fix: harden the per-user IPC endpoint

ipc.h

@@ -3,8 +3,6 @@
 
 #include <stddef.h>
 
-#define IPCPATH "/tmp/strans.%d"
-
 /*
  * Request: [flags, modifiers, key byte 0, ..., key byte 3].
  * Flags request preedit and distinguish lifecycle reset from physical Escape.
@@ -61,5 +59,7 @@ int	ipcpackresp(unsigned char*, size_t, int, const char*, size_t, const char*, s
 int	ipcreadn(int, void*, size_t);
 int	ipcsend(int, const void*, size_t);
 int	ipcreadresp(int, int, char*, size_t, char*, size_t, Ipcresp*);
+int	ipcpath(char*, size_t);
+int	ipcconnect(void);
 
 #endif