => listeners.onAlarm.push(fn) },
         create: (...args) => mockFns['alarms.create'](...args),
     },
+    webNavigation: {
+        onCommitted: { addListener: (fn) => listeners.onCommitted.push(fn) },
+    },
 };