diff --git a/docs/TODO.md b/docs/TODO.md
index f6ba1b1..a1a0df6 100644
--- a/docs/TODO.md
+++ b/docs/TODO.md
@@ -44,13 +44,13 @@
 
 ## 2. Next Up (Phase 1: Read/Browse Implementation)
 
-- [ ] **Task 1: OpenProject REST API v3 Client Layer**
-  - [ ] Implement `src/config/index.ts` to parse and validate `OPENPROJECT_BASE_URL`, `OPENPROJECT_API_KEY`, and `OPENPROJECT_READ_ONLY` (or `--read-only`) via Zod.
-  - [ ] Implement `src/context.ts` providing `RequestContext` interface and `AsyncLocalStorage` scoping (`getRequestContext`, `runWithContext`) for concurrent multi-user safety.
-  - [ ] Implement `src/client/api-client.ts` with native `fetch`, HTTP Basic Auth injection, error normalization, and rate/timeout handling.
-  - [ ] Implement `src/client/hal-parser.ts` to unpack HAL+JSON (`_links`, `_embedded`) into clean, token-efficient JSON models.
-  - [ ] Implement `src/client/filter-builder.ts` to translate LLM-friendly filter arguments into OpenProject's JSON filter syntax.
-  - [ ] Add unit tests in `tests/client.test.ts` verifying authentication headers, response parsing, and error sanitization against live container.
+- [x] **Task 1: OpenProject REST API v3 Client Layer**
+  - [x] Implement `src/config/index.ts` to parse and validate `OPENPROJECT_BASE_URL`, `OPENPROJECT_API_KEY`, and `OPENPROJECT_READ_ONLY` (or `--read-only`) via Zod.
+  - [x] Implement `src/context.ts` providing `RequestContext` interface and `AsyncLocalStorage` scoping (`getRequestContext`, `runWithContext`) for concurrent multi-user safety.
+  - [x] Implement `src/client/api-client.ts` with native `fetch`, HTTP Basic Auth injection, error normalization, and rate/timeout handling.
+  - [x] Implement `src/client/hal-parser.ts` to unpack HAL+JSON (`_links`, `_embedded`) into clean, token-efficient JSON models.
+  - [x] Implement `src/client/filter-builder.ts` to translate LLM-friendly filter arguments into OpenProject's JSON filter syntax.
+  - [x] Add unit tests in `tests/client.test.ts` verifying authentication headers, response parsing, and error sanitization against live container.
 
 - [ ] **Task 2: Domain Services**
   - [ ] Implement `src/services/projects.ts` (`listProjects`, `getProject`).
diff --git a/src/client/api-client.ts b/src/client/api-client.ts
new file mode 100644
index 0000000..02ccec7
--- /dev/null
+++ b/src/client/api-client.ts
@@ -0,0 +1,332 @@
+/**
+ * OpenProject REST API v3 HTTP Client.
+ */
+
+import type { OpenProjectApiErrorPayload } from "./types.ts";
+
+export interface ClientOptions {
+  baseUrl: string;
+  apiKey: string;
+  timeoutMs?: number;
+  fetchFn?: (input: string | URL | Request, init?: RequestInit) => Promise<Response>;
+}
+
+// =============================================================================
+// Error Hierarchy
+// =============================================================================
+
+export class OpenProjectError extends Error {
+  readonly statusCode?: number;
+  readonly errorIdentifier?: string;
+  readonly details?: unknown;
+
+  constructor(
+    message: string,
+    options?: {
+      statusCode?: number;
+      errorIdentifier?: string;
+      details?: unknown;
+      cause?: unknown;
+    }
+  ) {
+    super(message);
+    this.name = "OpenProjectError";
+    this.statusCode = options?.statusCode;
+    this.errorIdentifier = options?.errorIdentifier;
+    this.details = options?.details;
+    if (options?.cause) {
+      this.cause = options.cause;
+    }
+  }
+}
+
+export class OpenProjectAuthenticationError extends OpenProjectError {
+  constructor(message = "Authentication failed. Please check your OpenProject API key.", options?: { errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 401, ...options });
+    this.name = "OpenProjectAuthenticationError";
+  }
+}
+
+export class OpenProjectForbiddenError extends OpenProjectError {
+  constructor(message = "Access forbidden. You do not have permission to access this resource.", options?: { errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 403, ...options });
