Merge branch 'main' into feature/user-management

AGENTS.md

@@ -483,6 +483,17 @@ downstream board's demand after its own board simultaneity factor to the chosen
 feeding circuit as a read-only virtual row. Recursive chains and several boards
 on one circuit are supported. A board-only link affects hierarchy but adds no
 load until a feeding circuit is selected.
+The distribution-board dialog can create one empty feeder circuit and link it
+in the same `distribution-board.create-feeder-circuit` project command. Its
+history inverse restores the complete previous board update before removing
+only the unchanged generated circuit; Redo reuses its UUID and BMK. No
+CircuitDeviceRow is created. The three-phase group is suggested, the optional
+circuit display name stays empty by default, and protection remains open for
+planner sizing. A circuit with exactly one downstream board and no device rows
+is rendered as one compact row using the live board number/name; several
+downstream boards or additional devices retain summary and child rows. Editing
+the name or remark of an empty reserve circuit changes the circuit itself and
+does not implicitly create a device row.
 Distribution-board floor assignment and a project-enabled supply type use
 `distribution-board.update`; both values are snapshot/export fields and one
 persistent undo step.

docs/circuit-list-editor-api.md

@@ -269,6 +269,13 @@ commands. Endpoints, payloads and calculation rules: `docs/estimate-balance.md`.
     submitted info fields, are restored together by persistent Undo/Redo
   - `fedFrom` remains free text for external feeds such as HAK, metering,
     transformer or generator and for supplementary notes
+- The project-command endpoint additionally accepts
+  `distribution-board.create-feeder-circuit` with an empty complete circuit
+  snapshot and an embedded version-2 `distribution-board.update`. Both writes
+  are one transaction, revision and Undo step. The generated circuit has no
+  device row; Redo keeps its UUID and BMK. The history-only inverse
+  `distribution-board.remove-feeder-circuit` restores the previous board values
+  and removes only the unchanged circuit.
 - `POST /projects/:projectId/distribution-boards/:distributionBoardId/copy`
   - body: `{ "name": "UV-02 Kopie", "expectedRevision": 14 }`
   - duplicates the complete distribution-board subtree with new owning UUIDs
@@ -346,7 +353,9 @@ commands. Endpoints, payloads and calculation rules: `docs/estimate-balance.md`.
   footer components. Circuit and component protection devices use their
   separate one-to-one DTOs. Calculated row, circuit, section and board totals
   remain included. Circuit totals contain the demand of linked downstream
-  boards. `downstreamBoardLoads` exposes those contributions as read-only rows;
+  boards. `downstreamBoardLoads` exposes those contributions as read-only
+  values; the grid combines exactly one downstream board without device rows
+  into the circuit row and keeps child rows for mixed or multiple loads.
   `feedingReference` resolves the current board/circuit labels by id.
 
 Response sketch:

docs/current-architecture.md

@@ -477,6 +477,21 @@ Verweise nicht. Der speisende Stromkreis muss zur speisenden Verteilung gehören
 Selbstverweise und Zyklen werden abgelehnt. Löschbefehle für referenzierte
 Verteilungen und Stromkreise, einschließlich Unterbaum- und Undo-Pfaden, werden
 vor der Datenbankänderung fachlich gesperrt.
+Im Bearbeiten-Dialog kann nach Auswahl der speisenden Verteilung direkt ein
+neuer Einspeiseabgang geplant werden. Die Oberfläche schlägt die dreiphasige
+Gruppe und das nächste BMK vor. Der Befehl
+`distribution-board.create-feeder-circuit` legt den leeren Stromkreis an und
+wendet die vollständige Verteilungsänderung in derselben Transaktion und
+Revision an; es entsteht keine Gerätezeile. Schutz und Leitung bleiben bewusst
+offen, weil sie aus Last und Verlegebedingungen geplant werden müssen. Undo
+stellt zuerst die vorherigen Verteilungswerte wieder her und entfernt danach
+nur den unveränderten erzeugten Stromkreis; Redo verwendet UUID und BMK erneut.
+Bei genau einer gespeisten Unterverteilung ohne Gerätezeilen projiziert das
+Grid nur eine kompakte Stromkreiszeile mit dem über die ID aufgelösten
+Verteilernamen. Erst mehrere Unterverteilungen oder zusätzliche Geräte erzeugen
+Sammel- und Unterzeilen. Anzeigename und Bemerkung eines leeren
+Reservestromkreises gehören zum Stromkreis und erzeugen beim Bearbeiten keine
+Gerätezeile.
 Die projektweite Circuit-Tree-Projektion berechnet rekursiv die Lasten aller
 Verteilungen. Die Leistung einer Unterverteilung nach ihrem eigenen
 Verteiler-GZF wird als virtuelle, schreibgeschützte Zeile genau dem gewählten

docs/print-view.md

@@ -38,8 +38,9 @@ automatisch bei späteren Änderungen in einem anderen Tab.
 3. **Verteilerpläne (quer, je Verteiler)** – Titelleiste mit
    Verteilernummer, Bezeichnung, Örtlichkeit, Netzart, „Gespeist von“ und
    P<sub>gl</sub>; darunter Kopfkomponenten, Gruppen, Stromkreise
-   (mehrzeilige mit Sammelzeile, eingerückten Gerätezeilen und
+   (reine 1:1-Einspeiseabgänge kompakt in einer Zeile; sonst mehrzeilig mit
-   schreibgeschützten Unterverteilungszeilen),
+   Sammelzeile, eingerückten Gerätezeilen und schreibgeschützten
+   Unterverteilungszeilen),
    Gruppensummen und Verteilersumme. Fehlende Kabelangaben sind als „offen“
    markiert. Die Titelleiste steht im Tabellenkopf und wiederholt sich beim
    Drucken auf Folgeseiten.

src/app/globals.css

@@ -1551,6 +1551,10 @@ a.kpi:hover {
   background: var(--panel-bg-subtle);
 }
 
+.tree-grid .feeder-circuit-row td:nth-child(2) {
+  font-weight: 600;
+}
+
 .tree-grid .device-row td:first-child {
   color: var(--text-faint);
 }

src/app/projects/[projectId]/page.tsx

@@ -47,6 +47,7 @@ import {
 import {
   copyGlobalDeviceToProject,
   copyDistributionBoard,
+  createFeederCircuitAndUpdateDistributionBoard,
   copyProjectDeviceToGlobal,
   createDistributionBoard,
   createProjectDevice,
@@ -71,6 +72,12 @@ import {
   updateProjectDevice,
   updateProjectSettings,
 } from "../../../frontend/utils/api";
+import { createClientId } from "../../../frontend/utils/client-id";
+import {
+  buildFeederCircuitSnapshot,
+  getDefaultFeederCircuitSection,
+  getNextFeederCircuitIdentifier,
+} from "../../../frontend/utils/distribution-board-feeder-circuit";
 import type {
   BuildingDto,
   CircuitListDto,
@@ -146,6 +153,7 @@ const boardFilterCollapsedStorageKey =
   "leistungsbilanz:overview-filter-collapsed:distribution-boards";
 const projectDeviceFilterCollapsedStorageKey =
   "leistungsbilanz:overview-filter-collapsed:project-devices";
+const createFeederCircuitSelectValue = "__create_feeder_circuit__";
 
