diff --git a/components/contacts/__tests__/contact-form.test.tsx b/components/contacts/__tests__/contact-form.test.tsx
index ef207dbdc..8dfeb0600 100644
--- a/components/contacts/__tests__/contact-form.test.tsx
+++ b/components/contacts/__tests__/contact-form.test.tsx
@@ -579,3 +579,112 @@ describe('ContactForm', () => {
     expect(options).toContain('Team (userb@example.org)');
   });
 });
+
+// pim-4: saving never rewrites what the user didn't touch.
+describe('ContactForm keeps what was not edited', () => {
+  // As a card with a structured German address comes from ContactCard/get.
+  const home = {
+    '@type': 'Address',
+    contexts: { private: true },
+    countryCode: 'DE',
+    full: 'Hauptstraße 1, 3. OG, 10000 Berlin',
+    isOrdered: true,
+    defaultSeparator: ', ',
+    components: [
+      { kind: 'name', value: 'Hauptstraße' },
+      { kind: 'separator', value: ' ' },
+      { kind: 'number', value: '1' },
+      { kind: 'apartment', value: '3. OG' },
+      { kind: 'postcode', value: '10000' },
+      { kind: 'locality', value: 'Berlin' },
+      { kind: 'country', value: 'Germany' },
+    ],
+  };
+  const office = {
+    components: [
+      { kind: 'number', value: '1' },
+      { kind: 'name', value: 'Main Street' },
+      { kind: 'locality', value: 'Springfield' },
+      { kind: 'region', value: 'IL' },
+      { kind: 'postcode', value: '62701' },
+      { kind: 'country', value: 'USA' },
+    ],
+    contexts: { work: true },
+  };
+  const card: ContactCard = {
+    ...existingContact,
+    nicknames: { nick: { name: 'Ali', contexts: { private: true } } },
+    emails: { home: { address: 'alice@example.com', pref: 1, label: 'main' }, w: { address: 'alice@work.example', contexts: { work: true } } },
+    addresses: { home, office } as ContactCard['addresses'],
+  };
+
+  async function save(change: () => void) {
+    const onSave = vi.fn().mockResolvedValue(undefined);
+    render(<ContactForm contact={card} onSave={onSave} onCancel={vi.fn()} />);
+    change();
+    fireEvent.submit(screen.getByText('save').closest('form')!);
+    await waitFor(() => expect(onSave).toHaveBeenCalledOnce());
+    return onSave.mock.calls[0][0] as Partial<ContactCard>;
+  }
+
+  it('sends only the nickname when only the nickname changed', async () => {
+    const data = await save(() => fireEvent.change(screen.getByDisplayValue('Ali'), { target: { value: 'Lissy' } }));
+    expect(Object.keys(data)).toEqual(['nicknames']);
+    // The nickname keeps its key and its contexts.
+    expect(data.nicknames).toEqual({ nick: { name: 'Lissy', contexts: { private: true } } });
+  });
+
+  it("shows street and number in the address's own order, German fields as Street, Postcode + City", () => {
+    render(<ContactForm contact={card} onSave={vi.fn()} onCancel={vi.fn()} />);
+    expect(screen.getByDisplayValue('Hauptstraße 1')).toBeInTheDocument();
+    expect(screen.getByDisplayValue('1 Main Street')).toBeInTheDocument();
+    const berlin = screen.getByDisplayValue('Berlin');
+    const postcode = screen.getByDisplayValue('10000');
+    // Postcode comes before the city for Germany, after it for the US.
+    expect(postcode.compareDocumentPosition(berlin) & Node.DOCUMENT_POSITION_FOLLOWING).toBeTruthy();
+    const springfield = screen.getByDisplayValue('Springfield');
+    const zip = screen.getByDisplayValue('62701');
+    expect(springfield.compareDocumentPosition(zip) & Node.DOCUMENT_POSITION_FOLLOWING).toBeTruthy();
+  });
+
+  it('keeps an untouched address exactly as stored when another address is edited', async () => {
+    const data = await save(() => fireEvent.change(screen.getByDisplayValue('62701'), { target: { value: '62702' } }));
+    expect(data.addresses!.home).toBe(home);
+    expect(data.addresses!.office.components!.find(c => c.kind === 'postcode')!.value).toBe('62702');
+    expect('emails' in data).toBe(false);
+  });
+
+  it('saves an edited German address in German order and keeps the parts the form does not show', async () => {
+    const data = await save(() => fireEvent.change(screen.getByDisplayValue('Hauptstraße 1'), { target: { value: 'Hauptstraße 12a' } }));
+    const saved = data.addresses!.home;
+    expect(saved.components!.map(c => `${c.kind}:${c.value}`)).toEqual([
+      'name:Hauptstraße', 'separator: ', 'number:12a', 'apartment:3. OG', 'postcode:10000', 'separator: ', 'locality:Berlin', 'country:Germany',
+    ]);
+    expect(saved).toMatchObject({ '@type': 'Address', countryCode: 'DE', contexts: { private: true }, isOrdered: true, defaultSeparator: ', ' });
+    // The old one-line text would contradict the new parts.
+    expect(saved.full).toBeUndefined();
+    expect(data.addresses!.office).toBe(office);
+  });
+
+  it('keeps an untouched email with its key, pref and label when another is edited', async () => {
+    const data = await save(() => fireEvent.change(screen.getByDisplayValue('alice@work.example'), { target: { value: 'alice@new.example' } }));
+    expect(data.emails!.home).toBe(card.emails!.home);
+    expect(data.emails!.w).toEqual({ address: 'alice@new.example', contexts: { work: true } });
+  });
+
+  it('still sends every field of a new contact, its address in the order of the country typed', async () => {
+    const onSave = vi.fn().mockResolvedValue(undefined);
+    render(<ContactForm onSave={onSave} onCancel={vi.fn()} />);
+    fireEvent.change(screen.getByPlaceholderText('given_name'), { target: { value: 'Jane' } });
+    fireEvent.click(screen.getByText('addresses'));
+    fireEvent.click(screen.getByText('add_address'));
+    fireEvent.change(screen.getByPlaceholderText('street'), { target: { value: 'Hauptstraße 5' } });
+    fireEvent.change(screen.getByPlaceholderText('country'), { target: { value: 'Deutschland' } });
+    fireEvent.submit(screen.getByText('save').closest('form')!);
+    await waitFor(() => expect(onSave).toHaveBeenCalledOnce());
+    const data = onSave.mock.calls[0][0] as Partial<ContactCard>;
+    expect('emails' in data && 'notes' in data && 'name' in data).toBe(true);
+    expect(data.addresses!.a0).toMatchObject({ countryCode: 'DE' });
+    expect(data.addresses!.a0.components!.map(c => `${c.kind}:${c.value}`)).toEqual(['name:Hauptstraße', 'separator: ', 'number:5', 'country:Deutschland']);
+  });
+});
diff --git a/components/contacts/contact-detail.tsx b/components/contacts/contact-detail.tsx
index 1537c9814..1c35b2977 100644
--- a/components/contacts/contact-detail.tsx
+++ b/components/contacts/contact-detail.tsx
@@ -8,6 +8,7 @@ import { Avatar } from "@/components/ui/avatar";
 import { MailtoLink } from "@/components/ui/mailto-link";
 import { Button } from "@/components/ui/button";
 import { cn } from "@/lib/utils";
+import { formatAddressLines } from "@/lib/address-format";
 import type { ContactCard, AnniversaryDate } from "@/lib/jmap/types";
 import { getContactDisplayName, getContactPrimaryEmail, getContactPhotoRef } from "@/stores/contact-store";
 import { ContactActivity } from "./contact-activity";
@@ -268,23 +269,14 @@ export function ContactDetail({ contact, onEdit, onDelete, onAddToGroup, onDupli
               })}
 