+    this.name = "OpenProjectForbiddenError";
+  }
+}
+
+export class OpenProjectNotFoundError extends OpenProjectError {
+  constructor(message = "Resource not found.", options?: { errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 404, ...options });
+    this.name = "OpenProjectNotFoundError";
+  }
+}
+
+export class OpenProjectConflictError extends OpenProjectError {
+  constructor(message = "Conflict updating resource. Lock version mismatch.", options?: { errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 409, ...options });
+    this.name = "OpenProjectConflictError";
+  }
+}
+
+export class OpenProjectValidationError extends OpenProjectError {
+  constructor(message = "Validation failed for request data.", options?: { errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 422, ...options });
+    this.name = "OpenProjectValidationError";
+  }
+}
+
+export class OpenProjectRateLimitError extends OpenProjectError {
+  readonly retryAfter?: number;
+
+  constructor(message = "Rate limit exceeded. Please wait before retrying.", options?: { retryAfter?: number; errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: 429, ...options });
+    this.name = "OpenProjectRateLimitError";
+    this.retryAfter = options?.retryAfter;
+  }
+}
+
+export class OpenProjectServerError extends OpenProjectError {
+  constructor(message = "OpenProject internal server error.", options?: { statusCode?: number; errorIdentifier?: string; details?: unknown; cause?: unknown }) {
+    super(message, { statusCode: options?.statusCode ?? 500, ...options });
+    this.name = "OpenProjectServerError";
+  }
+}
+
+export class OpenProjectNetworkError extends OpenProjectError {
+  constructor(message = "Network error connecting to OpenProject instance.", options?: { cause?: unknown }) {
+    super(message, options);
+    this.name = "OpenProjectNetworkError";
+  }
+}
+
+// =============================================================================
+// OpenProject Client Implementation
+// =============================================================================
+
+export class OpenProjectClient {
+  readonly baseUrl: string;
+  private readonly apiKey: string;
+  private readonly timeoutMs: number;
+  private readonly fetchFn: (input: string | URL | Request, init?: RequestInit) => Promise<Response>;
+  private readonly authHeader: string;
+
+  constructor(options: ClientOptions) {
+    this.baseUrl = options.baseUrl.replace(/\/+$/, "");
+    this.apiKey = options.apiKey;
+    this.timeoutMs = options.timeoutMs ?? 30000;
+    this.fetchFn = options.fetchFn ?? fetch;
+    this.authHeader = `Basic ${btoa(`apikey:${this.apiKey}`)}`;
+  }
+
+  /**
+   * Performs an HTTP GET request to OpenProject API v3.
+   */
+  async get<T>(
+    path: string,
+    query?: Record<string, string | number | boolean | undefined | null>
+  ): Promise<T> {
+    const url = this.resolveUrl(path, query);
+    return this.request<T>(url, { method: "GET" });
+  }
+
+  /**
+   * Performs an HTTP POST request to OpenProject API v3.
+   */
+  async post<T>(path: string, body?: unknown): Promise<T> {
+    const url = this.resolveUrl(path);
+    return this.request<T>(url, {
+      method: "POST",
+      body: body !== undefined ? JSON.stringify(body) : undefined,
+    });
+  }
+
+  /**
+   * Performs an HTTP PATCH request to OpenProject API v3.
+   */
+  async patch<T>(path: string, body?: unknown): Promise<T> {
+    const url = this.resolveUrl(path);
+    return this.request<T>(url, {
+      method: "PATCH",
+      body: body !== undefined ? JSON.stringify(body) : undefined,
+    });
+  }
+
+  /**
+   * Performs an HTTP DELETE request to OpenProject API v3.
+   */
+  async delete<T>(path: string): Promise<T> {
+    const url = this.resolveUrl(path);
+    return this.request<T>(url, { method: "DELETE" });
+  }
+
+  /**
+   * Resolves a path or full URL against the client's baseUrl and appends query parameters.