 export default function ProjectDetailPage() {
   const params = useParams<{ projectId: string }>();
@@ -175,6 +183,12 @@ export default function ProjectDetailPage() {
   const [editingBoardCopyName, setEditingBoardCopyName] = useState("");
   const [editingFeedingBoardId, setEditingFeedingBoardId] = useState("");
   const [editingFeedingCircuitId, setEditingFeedingCircuitId] = useState("");
+  const [isCreatingFeederCircuit, setIsCreatingFeederCircuit] =
+    useState(false);
+  const [editingFeederCircuitSectionId, setEditingFeederCircuitSectionId] =
+    useState("");
+  const [editingFeederCircuitDisplayName, setEditingFeederCircuitDisplayName] =
+    useState("");
   const [editingBoardInfo, setEditingBoardInfo] =
     useState<DistributionBoardInfoDraft>(
       toDistributionBoardInfoDraft({
@@ -350,6 +364,21 @@ export default function ProjectDetailPage() {
   const selectedFeedingCircuit = selectedFeedingCircuits.find(
     ({ circuit }) => circuit.id === editingFeedingCircuitId
   );
+  const feederCircuitSections =
+    selectedFeedingTree?.sections.filter(
+      (section) => section.category !== undefined
+    ) ?? [];
+  const selectedNewFeederCircuitSection = feederCircuitSections.find(
+    (section) => section.id === editingFeederCircuitSectionId
+  );
+  const newFeederCircuitIdentifier = selectedNewFeederCircuitSection
+    ? getNextFeederCircuitIdentifier(selectedNewFeederCircuitSection)
+    : null;
+  const selectedFeedingCircuitCategory =
+    selectedFeedingCircuit?.section.category ??
+    (isCreatingFeederCircuit
+      ? selectedNewFeederCircuitSection?.category
+      : undefined);
   const selectedFeedingBoard = boards.find(
     (board) => board.id === editingFeedingBoardId
   );
@@ -556,6 +585,9 @@ export default function ProjectDetailPage() {
     setEditingBoardInfo(toDistributionBoardInfoDraft(board));
     setEditingFeedingBoardId(board.feedingDistributionBoardId ?? "");
     setEditingFeedingCircuitId(board.feedingCircuitId ?? "");
+    setIsCreatingFeederCircuit(false);
+    setEditingFeederCircuitSectionId("");
+    setEditingFeederCircuitDisplayName("");
   }
 
   function openBoardCreator() {
@@ -584,28 +616,56 @@ export default function ProjectDetailPage() {
     setIsSaving(true);
     setError(null);
     try {
-      const result = await updateDistributionBoard(
+      const boardInput = {
-        projectId,
-        editingBoard.id,
-        {
         floorId: editingBoardFloorId || null,
         supplyType: editingBoardSupplyType,
         simultaneityFactor,
         feedingDistributionBoardId: editingFeedingBoardId || null,
         feedingCircuitId: editingFeedingCircuitId || null,
         ...fromDistributionBoardInfoDraft(editingBoardInfo),
+      };
+      let result;
+      if (isCreatingFeederCircuit) {
+        if (!editingFeedingBoardId || !selectedFeedingTree) {
+          throw new Error("Bitte eine speisende Verteilung wählen.");
+        }
+        if (!selectedNewFeederCircuitSection) {
+          throw new Error(
+            "Bitte eine Stromkreisgruppe für den neuen Abgang wählen."
+          );
+        }
+        const circuit = buildFeederCircuitSnapshot({
+          id: createClientId(),
+          tree: selectedFeedingTree,
+          sectionId: selectedNewFeederCircuitSection.id,
+          displayName: editingFeederCircuitDisplayName,
+        });
+        result = await createFeederCircuitAndUpdateDistributionBoard(
+          projectId,
+          editingBoard.id,
+          {
+            ...boardInput,
+            feedingDistributionBoardId: editingFeedingBoardId,
+            feedingCircuitId: circuit.id,
           },
+          circuit,
           project.currentRevision
         );
-      setBoards((current) =>
+      } else {
-        current.map((board) =>
+        result = await updateDistributionBoard(
-          board.id === result.distributionBoard.id
+          projectId,
-            ? result.distributionBoard
+          editingBoard.id,
-            : board
+          boardInput,
-        )
+          project.currentRevision
         );
+      }
       applyProjectRevision(result.history.currentRevision);
-      setCircuitTrees((await getProjectCircuitTrees(projectId)).trees);
+      const [updatedBoards, updatedTrees] = await Promise.all([
+        listDistributionBoards(projectId),
+        getProjectCircuitTrees(projectId),
+      ]);
+      setBoards(updatedBoards);
+      setCircuitTrees(updatedTrees.trees);
       setEditingBoard(null);
     } catch (err) {
       setError(
@@ -1567,8 +1627,16 @@ export default function ProjectDetailPage() {
                   className="form-select"
                   id="feeding-distribution-board"
                   onChange={(event) => {
-                    setEditingFeedingBoardId(event.target.value);
+                    const boardId = event.target.value;
+                    setEditingFeedingBoardId(boardId);
                     setEditingFeedingCircuitId("");
+                    setIsCreatingFeederCircuit(false);
+                    setEditingFeederCircuitSectionId(
+                      getDefaultFeederCircuitSection(
+                        circuitTreeByBoardId.get(boardId)
+                      )?.id ?? ""
+                    );
+                    setEditingFeederCircuitDisplayName("");
                   }}
                   value={editingFeedingBoardId}
                 >
@@ -1588,10 +1656,31 @@ export default function ProjectDetailPage() {
                   className="form-select"
                   disabled={!editingFeedingBoardId}
                   id="feeding-circuit"
-                  onChange={(event) => setEditingFeedingCircuitId(event.target.value)}
+                  onChange={(event) => {
-                  value={editingFeedingCircuitId}
+                    if (event.target.value === createFeederCircuitSelectValue) {
+                      setEditingFeedingCircuitId("");
+                      setIsCreatingFeederCircuit(true);
+                      setEditingFeederCircuitSectionId(
+                        (current) =>
+                          current ||
+                          getDefaultFeederCircuitSection(selectedFeedingTree)?.id ||
+                          ""
+                      );
+                      return;
+                    }
+                    setIsCreatingFeederCircuit(false);
+                    setEditingFeedingCircuitId(event.target.value);
+                  }}
+                  value={
+                    isCreatingFeederCircuit
+                      ? createFeederCircuitSelectValue
+                      : editingFeedingCircuitId
+                  }
                 >
                   <option value="">Nur Verteilung bekannt</option>
+                  <option value={createFeederCircuitSelectValue}>
+                    + Neuen Einspeiseabgang anlegen …
+                  </option>
                   {selectedFeedingCircuits.map(({ circuit }) => (
                     <option key={circuit.id} value={circuit.id}>
                       {circuit.equipmentIdentifier}
@@ -1600,7 +1689,62 @@ export default function ProjectDetailPage() {
                   ))}
                 </select>
               </div>
-              {editingFeedingBoardId && !editingFeedingCircuitId ? (
+              {isCreatingFeederCircuit ? (
+                <div className="col-12">
+                  <div className="border rounded p-3">
+                    <div className="row g-3">
+                      <div className="col-12 col-md-6">
+                        <label className="form-label" htmlFor="new-feeder-circuit-section">
+                          Stromkreisgruppe
+                        </label>
+                        <select
+                          className="form-select"
+                          id="new-feeder-circuit-section"
+                          onChange={(event) =>
+                            setEditingFeederCircuitSectionId(event.target.value)
+                          }
+                          required
+                          value={editingFeederCircuitSectionId}
+                        >
+                          {feederCircuitSections.map((section) => (
+                            <option key={section.id} value={section.id}>
+                              {section.displayName}
+                            </option>
+                          ))}
+                        </select>
+                        <div className="form-text">
+                          Vorgesehenes BMK: {newFeederCircuitIdentifier ?? "–"}
+                        </div>
+                      </div>
+                      <div className="col-12 col-md-6">
+                        <label className="form-label" htmlFor="new-feeder-circuit-name">
+                          Abgangsbezeichnung (optional)
+                        </label>
+                        <input
+                          className="form-control"
+                          id="new-feeder-circuit-name"
+                          onChange={(event) =>
+                            setEditingFeederCircuitDisplayName(event.target.value)
+                          }
+                          placeholder="z. B. Steigetrasse Ost"
+                          value={editingFeederCircuitDisplayName}
+                        />
+                        <div className="form-text">
+                          Ohne Zusatzbezeichnung wird der Name der gespeisten
+                          Verteilung angezeigt.
+                        </div>
+                      </div>
+                    </div>
+                    <div className="form-text mt-2">
+                      Der Abgang wird erst beim Speichern angelegt und gemeinsam
+                      mit dieser Verteilung verknüpft. Es entsteht keine Gerätezeile.
+                    </div>
+                  </div>
+                </div>
+              ) : null}
+              {editingFeedingBoardId &&
+              !editingFeedingCircuitId &&
+              !isCreatingFeederCircuit ? (
                 <div className="col-12">
                   <div className="alert alert-warning mb-0 py-2">
                     Ohne speisenden Abgang wird die Hierarchie angezeigt, die
@@ -1618,8 +1762,8 @@ export default function ProjectDetailPage() {
                   </div>
                 </div>
               ) : null}
-              {selectedFeedingCircuit &&
+              {selectedFeedingCircuitCategory !== undefined &&
-              selectedFeedingCircuit.section.category !== "three_phase" ? (
+              selectedFeedingCircuitCategory !== "three_phase" ? (
                 <div className="col-12">
                   <div className="alert alert-warning mb-0 py-2">
                     Der gewählte Abgang ist 1-phasig. Bitte prüfen, ob diese

