Stop merging unrelated emails into a customer's other open ticket

Inbound email with no In-Reply-To/References match against a tracked
message now always opens a new ticket, instead of falling back to the
customer's most recent open ticket. That fallback made sense for
Telegram/website chat (no subject, single running stream) but was
wrong for email, where an unrelated new request from a repeat
customer got silently appended to whatever ticket happened to still
be open.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gh2UXUQUVBWroWEnn1FLFG

src/lib/tickets/service.ts

@@ -310,10 +310,12 @@ export async function recordChatInboundMessage(params: {
 }
 
 /**
- * Records an inbound email. Prefers exact thread matching via
- * In-Reply-To/References (so a reply to a specific closed ticket lands on
- * that ticket, not a random other open one); falls back to the same
- * find-or-create-open-ticket heuristic used for Telegram.
+ * Records an inbound email. Threads it onto an existing ticket only via
+ * exact In-Reply-To/References matching. Unlike Telegram/the website widget
+ * (a continuous chat stream with no subject), email always carries a
+ * distinct subject per conversation — so a message with no header match is
+ * always a new, unrelated request and must become its own ticket, even if
+ * the customer already has another ticket open.
  */
 export async function recordEmailInboundMessage(params: {
   fromEmail: string;
@@ -330,7 +332,7 @@ export async function recordEmailInboundMessage(params: {
   const matchedTicketId = await findTicketIdByEmailReferences(params.referencedMessageIds);
   let ticket = matchedTicketId
     ? await db.query.tickets.findFirst({ where: eq(tickets.id, matchedTicketId) })
-    : await findOpenTicketForCustomer(customer.id);
+    : null;
 
   let ticketIsNew = false;
   if (!ticket) {