+   */
+  resolveUrl(
+    path: string,
+    query?: Record<string, string | number | boolean | undefined | null>
+  ): string {
+    let resolved: string;
+
+    if (path.startsWith("http://") || path.startsWith("https://")) {
+      resolved = path;
+    } else {
+      let normalizedPath = path.startsWith("/") ? path : `/${path}`;
+      if (!normalizedPath.startsWith("/api/v3")) {
+        normalizedPath = `/api/v3${normalizedPath}`;
+      }
+      resolved = `${this.baseUrl}${normalizedPath}`;
+    }
+
+    if (!query) {
+      return resolved;
+    }
+
+    const url = new URL(resolved);
+    for (const [key, value] of Object.entries(query)) {
+      if (value !== undefined && value !== null) {
+        url.searchParams.set(key, String(value));
+      }
+    }
+    return url.toString();
+  }
+
+  /**
+   * Sanitizes strings (e.g. error messages) to ensure credentials are never leaked.
+   */
+  private sanitize(text: string): string {
+    if (!this.apiKey) {
+      return text;
+    }
+    let sanitized = text.replaceAll(this.apiKey, "[REDACTED_API_KEY]");
+    const base64Auth = btoa(`apikey:${this.apiKey}`);
+    sanitized = sanitized.replaceAll(base64Auth, "[REDACTED_AUTH]");
+    return sanitized;
+  }
+
+  /**
+   * Executes an HTTP request with timeout, authentication, and error normalization.
+   */
+  private async request<T>(url: string, init: RequestInit): Promise<T> {
+    const headers = new Headers(init.headers);
+    headers.set("Authorization", this.authHeader);
+    headers.set("Accept", "application/hal+json, application/json");
+    if (init.body && !headers.has("Content-Type")) {
+      headers.set("Content-Type", "application/json");
+    }
+
+    let signal = init.signal;
+    let timeoutId: ReturnType<typeof setTimeout> | undefined;
+
+    if (!signal) {
+      if (typeof AbortSignal !== "undefined" && "timeout" in AbortSignal) {
+        signal = AbortSignal.timeout(this.timeoutMs);
+      } else {
+        const controller = new AbortController();
+        timeoutId = setTimeout(() => controller.abort(), this.timeoutMs);
+        signal = controller.signal;
+      }
+    }
+
+    try {
+      const response = await this.fetchFn(url, {
+        ...init,
+        headers,
+        signal,
+      });
+
+      if (timeoutId) {
+        clearTimeout(timeoutId);
+      }
+
+      if (response.status === 204) {
+        return undefined as unknown as T;
+      }
+
+      const contentType = response.headers.get("content-type") || "";
+      const isJson = contentType.includes("application/json") || contentType.includes("application/hal+json");
+
+      if (!response.ok) {
+        let errorPayload: OpenProjectApiErrorPayload | undefined;
+        let rawErrorBody: string | undefined;
+
+        if (isJson) {
+          try {
+            errorPayload = (await response.json()) as OpenProjectApiErrorPayload;
+          } catch {
+            // Ignore JSON parse failure on error body
+          }
+        } else {
+          try {
+            rawErrorBody = await response.text();
+          } catch {
+            // Ignore text parse failure
+          }
+        }
+
+        const message = errorPayload?.message
+          ? this.sanitize(errorPayload.message)
+          : rawErrorBody
+          ? this.sanitize(rawErrorBody.slice(0, 300))
+          : `HTTP ${response.status} ${response.statusText}`;
+
+        const errorIdentifier = errorPayload?.errorIdentifier;
+        const details = errorPayload?.errors;
+
+        switch (response.status) {
+          case 401:
+            throw new OpenProjectAuthenticationError(message, { errorIdentifier, details });
+          case 403:
+            throw new OpenProjectForbiddenError(message, { errorIdentifier, details });
+          case 404:
+            throw new OpenProjectNotFoundError(message, { errorIdentifier, details });
+          case 409:
+            throw new OpenProjectConflictError(message, { errorIdentifier, details });
+          case 422:
+            throw new OpenProjectValidationError(message, { errorIdentifier, details });
