diff --git a/lib/__tests__/account-state-manager.test.ts b/lib/__tests__/account-state-manager.test.ts
index 658fe2c5..7f61265f 100644
--- a/lib/__tests__/account-state-manager.test.ts
+++ b/lib/__tests__/account-state-manager.test.ts
@@ -58,7 +58,7 @@ describe('snapshotAccount / restoreAccount', () => {
     expect(useVacationStore.getState().isEnabled).toBe(true);
   });
 
-  it('CHARACTERISATION: only snapshotted fields are restored; others survive', () => {
+  it('resets fields outside the snapshot subset to their defaults (no cross-account leak)', () => {
     // isLoading is NOT part of the email snapshot subset.
     useEmailStore.setState({ selectedMailbox: 'a-in', isLoading: false });
     snapshotAccount('A');
@@ -66,11 +66,11 @@ describe('snapshotAccount / restoreAccount', () => {
 
     restoreAccount('A');
 
-    expect(useEmailStore.getState().selectedMailbox).toBe('a-in'); // restored
-    expect(useEmailStore.getState().isLoading).toBe(true); // NOT restored (merge)
+    expect(useEmailStore.getState().selectedMailbox).toBe('a-in'); // captured → restored
+    expect(useEmailStore.getState().isLoading).toBe(false); // uncaptured → reset, not leaked
   });
 
-  it('CHARACTERISATION: snapshot stores array references, not deep clones', () => {
+  it('decouples the snapshot from later in-place mutation of the source array', () => {
     const arr = [makeEmail({ id: '1' })];
     useEmailStore.setState({ emails: arr });
     snapshotAccount('A');
@@ -78,8 +78,8 @@ describe('snapshotAccount / restoreAccount', () => {
     useEmailStore.setState({ emails: [] });
 
     restoreAccount('A');
-    // The post-snapshot mutation leaked into the snapshot.
-    expect(useEmailStore.getState().emails.map((e) => e.id)).toEqual(['1', '2']);
+    // The post-snapshot mutation did NOT leak into the snapshot.
+    expect(useEmailStore.getState().emails.map((e) => e.id)).toEqual(['1']);
   });
 
   it('returns false and leaves stores untouched for an unknown account', () => {
diff --git a/lib/__tests__/download-filename.test.ts b/lib/__tests__/download-filename.test.ts
index 455483c9..7302713f 100644
--- a/lib/__tests__/download-filename.test.ts
+++ b/lib/__tests__/download-filename.test.ts
@@ -41,11 +41,11 @@ describe('emailExportFilename', () => {
     expect(emailExportFilename(makeEmail({}), '{unknown_token}')).toBe('email.eml');
   });
 
-  it('CHARACTERISATION: per-token sanitise caps each value at 80 chars', () => {
-    // sanitizePart defaults to maxLen=80, applied per {token} during render —
-    // so a single long {subject} is truncated to 80 well before the 200 cap.
+  it('lets a single long token reach the 200-char filename cap', () => {
+    // Each {token} is now capped at FILENAME_MAX_LEN (200), so the overall
+    // filename limit governs instead of an earlier 80-char per-token cap.
     const out = emailExportFilename(makeEmail({ subject: 'a'.repeat(300) }), '{subject}');
-    expect(out).toBe('a'.repeat(80) + '.eml');
+    expect(out).toBe('a'.repeat(200) + '.eml');
   });
 });
 
diff --git a/lib/account-state-manager.ts b/lib/account-state-manager.ts
index 7fba8a3d..10dc9fe8 100644
--- a/lib/account-state-manager.ts
+++ b/lib/account-state-manager.ts
@@ -37,33 +37,37 @@ export function snapshotAccount(accountId: string): void {
   const identityState = useIdentityStore.getState();
   const vacationState = useVacationStore.getState();
 
+  // Copy the captured collections so the snapshot is decoupled from the live
+  // store: a later in-place mutation (e.g. an array push/splice, or stamping
+  // fields onto a shared email object) must not retroactively corrupt a
+  // snapshot taken earlier.
   cache.set(accountId, {
     email: {
-      emails: emailState.emails,
-      mailboxes: emailState.mailboxes,
+      emails: [...emailState.emails],
+      mailboxes: [...emailState.mailboxes],
       selectedEmail: emailState.selectedEmail,
       selectedMailbox: emailState.selectedMailbox,
       searchQuery: emailState.searchQuery,
-      quota: emailState.quota,
+      quota: emailState.quota ? { ...emailState.quota } : emailState.quota,
     },
     contact: {
-      contacts: contactState.contacts,
-      addressBooks: contactState.addressBooks,
+      contacts: [...contactState.contacts],
+      addressBooks: [...contactState.addressBooks],
       supportsSync: contactState.supportsSync,
     },
     calendar: {
-      calendars: calendarState.calendars,
-      events: calendarState.events,
-      selectedCalendarIds: calendarState.selectedCalendarIds,
+      calendars: [...calendarState.calendars],
+      events: [...calendarState.events],
+      selectedCalendarIds: [...calendarState.selectedCalendarIds],
       viewMode: calendarState.viewMode,
       supportsCalendar: calendarState.supportsCalendar,
     },
     filter: {
-      rules: filterState.rules,
+      rules: [...filterState.rules],
       isSupported: filterState.isSupported,
     },
     identity: {
-      identities: identityState.identities,
+      identities: [...identityState.identities],
       preferredPrimaryId: identityState.preferredPrimaryId,
     },
     vacation: {
@@ -73,11 +77,22 @@ export function snapshotAccount(accountId: string): void {
   });
 }
 
