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+# Design Specification: Domain Services Layer
+
+- **Date**: 2026-09-05
+- **Status**: Draft (Under Review)
+- **Target**: `openproject-mcp` Phase 1 (Task 2: Domain Services)
+- **Author**: Antigravity Agent & User Pairing
+
+---
+
+## 1. Executive Summary
+
+This specification defines the Domain Services layer for `openproject-mcp`. The Domain Services layer sits directly between the OpenProject REST API v3 client (`src/client/`) and the upcoming MCP tools layer (`src/tools/`).
+
+Domain services provide stateless, strongly-typed TypeScript functions that abstract OpenProject REST endpoints, automate HAL+JSON unpack/normalization, apply LLM-friendly filter translation, and integrate seamlessly with `RequestContext` via `AsyncLocalStorage`.
+
+---
+
+## 2. Architecture & Design Principles
+
+### 2.1. Stateless Functional Modules with Optional Client Override
+Each domain service is implemented as a functional module exporting standalone asynchronous functions. Every function accepts an optional `client?: OpenProjectClient` parameter as its final argument:
+- **Default Execution**: If `client` is omitted, the service resolves the client from the active execution context via `getRequestContext().client`. This enables MCP tool handlers to call service functions with zero boilerplate.
+- **Testing Ergonomics**: If `client` is explicitly provided, the service uses that instance directly. This allows unit tests to test services with mock clients without requiring `AsyncLocalStorage` setup.
+
+### 2.2. Directory & File Organization
+All domain service code is placed in `src/services/`:
+- `src/services/projects.ts`: Project listing, details, and schema inspection.
+- `src/services/work-packages.ts`: Work package browsing, details, and search.
+- `src/services/queries.ts`: Saved query listing, query configuration details, and query result execution.
+- `src/services/metadata.ts`: System taxonomies including statuses, work package types, priorities, and users.
+- `src/services/index.ts`: Unified barrel export for all domain services and related parameter types.
+
+---
+
+## 3. Detailed Component Specifications
+
+### 3.1. Client Resolution Helper
+A shared internal utility function `resolveClient(client?: OpenProjectClient): OpenProjectClient` will be used across all service modules:
+```typescript
+import { getRequestContext } from "../context.ts";
+import type { OpenProjectClient } from "../client/api-client.ts";
+
+export function resolveClient(client?: OpenProjectClient): OpenProjectClient {
+  return client ?? getRequestContext().client;
+}
+```
+
+### 3.2. Projects Service (`src/services/projects.ts`)
+Interacts with `/api/v3/projects`.
+
+#### Types & Interfaces
+```typescript
+export interface ListProjectsParams {
+  pageSize?: number;
+  offset?: number;
+  sortBy?: string;
+  filters?: FilterElement[];
+}
+```
+
+#### Functions
+1. `listProjects(params?: ListProjectsParams, client?: OpenProjectClient): Promise<PaginatedResult<ProjectSummary>>`
+   - Endpoint: `GET /api/v3/projects`
+   - Query Parameters: `pageSize`, `offset`, `sortBy`, `filters` (JSON stringified).
+   - Response Normalization: `unpackCollection(response, normalizeProjectSummary)`.
+
+2. `getProject(idOrIdentifier: number | string, client?: OpenProjectClient): Promise<ProjectDetail>`
+   - Endpoint: `GET /api/v3/projects/{idOrIdentifier}`
+   - Response Normalization: `normalizeProject(response)`.
+
+3. `getProjectSchema(client?: OpenProjectClient): Promise<Record<string, unknown>>`
+   - Endpoint: `GET /api/v3/projects/schema`
+   - Returns the schema definition object for projects.
+
+---
+
+### 3.3. Work Packages Service (`src/services/work-packages.ts`)
+Interacts with `/api/v3/work_packages` and project-scoped work package endpoints.
+
+#### Types & Interfaces
+```typescript
+export interface ListWorkPackagesParams extends WorkPackageFilterParams {
+  pageSize?: number;
+  offset?: number;
+  sortBy?: string;
+}
+
+export interface SearchWorkPackagesOptions {
+  projectId?: number | string;
+  pageSize?: number;
+  offset?: number;
+}
+```
+
+#### Functions
+1. `listWorkPackages(params?: ListWorkPackagesParams, client?: OpenProjectClient): Promise<PaginatedResult<WorkPackageSummary>>`
+   - Builds filter array using `buildWorkPackageFilters(params)`.
+   - Endpoint: `GET /api/v3/work_packages`
+   - Query Parameters: `pageSize`, `offset`, `sortBy`, `filters` (JSON stringified).
+   - Response Normalization: `unpackCollection(response, normalizeWorkPackageSummary)`.
+
+2. `getWorkPackage(id: number, client?: OpenProjectClient): Promise<WorkPackageDetail>`
+   - Endpoint: `GET /api/v3/work_packages/{id}`
+   - Response Normalization: `normalizeWorkPackage(response)`.
+
+3. `searchWorkPackages(query: string, options?: SearchWorkPackagesOptions, client?: OpenProjectClient): Promise<PaginatedResult<WorkPackageSummary>>`
+   - Convenience wrapper around `listWorkPackages` setting `subject: query` and optional `projectId`.