+          case 429: {
+            const retryAfterHeader = response.headers.get("retry-after");
+            const retryAfter = retryAfterHeader ? parseInt(retryAfterHeader, 10) : undefined;
+            throw new OpenProjectRateLimitError(message, { retryAfter, errorIdentifier, details });
+          }
+          default:
+            if (response.status >= 500) {
+              throw new OpenProjectServerError(message, { statusCode: response.status, errorIdentifier, details });
+            }
+            throw new OpenProjectError(message, { statusCode: response.status, errorIdentifier, details });
+        }
+      }
+
+      if (isJson) {
+        return (await response.json()) as T;
+      }
+
+      return (await response.text()) as unknown as T;
+    } catch (error) {
+      if (timeoutId) {
+        clearTimeout(timeoutId);
+      }
+
+      if (error instanceof OpenProjectError) {
+        throw error;
+      }
+
+      const isTimeout =
+        (error as { name?: string })?.name === "TimeoutError" ||
+        (error as { name?: string })?.name === "AbortError";
+
+      if (isTimeout) {
+        throw new OpenProjectNetworkError(
+          `Request to OpenProject timed out after ${this.timeoutMs}ms.`,
+          { cause: error }
+        );
+      }
+
+      const rawMsg = (error as Error)?.message ?? String(error);
+      throw new OpenProjectNetworkError(
+        `Failed to connect to OpenProject: ${this.sanitize(rawMsg)}`,
+        { cause: error }
+      );
+    }
+  }
+}
diff --git a/src/client/filter-builder.ts b/src/client/filter-builder.ts
new file mode 100644
index 0000000..3e8f0bb
--- /dev/null
+++ b/src/client/filter-builder.ts
@@ -0,0 +1,157 @@
+/**
+ * Filter Builder for OpenProject REST API v3 JSON filter syntax.
+ */
+
+import type {
+  FilterElement,
+  FilterOperator,
+  WorkPackageFilterParams,
+} from "./types.ts";
+
+/**
+ * Fluent builder for creating OpenProject API v3 filter arrays.
+ */
+export class FilterBuilder {
+  private filters: FilterElement[] = [];
+
+  /**
+   * Adds an arbitrary property filter.
+   */
+  add(
+    property: string,
+    operator: FilterOperator,
+    values: (string | number | boolean)[] = []
+  ): this {
+    this.filters.push({
+      [property]: {
+        operator,
+        values: values.map(String),
+      },
+    });
+    return this;
+  }
+
+  /**
+   * Filters by project ID or identifier.
+   */
+  project(projectId: number | string): this {
+    return this.add("project", "=", [projectId]);
+  }
+
+  /**
+   * Filters by work package status.
+   * Accepts "open", "closed", or specific numeric/string status IDs.
+   */
+  status(status: "open" | "closed" | string | number): this {
+    if (status === "open") {
+      return this.add("status", "o", []);
+    }
+    if (status === "closed") {
+      return this.add("status", "c", []);
+    }
+    return this.add("status", "=", [status]);
+  }
+
+  /**
+   * Filters by work package type ID.
+   */
+  type(typeId: number | string): this {
+    return this.add("type", "=", [typeId]);
+  }
+
+  /**
+   * Filters by assignee user ID or "me".
+   */
+  assignee(assigneeId: number | string): this {
+    return this.add("assignee", "=", [assigneeId]);
+  }
+
+  /**
+   * Filters by author user ID.
+   */
+  author(authorId: number | string): this {
+    return this.add("author", "=", [authorId]);
+  }
+
+  /**
+   * Filters by priority ID.
+   */
+  priority(priorityId: number | string): this {
+    return this.add("priority", "=", [priorityId]);
+  }
+
+  /**
+   * Filters by subject (substring match).
+   */
+  subject(text: string): this {
+    return this.add("subject", "~", [text]);
+  }
+
+  /**
+   * Returns the constructed filter array.
+   */
+  build(): FilterElement[] {
+    return [...this.filters];
+  }
+
+  /**
+   * Serializes the filter array into JSON string expected by OpenProject API v3.
+   */
+  toJSON(): string {
+    return JSON.stringify(this.filters);
+  }
+}
+
+/**
+ * Builds an OpenProject API v3 filter array from a WorkPackageFilterParams object.
