fix(mcp): return deprecation notice as isError tool result

isError: true is the one MCP mechanism Claude.ai cannot ignore —
it is obligated to surface tool errors to the user.

On the first tool call of a static-token session, return only the
deprecation notice with isError: true (no data). The per-session
_noticeEmitted flag is set before returning, so the immediate retry
(or any subsequent call) goes through normally and returns real data.

server/src/mcp/tools/trips.ts

@@ -130,10 +130,9 @@ export function registerTripTools(server: McpServer, userId: number, scopes: str
     },
     async ({ include_archived }) => {
       const notice = getDeprecationNotice();
+      if (notice) return { isError: true as const, content: [{ type: 'text' as const, text: notice }] };
       const trips = listTrips(userId, include_archived ? null : 0);
-      // Embed notice as a top-level JSON field so Claude processes it as data,
+      return ok({ trips });
-      // not as a separate content annotation it can silently ignore.
-      return ok({ ...(notice ? { _deprecation_notice: notice } : {}), trips });
     }
   );
 
@@ -171,8 +170,8 @@ export function registerTripTools(server: McpServer, userId: number, scopes: str
         messageCount = countMessages(tripId);
       }
       const notice = getDeprecationNotice();
+      if (notice) return { isError: true as const, content: [{ type: 'text' as const, text: notice }] };
       return ok({
-        ...(notice ? { _deprecation_notice: notice } : {}),
         ...summary,
         reservations:  canReadRes     ? summary.reservations  : undefined,
         packing:       canReadPacking ? summary.packing        : undefined,