src/db/repositories/circuit-structure-project-command.repository.ts

@@ -40,7 +40,7 @@ export class CircuitStructureProjectCommandRepository
       this.database,
       input,
       (tx) =>
-        this.applyCommand(
+        this.applyInTransaction(
           tx,
           input.projectId,
           input.source,
@@ -49,7 +49,11 @@ export class CircuitStructureProjectCommandRepository
     );
   }
 
-  private applyCommand(
+  /**
+   * Applies the circuit write inside an already-owned project transaction.
+   * Composite project commands use this without creating a second revision.
+   */
+  applyInTransaction(
     database: AppDatabase,
     projectId: string,
     source: ExecuteCircuitStructureCommandInput["source"],

src/db/repositories/distribution-board-structure-project-command.repository.ts

@@ -1,4 +1,5 @@
 import { and, asc, eq, inArray } from "drizzle-orm";
+import { isDeepStrictEqual } from "node:util";
 import {
   assertDistributionBoardDeleteProjectCommand,
   assertDistributionBoardInsertProjectCommand,
@@ -17,6 +18,20 @@ import {
   type DistributionBoardUpdateProjectCommand,
   type DistributionBoardUpdateValues,
 } from "../../domain/models/distribution-board-project-command.model.js";
+import {
+  assertDistributionBoardFeederCircuitProjectCommand,
+  createDistributionBoardCreateFeederCircuitProjectCommand,
+  createDistributionBoardRemoveFeederCircuitProjectCommand,
+  distributionBoardCreateFeederCircuitCommandType,
+  distributionBoardRemoveFeederCircuitCommandType,
+  type DistributionBoardFeederCircuitProjectCommand,
+} from "../../domain/models/distribution-board-feeder-circuit-project-command.model.js";
+import {
+  circuitDeleteCommandType,
+  circuitInsertCommandType,
+  createCircuitDeleteProjectCommand,
+  createCircuitInsertProjectCommand,
+} from "../../domain/models/circuit-structure-project-command.model.js";
 import type {
   DistributionBoardStructureProjectCommandStore,
   ExecuteDistributionBoardStructureCommandInput,
@@ -31,6 +46,7 @@ import { floors } from "../schema/floors.js";
 import { projects } from "../schema/projects.js";
 import { executeProjectCommandTransaction } from "./project-command-transaction.persistence.js";
 import { assertBoardsAreNotReferencedAsFeeders } from "./distribution-board-feeding-deletion-guard.persistence.js";
+import { CircuitStructureProjectCommandRepository } from "./circuit-structure-project-command.repository.js";
 
 export class DistributionBoardStructureProjectCommandRepository
   implements DistributionBoardStructureProjectCommandStore
@@ -62,6 +78,30 @@ export class DistributionBoardStructureProjectCommandRepository
     );
   }
 
+  executeFeederCircuit(
+    input: Omit<
+      ExecuteDistributionBoardStructureCommandInput,
+      "command"
+    > & {
+      command: DistributionBoardFeederCircuitProjectCommand;
+    }
+  ) {
+    assertDistributionBoardFeederCircuitProjectCommand(input.command);
+    if (
+      input.source === "user" &&
+      input.command.type === distributionBoardRemoveFeederCircuitCommandType
+    ) {
+      throw new Error(
+        "Generated feeder circuits may only be removed through project history."
+      );
+    }
+    return executeProjectCommandTransaction(
+      this.database,
+      input,
+      (tx) => this.applyFeederCircuitCommand(tx, input)
+    );
+  }
+
   private applyCommand(
     database: AppDatabase,
     projectId: string,
@@ -367,6 +407,64 @@ export class DistributionBoardStructureProjectCommandRepository
     return inverse;
   }
 
+  private applyFeederCircuitCommand(
+    database: AppDatabase,
+    input: Omit<
+      ExecuteDistributionBoardStructureCommandInput,
+      "command"
+    > & {
+      command: DistributionBoardFeederCircuitProjectCommand;
+    }
+  ): DistributionBoardFeederCircuitProjectCommand {
+    const circuitRepository =
+      new CircuitStructureProjectCommandRepository(database);
+    const { circuit, boardUpdate } = input.command.payload;
+    if (
+      input.command.type === distributionBoardCreateFeederCircuitCommandType
+    ) {
+      const circuitInverse = circuitRepository.applyInTransaction(
+        database,
+        input.projectId,
+        input.source,
+        createCircuitInsertProjectCommand(circuit)
+      );
+      if (circuitInverse.type !== circuitDeleteCommandType) {
+        throw new Error("Created feeder circuit returned an invalid inverse.");
+      }
+      const boardInverse = this.update(database, {
+        ...input,
+        command: boardUpdate,
+      });
+      return createDistributionBoardRemoveFeederCircuitProjectCommand(
+        circuit,
+        boardInverse
+      );
+    }
+
+    const boardInverse = this.update(database, {
+      ...input,
+      command: boardUpdate,
+    });
+    const circuitInverse = circuitRepository.applyInTransaction(
+      database,
+      input.projectId,
+      input.source,
+      createCircuitDeleteProjectCommand(circuit.id, circuit.circuitListId)
+    );
+    if (
+      circuitInverse.type !== circuitInsertCommandType ||
+      !isDeepStrictEqual(circuitInverse.payload.circuit, circuit)
+    ) {
+      throw new Error(
+        "Generated feeder circuit changed before history removal."
+      );
+    }
+    return createDistributionBoardCreateFeederCircuitProjectCommand(
+      circuit,
+      boardInverse
+    );
+  }
+
   private assertFeedingReference(
     database: AppDatabase,
     projectId: string,