+ */
+export function buildWorkPackageFilters(
+  params: WorkPackageFilterParams
+): FilterElement[] {
+  const builder = new FilterBuilder();
+
+  if (params.projectId !== undefined && params.projectId !== "") {
+    builder.project(params.projectId);
+  }
+
+  if (params.status !== undefined && params.status !== "") {
+    builder.status(params.status);
+  }
+
+  if (params.typeId !== undefined && params.typeId !== "") {
+    builder.type(params.typeId);
+  }
+
+  if (params.assigneeId !== undefined && params.assigneeId !== "") {
+    builder.assignee(params.assigneeId);
+  }
+
+  if (params.authorId !== undefined && params.authorId !== "") {
+    builder.author(params.authorId);
+  }
+
+  if (params.priorityId !== undefined && params.priorityId !== "") {
+    builder.priority(params.priorityId);
+  }
+
+  if (params.subject !== undefined && params.subject.trim() !== "") {
+    builder.subject(params.subject.trim());
+  }
+
+  if (params.customFilters && params.customFilters.length > 0) {
+    for (const filter of params.customFilters) {
+      for (const [prop, criteria] of Object.entries(filter)) {
+        builder.add(prop, criteria.operator, criteria.values);
+      }
+    }
+  }
+
+  return builder.build();
+}
+
+/**
+ * Serializes a filter array to a JSON string for use in query parameters.
+ */
+export function serializeFilters(filters: FilterElement[]): string {
+  return JSON.stringify(filters);
+}
diff --git a/src/client/hal-parser.ts b/src/client/hal-parser.ts
new file mode 100644
index 0000000..9ca3d54
--- /dev/null
+++ b/src/client/hal-parser.ts
@@ -0,0 +1,385 @@
+/**
+ * HAL+JSON Normalization and Parsing Utilities.
+ * Unpacks nested HAL links and embedded data into token-efficient JSON models.
+ */
+
+import type {
+  HalCollection,
+  HalLink,
+  HalResource,
+  PaginatedResult,
+  PriorityItem,
+  ProjectDetail,
+  ProjectSummary,
+  QueryDetail,
+  QuerySummary,
+  StatusItem,
+  TypeItem,
+  UserItem,
+  WorkPackageDetail,
+  WorkPackageSummary,
+} from "./types.ts";
+
+/**
+ * Extracts a numeric entity ID from an OpenProject HAL href URL.
+ * e.g. "/api/v3/projects/4" -> 4
+ */
+export function extractIdFromHref(href?: string | null): number | undefined {
+  if (!href) return undefined;
+  const match = href.match(/\/(\d+)(?:[/?#]|$)/);
+  if (match && match[1]) {
+    return parseInt(match[1], 10);
+  }
+  return undefined;
+}
+
+/**
+ * Resolves a HAL link into its extracted ID, title, and href.
+ */
+export function resolveLink(
+  link?: HalLink | null
+): { id?: number; title?: string; href?: string } | undefined {
+  if (!link || !link.href) return undefined;
+  return {
+    id: extractIdFromHref(link.href),
+    title: link.title,
+    href: link.href,
+  };
+}
+
+/**
+ * Extracts raw plain text from an OpenProject formatted text field.
+ */
+export function extractRawText(field: unknown): string {
+  if (!field) return "";
+  if (typeof field === "string") return field;
+  if (typeof field === "object" && field !== null) {
+    const obj = field as Record<string, unknown>;
+    if (typeof obj.raw === "string") return obj.raw;
+    if (typeof obj.html === "string") return obj.html;
+  }
+  return String(field);
+}
+
+/**
+ * Unpacks a HAL Collection into a standard PaginatedResult using a transformer function.
+ */
+export function unpackCollection<TItem = HalResource, TResult = unknown>(
+  collection: HalCollection<TItem>,
+  itemTransformer: (item: TItem) => TResult
+): PaginatedResult<TResult> {
+  const rawElements = collection._embedded?.elements ?? [];
+  return {
+    items: rawElements.map(itemTransformer),
+    total: collection.total ?? rawElements.length,
+    count: collection.count ?? rawElements.length,
+    pageSize: collection.pageSize ?? rawElements.length,
+    offset: collection.offset ?? 1,
+  };
+}
+
+/**
+ * Normalizes a project HAL resource into a token-efficient ProjectSummary.
+ */
+export function normalizeProjectSummary(resource: HalResource): ProjectSummary {
+  const selfHref = (resource._links?.self as HalLink | undefined)?.href;
+  return {
+    id: resource.id ?? extractIdFromHref(selfHref) ?? 0,
+    identifier: String(resource.identifier ?? ""),
+    name: String(resource.name ?? ""),
+    active: Boolean(resource.active),
+    public: Boolean(resource.public),
+    description: extractRawText(resource.description),
+    createdAt: typeof resource.createdAt === "string" ? resource.createdAt : undefined,
+    updatedAt: typeof resource.updatedAt === "string" ? resource.updatedAt : undefined,
+  };
+}
+
+/**
+ * Normalizes a project HAL resource into a complete ProjectDetail.
