fix(review round 2): daemon symlink tars, orphan-safe removes, unique seed names, git ctx, IsErrNotFound, collision-free slugs, branch validation; web first-run WS, draft reset, IME guard, churn fix, test swap repair; 106 daemon + 190 web tests green

daemon/api.go

@@ -280,6 +280,10 @@ func (s *Server) handleSpawn(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "repo must look like group/project")
 		return
 	}
+	if body.Branch != "" && !branchRe.MatchString(body.Branch) {
+		writeError(w, http.StatusBadRequest, "invalid branch name")
+		return
+	}
 	res, err := s.spawn.Start(r.Context(), body.Repo, body.Branch)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, err.Error())