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+# Facets Predicate Filtering Implementation Plan
+
+> **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.
+
+**Goal:** Add predicate-based filtering (`$all`, `$any`, `$not`, `$exists`, `$in`, `$contains`, `$hasPrefix`) to the catalog `/entity-facets` endpoint, mirroring the pattern already used by `/entities/by-query`.
+
+**Architecture:** Add a POST variant of `/entity-facets` that accepts a JSON body with `query` (predicate) and `facets`. The client routes to POST when a `query` field is present, otherwise falls back to the existing GET endpoint. The backend validates the predicate with zod, then passes it through to `applyEntityFilterToQuery` which already supports both `filter` and `query`.
+
+**Tech Stack:** TypeScript, Express, Knex, zod, OpenAPI
+
+---
+
+### Task 1: Backend internal types — add `query` to `EntityFacetsRequest`
+
+**Files:**
+
+- Modify: `plugins/catalog-backend/src/catalog/types.ts:118-137`
+
+**Step 1: Add `query` field to `EntityFacetsRequest`**
+
+In `plugins/catalog-backend/src/catalog/types.ts`, add an optional `query` field to `EntityFacetsRequest` after the existing `filter` field:
+
+```typescript
+export interface EntityFacetsRequest {
+  filter?: EntityFilter;
+  /** Predicate-based query for filtering entities. */
+  query?: FilterPredicate;
+  facets: string[];
+  credentials: BackstageCredentials;
+}
+```
+
+`FilterPredicate` is already imported at the top of this file from `@backstage/filter-predicates`.
+
+**Step 2: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass (the new field is optional, so no callers break).
+
+**Step 3: Commit**
+
+```
+feat(catalog): add query predicate field to EntityFacetsRequest
+```
+
+---
+
+### Task 2: DefaultEntitiesCatalog — pass `query` through to filter application
+
+**Files:**
+
+- Modify: `plugins/catalog-backend/src/service/DefaultEntitiesCatalog.ts:675-712`
+
+**Step 1: Update the `facets` method to pass `query` to `applyEntityFilterToQuery`**
+
+Change the filter application block (lines 689-696) from:
+
+```typescript
+if (request.filter) {
+  applyEntityFilterToQuery({
+    filter: request.filter,
+    targetQuery: query,
+    onEntityIdField: 'search.entity_id',
+    knex: this.database,
+  });
+}
+```
+
+To:
+
+```typescript
+if (request.filter || request.query) {
+  applyEntityFilterToQuery({
+    filter: request.filter,
+    query: request.query,
+    targetQuery: query,
+    onEntityIdField: 'search.entity_id',
+    knex: this.database,
+  });
+}
+```
+
+**Step 2: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 3: Commit**
+
+```
+feat(catalog): support query predicates in DefaultEntitiesCatalog.facets
+```
+
+---
+
+### Task 3: Backend router — add POST `/entity-facets` handler
+
+**Files:**
+
+- Modify: `plugins/catalog-backend/src/service/createRouter.ts:552-574`
+- Create: `plugins/catalog-backend/src/service/request/parseEntityFacetsQuery.ts`
+
+**Step 1: Create the request parser for POST facets**
+
+Create `plugins/catalog-backend/src/service/request/parseEntityFacetsQuery.ts`:
+
+```typescript
+/*
+ * Copyright 2026 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { InputError } from '@backstage/errors';
+import {
+  createZodV3FilterPredicateSchema,
+  FilterPredicate,
+} from '@backstage/filter-predicates';
+import { z } from 'zod/v3';
+import { fromZodError } from 'zod-validation-error/v3';
+
+const filterPredicateSchema = createZodV3FilterPredicateSchema(z);
+
+export interface ParsedEntityFacetsQuery {
+  facets: string[];
+  query?: FilterPredicate;
+}
+
+export function parseEntityFacetsQuery(
+  body: Record<string, unknown>,
+): ParsedEntityFacetsQuery {
+  // Parse facets
+  if (!Array.isArray(body.facets) || body.facets.length === 0) {
+    throw new InputError('Missing or empty facets parameter');
+  }
+  const facets = body.facets.filter(
+    (f): f is string => typeof f === 'string' && f.length > 0,
+  );
+  if (facets.length === 0) {
+    throw new InputError('Missing or empty facets parameter');
+  }
+
+  // Parse query predicate
+  let query: FilterPredicate | undefined;
+  if (body.query !== undefined) {
+    if (
+      typeof body.query !== 'object' ||
+      body.query === null ||
+      Array.isArray(body.query)
+    ) {
+      throw new InputError('Query must be an object');
+    }
+    const result = filterPredicateSchema.safeParse(body.query);
+    if (!result.success) {
