diff --git a/public/index.html b/public/index.html
index fb3c8ff..f9d9884 100644
--- a/public/index.html
+++ b/public/index.html
@@ -472,6 +472,8 @@ const flowState = {
   currentIntent: null,
   sessionToken: '',
   sessionExpiresAt: '',
+  sessionWallet: '',
+  sessionRefreshInFlight: null,
 };
 
 const continueAction = document.getElementById('continue-action');
@@ -519,6 +521,7 @@ function getStoredAcknowledgement() {
       if (parsed && (parsed.code || parsed.token)) {
         flowState.sessionToken = typeof parsed.session_token === 'string' ? parsed.session_token : '';
         flowState.sessionExpiresAt = typeof parsed.session_expires_at === 'string' ? parsed.session_expires_at : '';
+        flowState.sessionWallet = typeof parsed.wallet === 'string' ? parsed.wallet : '';
         return parsed;
       }
     } catch (err) {
@@ -609,7 +612,92 @@ function formatQuoteDisplay(quote) {
   return null;
 }
 
-async function postJSON(url, payload) {
+function clearFlowSession(reason) {
+  flowState.sessionToken = '';
+  flowState.sessionExpiresAt = '';
+  flowState.sessionWallet = '';
+  if (reason) {
+    console.warn('wallet session cleared:', reason);
+  }
+}
+
+function captureFlowSessionHeaders(res) {
+  const token = String(res.headers.get('x-edut-session') || '').trim();
+  if (token) {
+    flowState.sessionToken = token;
+  }
+  const expiresAt = String(res.headers.get('x-edut-session-expires-at') || '').trim();
+  if (expiresAt) {
+    flowState.sessionExpiresAt = expiresAt;
+  }
+}
+
+function parseApiError(text, status) {
+  if (!text) {
+    return { message: 'HTTP ' + status, code: '' };
+  }
+  try {
+    const parsed = JSON.parse(text);
+    if (parsed && typeof parsed === 'object') {
+      return {
+        message: String(parsed.error || ('HTTP ' + status)),
+        code: String(parsed.code || ''),
+      };
+    }
+  } catch (err) {
+    // fall back to raw text
+  }
+  return { message: text, code: '' };
+}
+
+function isTerminalSessionCode(code) {
+  const normalized = String(code || '').toLowerCase();
+  return normalized === 'wallet_session_invalid' ||
+    normalized === 'wallet_session_expired' ||
+    normalized === 'wallet_session_revoked' ||
+    normalized === 'wallet_session_mismatch';
+}
+
+async function maybeRefreshFlowSession(wallet, requestUrl) {
+  if (!flowState.sessionToken || !wallet || !flowState.sessionExpiresAt) {
+    return;
+  }
+  if (String(requestUrl || '').indexOf('/secret/wallet/session/') === 0) {
+    return;
+  }
+  const expiresAt = Date.parse(flowState.sessionExpiresAt);
+  if (!Number.isFinite(expiresAt)) {
+    return;
+  }
+  if ((expiresAt - Date.now()) > (5 * 60 * 1000)) {
+    return;
+  }
+  if (flowState.sessionRefreshInFlight) {
+    await flowState.sessionRefreshInFlight;
+    return;
+  }
+  flowState.sessionRefreshInFlight = postJSON(
+    '/secret/wallet/session/refresh',
+    { wallet },
+    { wallet, skipSessionRefresh: true },
+  ).then(function (out) {
+    if (out && typeof out.session_token === 'string') {
+      flowState.sessionToken = out.session_token;
+    }
+    if (out && typeof out.session_expires_at === 'string') {
+      flowState.sessionExpiresAt = out.session_expires_at;
+    }
+  }).finally(function () {
+    flowState.sessionRefreshInFlight = null;
+  });
+  await flowState.sessionRefreshInFlight;
+}
+
+async function postJSON(url, payload, options) {
+  const opts = options || {};
+  if (!opts.skipSessionRefresh) {
+    await maybeRefreshFlowSession(opts.wallet || flowState.sessionWallet || '', url);
+  }
   const headers = {
     'Content-Type': 'application/json',
   };
@@ -622,11 +710,17 @@ async function postJSON(url, payload) {
     headers,
     body: JSON.stringify(payload),
   });
+  captureFlowSessionHeaders(res);
+  const text = await res.text();
   if (!res.ok) {
-    const detail = await res.text();
-    throw new Error(detail || ('HTTP ' + res.status));
+    const detail = parseApiError(text, res.status);
+    if (isTerminalSessionCode(detail.code)) {
+      clearFlowSession(detail.code);
+    }
+    throw new Error(detail.message);
   }
-  return res.json();
+  if (!text) return {};
+  return JSON.parse(text);
 }
 