               {addresses.map((a, i) => {
-                const lines: string[] = [];
-                if (a.full || a.fullAddress) {
-                  lines.push((a.full || a.fullAddress) as string);
-                } else if (a.components && a.components.length > 0) {
-                  const joined = a.components.filter(c => c.kind !== 'separator').map(c => c.value).filter(Boolean).join(", ");
-                  if (joined) lines.push(joined);
-                } else {
-                  const parts = [a.street, [a.postcode, a.locality].filter(Boolean).join(" "), a.region, a.country]
-                    .map(s => (typeof s === "string" ? s.trim() : ""))
-                    .filter(Boolean) as string[];
-                  lines.push(...parts);
-                }
+                // One line per part, in the order of the address's country:
+                // "Hauptstraße 1" / "10000 Berlin" / "Germany".
+                const lines = formatAddressLines(a, locale);
                 return (
                   <FieldRow key={`ad${i}`} icon={MapPin} label={formatContexts(a.contexts, contextLabel) || t("detail.address_default_label")}>
-                    <div className="text-sm space-y-0.5">
+                    <div className="text-sm space-y-0.5" data-testid="contact-address">
                       {lines.map((line, idx) => (
-                        <div key={idx}>{line}</div>
+                        <div key={idx} data-address-line="">{line}</div>
                       ))}
                       {a.timeZone && (
                         <div className="text-xs text-muted-foreground">{t("detail.timezone")}: {a.timeZone}</div>
diff --git a/components/contacts/contact-form.tsx b/components/contacts/contact-form.tsx
index bea3db826..c506aab54 100644
--- a/components/contacts/contact-form.tsx
+++ b/components/contacts/contact-form.tsx
@@ -2,7 +2,7 @@
 
 import { useState, useMemo, useCallback, useRef, useEffect, useId } from "react";
 import { useCloseBesideControls } from "@/hooks/use-close-beside-controls";
-import { useTranslations } from "next-intl";
+import { useLocale, useTranslations } from "next-intl";
 import { X, Plus, ChevronDown, ChevronRight, User, Building, MapPin, Globe, Cake, Heart, Tag, StickyNote, Mail, Phone, Calendar, UserCircle, Book, Camera, Trash2, MoreHorizontal } from "@/components/icons";
 import { Button } from "@/components/ui/button";
 import { IconButton } from "@/components/ui/icon-button";
@@ -11,38 +11,47 @@ import { Avatar } from "@/components/ui/avatar";
 import { findContactPhotoEntry, getContactPhotoRef, type ContactPhotoRef } from "@/stores/contact-store";
 import type { ContactSaveOptions } from "@/lib/contact-media";
 import { cn } from "@/lib/utils";
+import { addressStyle, addressToParts, countryCodeFromName, partsToComponents, type AddressStyle } from "@/lib/address-format";
 import { useBottomControls } from "@/hooks/use-bottom-controls";
 import type { ContactCard, ContactOnlineService, ContactAnniversary, ContactPersonalInfo, AddressBook, AnniversaryDate, PartialDate, ContactAddress, ContactMedia } from "@/lib/jmap/types";
 
+// Each row of a list field keeps the `key` of the card's entry it was read
+// from, so Save can send an entry the user didn't touch back unchanged.
 interface EmailEntry {
+  key?: string;
   address: string;
   context: "work" | "private" | "";
 }
 
 interface PhoneEntry {
+  key?: string;
   number: string;
   context: "work" | "private" | "";
   feature: "voice" | "mobile" | "fax" | "pager" | "video" | "text" | "";
 }
 
 interface OnlineServiceEntry {
+  key?: string;
   uri: string;
   service: string;
   label: string;
 }
 
 interface AnniversaryEntry {
+  key?: string;
   date: string;
   kind: "birth" | "death" | "wedding" | "other";
 }
 
 interface PersonalInfoEntry {
+  key?: string;
   value: string;
   kind: "expertise" | "hobby" | "interest" | "other";
   level: "high" | "medium" | "low" | "";
 }
 
 interface AddressEntry {
+  key?: string;
   street: string;
   locality: string;
   region: string;
@@ -125,6 +134,62 @@ function mediaForPhotoEdit(
   return { media, photoKey };
 }
 
+/**
+ * The map to save for a list field (emails, phones, addresses...). A row the
+ * user didn't touch goes back exactly as the card had it, under its key. An
+ * edited row is built on the card's entry (`previous`), so properties the
+ * form doesn't show stay; a new row gets a key no other entry uses.
+ */
+function entriesToSave<E extends { key?: string }, V>(
+  rows: E[],
+  initialRows: E[],
+  original: Record<string, V> | undefined,
+  prefix: string,
+  build: (row: E, previous: V | undefined, before: E | undefined) => V,
+): Record<string, V> {
+  const out: Record<string, V> = {};
+  const taken = new Set(rows.map(r => r.key).filter((k): k is string => !!k && !!original?.[k]));
+  let n = 0;
+  const freshKey = () => {
+    let key = `${prefix}${n++}`;
+    while (taken.has(key)) key = `${prefix}${n++}`;
+    taken.add(key);
+    return key;
+  };
+  for (const row of rows) {
+    const previous = row.key ? original?.[row.key] : undefined;
+    const before = previous !== undefined ? initialRows.find(r => r.key === row.key) : undefined;
+    if (previous !== undefined && before && JSON.stringify(before) === JSON.stringify(row)) {
+      out[row.key!] = previous;
+    } else {
+      out[previous !== undefined ? row.key! : freshKey()] = build(row, previous, before);
+    }
+  }
+  return out;
+}
+
+/** `contexts` for a row: the card's own when the select wasn't changed. */
+function contextsToSave(context: string, previous: Record<string, boolean> | undefined, before: { context: string } | undefined): Record<string, boolean> | undefined {
+  if (before && before.context === context) return previous;
+  return context ? { [context]: true } : undefined;
+}
+
+/** A card's first entry of a map with one field changed, the others kept; undefined when none is left. */
+function firstEntryToSave<V extends object>(original: Record<string, V> | undefined, fallbackKey: string, value: V | null): Record<string, V> | undefined {
+  const entries = Object.entries(original ?? {});
+  const [firstKey, first] = entries[0] ?? [fallbackKey, undefined];
+  const rest = entries.slice(1);
+  const out: Record<string, V> = {};
+  if (value) out[firstKey] = { ...(first ?? {}), ...value } as V;
+  for (const [k, v] of rest) out[k] = v;
+  return Object.keys(out).length > 0 ? out : undefined;
+}
+
+/** Drops keys whose value is undefined, so a built entry has no empty properties. */
+function compact<T extends object>(obj: T): T {
+  return Object.fromEntries(Object.entries(obj).filter(([, v]) => v !== undefined)) as T;
+}
+
 function FormSection({ icon: Icon, title, children, collapsible, defaultOpen = true }: {
   icon: React.ComponentType<{ className?: string }>;
   title: string;
@@ -221,6 +286,7 @@ function Select({ value, onChange, children, className, id, "aria-label": ariaLa
 export function ContactForm({ contact, addressBooks, allKeywords, defaultAddressBookId, prefill, onSave, onCancel, loadCurrentMedia, onDirtyChange }: ContactFormProps) {
   const t = useTranslations("contacts.form");
   const tx = useTranslations("ux_pim_contact");
+  const locale = useLocale();
   const isEditing = !!contact;
   // The header's close goes to its start when the window's own close is at its end.
   const [header, setHeader] = useState<HTMLDivElement | null>(null);
@@ -283,25 +349,12 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
     return pd;
   }
 