src/domain/models/distribution-board-feeder-circuit-project-command.model.ts

@@ -0,0 +1,132 @@
+import {
+  assertCircuitInsertProjectCommand,
+  circuitInsertCommandType,
+  circuitStructureCommandSchemaVersion,
+  type CircuitSnapshot,
+} from "./circuit-structure-project-command.model.js";
+import {
+  assertDistributionBoardUpdateProjectCommand,
+  type DistributionBoardUpdateProjectCommand,
+} from "./distribution-board-project-command.model.js";
+import type { SerializedProjectCommand } from "./project-command.model.js";
+
+export const distributionBoardCreateFeederCircuitCommandType =
+  "distribution-board.create-feeder-circuit" as const;
+export const distributionBoardRemoveFeederCircuitCommandType =
+  "distribution-board.remove-feeder-circuit" as const;
+export const distributionBoardFeederCircuitCommandSchemaVersion = 1 as const;
+
+export interface DistributionBoardFeederCircuitCommandPayload {
+  circuit: CircuitSnapshot;
+  boardUpdate: DistributionBoardUpdateProjectCommand;
+}
+
+export interface DistributionBoardCreateFeederCircuitProjectCommand
+  extends SerializedProjectCommand<DistributionBoardFeederCircuitCommandPayload> {
+  schemaVersion: typeof distributionBoardFeederCircuitCommandSchemaVersion;
+  type: typeof distributionBoardCreateFeederCircuitCommandType;
+}
+
+export interface DistributionBoardRemoveFeederCircuitProjectCommand
+  extends SerializedProjectCommand<DistributionBoardFeederCircuitCommandPayload> {
+  schemaVersion: typeof distributionBoardFeederCircuitCommandSchemaVersion;
+  type: typeof distributionBoardRemoveFeederCircuitCommandType;
+}
+
+export type DistributionBoardFeederCircuitProjectCommand =
+  | DistributionBoardCreateFeederCircuitProjectCommand
+  | DistributionBoardRemoveFeederCircuitProjectCommand;
+
+export function createDistributionBoardCreateFeederCircuitProjectCommand(
+  circuit: CircuitSnapshot,
+  boardUpdate: DistributionBoardUpdateProjectCommand
+): DistributionBoardCreateFeederCircuitProjectCommand {
+  const command: DistributionBoardCreateFeederCircuitProjectCommand = {
+    schemaVersion: distributionBoardFeederCircuitCommandSchemaVersion,
+    type: distributionBoardCreateFeederCircuitCommandType,
+    payload: { circuit, boardUpdate },
+  };
+  assertDistributionBoardFeederCircuitProjectCommand(command);
+  return command;
+}
+
+export function createDistributionBoardRemoveFeederCircuitProjectCommand(
+  circuit: CircuitSnapshot,
+  boardUpdate: DistributionBoardUpdateProjectCommand
+): DistributionBoardRemoveFeederCircuitProjectCommand {
+  const command: DistributionBoardRemoveFeederCircuitProjectCommand = {
+    schemaVersion: distributionBoardFeederCircuitCommandSchemaVersion,
+    type: distributionBoardRemoveFeederCircuitCommandType,
+    payload: { circuit, boardUpdate },
+  };
+  assertDistributionBoardFeederCircuitProjectCommand(command);
+  return command;
+}
+
+export function assertDistributionBoardFeederCircuitProjectCommand(
+  command: SerializedProjectCommand<unknown>
+): asserts command is DistributionBoardFeederCircuitProjectCommand {
+  if (
+    command.schemaVersion !==
+      distributionBoardFeederCircuitCommandSchemaVersion ||
+    (command.type !== distributionBoardCreateFeederCircuitCommandType &&
+      command.type !== distributionBoardRemoveFeederCircuitCommandType) ||
+    !isPlainObject(command.payload)
+  ) {
+    throw new Error("Unsupported distribution-board feeder-circuit command.");
+  }
+
+  const { circuit, boardUpdate } = command.payload;
+  if (!isPlainObject(boardUpdate)) {
+    throw new Error("Feeder-circuit command requires a board update.");
+  }
+  assertCircuitInsertProjectCommand({
+    schemaVersion: circuitStructureCommandSchemaVersion,
+    type: circuitInsertCommandType,
+    payload: { circuit },
+  });
+  const boardUpdateCommand =
+    boardUpdate as unknown as SerializedProjectCommand<unknown>;
+  assertDistributionBoardUpdateProjectCommand(boardUpdateCommand);
+
+  const typedCircuit = circuit as CircuitSnapshot;
+  const typedBoardUpdate: DistributionBoardUpdateProjectCommand =
+    boardUpdateCommand;
+  if (typedCircuit.deviceRows.length !== 0 || !typedCircuit.isReserve) {
+    throw new Error(
+      "A generated feeder circuit must be empty before the board load is linked."
+    );
+  }
+  const feedingBoard = getChangeValue(
+    typedBoardUpdate,
+    "feedingDistributionBoardId"
+  );
+  const feedingCircuit = getChangeValue(
+    typedBoardUpdate,
+    "feedingCircuitId"
+  );
+  if (feedingBoard === undefined || feedingCircuit === undefined) {
+    throw new Error(
+      "Feeder-circuit commands must update both logical feeding references."
+    );
+  }
+  if (
+    command.type === distributionBoardCreateFeederCircuitCommandType &&
+    (typeof feedingBoard !== "string" || feedingCircuit !== typedCircuit.id)
+  ) {
+    throw new Error(
+      "The created feeder circuit must be linked by the distribution-board update."
+    );
+  }
+}
+
+function getChangeValue(
+  command: DistributionBoardUpdateProjectCommand,
+  field: "feedingDistributionBoardId" | "feedingCircuitId"
+) {
+  return command.payload.changes.find((change) => change.field === field)?.value;
+}
+
+function isPlainObject(value: unknown): value is Record<string, unknown> {
+  return value !== null && typeof value === "object" && !Array.isArray(value);
+}

src/domain/ports/distribution-board-structure-project-command.store.ts

@@ -1,5 +1,6 @@
 import type { DistributionBoardStructureProjectCommand } from "../models/distribution-board-structure-project-command.model.js";
 import type { DistributionBoardUpdateProjectCommand } from "../models/distribution-board-project-command.model.js";
+import type { DistributionBoardFeederCircuitProjectCommand } from "../models/distribution-board-feeder-circuit-project-command.model.js";
 import type {
   AppendedProjectRevision,
   ProjectRevisionSource,
@@ -35,4 +36,15 @@ export interface DistributionBoardStructureProjectCommandStore {
     revision: AppendedProjectRevision;
     inverse: DistributionBoardUpdateProjectCommand;
   };
+  executeFeederCircuit(
+    input: Omit<
+      ExecuteDistributionBoardStructureCommandInput,
+      "command"
+    > & {
+      command: DistributionBoardFeederCircuitProjectCommand;
+    }
+  ): {
+    revision: AppendedProjectRevision;
+    inverse: DistributionBoardFeederCircuitProjectCommand;
+  };
 }