+      throw new InputError(`Invalid query: ${fromZodError(result.error)}`);
+    }
+    query = result.data;
+  }
+
+  return { facets, query };
+}
+```
+
+**Step 2: Add the POST handler in createRouter.ts**
+
+After the existing `.get('/entity-facets', ...)` block (which ends around line 574), add a new `.post('/entity-facets', ...)` handler. Change line 574 from:
+
+```typescript
+      });
+```
+
+to:
+
+```typescript
+      })
+      .post('/entity-facets', async (req, res) => {
+        const auditorEvent = await auditor.createEvent({
+          eventId: 'entity-facets',
+          request: req,
+        });
+
+        try {
+          const { facets, query } = parseEntityFacetsQuery(req.body ?? {});
+
+          const response = await entitiesCatalog.facets({
+            filter: undefined,
+            query,
+            facets,
+            credentials: await httpAuth.credentials(req),
+          });
+
+          await auditorEvent?.success();
+
+          res.status(200).json(response);
+        } catch (err) {
+          await auditorEvent?.fail({
+            error: err,
+          });
+          throw err;
+        }
+      });
+```
+
+Add the import at the top of createRouter.ts, alongside the other request parser imports:
+
+```typescript
+import { parseEntityFacetsQuery } from './request/parseEntityFacetsQuery';
+```
+
+**Step 3: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 4: Commit**
+
+```
+feat(catalog): add POST /entity-facets endpoint with predicate support
+```
+
+---
+
+### Task 4: Backend router tests — test the POST endpoint
+
+**Files:**
+
+- Modify: `plugins/catalog-backend/src/service/createRouter.test.ts`
+- Create: `plugins/catalog-backend/src/service/request/parseEntityFacetsQuery.test.ts`
+
+**Step 1: Write unit tests for `parseEntityFacetsQuery`**
+
+Create `plugins/catalog-backend/src/service/request/parseEntityFacetsQuery.test.ts`:
+
+```typescript
+/*
+ * Copyright 2026 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { parseEntityFacetsQuery } from './parseEntityFacetsQuery';
+
+describe('parseEntityFacetsQuery', () => {
+  it('parses facets with no query', () => {
+    expect(parseEntityFacetsQuery({ facets: ['kind'] })).toEqual({
+      facets: ['kind'],
+      query: undefined,
+    });
+  });
+
+  it('parses facets with a simple query', () => {
+    expect(
+      parseEntityFacetsQuery({
+        facets: ['spec.type'],
+        query: { kind: 'Component' },
+      }),
+    ).toEqual({
+      facets: ['spec.type'],
+      query: { kind: 'Component' },
+    });
+  });
+
+  it('parses facets with complex predicate query', () => {
+    const query = {
+      $all: [{ kind: 'Component' }, { 'spec.lifecycle': 'production' }],
+    };
+    expect(parseEntityFacetsQuery({ facets: ['spec.type'], query })).toEqual({
+      facets: ['spec.type'],
+      query,
+    });
+  });
+
+  it('throws on missing facets', () => {
+    expect(() => parseEntityFacetsQuery({})).toThrow(
+      'Missing or empty facets parameter',
+    );
+  });
+
+  it('throws on empty facets array', () => {
+    expect(() => parseEntityFacetsQuery({ facets: [] })).toThrow(
+      'Missing or empty facets parameter',
+    );
+  });
+
+  it('throws on invalid query (not an object)', () => {
+    expect(() =>
+      parseEntityFacetsQuery({ facets: ['kind'], query: 'bad' }),
+    ).toThrow('Query must be an object');
+  });
+
+  it('throws on invalid query (array)', () => {
+    expect(() =>
+      parseEntityFacetsQuery({ facets: ['kind'], query: [] }),
+    ).toThrow('Query must be an object');
+  });
+});
+```
+
+**Step 2: Run the parser tests**
+
+Run: `CI=1 yarn --cwd plugins/catalog-backend test src/service/request/parseEntityFacetsQuery.test.ts`
+Expected: All tests pass.
+
+**Step 3: Add route-level tests in `createRouter.test.ts`**
+
+Add a new describe block for `POST /entity-facets` and `GET /entity-facets` to the existing test file. Find a suitable location (near end of the `'createRouter readonly disabled'` describe block, before its closing `}`). The test should exercise both the POST and GET routes using the mocked `entitiesCatalog.facets`.
+
+Look at how other route tests are structured in the file (e.g. `POST /entities/by-query`) and follow the same pattern with `request(app).post(...)`.
+
+**Step 4: Run the router tests**
+
+Run: `CI=1 yarn --cwd plugins/catalog-backend test src/service/createRouter.test.ts`
+Expected: All tests pass.