-  // Extract flat address fields from RFC 9553 components format
-  function addressToFlat(a: ContactAddress): AddressEntry {
-    if (a.components && a.components.length > 0) {
-      const findComp = (kind: string) => a.components!.filter(c => c.kind === kind).map(c => c.value).join(' ');
-      return {
-        street: findComp('name') || findComp('number') ? [findComp('number'), findComp('name')].filter(Boolean).join(' ') : '',
-        locality: findComp('locality'),
-        region: findComp('region'),
-        postcode: findComp('postcode'),
-        country: findComp('country'),
-        context: a.contexts?.work ? 'work' : a.contexts?.private ? 'private' : '',
-      };
-    }
+  // The form's fields for an address: street name and house number in one
+  // field, in the order of the address's country ("Hauptstraße 1").
+  function addressToFlat(key: string, a: ContactAddress): AddressEntry {
     return {
-      street: a.street || '',
-      locality: a.locality || '',
-      region: a.region || '',
-      postcode: a.postcode || '',
-      country: a.country || '',
+      key,
+      ...addressToParts(a, locale),
       context: a.contexts?.work ? 'work' : a.contexts?.private ? 'private' : '',
     };
   }
@@ -318,7 +371,8 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
 
   const [emails, setEmails] = useState<EmailEntry[]>(() => {
     if (contact?.emails) {
-      return Object.values(contact.emails).map(e => ({
+      return Object.entries(contact.emails).map(([key, e]) => ({
+        key,
         address: e.address,
         context: e.contexts?.work ? "work" : e.contexts?.private ? "private" : "",
       }));
@@ -328,7 +382,8 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
 
   const [phones, setPhones] = useState<PhoneEntry[]>(() => {
     if (contact?.phones) {
-      return Object.values(contact.phones).map(p => ({
+      return Object.entries(contact.phones).map(([key, p]) => ({
+        key,
         number: p.number,
         context: p.contexts?.work ? "work" : p.contexts?.private ? "private" : "",
         // RFC 9553 calls it "mobile"; cards saved by older versions of this form say "cell".
@@ -372,14 +427,15 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
 
   const [addresses, setAddresses] = useState<AddressEntry[]>(() => {
     if (contact?.addresses) {
-      return Object.values(contact.addresses).map(a => addressToFlat(a));
+      return Object.entries(contact.addresses).map(([key, a]) => addressToFlat(key, a));
     }
     return [];
   });
 
   const [onlineServices, setOnlineServices] = useState<OnlineServiceEntry[]>(() => {
     if (contact?.onlineServices) {
-      return Object.values(contact.onlineServices).map(s => ({
+      return Object.entries(contact.onlineServices).map(([key, s]) => ({
+        key,
         uri: s.uri,
         service: s.service || "",
         label: s.label || "",
@@ -390,7 +446,8 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
 
   const [anniversaries, setAnniversaries] = useState<AnniversaryEntry[]>(() => {
     if (contact?.anniversaries) {
-      return Object.values(contact.anniversaries).map(a => ({
+      return Object.entries(contact.anniversaries).map(([key, a]) => ({
+        key,
         date: anniversaryDateToString(a.date),
         kind: a.kind,
       }));
@@ -400,7 +457,8 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
 
   const [personalInfoEntries, setPersonalInfoEntries] = useState<PersonalInfoEntry[]>(() => {
     if (contact?.personalInfo) {
-      return Object.values(contact.personalInfo).map(p => ({
+      return Object.entries(contact.personalInfo).map(([key, p]) => ({
+        key,
         value: p.value,
         kind: p.kind,
         level: p.level || "",
@@ -475,6 +533,32 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
     keywordsStr, categoryDraft, note, genderSex, genderIdentity, calendarUri, schedulingUri, freeBusyUri, selectedBookId,
   ]);
   const [initialFields] = useState(fields);
+
+  // What each card property is built from. Saving an existing card sends only
+  // the properties whose fields changed, so the rest stay exactly as stored,
+  // structured address parts included (#pim-4).
+  const personNamed = !!(givenName.trim() || surname.trim());
+  const propertyFields: Record<string, unknown> = {
+    name: [prefix, givenName, additionalName, surname, suffix, isOrg, isOrg || !personNamed ? organization : ""],
+    nicknames: nickname,
+    emails,
+    phones,
+    titles: [jobTitle, role],
+    organizations: [organization, department],
+    addresses,
+    onlineServices,
+    anniversaries,
+    personalInfo: personalInfoEntries,
+    keywords: [keywordsStr, categoryDraft],
+    notes: note,
+    speakToAs: [genderSex, genderIdentity],
+    calendarUri: [calendarUri, freeBusyUri],
+    freeBusyUri: [calendarUri, freeBusyUri],
+    schedulingUri,
+    addressBookIds: selectedBookId,
+  };
+  const [initialPropertyFields] = useState(() => JSON.stringify(propertyFields));
+  const [initialRows] = useState(() => ({ emails, phones, addresses, onlineServices, anniversaries, personalInfoEntries, department }));
   const dirty = fields !== initialFields || photoEdit.kind !== "unchanged";
   useEffect(() => { onDirtyChange?.(dirty); }, [dirty, onDirtyChange]);
   const footerRef = useBottomControls();
@@ -547,27 +631,21 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
       }
     }
 
-    const emailsMap: Record<string, { address: string; contexts?: Record<string, boolean> }> = {};
-    validEmails.forEach((entry, i) => {
-      const obj: { address: string; contexts?: Record<string, boolean> } = { address: entry.address.trim() };
-      if (entry.context) {
-        obj.contexts = { [entry.context]: true };
-      }
-      emailsMap[`e${i}`] = obj;
-    });
+    type Email = NonNullable<ContactCard["emails"]>[string];
+    type PhoneValue = NonNullable<ContactCard["phones"]>[string];
+    const emailsMap = entriesToSave<EmailEntry, Email>(validEmails, initialRows.emails, contact?.emails, "e", (row, previous, before) => compact({
+      ...previous,
+      address: row.address.trim(),
+      contexts: contextsToSave(row.context, previous?.contexts, before),
+    }));
 
     const validPhones = phones.filter(p => p.number.trim());
-    const phonesMap: Record<string, { number: string; contexts?: Record<string, boolean>; features?: Record<string, boolean> }> = {};
-    validPhones.forEach((entry, i) => {
-      const obj: { number: string; contexts?: Record<string, boolean>; features?: Record<string, boolean> } = { number: entry.number.trim() };
-      if (entry.context) {
-        obj.contexts = { [entry.context]: true };
-      }
-      if (entry.feature) {
-        obj.features = { [entry.feature]: true };
-      }
-      phonesMap[`p${i}`] = obj;
-    });
+    const phonesMap = entriesToSave<PhoneEntry, PhoneValue>(validPhones, initialRows.phones, contact?.phones, "p", (row, previous, before) => compact({
+      ...previous,
+      number: row.number.trim(),
+      contexts: contextsToSave(row.context, previous?.contexts, before),
+      features: before && before.feature === row.feature ? previous?.features : row.feature ? { [row.feature]: true } : undefined,
+    }));
 
     // Emit JSContact-standard kinds (RFC 9553) so the JMAP server stores them losslessly.
     const nameComponents = [];
@@ -597,41 +675,58 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
     if (jobTitle.trim()) titlesMap["t0"] = { name: jobTitle.trim(), kind: "title" };
     if (role.trim()) titlesMap["t1"] = { name: role.trim(), kind: "role" };
 
-    const orgUnits = department.trim() ? [{ name: department.trim() }] : undefined;
+    const firstOrg = Object.values(contact?.organizations ?? {})[0];
+    const orgUnits = firstOrg && department === initialRows.department
+      ? firstOrg.units
+      : department.trim() ? [{ name: department.trim() }] : undefined;
 