src/domain/services/project-command.service.ts

@@ -45,6 +45,11 @@ import {
   assertDistributionBoardUpdateProjectCommand,
   distributionBoardUpdateCommandType,
 } from "../models/distribution-board-project-command.model.js";
+import {
+  assertDistributionBoardFeederCircuitProjectCommand,
+  distributionBoardCreateFeederCircuitCommandType,
+  distributionBoardRemoveFeederCircuitCommandType,
+} from "../models/distribution-board-feeder-circuit-project-command.model.js";
 import {
   assertDistributionBoardComponentDeleteProjectCommand,
   assertDistributionBoardComponentInsertProjectCommand,
@@ -418,6 +423,14 @@ export class ProjectCommandService implements ProjectCommandExecutor {
           command: input.command,
         }).revision;
       }
+      case distributionBoardCreateFeederCircuitCommandType:
+      case distributionBoardRemoveFeederCircuitCommandType: {
+        assertDistributionBoardFeederCircuitProjectCommand(input.command);
+        return this.distributionBoardStructureStore.executeFeederCircuit({
+          ...input,
+          command: input.command,
+        }).revision;
+      }
       case distributionBoardComponentInsertCommandType: {
         assertDistributionBoardComponentInsertProjectCommand(
           input.command

src/frontend/components/circuit-tree-editor.tsx

@@ -1766,7 +1766,7 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
     const currentDisplay =
       mode === "replaceWithTypedChar" && cell.cellKey !== "phaseType"
         ? typedChar ?? ""
-        : String(visibleCell.value ?? "");
+        : String(visibleCell.editValue ?? visibleCell.value ?? "");
     focusTokenRef.current += 1;
     setEditingCell({
       ...cell,
@@ -4077,7 +4077,9 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
                   key={row.rowKey}
                   className={`${
                     row.rowType === "circuitSummary"
-                      ? "summary-row"
+                      ? row.downstreamBoardLoad
+                        ? "feeder-circuit-row"
+                        : "summary-row"
                       : row.rowType === "deviceRow"
                         ? "device-row"
                         : row.rowType === "downstreamBoardLoad"
@@ -4708,11 +4710,19 @@ export function CircuitTreeEditor(props: { projectId: string; circuitListId: str
                           tabIndex={-1}
                         />
                         <IconButton
-                          disabled={isSaving}
+                          disabled={
+                            isSaving ||
+                            (row.circuit.downstreamBoardLoads?.length ?? 0) > 0
+                          }
                           icon={Trash2}
                           label="Stromkreis löschen"
                           onClick={() => void handleDeleteCircuit(row.circuit!.id)}
                           tabIndex={-1}
+                          title={
+                            (row.circuit.downstreamBoardLoads?.length ?? 0) > 0
+                              ? "Speist eine Unterverteilung – zuerst deren Einspeisung ändern"
+                              : undefined
+                          }
                           variant="danger"
                         />
                       </>

src/frontend/print/print-document.tsx

@@ -431,6 +431,25 @@ function CircuitRows({ circuit }: { circuit: CircuitTreeCircuitDto }) {
       </tr>
     );
   }
+  if (rows.length === 0 && downstreamBoards.length === 1) {
+    const boardLabel =
+      downstreamBoards[0].boardNumber ?? downstreamBoards[0].name;
+    return (
+      <tr className="pd-circuit">
+        <td className="pd-bmk">{circuit.equipmentIdentifier}</td>
+        <td>
+          {boardLabel}
+          {circuit.displayName ? (
+            <span className="pd-sub"> · {circuit.displayName}</span>
+          ) : null}
+        </td>
+        <td>–</td>
+        <td /><td /><td />
+        <td className="pd-r"><strong>{formatKilowatt(circuit.circuitTotalPower)}</strong></td>
+        {circuitCells}
+      </tr>
+    );
+  }
   if (rows.length === 1 && downstreamBoards.length === 0) {
     const row = rows[0];
     const title = circuit.displayName ?? row.displayName;

src/frontend/utils/api.ts

@@ -366,10 +366,7 @@ export function createDistributionBoard(
   );
 }
 
-export function updateDistributionBoard(
+export type UpdateDistributionBoardInput = {
-  projectId: string,
-  distributionBoardId: string,
-  input: {
   floorId: string | null;
   supplyType: NonNullable<DistributionBoardDto["supplyType"]>;
   simultaneityFactor: number;
@@ -379,7 +376,12 @@ export function updateDistributionBoard(
       DistributionBoardDto,
       "feedingDistributionBoardId" | "feedingCircuitId"
     >
-    >,
+  >;
+
+export function updateDistributionBoard(
+  projectId: string,
+  distributionBoardId: string,
+  input: UpdateDistributionBoardInput,
   expectedRevision: number
 ) {
   return request<DistributionBoardCommandResultDto>(
@@ -391,6 +393,41 @@ export function updateDistributionBoard(
   );
 }
 
+export function createFeederCircuitAndUpdateDistributionBoard(
+  projectId: string,
+  distributionBoardId: string,
+  input: UpdateDistributionBoardInput & {
+    feedingDistributionBoardId: string;
+    feedingCircuitId: string;
+  },
+  circuit: CircuitSnapshot,
+  expectedRevision: number
+) {
+  return executeProjectCommand(
+    projectId,
+    expectedRevision,
+    {
+      schemaVersion: 1,
+      type: "distribution-board.create-feeder-circuit",
+      payload: {
+        circuit,
+        boardUpdate: {
+          schemaVersion: 2,
+          type: "distribution-board.update",
+          payload: {
+            distributionBoardId,
+            changes: Object.entries(input).map(([field, value]) => ({
+              field,
+              value,
+            })),
+          },
+        },
+      },
+    },
+    "Einspeiseabgang anlegen und Verteilung verknüpfen"
+  );
+}
+
 export const documentLogoUrl = "/api/document-branding/logo";
 
 export function getDocumentBranding() {

src/frontend/utils/circuit-grid-model.ts

@@ -617,7 +617,11 @@ export function getCellKind(rowType: RowType, key: CellKey): CellKind {
   if (rowType === "deviceRow") return deviceFieldKeys.has(key) ? "deviceField" : "readonly";
   if (rowType === "downstreamBoardLoad") return "readonly";
   if (rowType === "circuitSummary") return circuitFieldKeys.has(key) ? "circuitField" : "readonly";
-  if (rowType === "reserveCircuit" || rowType === "circuitCompact") {
+  if (rowType === "reserveCircuit") {
+    if (circuitFieldKeys.has(key)) return "circuitField";
+    if (deviceFieldKeys.has(key)) return "deviceField";
+  }
+  if (rowType === "circuitCompact") {
     if (deviceFieldKeys.has(key)) return "deviceField";
     if (circuitFieldKeys.has(key)) return "circuitField";
   }

src/frontend/utils/circuit-grid-projection.ts

@@ -37,6 +37,8 @@ export interface VisibleGridCell {
   editable: boolean;
   kind: CellKind;
   value: GridValue;
+  /** Separate persisted value when the displayed value is derived. */
+  editValue?: GridValue;
 }
 
 export interface VisibleGridRow {
@@ -144,6 +146,7 @@ function makeVisibleGridRow(
     const kind = getCellKind(rowType, column.key);
     const editable = kind === "circuitField" || kind === "deviceField";
     let value: GridValue;
+    let editValue: GridValue | undefined;
 
     if (rowType === "downstreamBoardLoad" && downstreamBoardLoad) {
       value = column.key === "displayName"
@@ -155,6 +158,35 @@ function makeVisibleGridRow(
             : column.key === "remark"
               ? "Automatisch aus der verknüpften Verteilung"
               : undefined;
+    } else if (
+      rowType === "circuitSummary" &&
+      circuit &&
+      downstreamBoardLoad &&
+      circuit.deviceRows.length === 0
+    ) {
+      if (column.key === "displayName") {
+        const boardLabel =
+          downstreamBoardLoad.boardNumber ?? downstreamBoardLoad.name;
+        value = circuit.displayName
+          ? `${boardLabel} · ${circuit.displayName}`
+          : boardLabel;
+        editValue = circuit.displayName ?? "";
+      } else if (column.key === "cosPhi") {
+        value = circuit.circuitCosPhi;
+      } else if (
+        kind === "computed" &&
+        circuitOnlyColumns.has(column.key)
+      ) {
+        value = getCircuitValue(circuit, column.key);
+      } else if (kind === "circuitField") {
+        value = getCircuitValue(circuit, column.key);
+      } else if (column.key === "rowTotalPower") {
+        value = circuit.circuitTotalPower;
+      } else if (column.key === "circuitTotalPower") {
+        value = circuit.circuitTotalPower;
+      } else if (column.key === "voltage") {
+        value = circuit.voltage;
+      }
     } else if (rowType === "placeholder") {
       value = column.key === "equipmentIdentifier" ? "-frei-" : undefined;
     } else if (kind === "deviceField" && device) {
@@ -178,7 +210,7 @@ function makeVisibleGridRow(
       value = circuit.voltage;
     }
 
