444 bytes

#include<string>
#define F r.find(
#define U(S,n)p=F s(S)+b[i]);if(p-size_t(-1)){b.replace(i,1,r.substr(p+n+1,F'/',n+p)-p-2));r.replace(p+1,F'/',p+1)-p,"");}
#define V(A)i<A.size();++i,c
using s=std::string;s m(s a){s b,r="/a@/b8/c(/d6/e3/f#/g9/h#/i1//i!/k</l1//li/o0/q9/s5//s$/t+/v>/wuu//w2u/x%/y?/";int c=1,i=0;for(;V(a)=1){for(;a[i]==a[i+1]&&1+V(a)++);b+=(c-1?std::to_string(c):"")+a[i];}for(i=0;V(b)){auto U("/",1)else{U("//",2)}}return b;}