+
+**Step 5: Commit**
+
+```
+test(catalog): add tests for POST /entity-facets endpoint
+```
+
+---
+
+### Task 5: OpenAPI schema — add POST operation for `/entity-facets`
+
+**Files:**
+
+- Modify: `plugins/catalog-backend/src/schema/openapi.yaml:1160-1196`
+
+**Step 1: Add POST operation to the `/entity-facets` path**
+
+After the existing `get` operation block (which ends at line 1196 with `- $ref: '#/components/parameters/filter'`), add:
+
+```yaml
+post:
+  operationId: QueryEntityFacetsByPredicate
+  tags:
+    - Entity
+  description: Get entity facets using predicate-based filters.
+  responses:
+    '200':
+      description: Ok
+      content:
+        application/json:
+          schema:
+            $ref: '#/components/schemas/EntityFacetsResponse'
+    '400':
+      $ref: '#/components/responses/ErrorResponse'
+    default:
+      $ref: '#/components/responses/ErrorResponse'
+  security:
+    - {}
+    - JWT: []
+  requestBody:
+    required: true
+    content:
+      application/json:
+        schema:
+          type: object
+          required:
+            - facets
+          properties:
+            facets:
+              type: array
+              items:
+                type: string
+            query:
+              $ref: '#/components/schemas/JsonObject'
+```
+
+**Step 2: Commit**
+
+```
+feat(catalog): add POST /entity-facets to OpenAPI schema
+```
+
+---
+
+### Task 6: Generated OpenAPI client — add `queryEntityFacetsByPredicate` method
+
+**Files:**
+
+- Modify: `packages/catalog-client/src/schema/openapi/generated/apis/Api.client.ts`
+- Create: `packages/catalog-client/src/schema/openapi/generated/models/QueryEntityFacetsByPredicateRequest.model.ts`
+
+**Step 1: Create the request model**
+
+Create `packages/catalog-client/src/schema/openapi/generated/models/QueryEntityFacetsByPredicateRequest.model.ts`:
+
+```typescript
+// ******************************************************************
+// * THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY. *
+// ******************************************************************
+
+/**
+ * @public
+ */
+export interface QueryEntityFacetsByPredicateRequest {
+  facets: Array<string>;
+  /**
+   * A type representing all allowed JSON object values.
+   */
+  query?: { [key: string]: any };
+}
+```
+
+**Step 2: Add the request type and method to the API client**
+
+In `packages/catalog-client/src/schema/openapi/generated/apis/Api.client.ts`:
+
+Add the import near the other model imports:
+
+```typescript
+import { QueryEntityFacetsByPredicateRequest } from '../models/QueryEntityFacetsByPredicateRequest.model';
+```
+
+Add the request type alongside the other exported types (after `QueryEntitiesByPredicate`):
+
+```typescript
+export type QueryEntityFacetsByPredicate = {
+  body: QueryEntityFacetsByPredicateRequest;
+};
+```
+
+Add the method after the `getEntityFacets` method:
+
+```typescript
+  public async queryEntityFacetsByPredicate(
+    // @ts-ignore
+    request: QueryEntityFacetsByPredicate,
+    options?: RequestOptions,
+  ): Promise<TypedResponse<EntityFacetsResponse>> {
+    const baseUrl = await this.discoveryApi.getBaseUrl(pluginId);
+
+    const uriTemplate = `/entity-facets`;
+
+    const uri = parser.parse(uriTemplate).expand({});
+
+    return await this.fetchApi.fetch(`${baseUrl}${uri}`, {
+      headers: {
+        'Content-Type': 'application/json',
+        ...(options?.token && { Authorization: `Bearer ${options?.token}` }),
+      },
+      method: 'POST',
+      body: JSON.stringify(request.body),
+    });
+  }
+```
+
+**Step 3: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 4: Commit**
+
+```
+feat(catalog): add queryEntityFacetsByPredicate to generated OpenAPI client
+```
+
+---
+
+### Task 7: Client types — add `query` field to `GetEntityFacetsRequest`
+
+**Files:**
+
+- Modify: `packages/catalog-client/src/types/api.ts:261-323`
+
+**Step 1: Add `query` field to `GetEntityFacetsRequest`**
+
+Add after the existing `filter` field (line 299):
+
+```typescript
+  /**
+   * If given, return only entities that match the given predicate query.
+   *
+   * @remarks
+   *
+   * Supports operators like `$all`, `$any`, `$not`, `$exists`, `$in`,
+   * `$contains`, and `$hasPrefix`. When both `filter` and `query` are
+   * provided, they are combined with `$all`.
+   */
+  query?: FilterPredicate;
+```
+
+`FilterPredicate` is already imported at the top of this file.