-    return { cellKey: column.key, editable, kind, value };
+    return { cellKey: column.key, editable, kind, value, editValue };
   });
 
   return {
@@ -247,6 +279,19 @@ export function buildVisibleGridRowsWithStructure(
       const downstreamLoads = circuit.downstreamBoardLoads ?? [];
       if (circuit.deviceRows.length === 0 && downstreamLoads.length === 0) {
         rows.push(makeVisibleGridRow("reserveCircuit", section.id, circuit));
+      } else if (
+        circuit.deviceRows.length === 0 &&
+        downstreamLoads.length === 1
+      ) {
+        rows.push(
+          makeVisibleGridRow(
+            "circuitSummary",
+            section.id,
+            circuit,
+            undefined,
+            downstreamLoads[0]
+          )
+        );
       } else if (circuit.deviceRows.length === 1 && downstreamLoads.length === 0) {
         rows.push(makeVisibleGridRow("circuitCompact", section.id, circuit, circuit.deviceRows[0]));
       } else {

src/frontend/utils/distribution-board-feeder-circuit.ts

@@ -0,0 +1,68 @@
+import type { CircuitSnapshot } from "../../domain/models/circuit-structure-project-command.model.js";
+import type {
+  CircuitTreeResponseDto,
+  CircuitTreeSectionDto,
+} from "../types";
+import { buildCircuitInsertSnapshot } from "./circuit-structure-command";
+
+export function getDefaultFeederCircuitSection(
+  tree: CircuitTreeResponseDto | undefined
+) {
+  if (!tree) return undefined;
+  return (
+    tree.sections.find((section) => section.category === "three_phase") ??
+    tree.sections.find((section) => section.category !== undefined)
+  );
+}
+
+export function getNextFeederCircuitIdentifier(
+  section: CircuitTreeSectionDto
+) {
+  let highestSuffix = 0;
+  for (const circuit of section.circuits) {
+    if (!circuit.equipmentIdentifier.startsWith(section.prefix)) continue;
+    const suffix = circuit.equipmentIdentifier.slice(section.prefix.length);
+    if (!/^\d+$/.test(suffix)) continue;
+    highestSuffix = Math.max(highestSuffix, Number(suffix));
+  }
+  return `${section.prefix}${highestSuffix + 1}`;
+}
+
+export function buildFeederCircuitSnapshot(input: {
+  id: string;
+  tree: CircuitTreeResponseDto;
+  sectionId: string;
+  displayName: string;
+}): CircuitSnapshot {
+  const section = input.tree.sections.find(
+    (candidate) => candidate.id === input.sectionId
+  );
+  if (!section || !section.category) {
+    throw new Error("Die gewählte Stromkreisgruppe ist nicht verfügbar.");
+  }
+  const snapshot = buildCircuitInsertSnapshot({
+    id: input.id,
+    circuitListId: input.tree.circuitListId,
+    category: section.category,
+    deviceRows: [],
+    values: {
+      sectionId: section.id,
+      equipmentIdentifier: getNextFeederCircuitIdentifier(section),
+      displayName: input.displayName.trim() || undefined,
+      sortOrder:
+        section.circuits.length === 0
+          ? 10
+          : Math.max(...section.circuits.map((circuit) => circuit.sortOrder)) +
+            10,
+      voltage:
+        section.category === "three_phase"
+          ? input.tree.threePhaseVoltageV
+          : input.tree.singlePhaseVoltageV,
+      isReserve: true,
+    },
+  });
+  // A distribution-board feeder is not a generic final circuit. Its protection
+  // must be selected from the calculated load and cable, so no 16 A group
+  // default is persisted here.
+  return { ...snapshot, protectionDevice: null };
+}

src/frontend/utils/project-version-history.ts

@@ -32,6 +32,10 @@ const commandTypeLabels: Record<string, string> = {
   "project.update-settings": "Projekteinstellungen bearbeitet",
   "distribution-board.insert": "Verteilung angelegt",
   "distribution-board.update": "Verteilung bearbeitet",
+  "distribution-board.create-feeder-circuit":
+    "Einspeiseabgang angelegt und verknüpft",
+  "distribution-board.remove-feeder-circuit":
+    "Einspeiseabgang und Verknüpfung entfernt",
   "distribution-board.delete": "Verteilung entfernt",
   "distribution-board.insert-subtree": "Verteilung vollständig eingefügt",
   "distribution-board.delete-subtree": "Verteilung vollständig entfernt",

tests/circuit-grid-model.test.ts

@@ -133,7 +133,9 @@ describe("circuit grid model", () => {
     assert.equal(getCellKind("circuitCompact", "equipmentIdentifier"), "circuitField");
     assert.equal(getCellKind("circuitSummary", "displayName"), "circuitField");
     assert.equal(getCellKind("deviceRow", "displayName"), "deviceField");
-    assert.equal(getCellKind("reserveCircuit", "remark"), "deviceField");
+    assert.equal(getCellKind("reserveCircuit", "displayName"), "circuitField");
+    assert.equal(getCellKind("reserveCircuit", "remark"), "circuitField");
+    assert.equal(getCellKind("reserveCircuit", "powerPerUnit"), "deviceField");
     assert.equal(getCellKind("placeholder", "displayName"), "deviceField");
     assert.equal(getCellKind("deviceRow", "equipmentIdentifier"), "readonly");
     assert.equal(getCellKind("circuitSummary", "controlRequirement"), "circuitField");

tests/circuit-grid-projection.test.ts

@@ -179,9 +179,10 @@ describe("circuit grid projection", () => {
     );
   });
 