+
+---
+
+### 3.4. Queries Service (`src/services/queries.ts`)
+Interacts with `/api/v3/queries`.
+
+#### Types & Interfaces
+```typescript
+export interface ListQueriesParams {
+  projectId?: number | string;
+  pageSize?: number;
+  offset?: number;
+}
+
+export interface QueryResultsParams {
+  pageSize?: number;
+  offset?: number;
+}
+```
+
+#### Functions
+1. `listQueries(params?: ListQueriesParams, client?: OpenProjectClient): Promise<PaginatedResult<QuerySummary>>`
+   - Endpoint: `GET /api/v3/queries`
+   - If `projectId` is provided, adds project filter: `[{"project":{"operator":"=","values":[String(projectId)]}}]`.
+   - Query Parameters: `pageSize`, `offset`, `filters`.
+   - Response Normalization: `unpackCollection(response, normalizeQuerySummary)`.
+
+2. `getQuery(id: number, client?: OpenProjectClient): Promise<QueryDetail>`
+   - Endpoint: `GET /api/v3/queries/{id}`
+   - Response Normalization: `normalizeQuery(response)`.
+
+3. `getQueryResults(id: number, params?: QueryResultsParams, client?: OpenProjectClient): Promise<PaginatedResult<WorkPackageSummary>>`
+   - Endpoint: `GET /api/v3/queries/{id}/results`
+   - Query Parameters: `pageSize`, `offset`.
+   - Response Normalization: `unpackCollection(response, normalizeWorkPackageSummary)`.
+
+---
+
+### 3.5. Metadata Service (`src/services/metadata.ts`)
+Interacts with `/api/v3/statuses`, `/api/v3/types`, `/api/v3/priorities`, and `/api/v3/users`.
+
+#### Types & Interfaces
+```typescript
+export interface ListTypesParams {
+  projectId?: number | string;
+}
+
+export interface ListUsersParams {
+  pageSize?: number;
+  offset?: number;
+  status?: string;
+}
+```
+
+#### Functions
+1. `listStatuses(client?: OpenProjectClient): Promise<StatusItem[]>`
+   - Endpoint: `GET /api/v3/statuses`
+   - Unpacks collection and extracts elements normalized via `normalizeStatus`.
+
+2. `listTypes(params?: ListTypesParams, client?: OpenProjectClient): Promise<TypeItem[]>`
+   - Endpoint: If `projectId` provided: `GET /api/v3/projects/{projectId}/types`, else: `GET /api/v3/types`.
+   - Unpacks collection and extracts elements normalized via `normalizeType`.
+
+3. `listPriorities(client?: OpenProjectClient): Promise<PriorityItem[]>`
+   - Endpoint: `GET /api/v3/priorities`
+   - Unpacks collection and extracts elements normalized via `normalizePriority`.
+
+4. `listUsers(params?: ListUsersParams, client?: OpenProjectClient): Promise<PaginatedResult<UserItem>>`
+   - Endpoint: `GET /api/v3/users`
+   - Query Parameters: `pageSize`, `offset`.
+   - Response Normalization: `unpackCollection(response, normalizeUser)`.
+
+---
+
+## 4. Error Handling & Security
+
+1. **Passthrough of Typed Errors**: Service methods do not swallow or alter domain-specific exceptions raised by `OpenProjectClient` (`OpenProjectNotFoundError`, `OpenProjectAuthenticationError`, `OpenProjectForbiddenError`, `OpenProjectValidationError`, `OpenProjectRateLimitError`).
+2. **Credential Sanitization**: The underlying HTTP client already strips API keys from exception messages. Services maintain this safety by avoiding string concatenation containing raw configuration.
+3. **Parameter Validation**: Input validation schemas will be enforced at the MCP tool boundary (Task 3 via Zod). Service functions enforce basic defensive checks (e.g. non-empty IDs).
+
+---
+
+## 5. Testing & Verification Strategy
+
+### 5.1. Unit Testing with Mocked Fetch (`tests/services.test.ts`)
+- Verify correct URL paths and query parameter encoding for all service functions.
+- Verify fallback to `getRequestContext().client` when called inside `runWithContext`.
+- Verify behavior when explicit client parameter is provided.
+- Verify error propagation when mock returns 404 or 403.
+
+### 5.2. Live Container Integration Testing
+- Verify against running local OpenProject 17 container using seeded data:
+  - Project `mcp-test-project` (ID 4) returned by `listProjects` and `getProject`.
+  - Seeded work packages (IDs 38-41) returned by `listWorkPackages` and `getWorkPackage`.
+  - Saved query `MCP Active Tasks` (ID 30) returned by `listQueries`, `getQuery`, and `getQueryResults`.
+  - Taxonomies returned by `listStatuses`, `listTypes`, `listPriorities`, and `listUsers`.
+
+---
+
+## 6. Out of Scope (Future Tasks)
+- MCP Tool registration and Zod schemas (Task 3: MCP Tool Definitions).
+- Mutating operations such as creating/updating work packages (Phase 2).
+- File attachment downloads and wikis (Phase 3).