office: promise an attach line only when a session was actually built

bin/office

@@ -364,8 +364,6 @@ def run_on_remote(host, folder, opts):
         sys.stdout.write(out.stdout)
     if out.returncode != 0:
         raise h.Refused(3, "the other machine refused: %s" % (out.stderr or out.stdout).strip()[:300])
-    h.say("")
-    h.say("switch to it:  tuios attach --host %s %s" % (host, opts["session"] or os.path.basename(folder)))
     return 0
 
 
@@ -786,6 +784,14 @@ def main():
         sys.executable,
         [sys.executable, os.path.join(HERE, "board"), "--folder", folder],
     )
+    if code == 0:
+        # Only now is there a session worth attaching to. Promising one earlier
+        # is how a person ends up trying to attach to a session that was never
+        # created, because the project was still waiting for its first commit.
+        client = opts.get("client_host") or ""
+        h.say("")
+        h.say("switch to it:  tuios attach%s %s"
+              % (" --host " + client if client else "", session))
     return code