+
+**Step 2: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 3: Commit**
+
+```
+feat(catalog): add query predicate to GetEntityFacetsRequest
+```
+
+---
+
+### Task 8: Client implementation — route to POST when `query` is present
+
+**Files:**
+
+- Modify: `packages/catalog-client/src/CatalogClient.ts:478-491`
+
+**Step 1: Update `getEntityFacets` to route to POST when `query` is present**
+
+Replace the current `getEntityFacets` method (lines 478-491) with:
+
+```typescript
+  async getEntityFacets(
+    request: GetEntityFacetsRequest,
+    options?: CatalogRequestOptions,
+  ): Promise<GetEntityFacetsResponse> {
+    const { filter, query, facets } = request;
+
+    // Route to POST endpoint if query predicate is provided
+    if (query || filter) {
+      return this.getEntityFacetsByPredicate(request, options);
+    }
+
+    return await this.requestOptional(
+      await this.apiClient.getEntityFacets(
+        {
+          query: { facet: facets },
+        },
+        options,
+      ),
+    );
+  }
+```
+
+**Step 2: Add the private `getEntityFacetsByPredicate` method**
+
+Add after `getEntityFacets`:
+
+```typescript
+  /**
+   * Get entity facets using predicate-based filters (POST endpoint).
+   * @internal
+   */
+  private async getEntityFacetsByPredicate(
+    request: GetEntityFacetsRequest,
+    options?: CatalogRequestOptions,
+  ): Promise<GetEntityFacetsResponse> {
+    const { filter, query, facets } = request;
+
+    let filterPredicate: FilterPredicate | undefined;
+    if (query !== undefined) {
+      if (
+        typeof query !== 'object' ||
+        query === null ||
+        Array.isArray(query)
+      ) {
+        throw new InputError('Query must be an object');
+      }
+      filterPredicate = query;
+    }
+    if (filter !== undefined) {
+      const converted = convertFilterToPredicate(filter);
+      filterPredicate = filterPredicate
+        ? { $all: [filterPredicate, converted] }
+        : converted;
+    }
+
+    return await this.requestOptional(
+      await this.apiClient.queryEntityFacetsByPredicate(
+        {
+          body: {
+            facets,
+            ...(filterPredicate && {
+              query: filterPredicate as unknown as { [key: string]: any },
+            }),
+          },
+        },
+        options,
+      ),
+    );
+  }
+```
+
+Make sure `InputError` is imported from `@backstage/errors` and `convertFilterToPredicate` is imported from `./utils` (check existing imports — `convertFilterToPredicate` is already used by `queryEntitiesByPredicate`).
+
+**Step 3: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 4: Run existing client tests**
+
+Run: `CI=1 yarn --cwd packages/catalog-client test`
+Expected: All tests pass.
+
+**Step 5: Commit**
+
+```
+feat(catalog): route facets requests to POST when query is present
+```
+
+---
+
+### Task 9: Generate API reports and create changesets
+
+**Files:**
+
+- Create: `.changeset/<name>.md` (two changesets)
+
+**Step 1: Run API reports**
+
+Run: `yarn build:api-reports` in project root.
+
+**Step 2: Create changeset for catalog-backend**
+
+Create `.changeset/facets-predicate-backend.md`:
+
+```markdown
+---
+'@backstage/plugin-catalog-backend': minor
+---
+
+Added support for predicate-based filtering on the `/entity-facets` endpoint via a new `POST` method. Supports `$all`, `$any`, `$not`, `$exists`, `$in`, `$contains`, and `$hasPrefix` operators.
+```
+
+**Step 3: Create changeset for catalog-client**
+
+Create `.changeset/facets-predicate-client.md`:
+
+```markdown
+---
+'@backstage/catalog-client': minor
+---
+
+Added support for the `query` field in `getEntityFacets` requests, enabling predicate-based filtering with `$all`, `$any`, `$not`, `$exists`, `$in`, `$contains`, and `$hasPrefix` operators.
+```
+
+**Step 4: Commit changesets and API reports**
+
+```
+chore: add changesets and API reports for facets predicate support
+```
+
+---
+
+### Task 10: Final verification
+
+**Step 1: Run type checker**
+
+Run: `yarn tsc` in project root.
+Expected: Should pass.
+
+**Step 2: Run backend tests**
+
+Run: `CI=1 yarn --cwd plugins/catalog-backend test`
+Expected: All tests pass.
+
+**Step 3: Run client tests**
+
+Run: `CI=1 yarn --cwd packages/catalog-client test`
+Expected: All tests pass.
+
+**Step 4: Run linter**
+
+Run: `yarn lint --fix` in project root.
+Expected: Should pass.