Extract provision_merchant() service for shared use

Both _auto_create_merchant (lazy GET fallback in views_api) and
LNbits' _create_default_merchant (eager signup hook) used to
reimplement merchant + zone + stall creation independently. Moves the
canonical implementation to services.provision_merchant() so both
call sites stay in lockstep — future changes (NIP-17 kind 10050 relay
list, additional default zones, etc.) only happen in one place.

- services.provision_merchant(user_id, wallet_id, public_key,
  private_key, display_name, config): creates merchant if absent,
  default 'Online' zone, default '<username>'s Store' stall, and
  publishes the kind 30017 stall event. Idempotent on the merchant
  pubkey: returns the existing merchant unchanged if one exists.
- views_api._auto_create_merchant: now a 10-line wrapper that loads
  the account, generates fallback keys if missing, then delegates.

The LNbits-side hook (lnbits/core/services/users.py:_create_default_merchant)
will be updated in a companion commit to also call this service.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services.py

@@ -12,9 +12,11 @@ from .crud import (
     CustomerProfile,
     create_customer,
     create_direct_message,
+    create_merchant,
     create_order,
     create_product,
     create_stall,
+    create_zone,
     get_customer,
     get_last_direct_messages_created_at,
     get_last_product_update_time,
@@ -42,6 +44,7 @@ from .models import (
     DirectMessage,
     DirectMessageType,
     Merchant,
+    MerchantConfig,
     Nostrable,
     Order,
     OrderContact,
@@ -49,11 +52,13 @@ from .models import (
     OrderItem,
     OrderStatusUpdate,
     PartialDirectMessage,
+    PartialMerchant,
     PartialOrder,
     PaymentOption,
     PaymentRequest,
     Product,
     Stall,
+    Zone,
 )
 from .nostr.event import NostrEvent
 from .nostr.nip59 import unwrap_message, wrap_message
@@ -180,6 +185,72 @@ async def sign_and_send_to_nostr(
     return event
 
 
+async def provision_merchant(
+    user_id: str,
+    wallet_id: str,
+    public_key: str,
+    private_key: str,
+    display_name: Optional[str] = None,
+    config: Optional[MerchantConfig] = None,
+) -> Merchant:
+    """
+    Provision a merchant with a default shipping zone and default stall,
+    and publish the stall to Nostr relays.
+
+    Single source of truth used by:
+    - LNbits user-creation hook (eager, on signup) — see
+      lnbits/core/services/users.py:_create_default_merchant
+    - nostrmarket views_api._auto_create_merchant (lazy, on first GET
+      /api/v1/merchant when a merchant is missing).
+
+    Idempotent on the merchant: if a merchant with this pubkey already
+    exists, returns it without recreating zone/stall.
+    """
+    existing = await get_merchant_by_pubkey(public_key)
+    if existing:
+        return existing
+
+    partial_merchant = PartialMerchant(
+        private_key=private_key,
+        public_key=public_key,
+        config=config or MerchantConfig(),
+    )
+    merchant = await create_merchant(user_id, partial_merchant)
+
+    online_zone = Zone(
+        id=f"online-{merchant.public_key}",
+        name="Online",
+        currency="sat",
+        cost=0,
+        countries=["Free (digital)"],
+    )
+    await create_zone(merchant.id, online_zone)
+
+    name = display_name or "My"
+    default_stall = Stall(
+        wallet=wallet_id,
+        name=f"{name}'s Store",
+        currency="sat",
+        shipping_zones=[online_zone],
+    )
+    default_stall = await create_stall(merchant.id, default_stall)
+
+    # Publish the kind 30017 stall event so customers' clients can resolve
+    # the stall name when they fetch products. Non-fatal on failure: a
+    # later product publish (or webapp self-heal) will retry.
+    try:
+        stall_event = await sign_and_send_to_nostr(merchant, default_stall)
+        default_stall.event_id = stall_event.id
+        await update_stall(merchant.id, default_stall)
+    except Exception as ex:
+        logger.warning(
+            f"[NOSTRMARKET] Failed to publish default stall for "
+            f"merchant {merchant.id}: {ex}"
+        )
+
+    return merchant
+
+
 async def handle_order_paid(order_id: str, merchant_pubkey: str):
     try:
         order = await update_order_paid_status(order_id, True)