-    const addressesMap: Record<string, ContactCard["addresses"] extends Record<string, infer V> ? V : never> = {};
-    addresses.filter(a => a.street.trim() || a.locality.trim() || a.country.trim()).forEach((a, i) => {
-      const components: Array<{ kind: string; value: string }> = [];
-      if (a.street.trim()) components.push({ kind: "name", value: a.street.trim() });
-      if (a.locality.trim()) components.push({ kind: "locality", value: a.locality.trim() });
-      if (a.region.trim()) components.push({ kind: "region", value: a.region.trim() });
-      if (a.postcode.trim()) components.push({ kind: "postcode", value: a.postcode.trim() });
-      if (a.country.trim()) components.push({ kind: "country", value: a.country.trim() });
-      const obj: Record<string, unknown> = { components, isOrdered: true, defaultSeparator: ", " };
-      if (a.context) obj.contexts = { [a.context]: true };
-      // @ts-expect-error - dynamic build
-      addressesMap[`a${i}`] = obj;
-    });
+    // An address the user didn't touch goes back as the card had it. An edited
+    // one is rebuilt in its country's order ("Hauptstraße" + "1", then
+    // postcode and city), keeping the parts the form doesn't show.
+    const addressesMap = entriesToSave<AddressEntry, ContactAddress>(
+      addresses.filter(a => a.street.trim() || a.locality.trim() || a.region.trim() || a.postcode.trim() || a.country.trim()),
+      initialRows.addresses, contact?.addresses, "a",
+      (row, previous, before) => {
+        const { components: previousComponents, full: _full, fullAddress: _fullAddress, street: _s, locality: _l, region: _r, postcode: _p, country: _c, ...kept } = previous ?? {};
+        void _full; void _fullAddress; void _s; void _l; void _r; void _p; void _c;
+        const countryCode = before && before.country === row.country
+          ? previous?.countryCode
+          : countryCodeFromName(row.country) ?? undefined;
+        return compact({
+          ...kept,
+          components: partsToComponents(row, previousComponents ?? [], locale, countryCode),
+          isOrdered: true,
+          defaultSeparator: previous?.defaultSeparator ?? ", ",
+          countryCode,
+          contexts: contextsToSave(row.context, previous?.contexts, before),
+        });
+      },
+    );
 
-    const onlineServicesMap: Record<string, ContactOnlineService> = {};
-    onlineServices.filter(s => s.uri.trim()).forEach((s, i) => {
-      const obj: ContactOnlineService = { uri: s.uri.trim() };
-      if (s.service.trim()) obj.service = s.service.trim();
-      if (s.label.trim()) obj.label = s.label.trim();
-      onlineServicesMap[`os${i}`] = obj;
-    });
+    const onlineServicesMap = entriesToSave<OnlineServiceEntry, ContactOnlineService>(
+      onlineServices.filter(s => s.uri.trim()), initialRows.onlineServices, contact?.onlineServices, "os",
+      (row, previous) => compact({
+        ...previous,
+        uri: row.uri.trim(),
+        service: row.service.trim() || undefined,
+        label: row.label.trim() || undefined,
+      }),
+    );
 
-    const anniversariesMap: Record<string, ContactAnniversary> = {};
-    anniversaries.filter(a => a.date.trim()).forEach((a, i) => {
-      anniversariesMap[`an${i}`] = { date: stringToPartialDate(a.date.trim()), kind: a.kind };
-    });
+    const anniversariesMap = entriesToSave<AnniversaryEntry, ContactAnniversary>(
+      anniversaries.filter(a => a.date.trim()), initialRows.anniversaries, contact?.anniversaries, "an",
+      (row, previous) => ({ ...previous, date: stringToPartialDate(row.date.trim()), kind: row.kind }),
+    );
 
-    const personalInfoMap: Record<string, ContactPersonalInfo> = {};
-    personalInfoEntries.filter(p => p.value.trim()).forEach((p, i) => {
-      const obj: ContactPersonalInfo = { value: p.value.trim(), kind: p.kind };
-      if (p.level) obj.level = p.level as "high" | "medium" | "low";
-      personalInfoMap[`pi${i}`] = obj;
-    });
+    const personalInfoMap = entriesToSave<PersonalInfoEntry, ContactPersonalInfo>(
+      personalInfoEntries.filter(p => p.value.trim()), initialRows.personalInfoEntries, contact?.personalInfo, "pi",
+      (row, previous) => compact({
+        ...previous,
+        value: row.value.trim(),
+        kind: row.kind,
+        level: (row.level || undefined) as ContactPersonalInfo["level"],
+      }),
+    );
 
     const keywordsMap: Record<string, boolean> = {};
     keywordsStr.split(",").map(k => k.trim()).filter(Boolean).forEach(k => {
@@ -651,21 +746,18 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
     const data: Partial<ContactCard> = {
       name: nameValue,
       ...(kindValue ? { kind: kindValue } : {}),
-      nicknames: nickname.trim() ? { n0: { name: nickname.trim() } } : undefined,
+      // The form edits the first nickname, note and organization; others stay.
+      nicknames: firstEntryToSave(contact?.nicknames, "n0", nickname.trim() ? { name: nickname.trim() } : null),
       emails: Object.keys(emailsMap).length > 0 ? emailsMap : undefined,
       phones: Object.keys(phonesMap).length > 0 ? phonesMap : undefined,
       titles: Object.keys(titlesMap).length > 0 ? titlesMap : undefined,
-      organizations: orgName
-        ? { o0: { name: orgName, units: orgUnits } }
-        : undefined,
+      organizations: firstEntryToSave(contact?.organizations, "o0", orgName ? { name: orgName, units: orgUnits } : null),
       addresses: Object.keys(addressesMap).length > 0 ? addressesMap : undefined,
       onlineServices: Object.keys(onlineServicesMap).length > 0 ? onlineServicesMap : undefined,
       anniversaries: Object.keys(anniversariesMap).length > 0 ? anniversariesMap : undefined,
       personalInfo: Object.keys(personalInfoMap).length > 0 ? personalInfoMap : undefined,
       keywords: Object.keys(keywordsMap).length > 0 ? keywordsMap : undefined,
-      notes: note.trim()
-        ? { n0: { note: note.trim() } }
-        : undefined,
+      notes: firstEntryToSave(contact?.notes, "n0", note.trim() ? { note: note.trim() } : null),
       speakToAs: (genderSex.trim() || genderIdentity.trim())
         ? {
             grammaticalGender: genderSex.trim() || undefined,
@@ -678,6 +770,15 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
       ...(selectedBookId ? { addressBookIds: { [selectedBookId]: true } } : {}),
     };
 