+ */
+export function normalizeProject(resource: HalResource): ProjectDetail {
+  const summary = normalizeProjectSummary(resource);
+  const parentLink = resource._links?.parent as HalLink | undefined;
+  const statusLink = resource._links?.status as HalLink | undefined;
+
+  return {
+    ...summary,
+    parentId: extractIdFromHref(parentLink?.href) ?? null,
+    parentName: parentLink?.title ?? null,
+    status: statusLink?.title ?? (typeof resource.status === "string" ? resource.status : null),
+    statusExplanation: extractRawText(resource.statusExplanation) || null,
+  };
+}
+
+/**
+ * Normalizes a work package HAL resource into a token-efficient WorkPackageSummary.
+ */
+export function normalizeWorkPackageSummary(resource: HalResource): WorkPackageSummary {
+  const links = resource._links ?? {};
+  const selfHref = (links.self as HalLink | undefined)?.href;
+  const typeLink = links.type as HalLink | undefined;
+  const statusLink = links.status as HalLink | undefined;
+  const priorityLink = links.priority as HalLink | undefined;
+  const projectLink = links.project as HalLink | undefined;
+  const authorLink = links.author as HalLink | undefined;
+  const assigneeLink = links.assignee as HalLink | undefined;
+
+  return {
+    id: resource.id ?? extractIdFromHref(selfHref) ?? 0,
+    subject: String(resource.subject ?? ""),
+    type: typeLink?.title ?? "",
+    typeId: extractIdFromHref(typeLink?.href),
+    status: statusLink?.title ?? "",
+    statusId: extractIdFromHref(statusLink?.href),
+    priority: priorityLink?.title,
+    priorityId: extractIdFromHref(priorityLink?.href),
+    project: projectLink?.title ?? "",
+    projectId: extractIdFromHref(projectLink?.href),
+    author: authorLink?.title,
+    authorId: extractIdFromHref(authorLink?.href),
+    assignee: assigneeLink?.title,
+    assigneeId: extractIdFromHref(assigneeLink?.href),
+    startDate: typeof resource.startDate === "string" ? resource.startDate : null,
+    dueDate: typeof resource.dueDate === "string" ? resource.dueDate : null,
+    estimatedTime: typeof resource.estimatedTime === "string" ? resource.estimatedTime : null,
+    spentTime: typeof resource.spentTime === "string" ? resource.spentTime : null,
+    percentageDone: typeof resource.percentageDone === "number" ? resource.percentageDone : null,
+    createdAt: typeof resource.createdAt === "string" ? resource.createdAt : undefined,
+    updatedAt: typeof resource.updatedAt === "string" ? resource.updatedAt : undefined,
+  };
+}
+
+/**
+ * Normalizes a work package HAL resource into a complete WorkPackageDetail.
+ */
+export function normalizeWorkPackage(resource: HalResource): WorkPackageDetail {
+  const summary = normalizeWorkPackageSummary(resource);
+  const links = resource._links ?? {};
+  const parentLink = links.parent as HalLink | undefined;
+
+  let parent: { id: number; subject?: string } | null = null;
+  if (parentLink?.href) {
+    const parentId = extractIdFromHref(parentLink.href);
+    if (parentId !== undefined) {
+      parent = {
+        id: parentId,
+        subject: parentLink.title,
+      };
+    }
+  }
+
+  const children: Array<{ id: number; subject?: string }> = [];
+  const rawChildren = links.children;
+  if (Array.isArray(rawChildren)) {
+    for (const child of rawChildren) {
+      const childLink = child as HalLink;
+      const childId = extractIdFromHref(childLink.href);
+      if (childId !== undefined) {
+        children.push({
+          id: childId,
+          subject: childLink.title,
+        });
+      }
+    }
+  }
+
+  // Extract custom fields if present (customFieldX keys)
+  const customFields: Record<string, unknown> = {};
+  for (const [key, val] of Object.entries(resource)) {
+    if (key.startsWith("customField")) {
+      customFields[key] = val;
+    }
+  }
+
+  return {
+    ...summary,
+    description: extractRawText(resource.description),
+    parent,
+    children: children.length > 0 ? children : undefined,
+    lockVersion: typeof resource.lockVersion === "number" ? resource.lockVersion : 0,
+    customFields: Object.keys(customFields).length > 0 ? customFields : undefined,
+  };
+}
+
+/**
+ * Normalizes a query HAL resource into a QuerySummary.
