Fix Live Activity lock screen rendering and polish multi-account auth.

Flatten widget layouts and use system colors so banner and expanded regions render on vibrant lock screens; migrate auth sessions per account to prevent double sign-in; scope app lock PIN to accounts; default clock description to "Clock In"; add architecture docs and deferred form validation on auth screens.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/(app)/invoices/edit/[id].tsx

@@ -22,6 +22,7 @@ import { fonts, spacing } from "@/constants/theme";
 import { useAppTheme } from "@/contexts/ThemeContext";
 import { formatCurrency } from "@/lib/format";
 import { getInvoiceStatus } from "@/lib/invoice-status";
+import { validateLineItems } from "@/lib/form-validation";
 import { useTabBarScrollPadding } from "@/lib/tab-bar-insets";
 import type { ThemeColors } from "@/lib/theme-palette";
 import { useThemedStyles } from "@/lib/use-themed-styles";
@@ -100,6 +101,8 @@ export default function InvoiceEditScreen() {
   const taxAmount = subtotal * (taxRate / 100);
   const total = subtotal + taxAmount;
   const currency = invoice?.currency ?? "USD";
+  const lineItemsError = validateLineItems(items);
+  const canSave = !lineItemsError;
 
   if (!id) {
     return <LoadingScreen message="Invalid invoice" />;
@@ -170,6 +173,7 @@ export default function InvoiceEditScreen() {
   }
 
   function handleSave() {
+    if (!canSave) return;
     setError(null);
 
     const parsedItems: Array<{
@@ -180,25 +184,11 @@ export default function InvoiceEditScreen() {
     }> = [];
 
     for (const item of items) {
-      const hours = Number(item.hours);
-      const rate = Number(item.rate);
-      if (!item.description.trim()) {
-        setError("Each line needs a description");
-        return;
-      }
-      if (Number.isNaN(hours) || hours < 0) {
-        setError("Hours must be a valid number");
-        return;
-      }
-      if (Number.isNaN(rate) || rate < 0) {
-        setError("Rate must be a valid number");
-        return;
-      }
       parsedItems.push({
         date: item.date,
         description: item.description.trim(),
-        hours,
-        rate,
+        hours: Number(item.hours),
+        rate: Number(item.rate),
       });
     }
 
@@ -274,10 +264,16 @@ export default function InvoiceEditScreen() {
             </View>
           </Card>
 
+          {lineItemsError ? <Text style={styles.error}>{lineItemsError}</Text> : null}
           {error ? <Text style={styles.error}>{error}</Text> : null}
 
           <View style={styles.actions}>
-            <Button title="Save changes" loading={updateInvoice.isPending} onPress={handleSave} />
+            <Button
+              title="Save changes"
+              loading={updateInvoice.isPending}
+              disabled={!canSave}
+              onPress={handleSave}
+            />
             {status !== "paid" ? (
               <Button
                 title={status === "draft" ? "Send invoice" : "Resend invoice"}

app/(app)/invoices/new.tsx

@@ -23,6 +23,11 @@ import { fonts, spacing } from "@/constants/theme";
 import { useAppTheme } from "@/contexts/ThemeContext";
 import { formatCurrency } from "@/lib/format";
 import { defaultDueDate, generateInvoiceNumber } from "@/lib/invoice-number";
+import {
+  isRequiredString,
+  isValidTaxRate,
+  validateLineItems,
+} from "@/lib/form-validation";
 import { useTabBarScrollPadding } from "@/lib/tab-bar-insets";
 import type { ThemeColors } from "@/lib/theme-palette";
 import { useThemedStyles } from "@/lib/use-themed-styles";
@@ -104,6 +109,19 @@ export default function NewInvoiceScreen() {
   const taxAmount = subtotal * (parsedTaxRate / 100);
   const total = subtotal + taxAmount;
 
+  const clientError = clientId ? undefined : "Select a client";
+  const invoiceNumberError = isRequiredString(invoiceNumber)
+    ? undefined
+    : "Invoice number is required";
+  const taxError = isValidTaxRate(taxRate) ? undefined : "Tax rate must be between 0 and 100";
+  const lineItemsError = validateLineItems(items);
+  const canCreate =
+    clientOptions.length > 0 &&
+    !clientError &&
+    !invoiceNumberError &&
+    !taxError &&
+    !lineItemsError;
+
   if (clientsQuery.isLoading) {
     return <LoadingScreen message="Loading…" />;
   }
@@ -140,18 +158,9 @@ export default function NewInvoiceScreen() {
   }
 
   function handleCreate() {
+    if (!canCreate) return;
     setError(null);
 
-    if (!clientId) {
-      setError("Select a client");
-      return;
-    }
-
-    if (!invoiceNumber.trim()) {
-      setError("Invoice number is required");
-      return;
-    }
-
     const parsedItems: Array<{
       date: Date;
       description: string;
@@ -160,41 +169,21 @@ export default function NewInvoiceScreen() {
     }> = [];
 
     for (const item of items) {
-      const hours = Number(item.hours);
-      const rate = Number(item.rate);
-      if (!item.description.trim()) {
-        setError("Each line needs a description");
-        return;
-      }
-      if (Number.isNaN(hours) || hours < 0) {
-        setError("Hours must be a valid number");
-        return;
-      }
-      if (Number.isNaN(rate) || rate < 0) {
-        setError("Rate must be a valid number");
-        return;
-      }
       parsedItems.push({
         date: item.date,
         description: item.description.trim(),
-        hours,
-        rate,
+        hours: Number(item.hours),
+        rate: Number(item.rate),
       });
     }
 
-    const tax = Number(taxRate);
-    if (Number.isNaN(tax) || tax < 0 || tax > 100) {
-      setError("Tax rate must be between 0 and 100");
-      return;
-    }
-
     createInvoice.mutate({
       clientId,
       invoiceNumber: invoiceNumber.trim(),
       issueDate,
       dueDate,
       notes,
-      taxRate: tax,
+      taxRate: Number(taxRate),
       currency,
       items: parsedItems,
       status: "draft",
@@ -232,6 +221,8 @@ export default function NewInvoiceScreen() {
                 placeholder="Select client…"
                 value={clientId}
                 options={clientOptions}
+                required
+                error={clientError}
                 onValueChange={setClientId}
               />
             )}
@@ -240,6 +231,8 @@ export default function NewInvoiceScreen() {
               value={invoiceNumber}
               onChangeText={setInvoiceNumber}
               autoCapitalize="characters"
+              required
+              error={invoiceNumberError}
             />
             <DateTimeField
               label="Issue date"
@@ -256,6 +249,7 @@ export default function NewInvoiceScreen() {
               value={taxRate}
               onChangeText={setTaxRate}
               keyboardType="decimal-pad"
+              error={taxError}
             />
             <Input
               label="Notes"
@@ -298,12 +292,13 @@ export default function NewInvoiceScreen() {
             </View>
           </Card>
 
+          {lineItemsError ? <Text style={styles.error}>{lineItemsError}</Text> : null}
           {error ? <Text style={styles.error}>{error}</Text> : null}
 
           <Button
             title="Create invoice"
             loading={createInvoice.isPending}
-            disabled={clientOptions.length === 0}
+            disabled={!canCreate}
             onPress={handleCreate}
           />
         </ScrollView>