+    // An existing card gets only what changed: every property left out stays
+    // on the server exactly as it is.
+    if (contact) {
+      const before = JSON.parse(initialPropertyFields) as Record<string, unknown>;
+      for (const [property, value] of Object.entries(propertyFields)) {
+        if (JSON.stringify(value) === JSON.stringify(before[property])) delete data[property as keyof ContactCard];
+      }
+    }
+
     setIsSaving(true);
     try {
       // `media` goes out only when the photo changed. An update without it
@@ -1029,31 +1130,61 @@ export function ContactForm({ contact, addressBooks, allKeywords, defaultAddress
           {/* Addresses */}
           <FormSection icon={MapPin} title={t("addresses")} collapsible defaultOpen={addresses.length > 0}>
             <div className="space-y-3">
-              {addresses.map((addr, i) => (
-                <div key={i} className="rounded-md border border-border/60 bg-muted/20 p-3 space-y-2 relative">
-                  <IconButton label={t("remove_entry")} onClick={() => setAddresses(addresses.filter((_, j) => j !== i))} className="absolute top-1 end-1">
-                    <X />
-                  </IconButton>
-                  <Input value={addr.street} onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], street: e.target.value }; setAddresses(n); }} placeholder={t("street")} aria-label={t("street")} />
-                  <div className="grid grid-cols-2 gap-2">
-                    <Input value={addr.locality} onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], locality: e.target.value }; setAddresses(n); }} placeholder={t("city")} aria-label={t("city")} />
-                    <Input value={addr.region} onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], region: e.target.value }; setAddresses(n); }} placeholder={t("region")} aria-label={t("region")} />
+              {addresses.map((addr, i) => {
+                const set = (name: keyof Omit<AddressEntry, "key">) => (e: React.ChangeEvent<HTMLInputElement | HTMLSelectElement>) => {
+                  const n = [...addresses];
+                  n[i] = { ...n[i], [name]: e.target.value };
+                  setAddresses(n);
+                };
+                const original = addr.key ? contact?.addresses?.[addr.key] : undefined;
+                const initialCountry = addr.key ? initialRows.addresses.find(a => a.key === addr.key)?.country : undefined;
+                const style: AddressStyle = addressStyle(addr.country, initialCountry === addr.country ? original?.countryCode : null, locale);
+                const field = (name: "locality" | "region" | "postcode", label: string, className?: string) => (
+                  <Input key={name} value={addr[name]} onChange={set(name)} placeholder={label} aria-label={label} className={className} />
+                );
+                const country = <Input key="country" value={addr.country} onChange={set("country")} placeholder={t("country")} aria-label={t("country")} />;
+                const context = (
+                  <Select key="context" value={addr.context} onChange={set("context")} aria-label={t("context_label")}>
+                    <option value="">-</option>
+                    <option value="work">{t("context_work")}</option>
+                    <option value="private">{tx("context_private")}</option>
+                  </Select>
+                );
+                return (
+                  <div key={addr.key ?? `new-${i}`} data-address-layout={style.town} className="rounded-md border border-border/60 bg-muted/20 p-3 space-y-2 relative">
+                    <IconButton label={t("remove_entry")} onClick={() => setAddresses(addresses.filter((_, j) => j !== i))} className="absolute top-1 end-1">
+                      <X />
+                    </IconButton>
+                    {/* Street and house number in one field, in the order the country writes them. */}
+                    <Input value={addr.street} onChange={set("street")} placeholder={t("street")} aria-label={t("street")} className="pe-10" />
+                    {style.town === "postcode-city" ? (
+                      <>
+                        <div className="grid grid-cols-3 gap-2">
+                          {field("postcode", t("postcode"))}
+                          {field("locality", t("city"), "col-span-2")}
+                        </div>
+                        <div className="grid grid-cols-3 gap-2">
+                          {field("region", t("region"))}
+                          {country}
+                          {context}
+                        </div>
+                      </>
+                    ) : (
+                      <>
+                        <div className="grid grid-cols-2 gap-2">
+                          {field("locality", t("city"))}
+                          {field("region", t("region"))}
+                        </div>
+                        <div className="grid grid-cols-3 gap-2">
+                          {field("postcode", t("postcode"))}
+                          {country}
+                          {context}
+                        </div>
+                      </>
+                    )}
                   </div>
-                  <div className="grid grid-cols-3 gap-2">
-                    <Input value={addr.postcode} onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], postcode: e.target.value }; setAddresses(n); }} placeholder={t("postcode")} aria-label={t("postcode")} />
-                    <Input value={addr.country} onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], country: e.target.value }; setAddresses(n); }} placeholder={t("country")} aria-label={t("country")} />
-                    <Select
-                      value={addr.context}
-                      onChange={(e) => { const n = [...addresses]; n[i] = { ...n[i], context: e.target.value as AddressEntry["context"] }; setAddresses(n); }}
-                      aria-label={t("context_label")}
-                    >
-                      <option value="">-</option>
-                      <option value="work">{t("context_work")}</option>
-                      <option value="private">{tx("context_private")}</option>
-                    </Select>
-                  </div>
-                </div>
-              ))}
+                );
+              })}
               <Button type="button" variant="ghost" size="sm" onClick={() => setAddresses([...addresses, { street: "", locality: "", region: "", postcode: "", country: "", context: "" }])} className="text-xs">
                 <Plus className="w-3 h-3 me-1" />
                 {t("add_address")}
diff --git a/integration/tests/25-ux-pim-contact.spec.ts b/integration/tests/25-ux-pim-contact.spec.ts
new file mode 100644
index 000000000..71d161c5f
--- /dev/null
+++ b/integration/tests/25-ux-pim-contact.spec.ts
@@ -0,0 +1,154 @@
+import { test, expect, type Page } from '@playwright/test';
+import { contextOptions } from './helpers/ent';
+import { JmapClient } from './helpers/jmap';
+import { accountSwitcher, neutralizeDevOverlay } from './helpers/app';
+
+/**
+ * Usability fix pim-4: saving a contact never rewrites an address the user
+ * didn't touch, and an edited address is saved in its country's order.
+ * Against a VM 106 Stalwart (1.0 and 0.16, which converts cards through
+ * vCard), every UI step is checked on the server.
+ *
+ * Account: dso-ux-pim (password IT_DSO_PASSWORD). The spec makes its own
+ * card, named "UXFIX-contact …", and removes it again.
+ */
+
+const PASSWORD = process.env.IT_DSO_PASSWORD ?? '';
+const A = 'dso-ux-pim@example.org';
+const CORE = 'urn:ietf:params:jmap:core';
+const CONTACTS = 'urn:ietf:params:jmap:contacts';
+const RUN = Date.now().toString(36);
+const PREFIX = 'UXFIX-contact';
+
+test.skip(!PASSWORD, 'Set IT_DSO_PASSWORD (vault "Stalwart test – dso-* throwaway accounts")');
+
+type Address = Record<string, unknown> & { components?: Array<{ kind: string; value: string }> };