-  it("renders linked downstream boards as separate read-only rows", () => {
+  it("renders one linked downstream board as one compact editable circuit row", () => {
     const feeder = {
       ...reserveCircuit,
+      displayName: undefined,
       isReserve: false,
       circuitTotalPower: 4,
       circuitApparentPower: 5,
@@ -202,19 +203,65 @@ describe("circuit grid projection", () => {
     assert.deepEqual(rows.map((row) => row.rowType), [
       "section",
       "circuitSummary",
-      "downstreamBoardLoad",
       "placeholder",
     ]);
-    const loadRow = rows[2];
+    const loadRow = rows[1];
     assert.equal(
       loadRow.cells.find((cell) => cell.cellKey === "displayName")?.value,
-      "Unterverteilung UV-02"
+      "UV-02"
+    );
+    assert.equal(
+      loadRow.cells.find((cell) => cell.cellKey === "displayName")?.editValue,
+      ""
     );
     assert.equal(
       loadRow.cells.find((cell) => cell.cellKey === "rowTotalPower")?.value,
       4
     );
-    assert.equal(loadRow.cells.every((cell) => !cell.editable), true);
+    assert.equal(
+      loadRow.cells.find((cell) => cell.cellKey === "displayName")?.kind,
+      "circuitField"
+    );
+  });
+
+  it("keeps separate read-only rows for several linked downstream boards", () => {
+    const feeder = {
+      ...reserveCircuit,
+      isReserve: false,
+      circuitTotalPower: 6,
+      circuitApparentPower: 7,
+      circuitCosPhi: 6 / 7,
+      downstreamBoardLoads: [
+        {
+          distributionBoardId: "board-a",
+          name: "Unterverteilung A",
+          boardNumber: "UV-A",
+          activePowerKw: 4,
+          apparentPowerKva: 5,
+          cosPhi: 0.8,
+        },
+        {
+          distributionBoardId: "board-b",
+          name: "Unterverteilung B",
+          boardNumber: "UV-B",
+          activePowerKw: 2,
+          apparentPowerKva: 2,
+          cosPhi: 1,
+        },
+      ],
+    };
+    const rows = buildVisibleGridRowsWithStructure(
+      [{ ...sections[0], circuits: [feeder] }],
+      { headerComponents: [], footerComponents: [] }
+    );
+    assert.deepEqual(rows.map((row) => row.rowType), [
+      "section",
+      "circuitSummary",
+      "downstreamBoardLoad",
+      "downstreamBoardLoad",
+      "placeholder",
+    ]);
+    assert.equal(rows[2].cells.every((cell) => !cell.editable), true);
   });
 
   it("shows circuit protection once on each visible circuit row", () => {

tests/distribution-board-feeder-circuit-project-command.repository.test.ts

@@ -0,0 +1,240 @@
+import path from "node:path";
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import { eq } from "drizzle-orm";
+import { migrate } from "drizzle-orm/better-sqlite3/migrator";
+import {
+  createDatabaseContext,
+  type DatabaseContext,
+} from "../src/db/database-context.js";
+import { DistributionBoardStructureProjectCommandRepository } from "../src/db/repositories/distribution-board-structure-project-command.repository.js";
+import { ProjectHistoryRepository } from "../src/db/repositories/project-history.repository.js";
+import { circuits } from "../src/db/schema/circuits.js";
+import { distributionBoards } from "../src/db/schema/distribution-boards.js";
+import { projects } from "../src/db/schema/projects.js";
+import {
+  assertDistributionBoardFeederCircuitProjectCommand,
+  createDistributionBoardCreateFeederCircuitProjectCommand,
+} from "../src/domain/models/distribution-board-feeder-circuit-project-command.model.js";
+import { createDistributionBoardUpdateProjectCommand } from "../src/domain/models/distribution-board-project-command.model.js";
+import {
+  createDistributionBoardInsertProjectCommand,
+  createDistributionBoardStructureSnapshot,
+} from "../src/domain/models/distribution-board-structure-project-command.model.js";
+import { buildCircuitInsertSnapshot } from "../src/frontend/utils/circuit-structure-command.js";
+
+function createTestDatabase(): DatabaseContext {
+  const context = createDatabaseContext(":memory:");
+  migrate(context.db, {
+    migrationsFolder: path.resolve("src", "db", "migrations"),
+  });
+  context.db
+    .insert(projects)
+    .values({ id: "project-1", name: "Test project" })
+    .run();
+  return context;
+}
+
+function setupBoards(
+  context: DatabaseContext,
+  repository: DistributionBoardStructureProjectCommandRepository
+) {
+  const source = createDistributionBoardStructureSnapshot(
+    "project-1",
+    "NSHV"
+  );
+  const downstream = createDistributionBoardStructureSnapshot(
+    "project-1",
+    "UV EG"
+  );
+  repository.execute({
+    projectId: "project-1",
+    expectedRevision: 0,
+    source: "user",
+    command: createDistributionBoardInsertProjectCommand(source),
+  });
+  repository.execute({
+    projectId: "project-1",
+    expectedRevision: 1,
+    source: "user",
+    command: createDistributionBoardInsertProjectCommand(downstream),
+  });
+  const section = source.sections.find(
+    (candidate) => candidate.key === "three_phase"
+  )!;
+  const circuit = {
+    ...buildCircuitInsertSnapshot({
+      id: "feeder-circuit",
+      circuitListId: source.circuitList.id,
+      category: "three_phase",
+      deviceRows: [],
+      values: {
+        sectionId: section.id,
+        equipmentIdentifier: `${section.prefix}1`,
+        displayName: undefined,
+        sortOrder: 10,
+        voltage: 400,
+        isReserve: true,
+      },
+    }),
+    protectionDevice: null,
+  };
+  const boardUpdate = createDistributionBoardUpdateProjectCommand(
+    downstream.distributionBoard.id,
+    {
+      feedingDistributionBoardId: source.distributionBoard.id,
+      feedingCircuitId: circuit.id,
+    }
+  );
+  const command =
+    createDistributionBoardCreateFeederCircuitProjectCommand(
+      circuit,
+      boardUpdate
+    );
+  return { source, downstream, circuit, command };
+}
+
+describe("distribution-board feeder-circuit project command", () => {
+  it("creates and links one feeder atomically and supports undo and redo", () => {
+    const context = createTestDatabase();
+    try {
+      const repository =
+        new DistributionBoardStructureProjectCommandRepository(context.db);
+      const history = new ProjectHistoryRepository(context.db);
+      const { source, downstream, circuit, command } = setupBoards(
+        context,
+        repository
+      );
+
+      repository.executeFeederCircuit({
+        projectId: "project-1",
+        expectedRevision: 2,
+        source: "user",
+        command,
+      });
+      assert.ok(
+        context.db
+          .select()
+          .from(circuits)
+          .where(eq(circuits.id, circuit.id))
+          .get()
+      );
+      assert.deepEqual(
+        context.db
+          .select({
+            boardId: distributionBoards.feedingDistributionBoardId,
+            circuitId: distributionBoards.feedingCircuitId,
+          })
+          .from(distributionBoards)
+          .where(eq(distributionBoards.id, downstream.distributionBoard.id))
+          .get(),
+        {
+          boardId: source.distributionBoard.id,
+          circuitId: circuit.id,
+        }
+      );
+
+      const undo = history.getNextCommand("project-1", "undo");
+      assert.ok(undo);
+      assertDistributionBoardFeederCircuitProjectCommand(undo.command);
+      repository.executeFeederCircuit({
+        projectId: "project-1",
+        expectedRevision: 3,
+        source: "undo",
+        historyTargetChangeSetId: undo.changeSetId,
+        command: undo.command,
+      });
+      assert.equal(
+        context.db
+          .select()
+          .from(circuits)
+          .where(eq(circuits.id, circuit.id))
+          .get(),
+        undefined
+      );
+      assert.deepEqual(
+        context.db
+          .select({
+            boardId: distributionBoards.feedingDistributionBoardId,
+            circuitId: distributionBoards.feedingCircuitId,
+          })
+          .from(distributionBoards)
+          .where(eq(distributionBoards.id, downstream.distributionBoard.id))
+          .get(),
+        { boardId: null, circuitId: null }
+      );
+
+      const redo = history.getNextCommand("project-1", "redo");
+      assert.ok(redo);
+      assertDistributionBoardFeederCircuitProjectCommand(redo.command);
+      repository.executeFeederCircuit({
+        projectId: "project-1",
+        expectedRevision: 4,
+        source: "redo",
+        historyTargetChangeSetId: redo.changeSetId,
+        command: redo.command,
+      });
+      assert.equal(
+        context.db
+          .select({ equipmentIdentifier: circuits.equipmentIdentifier })
+          .from(circuits)
+          .where(eq(circuits.id, circuit.id))
+          .get()?.equipmentIdentifier,
+        circuit.equipmentIdentifier
+      );
+    } finally {
+      context.close();
+    }
+  });
+
+  it("rolls back unlinking when the generated circuit changed before undo", () => {
+    const context = createTestDatabase();
+    try {
+      const repository =
+        new DistributionBoardStructureProjectCommandRepository(context.db);
+      const history = new ProjectHistoryRepository(context.db);
+      const { downstream, circuit, command } = setupBoards(context, repository);
+      repository.executeFeederCircuit({
+        projectId: "project-1",
+        expectedRevision: 2,
+        source: "user",
+        command,
+      });
+      context.db
+        .update(circuits)
+        .set({ displayName: "Außerhalb der Historie geändert" })
+        .where(eq(circuits.id, circuit.id))
+        .run();
+
+      const undo = history.getNextCommand("project-1", "undo");
+      assert.ok(undo);
+      assertDistributionBoardFeederCircuitProjectCommand(undo.command);
+      assert.throws(
+        () =>
+          repository.executeFeederCircuit({
+            projectId: "project-1",
+            expectedRevision: 3,
+            source: "undo",
+            historyTargetChangeSetId: undo.changeSetId,
+            command: undo.command,
+          }),
+        /changed before history removal/
+      );
+      const board = context.db
+        .select()
+        .from(distributionBoards)
+        .where(eq(distributionBoards.id, downstream.distributionBoard.id))
+        .get();
+      assert.equal(board?.feedingCircuitId, circuit.id);
+      assert.ok(
+        context.db
+          .select()
+          .from(circuits)
+          .where(eq(circuits.id, circuit.id))
+          .get()
+      );
+    } finally {
+      context.close();
+    }
+  });
+});