 function resolveLanguage(input) {
@@ -725,6 +819,10 @@ async function startWalletFlow() {
       throw new Error('Wallet connection was not approved.');
     }
     const address = accounts[0];
+    if (flowState.sessionWallet && flowState.sessionWallet.toLowerCase() !== address.toLowerCase()) {
+      clearFlowSession('wallet_changed');
+    }
+    flowState.sessionWallet = address;
     const chainIdHex = await window.ethereum.request({ method: 'eth_chainId' });
     const chainId = Number.parseInt(chainIdHex, 16);
 
@@ -734,7 +832,7 @@ async function startWalletFlow() {
       origin: window.location.origin,
       locale: localStorage.getItem('edut_lang') || 'en',
       chain_id: chainId,
-    });
+    }, { wallet: address });
     flowState.currentIntent = intent;
 
     const typedData = {
@@ -781,16 +879,17 @@ async function startWalletFlow() {
       address,
       chain_id: chainId,
       signature,
-    });
+    }, { wallet: address });
     flowState.sessionToken = verification.session_token || '';
     flowState.sessionExpiresAt = verification.session_expires_at || '';
+    flowState.sessionWallet = address;
 
     setFlowStatus('membership_quoting', 'Preparing membership mint...', false);
     const quote = await postJSON('/secret/membership/quote', {
       designation_code: verification.designation_code || intent.designation_code || null,
       address,
       chain_id: chainId,
-    });
+    }, { wallet: address });
 
     const txParams = quote.tx || {
       from: address,
@@ -823,7 +922,7 @@ async function startWalletFlow() {
       tx_hash: txHash,
       address,
       chain_id: chainId,
-    });
+    }, { wallet: address });
 
     if (confirmation.status !== 'membership_active') {
       throw new Error('Membership transaction did not activate.');
diff --git a/public/store/index.html b/public/store/index.html
index ce6149f..389906f 100644
--- a/public/store/index.html
+++ b/public/store/index.html
@@ -217,7 +217,9 @@
     offers: [],
     selectedOfferId: null,
     sessionToken: '',
+    sessionExpiresAt: '',
     sessionWallet: null,
+    sessionRefreshInFlight: null,
   };
 
   const walletLabel = document.getElementById('wallet-label');
@@ -404,6 +406,9 @@
       if (typeof parsed.session_token === 'string') {
         state.sessionToken = parsed.session_token.trim();
       }
+      if (typeof parsed.session_expires_at === 'string') {
+        state.sessionExpiresAt = parsed.session_expires_at.trim();
+      }
       if (typeof parsed.wallet === 'string') {
         state.sessionWallet = parsed.wallet.trim();
       }
@@ -412,6 +417,107 @@
     }
   }
 
