diff --git a/workspace-server/internal/handlers/registry.go b/workspace-server/internal/handlers/registry.go
index 97ef8537..4e3d6675 100644
--- a/workspace-server/internal/handlers/registry.go
+++ b/workspace-server/internal/handlers/registry.go
@@ -451,16 +451,17 @@ func (h *RegistryHandler) evaluateStatus(c *gin.Context, payload models.Heartbea
 		h.broadcaster.RecordAndBroadcast(ctx, "WORKSPACE_ONLINE", payload.WorkspaceID, map[string]interface{}{})
 	}
 
-	// Auto-recovery: if a workspace is marked "failed" or "provisioning" but is
-	// actively sending heartbeats, it has clearly booted successfully. Transition
-	// to "online" so the scheduler and dashboard reflect reality. This catches
-	// cases where the provisioner crashed mid-setup or an earlier error left the
-	// status stale.
-	if currentStatus == "failed" || currentStatus == "provisioning" {
-		if _, err := db.DB.ExecContext(ctx, `UPDATE workspaces SET status = 'online', updated_at = now() WHERE id = $1 AND status IN ('failed', 'provisioning')`, payload.WorkspaceID); err != nil {
-			log.Printf("Heartbeat: failed to auto-recover %s from %s to online: %v", payload.WorkspaceID, currentStatus, err)
+	// Auto-recovery: if a workspace is marked "provisioning" but is actively sending
+	// heartbeats, it has successfully started up. Transition to "online" so the scheduler
+	// and A2A proxy can dispatch tasks to it. The provisioner does not call
+	// /registry/register on container start — only the heartbeat loop does, so this
+	// transition is the only mechanism that moves newly-started workspaces out of
+	// the phantom-idle state. (#1784)
+	if currentStatus == "provisioning" {
+		if _, err := db.DB.ExecContext(ctx, `UPDATE workspaces SET status = 'online', updated_at = now() WHERE id = $1 AND status = 'provisioning'`, payload.WorkspaceID); err != nil {
+			log.Printf("Heartbeat: failed to transition %s from provisioning to online: %v", payload.WorkspaceID, err)
 		} else {
-			log.Printf("Heartbeat: auto-recovered %s from %s to online (heartbeat received)", payload.WorkspaceID, currentStatus)
+			log.Printf("Heartbeat: transitioned %s from provisioning to online (heartbeat received)", payload.WorkspaceID)
 		}
 		h.broadcaster.RecordAndBroadcast(ctx, "WORKSPACE_ONLINE", payload.WorkspaceID, map[string]interface{}{
 			"recovered_from": currentStatus,
diff --git a/workspace-server/internal/handlers/registry_test.go b/workspace-server/internal/handlers/registry_test.go
index 791f07dc..4d2cb904 100644
--- a/workspace-server/internal/handlers/registry_test.go
+++ b/workspace-server/internal/handlers/registry_test.go
@@ -134,6 +134,56 @@ func TestHeartbeatHandler_OfflineToOnline(t *testing.T) {
 	}
 }
 
+// ==================== Heartbeat — provisioning → online recovery (#1784) ====================
+
+func TestHeartbeatHandler_ProvisioningToOnline(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewRegistryHandler(broadcaster)
+
+	// Expect prevTask SELECT
+	mock.ExpectQuery("SELECT COALESCE\\(current_task").
+		WithArgs("ws-provisioning").
+		WillReturnRows(sqlmock.NewRows([]string{"current_task"}).AddRow(""))
+
+	// Expect heartbeat UPDATE
+	mock.ExpectExec("UPDATE workspaces SET").
+		WithArgs("ws-provisioning", 0.0, "", 1, 3000, "").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Expect evaluateStatus SELECT — currently provisioning
+	mock.ExpectQuery("SELECT status FROM workspaces WHERE id =").
+		WithArgs("ws-provisioning").
+		WillReturnRows(sqlmock.NewRows([]string{"status"}).AddRow("provisioning"))
+
+	// Expect status transition to online (#1784)
+	mock.ExpectExec("UPDATE workspaces SET status = 'online'").
+		WithArgs("ws-provisioning").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Expect RecordAndBroadcast INSERT for WORKSPACE_ONLINE
+	mock.ExpectExec("INSERT INTO structure_events").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+
+	body := `{"workspace_id":"ws-provisioning","error_rate":0.0,"sample_error":"","active_tasks":1,"uptime_seconds":3000}`
+	c.Request = httptest.NewRequest("POST", "/registry/heartbeat", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Heartbeat(c)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected status 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet sqlmock expectations: %v", err)
+	}
+}
+
 func TestHeartbeatHandler_BadJSON(t *testing.T) {
 	setupTestDB(t)
 	setupTestRedis(t)