-/** Restore cached store states for the given account. Returns false if no cache exists. */
+/**
+ * Restore cached store states for the given account. Returns false if no cache
+ * exists.
+ *
+ * The snapshot only captures a subset of each store's fields (the loaded data),
+ * so we reset every store to its baseline first. Without this, fields outside
+ * the captured subset (e.g. email selection, loading flags, tag counts) would
+ * carry over from whatever account was active, leaking state across accounts.
+ * `setState` merges, so the captured fields are then layered back on top.
+ */
 export function restoreAccount(accountId: string): boolean {
   const snapshot = cache.get(accountId);
   if (!snapshot) return false;
 
+  clearAllStores();
+
   useEmailStore.setState(snapshot.email);
   useContactStore.setState(snapshot.contact);
   useCalendarStore.setState(snapshot.calendar);
diff --git a/lib/download-filename.ts b/lib/download-filename.ts
index cbf4cad1..11dcc00e 100644
--- a/lib/download-filename.ts
+++ b/lib/download-filename.ts
@@ -64,6 +64,11 @@ export const BUNDLE_TOKENS: { token: string; description: string }[] = [
   { token: "day", description: "2-digit day" },
 ];
 
+// Overall cap for a generated filename stem. Also used as the per-token cap so
+// a single long token (e.g. {subject}) isn't truncated earlier than the final
+// filename would be.
+const FILENAME_MAX_LEN = 200;
+
 function sanitizePart(input: string, maxLen = 80): string {
   const cleaned = input
     .replace(SAFE_CHARS, "_")
@@ -173,7 +178,7 @@ function renderRaw(template: string, vars: Record<string, string>): string {
   return template.replace(/\{(\w+)\}/g, (_, key: string) => {
     const value = vars[key];
     if (value === undefined) return "";
-    return sanitizePart(value);
+    return sanitizePart(value, FILENAME_MAX_LEN);
   });
 }
 
@@ -184,9 +189,9 @@ export function emailExportFilename(
   const opts = typeof options === "string" ? { template: options } : options;
   const template = opts.template ?? DEFAULT_EMAIL_TEMPLATE;
   const rendered = renderRaw(template, emailVars(email));
-  const cleaned = sanitizePart(rendered, 200);
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN);
   const transformed = applyTransforms(cleaned, opts);
-  const stem = transformed.slice(0, 200) || "email";
+  const stem = transformed.slice(0, FILENAME_MAX_LEN) || "email";
   return `${stem}.eml`;
 }
 
@@ -199,7 +204,7 @@ export function attachmentDownloadFilename(
   const template = opts.template ?? DEFAULT_ATTACHMENT_TEMPLATE;
   if (!email) {
     const filename = (attachment.name || "attachment").trim();
-    const cleaned = sanitizePart(filename, 200) || "attachment";
+    const cleaned = sanitizePart(filename, FILENAME_MAX_LEN) || "attachment";
     return applyTransforms(cleaned, opts) || cleaned;
   }
   const vars = attachmentVars(email, attachment);
@@ -208,10 +213,10 @@ export function attachmentDownloadFilename(
     if (value === undefined) return "";
     // Preserve dots in {filename} so the original extension survives the
     // sanitiser (it strips trailing dots otherwise).
-    return key === "filename" ? value.replace(SAFE_CHARS, "_") : sanitizePart(value);
+    return key === "filename" ? value.replace(SAFE_CHARS, "_") : sanitizePart(value, FILENAME_MAX_LEN);
   });
   const templateMentionsExt = /\{(ext|filename)\}/.test(template);
-  const cleaned = sanitizePart(rendered, 200) || "attachment";
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN) || "attachment";
   if (templateMentionsExt) {
     return applyTransforms(cleaned, opts) || cleaned;
   }
@@ -235,9 +240,9 @@ export function bundleExportFilename(
   const opts = typeof options === "string" ? { template: options } : options;
   const template = opts.template ?? DEFAULT_BUNDLE_TEMPLATE;
   const rendered = renderRaw(template, bundleVars(count, iso));
-  const cleaned = sanitizePart(rendered, 200);
+  const cleaned = sanitizePart(rendered, FILENAME_MAX_LEN);
   const transformed = applyTransforms(cleaned, opts);
-  const stem = transformed.slice(0, 200) || "emails";
+  const stem = transformed.slice(0, FILENAME_MAX_LEN) || "emails";
   return `${stem}.zip`;
 }