+  function clearSession(reason) {
+    state.sessionToken = '';
+    state.sessionExpiresAt = '';
+    state.sessionWallet = null;
+    if (reason) {
+      setLog('Wallet session cleared: ' + reason + '.');
+    }
+  }
+
+  function captureSessionHeaders(response) {
+    const token = String(response.headers.get('x-edut-session') || '').trim();
+    if (!token) return;
+    state.sessionToken = token;
+    const expiresAt = String(response.headers.get('x-edut-session-expires-at') || '').trim();
+    if (expiresAt) {
+      state.sessionExpiresAt = expiresAt;
+    }
+    if (state.wallet) {
+      state.sessionWallet = state.wallet;
+    }
+  }
+
+  function parseApiErrorPayload(text, fallbackStatus) {
+    if (!text) {
+      return { error: 'HTTP ' + fallbackStatus, code: '' };
+    }
+    try {
+      const parsed = JSON.parse(text);
+      if (parsed && typeof parsed === 'object') {
+        return {
+          error: String(parsed.error || ('HTTP ' + fallbackStatus)),
+          code: String(parsed.code || ''),
+        };
+      }
+    } catch (err) {
+      // non-json response
+    }
+    return { error: text, code: '' };
+  }
+
+  function isTerminalSessionCode(code) {
+    const normalized = String(code || '').toLowerCase();
+    return normalized === 'wallet_session_invalid' ||
+      normalized === 'wallet_session_expired' ||
+      normalized === 'wallet_session_revoked' ||
+      normalized === 'wallet_session_mismatch';
+  }
+
+  async function maybeRefreshSession(pathHint) {
+    if (!state.sessionToken || !state.wallet || !state.sessionExpiresAt) {
+      return;
+    }
+    if (String(pathHint || '').indexOf('/secret/wallet/session/') === 0) {
+      return;
+    }
+    const expiresAt = Date.parse(state.sessionExpiresAt);
+    if (!Number.isFinite(expiresAt)) {
+      return;
+    }
+    if ((expiresAt - Date.now()) > (5 * 60 * 1000)) {
+      return;
+    }
+    if (state.sessionRefreshInFlight) {
+      await state.sessionRefreshInFlight;
+      return;
+    }
+    state.sessionRefreshInFlight = (async function () {
+      const response = await fetch('/secret/wallet/session/refresh', {
+        method: 'POST',
+        headers: authHeaders({ 'Content-Type': 'application/json' }),
+        body: JSON.stringify({ wallet: state.wallet }),
+      });
+      captureSessionHeaders(response);
+      const text = await response.text();
+      if (!response.ok) {
+        const detail = parseApiErrorPayload(text, response.status);
+        if (isTerminalSessionCode(detail.code)) {
+          clearSession(detail.code);
+        }
+        throw new Error(detail.error);
+      }
+      let payload = {};
+      try {
+        payload = text ? JSON.parse(text) : {};
+      } catch (err) {
+        // ignore parse error for non-essential refresh payload
+      }
+      if (payload && typeof payload.session_token === 'string') {
+        state.sessionToken = payload.session_token.trim();
+      }
+      if (payload && typeof payload.session_expires_at === 'string') {
+        state.sessionExpiresAt = payload.session_expires_at.trim();
+      }
+      state.sessionWallet = state.wallet;
+      setLog('Wallet session refreshed.');
+    })().finally(function () {
+      state.sessionRefreshInFlight = null;
+    });
+    await state.sessionRefreshInFlight;
+  }
+
   function authHeaders(extra) {
     const headers = Object.assign({}, extra || {});
     if (state.sessionToken) {
@@ -422,16 +528,42 @@
   }
 
   async function fetchJson(url) {
+    await maybeRefreshSession(url);
     const response = await fetch(url, {
       method: 'GET',
       headers: authHeaders(),
     });
+    captureSessionHeaders(response);
     if (!response.ok) {
-      throw new Error('HTTP ' + response.status);
+      const text = await response.text();
+      const detail = parseApiErrorPayload(text, response.status);
+      if (isTerminalSessionCode(detail.code)) {
+        clearSession(detail.code);
+      }
+      throw new Error(detail.error);
     }
     return response.json();
   }
 
+  async function postJson(url, payload) {
+    await maybeRefreshSession(url);
+    const response = await fetch(url, {
+      method: 'POST',
+      headers: authHeaders({ 'Content-Type': 'application/json' }),
+      body: JSON.stringify(payload),
+    });
+    captureSessionHeaders(response);
+    const text = await response.text();
+    if (!response.ok) {
+      const detail = parseApiErrorPayload(text, response.status);
+      if (isTerminalSessionCode(detail.code)) {
+        clearSession(detail.code);
+      }
+      throw new Error(detail.error);
+    }
+    return text ? JSON.parse(text) : {};
+  }
+
   async function loadOffers() {
     try {
       const payload = await fetchJson('/store/offers.json');
@@ -518,8 +650,9 @@
       state.wallet = accounts[0];
       state.ownershipProof = null;
       if (state.sessionWallet && state.wallet && state.sessionWallet.toLowerCase() !== state.wallet.toLowerCase()) {
-        state.sessionToken = '';
+        clearSession('wallet changed');
       }
+      state.sessionWallet = state.wallet;
       setLog('Wallet connected: ' + abbreviateWallet(state.wallet) + '.');
       await refreshMembershipState();
     } catch (err) {
@@ -623,17 +756,7 @@
         payload.ownership_proof = state.ownershipProof.signature;
       }
 
-      const response = await fetch('/marketplace/checkout/quote', {
-        method: 'POST',
-        headers: authHeaders({ 'Content-Type': 'application/json' }),
-        body: JSON.stringify(payload),
-      });
-
-      if (!response.ok) {
-        throw new Error('HTTP ' + response.status);
-      }
-
-      const quotePayload = await response.json();
+      const quotePayload = await postJson('/marketplace/checkout/quote', payload);
       const quoteId = quotePayload.quote_id || 'unknown';
       const amount = quotePayload.amount || quotePayload.amount_atomic || 'unknown';
       const total = quotePayload.total_amount || quotePayload.total_amount_atomic || amount;