+ */
+export function normalizeQuerySummary(resource: HalResource): QuerySummary {
+  const selfHref = (resource._links?.self as HalLink | undefined)?.href;
+  const projectLink = resource._links?.project as HalLink | undefined;
+
+  return {
+    id: resource.id ?? extractIdFromHref(selfHref) ?? 0,
+    name: String(resource.name ?? ""),
+    public: Boolean(resource.public),
+    starred: typeof resource.starred === "boolean" ? resource.starred : undefined,
+    projectId: extractIdFromHref(projectLink?.href) ?? null,
+    projectName: projectLink?.title ?? null,
+  };
+}
+
+/**
+ * Normalizes a query HAL resource into a complete QueryDetail.
+ */
+export function normalizeQuery(resource: HalResource): QueryDetail {
+  const summary = normalizeQuerySummary(resource);
+  const links = resource._links ?? {};
+
+  // Extract columns
+  const columns: string[] = [];
+  const rawColumns = links.columns;
+  if (Array.isArray(rawColumns)) {
+    for (const col of rawColumns) {
+      const link = col as HalLink;
+      columns.push(link.title ?? link.href?.split("/").pop() ?? "");
+    }
+  }
+
+  // Extract sortBy
+  const sortBy: Array<{ attribute: string; direction: "asc" | "desc" }> = [];
+  const rawSortBy = links.sortBy;
+  if (Array.isArray(rawSortBy)) {
+    for (const item of rawSortBy) {
+      const link = item as HalLink;
+      const title = link.title ?? "";
+      const isDesc = title.toLowerCase().includes("descending") || link.href?.endsWith("-desc");
+      const attr = link.href?.split("/").pop()?.replace(/-asc|-desc/, "") ?? title;
+      sortBy.push({ attribute: attr, direction: isDesc ? "desc" : "asc" });
+    }
+  }
+
+  // Extract filters
+  const filters: Array<{ field: string; operator: string; values: string[] }> = [];
+  if (Array.isArray(resource.filters)) {
+    for (const f of resource.filters as Array<Record<string, unknown>>) {
+      const fLinks = (f._links ?? {}) as Record<string, unknown>;
+      const opLink = fLinks.operator as HalLink | undefined;
+      const filterLink = fLinks.filter as HalLink | undefined;
+      const field = filterLink?.title ?? String(f.name ?? "");
+      const operator = opLink?.title ?? opLink?.href?.split("/").pop() ?? "";
+      const values: string[] = [];
+      if (Array.isArray(f.values)) {
+        values.push(...f.values.map(String));
+      }
+      filters.push({ field, operator, values });
+    }
+  }
+
+  const resultsLink = links.results as HalLink | undefined;
+
+  return {
+    ...summary,
+    columns,
+    sortBy: sortBy.length > 0 ? sortBy : undefined,
+    filters,
+    resultsHref: resultsLink?.href ?? undefined,
+  };
+}
+
+/**
+ * Normalizes a Status HAL resource.
+ */
+export function normalizeStatus(resource: HalResource): StatusItem {
+  return {
+    id: resource.id ?? extractIdFromHref((resource._links?.self as HalLink | undefined)?.href) ?? 0,
+    name: String(resource.name ?? ""),
+    isClosed: Boolean(resource.isClosed),
+    isDefault: typeof resource.isDefault === "boolean" ? resource.isDefault : undefined,
+    color: typeof resource.color === "string" ? resource.color : undefined,
+  };
+}
+
+/**
+ * Normalizes a Type HAL resource.
+ */
+export function normalizeType(resource: HalResource): TypeItem {
+  return {
+    id: resource.id ?? extractIdFromHref((resource._links?.self as HalLink | undefined)?.href) ?? 0,
+    name: String(resource.name ?? ""),
+    isMilestone: Boolean(resource.isMilestone),
+    isDefault: typeof resource.isDefault === "boolean" ? resource.isDefault : undefined,
+    color: typeof resource.color === "string" ? resource.color : undefined,
+  };
+}
+
+/**
+ * Normalizes a Priority HAL resource.