tests/distribution-board-feeder-circuit.test.ts

@@ -0,0 +1,168 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+  buildFeederCircuitSnapshot,
+  getDefaultFeederCircuitSection,
+  getNextFeederCircuitIdentifier,
+} from "../src/frontend/utils/distribution-board-feeder-circuit.js";
+import type { CircuitTreeResponseDto } from "../src/frontend/types.js";
+import { createFeederCircuitAndUpdateDistributionBoard } from "../src/frontend/utils/api.js";
+
+function tree(): CircuitTreeResponseDto {
+  return {
+    circuitListId: "list-main",
+    distributionBoardId: "board-main",
+    distributionBoardName: "NSHV",
+    currentRevision: 2,
+    singlePhaseVoltageV: 230,
+    threePhaseVoltageV: 400,
+    distributionBoardSimultaneityFactor: 1,
+    distributionBoardTotalPower: 0,
+    distributionBoardTotalPowerWithSimultaneityFactor: 0,
+    headerComponents: [],
+    footerComponents: [],
+    sections: [
+      {
+        id: "single",
+        key: "single_phase",
+        category: "single_phase",
+        groupNumber: 1,
+        displayName: "1-phasig 1",
+        prefix: "-2F1.",
+        sortOrder: 10,
+        sectionTotalPower: 0,
+        components: [],
+        circuits: [],
+      },
+      {
+        id: "three",
+        key: "three_phase",
+        category: "three_phase",
+        groupNumber: 1,
+        displayName: "3-phasig 1",
+        prefix: "-3F1.",
+        sortOrder: 20,
+        sectionTotalPower: 0,
+        components: [],
+        circuits: [
+          {
+            id: "existing-2",
+            circuitListId: "list-main",
+            sectionId: "three",
+            equipmentIdentifier: "-3F1.2",
+            sortOrder: 10,
+            isReserve: true,
+            circuitTotalPower: 0,
+            circuitApparentPower: 0,
+            circuitCosPhi: 1,
+            deviceRows: [],
+            downstreamBoardLoads: [],
+          },
+          {
+            id: "existing-5",
+            circuitListId: "list-main",
+            sectionId: "three",
+            equipmentIdentifier: "-3F1.5",
+            sortOrder: 30,
+            isReserve: true,
+            circuitTotalPower: 0,
+            circuitApparentPower: 0,
+            circuitCosPhi: 1,
+            deviceRows: [],
+            downstreamBoardLoads: [],
+          },
+        ],
+      },
+    ],
+  };
+}
+
+describe("distribution-board feeder circuit planning", () => {
+  it("prefers a three-phase section and does not fill BMK gaps", () => {
+    const input = tree();
+    const section = getDefaultFeederCircuitSection(input)!;
+    assert.equal(section.id, "three");
+    assert.equal(getNextFeederCircuitIdentifier(section), "-3F1.6");
+  });
+
+  it("builds an empty circuit with stable id, optional name and defaults", () => {
+    const input = tree();
+    const snapshot = buildFeederCircuitSnapshot({
+      id: "new-feeder",
+      tree: input,
+      sectionId: "three",
+      displayName: "  ",
+    });
+    assert.equal(snapshot.id, "new-feeder");
+    assert.equal(snapshot.equipmentIdentifier, "-3F1.6");
+    assert.equal(snapshot.displayName, null);
+    assert.equal(snapshot.sortOrder, 40);
+    assert.equal(snapshot.voltage, 400);
+    assert.equal(snapshot.isReserve, true);
+    assert.deepEqual(snapshot.deviceRows, []);
+    assert.equal(snapshot.protectionDevice, null);
+  });
+
+  it("sends circuit creation and board linking as one project command", async () => {
+    const input = tree();
+    const circuit = buildFeederCircuitSnapshot({
+      id: "new-feeder",
+      tree: input,
+      sectionId: "three",
+      displayName: "",
+    });
+    const requests: Array<{ url: string; method: string; body: any }> = [];
+    const originalFetch = globalThis.fetch;
+    globalThis.fetch = async (request, init) => {
+      requests.push({
+        url: String(request),
+        method: init?.method ?? "GET",
+        body: JSON.parse(String(init?.body)),
+      });
+      return new Response(JSON.stringify({}), {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      });
+    };
+    try {
+      await createFeederCircuitAndUpdateDistributionBoard(
+        "project-1",
+        "board-child",
+        {
+          floorId: null,
+          supplyType: "AV",
+          simultaneityFactor: 0.8,
+          feedingDistributionBoardId: "board-main",
+          feedingCircuitId: circuit.id,
+        },
+        circuit,
+        7
+      );
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+    assert.equal(requests.length, 1);
+    assert.equal(requests[0].url, "/api/projects/project-1/commands");
+    assert.equal(requests[0].method, "POST");
+    assert.equal(requests[0].body.expectedRevision, 7);
+    assert.equal(
+      requests[0].body.command.type,
+      "distribution-board.create-feeder-circuit"
+    );
+    assert.equal(requests[0].body.command.payload.circuit.id, "new-feeder");
+    assert.deepEqual(
+      requests[0].body.command.payload.boardUpdate.payload.changes
+        .filter((change: { field: string }) =>
+          change.field.startsWith("feeding")
+        )
+        .map((change: { field: string; value: unknown }) => [
+          change.field,
+          change.value,
+        ]),
+      [
+        ["feedingDistributionBoardId", "board-main"],
+        ["feedingCircuitId", "new-feeder"],
+      ]
+    );
+  });
+});