+type Card = Record<string, unknown> & {
+  id: string;
+  name?: { full?: string; components?: Array<{ kind: string; value: string }> };
+  nicknames?: Record<string, { name: string }>;
+  addresses?: Record<string, Address>;
+};
+
+async function defaultBook(c: JmapClient): Promise<string> {
+  const r = await c.request([['AddressBook/get', { accountId: c.accountId }, '0']], [CORE, CONTACTS]);
+  const list = r.methodResponses[0][1].list as Array<{ id: string; isDefault?: boolean }>;
+  return (list.find((b) => b.isDefault) ?? list[0]).id;
+}
+
+async function cards(c: JmapClient): Promise<Card[]> {
+  const r = await c.request([
+    ['ContactCard/query', { accountId: c.accountId, limit: 1000 }, 'q'],
+    ['ContactCard/get', { accountId: c.accountId, '#ids': { resultOf: 'q', name: 'ContactCard/query', path: '/ids' } }, 'g'],
+  ], [CORE, CONTACTS]);
+  const named = (card: Card) => card.name?.full ?? card.name?.components?.map((x) => x.value).join(' ') ?? '';
+  return (r.methodResponses[1][1].list as Card[]).filter((card) => named(card).startsWith(PREFIX));
+}
+
+async function getCard(c: JmapClient, id: string): Promise<Card> {
+  const r = await c.request([['ContactCard/get', { accountId: c.accountId, ids: [id] }, '0']], [CORE, CONTACTS]);
+  return r.methodResponses[0][1].list[0] as Card;
+}
+
+async function login(page: Page): Promise<void> {
+  await neutralizeDevOverlay(page);
+  await page.goto('/');
+  await page.locator('#username').waitFor({ state: 'visible', timeout: 60000 });
+  await page.fill('#username', A);
+  await page.fill('#password', PASSWORD);
+  await page.click('button[type="submit"]');
+  await accountSwitcher(page).waitFor({ state: 'visible', timeout: 60000 });
+}
+
+test.describe('Saving a contact keeps its address (pim-4)', () => {
+  test.afterAll(async () => {
+    const a = await JmapClient.connect(A, PASSWORD);
+    const ids = (await cards(a)).filter((card) => JSON.stringify(card.name).includes(RUN)).map((card) => card.id);
+    if (ids.length) await a.request([['ContactCard/set', { accountId: a.accountId, destroy: ids }, '0']], [CORE, CONTACTS]);
+  });
+
+  test('a nickname edit leaves a German address as stored, an address edit saves it in German order', async ({ browser }) => {
+    test.setTimeout(240_000);
+    const a = await JmapClient.connect(A, PASSWORD);
+    const surname = `Adresse ${RUN}`;
+    const created = await a.request([['ContactCard/set', {
+      accountId: a.accountId,
+      create: {
+        c: {
+          '@type': 'Card',
+          version: '1.0',
+          kind: 'individual',
+          addressBookIds: { [await defaultBook(a)]: true },
+          name: { '@type': 'Name', components: [{ kind: 'given', value: PREFIX }, { kind: 'surname', value: surname }], isOrdered: true },
+          phones: { p1: { '@type': 'Phone', number: '+49 30 123456', features: { voice: true }, contexts: { private: true } } },
+          addresses: {
+            home: {
+              '@type': 'Address',
+              contexts: { private: true },
+              countryCode: 'DE',
+              isOrdered: true,
+              defaultSeparator: ', ',
+              components: [
+                { kind: 'name', value: 'Hauptstraße' },
+                { kind: 'separator', value: ' ' },
+                { kind: 'number', value: '1' },
+                { kind: 'apartment', value: '3. OG' },
+                { kind: 'postcode', value: '10000' },
+                { kind: 'locality', value: 'Berlin' },
+                { kind: 'country', value: 'Germany' },
+              ],
+            },
+          },
+        },
+      },
+    }, '0']], [CORE, CONTACTS]);
+    const id = created.methodResponses[0][1].created?.c?.id as string | undefined;
+    expect(id, JSON.stringify(created.methodResponses[0][1].notCreated ?? {})).toBeTruthy();
+    // The address as this server keeps it (0.16 goes through vCard).
+    const stored = (await getCard(a, id!)).addresses!;
+    expect(Object.keys(stored)).toHaveLength(1);
+
+    const context = await browser.newContext(contextOptions());
+    const page = await context.newPage();
+    await login(page);
+    await page.goto('/contacts');
+    await page.getByPlaceholder('Search contacts...').fill(RUN);
+    await page.locator('[data-contact-id]', { hasText: surname }).first().click();
+
+    // The contact page lays the address out the German way, one line per part.
+    const addressLines = page.getByTestId('contact-address').first().locator('[data-address-line]');
+    await expect(addressLines).toHaveText(['Hauptstraße 1, 3. OG', '10000 Berlin', 'Germany']);
+    await expect(page.getByText('Home · Phone', { exact: true })).toBeVisible();
+
+    // 1. Only the nickname changes: the server's address stays exactly as it was.
+    await page.getByRole('button', { name: 'Edit contact' }).click();
+    await expect(page.getByLabel('Street')).toHaveValue('Hauptstraße 1');
+    await page.getByLabel('Nickname').fill('Adi');
+    await page.getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(page.getByText('Contact updated')).toBeVisible({ timeout: 30000 });
+    await expect.poll(async () => Object.values((await getCard(a, id!)).nicknames ?? {})[0]?.name, { timeout: 30000 }).toBe('Adi');
+    expect((await getCard(a, id!)).addresses).toEqual(stored);
+
+    // 2. The address is edited: saved in German order, apartment and context kept.
+    await page.getByRole('button', { name: 'Edit contact' }).click();
+    await page.getByLabel('Street').fill('Hauptstraße 12a');
+    await page.getByLabel('Postal code').fill('10115');
+    await page.getByRole('button', { name: 'Save', exact: true }).click();
+    await expect.poll(async () => {
+      const address = Object.values((await getCard(a, id!)).addresses ?? {})[0];
+      return address?.components?.map((x) => `${x.kind}:${x.value}`);
+    }, { timeout: 30000 }).toEqual([
+      'name:Hauptstraße', 'separator: ', 'number:12a', 'apartment:3. OG', 'postcode:10115', 'separator: ', 'locality:Berlin', 'country:Germany',
+    ]);
+    const edited = Object.values((await getCard(a, id!)).addresses!)[0];
+    expect(edited).toMatchObject({ countryCode: 'DE', contexts: { private: true }, isOrdered: true });
+    await expect(addressLines).toHaveText(['Hauptstraße 12a, 3. OG', '10115 Berlin', 'Germany']);
+
+    // A reload reads the card back from the server, not from the app's memory.
+    await page.reload();
+    await page.getByPlaceholder('Search contacts...').fill(RUN);
+    await page.locator('[data-contact-id]', { hasText: surname }).first().click();
+    await expect(addressLines).toHaveText(['Hauptstraße 12a, 3. OG', '10115 Berlin', 'Germany']);
+    await context.close();
+  });
+});
diff --git a/lib/__tests__/address-format.test.ts b/lib/__tests__/address-format.test.ts
new file mode 100644
index 000000000..c6fd7818e
--- /dev/null
+++ b/lib/__tests__/address-format.test.ts
@@ -0,0 +1,86 @@
+import { describe, it, expect } from 'vitest';
+import {
+  addressStyle,
+  addressToParts,
+  countryCodeFromName,
+  formatAddressLines,
+  partsToComponents,
+  splitStreet,
+} from '../address-format';
+import type { ContactAddress } from '@/lib/jmap/types';
+
+const german: ContactAddress = {
+  components: [
+    { kind: 'name', value: 'Hauptstraße' },
+    { kind: 'number', value: '1' },
+    { kind: 'postcode', value: '10000' },
+    { kind: 'locality', value: 'Berlin' },
+    { kind: 'country', value: 'Germany' },
+  ],
+};
+
+describe('address-format', () => {
+  it('knows countries by code and by name in several languages', () => {
+    expect(countryCodeFromName('Germany')).toBe('DE');
+    expect(countryCodeFromName('Deutschland')).toBe('DE');
+    expect(countryCodeFromName('Schweiz')).toBe('CH');
+    expect(countryCodeFromName('de')).toBe('DE');
+    expect(countryCodeFromName('USA')).toBe('US');
+    expect(countryCodeFromName('United Kingdom')).toBe('GB');
