feat: start on a blank container — spawn with empty:true and no repo (skip clone, default worker image); Spawn UI enables blank spawn without repo selection

daemon/api.go

@@ -373,7 +373,13 @@ func (s *Server) handleSpawn(w http.ResponseWriter, r *http.Request) {
 	if !decodeBody(w, r, &body) {
 		return
 	}
-	if !validRepoPath(body.Repo) {
+	// Blank-container spawns carry no repo; everything else must look like
+	// group/project.
+	if body.Repo == "" && !body.Empty {
+		writeError(w, http.StatusBadRequest, "repo required (or set empty for a blank container)")
+		return
+	}
+	if body.Repo != "" && !validRepoPath(body.Repo) {
 		writeError(w, http.StatusBadRequest, "repo must look like group/project")
 		return
 	}

daemon/api_extra_test.go

@@ -682,3 +682,20 @@ func TestRenameAndSetModelBodyValidation(t *testing.T) {
 		t.Fatalf("bad model body = %d, want 400", code)
 	}
 }
+
+func TestAPISpawnBlankContainerNoRepo(t *testing.T) {
+	ts, _ := newSpawnAPIServer(t)
+
+	// no repo and not empty → 400
+	if code, body := apiReq(t, http.MethodPost, ts.URL+"/api/spawn", testToken, `{"repo":""}`); code != http.StatusBadRequest {
+		t.Fatalf("no-repo non-empty spawn = %d %s, want 400", code, body)
+	}
+	// blank container: no repo required
+	code, body := apiReq(t, http.MethodPost, ts.URL+"/api/spawn", testToken, `{"empty":true}`)
+	if code != http.StatusCreated {
+		t.Fatalf("blank spawn = %d %s, want 201", code, body)
+	}
+	if !strings.Contains(body, `"sessionId"`) {
+		t.Fatalf("blank spawn body = %s, want sessionId", body)
+	}
+}

daemon/docker.go

@@ -298,9 +298,12 @@ func (s *Spawner) runJob(repo, branch, model string, empty bool, sessionID strin
 	lock.Lock()
 	defer lock.Unlock()
 
-	if err := s.cloneOrUpdate(s.ctx, repo, branch, slug); err != nil {
-		s.setJob(sessionID, repo, stateError, "", err.Error())
-		return
+	// blank-container spawn: nothing to clone or update
+	if repo != "" {
+		if err := s.cloneOrUpdate(s.ctx, repo, branch, slug); err != nil {
+			s.setJob(sessionID, repo, stateError, "", err.Error())
+			return
+		}
 	}
 	s.setJob(sessionID, repo, stateBuilding, "", "")
 	if err := s.ensureImage(s.ctx); err != nil {

daemon/spawner_test.go

@@ -1348,3 +1348,24 @@ func TestSpawnerEmptyScratch(t *testing.T) {
 		t.Fatalf("sessions volume missing: %v", binds)
 	}
 }
+
+func TestSpawnerEmptyScratchNoRepo(t *testing.T) {
+	f := newFakeDocker()
+	sp, _ := newTestSpawner(t, f)
+
+	res, err := sp.Start(context.Background(), "", "", "", true)
+	if err != nil {
+		t.Fatalf("Start with no repo: %v", err)
+	}
+	waitJobState(t, sp, res.SessionID, stateRunning)
+	creates := f.createsByName("lvmh-agent-")
+	if len(creates) != 1 {
+		t.Fatalf("creates = %d, want 1", len(creates))
+	}
+	for _, b := range creates[0].HostConfig.Binds {
+		if b == "lvmh-sessions:/pi-sessions" || b == "lvmh-pi-cache:/root/.pi/agent/cache" {
+			continue
+		}
+		t.Fatalf("blank spawn must mount no repo volume: %v", creates[0].HostConfig.Binds)
+	}
+}