+    expect(countryCodeFromName('Atlantis')).toBeNull();
+  });
+
+  it('puts the number after the street for Germany and before it for the US', () => {
+    expect(addressStyle('Germany').street).toBe('number-after');
+    expect(addressStyle('Österreich').street).toBe('number-after');
+    expect(addressStyle('Netherlands').street).toBe('number-after');
+    expect(addressStyle('United States').street).toBe('number-before');
+    expect(addressStyle('France')).toEqual({ street: 'number-before', town: 'postcode-city' });
+    expect(addressStyle('', 'CA').town).toBe('city-region-postcode');
+    // No country: the UI language's.
+    expect(addressStyle('', null, 'de').street).toBe('number-after');
+    expect(addressStyle('', null, 'en').street).toBe('number-before');
+  });
+
+  it('shows street and number in one field in the country\'s order', () => {
+    expect(addressToParts(german).street).toBe('Hauptstraße 1');
+    expect(addressToParts({ ...german, countryCode: 'US', components: [
+      { kind: 'number', value: '1' }, { kind: 'name', value: 'Main Street' }, { kind: 'country', value: 'USA' },
+    ] }).street).toBe('1 Main Street');
+    // A country this file doesn't know keeps the card's own order.
+    expect(addressToParts({ components: [
+      { kind: 'name', value: 'Ulitsa' }, { kind: 'number', value: '7' }, { kind: 'country', value: 'Atlantis' },
+    ] }).street).toBe('Ulitsa 7');
+  });
+
+  it('splits a typed street line where the country puts the number', () => {
+    expect(splitStreet('Hauptstraße 12a', 'number-after')).toEqual({ name: 'Hauptstraße', number: '12a' });
+    expect(splitStreet('Am Markt 3-5', 'number-after')).toEqual({ name: 'Am Markt', number: '3-5' });
+    expect(splitStreet('Am Markt', 'number-after')).toEqual({ name: 'Am Markt', number: '' });
+    expect(splitStreet('221B Baker Street', 'number-before')).toEqual({ name: 'Baker Street', number: '221B' });
+    expect(splitStreet('Baker Street 221', 'number-before')).toEqual({ name: 'Baker Street 221', number: '' });
+  });
+
+  it('builds components in the country\'s order, keeping parts the form doesn\'t show', () => {
+    const parts = { street: 'Hauptstraße 1', locality: 'Berlin', region: '', postcode: '10000', country: 'Germany' };
+    const components = partsToComponents(parts, [{ kind: 'apartment', value: '3. OG' }]);
+    expect(components.map(c => `${c.kind}:${c.value}`)).toEqual([
+      'name:Hauptstraße', 'separator: ', 'number:1', 'apartment:3. OG', 'postcode:10000', 'separator: ', 'locality:Berlin', 'country:Germany',
+    ]);
+    const us = partsToComponents({ street: '1 Main St', locality: 'Springfield', region: 'IL', postcode: '62701', country: 'USA' });
+    expect(us.map(c => `${c.kind}:${c.value}`)).toEqual([
+      'number:1', 'separator: ', 'name:Main St', 'locality:Springfield', 'region:IL', 'separator: ', 'postcode:62701', 'country:USA',
+    ]);
+  });
+
+  it('formats an address one line per part, for its country', () => {
+    expect(formatAddressLines(german)).toEqual(['Hauptstraße 1', '10000 Berlin', 'Germany']);
+    expect(formatAddressLines({ components: [
+      { kind: 'number', value: '1' }, { kind: 'name', value: 'Main St' }, { kind: 'locality', value: 'Springfield' },
+      { kind: 'region', value: 'IL' }, { kind: 'postcode', value: '62701' }, { kind: 'country', value: 'USA' },
+    ] })).toEqual(['1 Main St', 'Springfield, IL 62701', 'USA']);
+    expect(formatAddressLines({ street: '10 Downing Street', locality: 'London', postcode: 'SW1A 2AA', country: 'United Kingdom' }))
+      .toEqual(['10 Downing Street', 'London', 'SW1A 2AA', 'United Kingdom']);
+    expect(formatAddressLines({ full: 'Somewhere 1\n12345 Town' })).toEqual(['Somewhere 1', '12345 Town']);
+  });
+});
diff --git a/lib/address-format.ts b/lib/address-format.ts
new file mode 100644
index 000000000..4018a370b
--- /dev/null
+++ b/lib/address-format.ts
@@ -0,0 +1,262 @@
+import type { AddressComponent, ContactAddress } from "@/lib/jmap/types";
+
+/**
+ * Postal addresses laid out the way the address's country writes them.
+ *
+ * Two things differ between countries here: whether the house number comes
+ * after the street name ("Hauptstraße 1") or before it ("1 Main Street"), and
+ * whether the postcode leads the town line ("10115 Berlin", "75001 Paris"),
+ * follows it ("Springfield, IL 62701") or has a line of its own (UK).
+ */
+
+export type StreetOrder = "number-after" | "number-before";
+export type TownLine = "postcode-city" | "city-region-postcode" | "city-then-postcode";
+
+export interface AddressStyle {
+  street: StreetOrder;
+  town: TownLine;
+}
+
+const NUMBER_AFTER = [
+  "DE", "AT", "CH", "LI", "NL", "BE", "IT", "SM", "VA", "ES", "AD", "PT", "DK", "IS", "NO", "SE", "FI",
+  "PL", "CZ", "SK", "HU", "SI", "HR", "BA", "RS", "ME", "MK", "AL", "RO", "BG", "GR", "CY", "TR",
+  "EE", "LV", "LT", "RU", "UA", "BY", "MX", "AR", "BR", "CL", "UY", "PY", "BO", "PE", "VE", "EC",
+];
+const NUMBER_BEFORE = ["US", "CA", "GB", "IE", "FR", "MC", "LU", "AU", "NZ", "ZA", "IN", "SG", "PH", "MY", "IL", "HK"];
+const CITY_REGION_POSTCODE = ["US", "CA", "AU"];
+const CITY_THEN_POSTCODE = ["GB", "IE"];
+
+const KNOWN_CODES = [...NUMBER_AFTER, ...NUMBER_BEFORE];
+
+/** The style for an ISO 3166 code, or null for a country this file doesn't know. */
+export function styleForCountryCode(code: string | undefined | null): AddressStyle | null {
+  const cc = code?.trim().toUpperCase();
+  if (!cc) return null;
+  const c = cc === "UK" ? "GB" : cc;
+  if (!KNOWN_CODES.includes(c)) return null;
+  return {
+    street: NUMBER_AFTER.includes(c) ? "number-after" : "number-before",
+    town: CITY_REGION_POSTCODE.includes(c) ? "city-region-postcode"
+      : CITY_THEN_POSTCODE.includes(c) ? "city-then-postcode"
+        : "postcode-city",
+  };
+}
+
+// Country names as people type them: each known code's name in these
+// languages, plus a few short forms.
+const NAME_LOCALES = ["en", "de", "fr", "es", "it", "nl", "pt", "pl", "sv", "da", "nb", "fi", "cs", "sk", "hu", "tr", "ru", "uk", "ro", "el", "hr", "sl", "et", "lv", "lt", "ca"];
+const ALIASES: Record<string, string> = {
+  usa: "US", "u.s.a.": "US", "u.s.": "US", "united states of america": "US", america: "US",
+  uk: "GB", "u.k.": "GB", england: "GB", scotland: "GB", wales: "GB", "great britain": "GB", "northern ireland": "GB",
+  holland: "NL", brd: "DE", "bundesrepublik deutschland": "DE", "the netherlands": "NL",
+  "schweiz": "CH", "suisse": "CH", "svizzera": "CH", "österreich": "AT", "osterreich": "AT",
+};
+let nameIndex: Map<string, string> | null = null;
+
+function normalise(name: string): string {
+  return name.trim().toLowerCase().replace(/\s+/g, " ");
+}
+
+function countryNameIndex(): Map<string, string> {
+  if (nameIndex) return nameIndex;
+  const index = new Map<string, string>();
+  for (const [alias, code] of Object.entries(ALIASES)) index.set(alias, code);
+  for (const locale of NAME_LOCALES) {
+    let names: Intl.DisplayNames;
+    try {
+      names = new Intl.DisplayNames([locale], { type: "region" });
+    } catch {
+      continue;
+    }
+    for (const code of KNOWN_CODES) {
+      const name = names.of(code);
+      if (name && name !== code) {
+        const key = normalise(name);
+        if (!index.has(key)) index.set(key, code);
+      }
+    }
+  }
+  nameIndex = index;
+  return index;
+}
+
+/** The ISO code for a typed country ("Germany", "Deutschland", "DE"), or null. */
+export function countryCodeFromName(country: string | undefined | null): string | null {
+  const key = normalise(country ?? "");
+  if (!key) return null;
+  if (/^[a-z]{2}$/.test(key)) {
+    const code = key.toUpperCase() === "UK" ? "GB" : key.toUpperCase();
+    return KNOWN_CODES.includes(code) ? code : null;
+  }
+  return countryNameIndex().get(key) ?? null;
+}
+
+// The country a UI language most likely means, for addresses without one.
+const LANGUAGE_COUNTRY: Record<string, string> = {
+  de: "DE", nl: "NL", it: "IT", es: "ES", ca: "ES", pt: "PT", da: "DK", nb: "NO", sv: "SE", fi: "FI",
+  pl: "PL", cs: "CZ", sk: "SK", hu: "HU", ro: "RO", tr: "TR", et: "EE", lv: "LV", lt: "LT", ru: "RU",
+  uk: "UA", el: "GR", fr: "FR", en: "US",
+};
+
+/**
+ * The style for an address: from its country code, else its country's name,
+ * else the UI language's country, else US style.
+ */
+export function addressStyle(country: string | undefined | null, countryCode?: string | null, locale?: string): AddressStyle {
+  return styleForCountryCode(countryCode)
+    ?? styleForCountryCode(countryCodeFromName(country))
+    ?? styleForCountryCode(LANGUAGE_COUNTRY[(locale ?? "").split(/[-_]/)[0].toLowerCase()])
+    ?? { street: "number-before", town: "city-region-postcode" };
+}
+
+/** "Hauptstraße" + "1" as the country writes it. */
+export function joinStreet(name: string, number: string, order: StreetOrder): string {
+  const parts = order === "number-after" ? [name, number] : [number, name];
+  return parts.map(p => p.trim()).filter(Boolean).join(" ");
+}
+
+const HOUSE_NUMBER = String.raw`\d+\s?[a-zA-Z]?(?:\s?[-–/]\s?\d+\s?[a-zA-Z]?)?`;
+const NUMBER_LAST = new RegExp(String.raw`^(.*\S)\s+(${HOUSE_NUMBER})$`);
+const NUMBER_FIRST = new RegExp(String.raw`^(${HOUSE_NUMBER})\s+(\S.*)$`);
+
+/**
+ * Splits a typed street line into street name and house number where the
+ * number sits where the country puts it. Anything else stays whole as the
+ * name ("Am Markt", "Hauptstraße 1, Hinterhaus").
+ */
+export function splitStreet(line: string, order: StreetOrder): { name: string; number: string } {
+  const text = line.trim().replace(/\s+/g, " ");
+  if (order === "number-after") {
+    const m = NUMBER_LAST.exec(text);
+    if (m) return { name: m[1].replace(/,$/, ""), number: m[2] };
+  } else {
+    const m = NUMBER_FIRST.exec(text);
+    if (m) return { name: m[2], number: m[1].replace(/,$/, "") };
+  }
+  return { name: text, number: "" };
+}
+
+/** Kinds the contact form shows as fields of their own. */
+const FORM_KINDS = new Set(["name", "number", "locality", "region", "postcode", "country", "separator"]);
+/** Kinds that belong on the street line ("Hauptstraße 1, 3. OG"). */
+const STREET_EXTRAS = new Set(["apartment", "room", "floor", "building", "block", "direction", "landmark"]);
+
+function valuesOf(components: AddressComponent[], kind: string): string {
+  return components.filter(c => c.kind === kind).map(c => c.value?.trim()).filter(Boolean).join(" ");
+}
+
+/** The parts of an address as the contact form edits them. */
+export interface AddressParts {
+  street: string;
+  locality: string;
+  region: string;
+  postcode: string;
+  country: string;
+}
+
+/**
+ * The form's fields for an address. Street name and number become one line in
+ * the order of the address's country; for a country not known here, in the
+ * order the components have.
+ */
+export function addressToParts(address: ContactAddress, locale?: string): AddressParts {
+  const components = address.components ?? [];
+  if (components.length === 0) {
+    return {
+      street: address.street ?? "",
+      locality: address.locality ?? "",
+      region: address.region ?? "",
+      postcode: address.postcode ?? "",
+      country: address.country ?? "",
+    };
+  }
+  const country = valuesOf(components, "country");
+  const name = valuesOf(components, "name");
+  const number = valuesOf(components, "number");
+  const known = styleForCountryCode(address.countryCode) ?? styleForCountryCode(countryCodeFromName(country));
+  let order: StreetOrder;
+  if (known) order = known.street;
+  else {
+    const nameAt = components.findIndex(c => c.kind === "name");
+    const numberAt = components.findIndex(c => c.kind === "number");
+    order = nameAt >= 0 && numberAt >= 0
+      ? (numberAt > nameAt ? "number-after" : "number-before")
+      : addressStyle(country, null, locale).street;
+  }
+  return {
+    street: joinStreet(name, number, order),
+    locality: valuesOf(components, "locality"),
+    region: valuesOf(components, "region"),
+    postcode: valuesOf(components, "postcode"),
+    country,
+  };
+}
+
+const sep = (value: string): AddressComponent => ({ kind: "separator", value });
+
+/**
+ * RFC 9553 components for edited form fields, in the country's order, with
+ * separators inside a line and `defaultSeparator` (", ") between lines.
+ * Components the form doesn't show (apartment, district, PO box...) are kept
+ * from `previous`.
+ */
+export function partsToComponents(parts: AddressParts, previous: AddressComponent[] = [], locale?: string, countryCode?: string | null): AddressComponent[] {
+  const style = addressStyle(parts.country, countryCode, locale);
+  const { name, number } = splitStreet(parts.street, style.street);
+  const extras = previous.filter(c => !FORM_KINDS.has(c.kind) && c.value?.trim());
+  const comp = (kind: string, value: string): AddressComponent[] => value.trim() ? [{ kind, value: value.trim() }] : [];
+  const line = (...groups: AddressComponent[][]): AddressComponent[] => {
+    const filled = groups.filter(g => g.length > 0);
+    return filled.flatMap((g, i) => (i === 0 ? g : [sep(" "), ...g]));
+  };
+
+  const streetLine = style.street === "number-after"
+    ? line(comp("name", name), comp("number", number))
+    : line(comp("number", number), comp("name", name));
+  const streetExtras = extras.filter(c => STREET_EXTRAS.has(c.kind));
+  const otherExtras = extras.filter(c => !STREET_EXTRAS.has(c.kind));
+
+  const lines: AddressComponent[][] = [streetLine, ...streetExtras.map(c => [c]), ...otherExtras.map(c => [c])];
+  if (style.town === "postcode-city") {
+    lines.push(line(comp("postcode", parts.postcode), comp("locality", parts.locality)), comp("region", parts.region));
+  } else if (style.town === "city-region-postcode") {
+    lines.push(comp("locality", parts.locality), line(comp("region", parts.region), comp("postcode", parts.postcode)));
+  } else {
+    lines.push(comp("locality", parts.locality), comp("region", parts.region), comp("postcode", parts.postcode));
+  }
+  lines.push(comp("country", parts.country));
+  // Lines follow each other through defaultSeparator, so no separator between them.
+  return lines.filter(l => l.length > 0).flat();
+}
+
+/**
+ * An address as lines to show, laid out for its country: "Hauptstraße 1" /
+ * "10000 Berlin" / "Germany". Addresses without components show their `full`
+ * text or their flat fields.
+ */
+export function formatAddressLines(address: ContactAddress, locale?: string): string[] {
+  const components = (address.components ?? []).filter(c => c.kind !== "separator" && c.value?.trim());
+  if (components.length === 0) {
+    const full = address.full || address.fullAddress;
+    if (full) return full.split(/\r?\n/).map(l => l.trim()).filter(Boolean);
+  }
+  const parts = addressToParts(address, locale);
+  const style = addressStyle(parts.country, address.countryCode, locale);
+  const lines: string[] = [];
+  const extras = components.filter(c => !FORM_KINDS.has(c.kind));
+  const streetExtras = extras.filter(c => STREET_EXTRAS.has(c.kind)).map(c => c.value.trim());
+  const street = [parts.street, ...streetExtras].filter(Boolean).join(", ");
+  if (street) lines.push(street);
+  for (const c of extras.filter(c => !STREET_EXTRAS.has(c.kind))) lines.push(c.value.trim());
+  const join = (...xs: string[]) => xs.map(x => x.trim()).filter(Boolean).join(" ");
+  if (style.town === "postcode-city") {
+    lines.push(join(parts.postcode, parts.locality), parts.region);
+  } else if (style.town === "city-region-postcode") {
+    const regionPostcode = join(parts.region, parts.postcode);
+    lines.push([parts.locality.trim(), regionPostcode].filter(Boolean).join(", "));
+  } else {
+    lines.push(parts.locality, parts.region, parts.postcode);
+  }
+  lines.push(parts.country);
+  return lines.map(l => l.trim()).filter(Boolean);
+}