+ */
+export function normalizePriority(resource: HalResource): PriorityItem {
+  return {
+    id: resource.id ?? extractIdFromHref((resource._links?.self as HalLink | undefined)?.href) ?? 0,
+    name: String(resource.name ?? ""),
+    isActive: typeof resource.isActive === "boolean" ? resource.isActive : true,
+    isDefault: typeof resource.isDefault === "boolean" ? resource.isDefault : undefined,
+    color: typeof resource.color === "string" ? resource.color : undefined,
+  };
+}
+
+/**
+ * Normalizes a User HAL resource.
+ */
+export function normalizeUser(resource: HalResource): UserItem {
+  return {
+    id: resource.id ?? extractIdFromHref((resource._links?.self as HalLink | undefined)?.href) ?? 0,
+    name: String(resource.name ?? ""),
+    login: typeof resource.login === "string" ? resource.login : undefined,
+    email: typeof resource.email === "string" ? resource.email : undefined,
+    admin: typeof resource.admin === "boolean" ? resource.admin : undefined,
+    status: typeof resource.status === "string" ? resource.status : undefined,
+  };
+}
+
+/**
+ * Low-level cleaner that strips operational action links and flattens
+ * generic HAL resources for general token-efficient LLM consumption.
+ */
+export function unpackHalResource(resource: HalResource): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+
+  const operationalLinks = new Set([
+    "self", "schema", "update", "updateImmediately", "delete", "createWorkPackage",
+    "editWorkPackage", "createWorkPackageImmediate", "addAttachment", "addWatcher",
+    "removeWatcher", "addRelation", "addChild", "changeParent", "addComment",
+    "previewMarkup", "logTime", "move", "copy", "pdf", "generate_pdf", "atom",
+    "configureForm", "star", "unstar", "watch", "unwatch", "favor", "unfavor",
+  ]);
+
+  for (const [key, value] of Object.entries(resource)) {
+    if (key === "_links") {
+      const links = value as Record<string, HalLink | HalLink[] | undefined>;
+      const cleanedLinks: Record<string, unknown> = {};
+
+      for (const [linkRel, linkVal] of Object.entries(links)) {
+        if (operationalLinks.has(linkRel) || !linkVal) {
+          continue;
+        }
+
+        if (Array.isArray(linkVal)) {
+          cleanedLinks[linkRel] = linkVal.map((l) => ({
+            id: extractIdFromHref(l.href),
+            title: l.title ?? undefined,
+          }));
+        } else if (linkVal.href) {
+          cleanedLinks[linkRel] = {
+            id: extractIdFromHref(linkVal.href),
+            title: linkVal.title ?? undefined,
+          };
+        }
+      }
+
+      if (Object.keys(cleanedLinks).length > 0) {
+        result.links = cleanedLinks;
+      }
+    } else if (key === "_embedded") {
+      const embedded = value as Record<string, unknown>;
+      result.embedded = embedded;
+    } else if (key === "description" || key === "statusExplanation") {
+      result[key] = extractRawText(value);
+    } else {
+      result[key] = value;
+    }
+  }
+
+  return result;
+}
diff --git a/src/client/index.ts b/src/client/index.ts
new file mode 100644
index 0000000..4fb57ac
--- /dev/null
+++ b/src/client/index.ts
@@ -0,0 +1,4 @@
+export * from "./types.ts";
+export * from "./api-client.ts";
+export * from "./hal-parser.ts";
+export * from "./filter-builder.ts";
diff --git a/src/client/types.ts b/src/client/types.ts
new file mode 100644
index 0000000..f48945e
--- /dev/null
+++ b/src/client/types.ts
@@ -0,0 +1,195 @@
+/**
+ * OpenProject REST API v3 Types and Domain Interfaces.
+ */
+
+// =============================================================================
+// HAL+JSON Primitive Interfaces
+// =============================================================================
+
+export interface HalLink {
+  href: string | null;
+  title?: string;
+  templated?: boolean;
+  method?: string;
+  type?: string;
+  payload?: Record<string, unknown>;
+  [key: string]: unknown;
+}
+
+export type HalLinks = Record<string, HalLink | HalLink[] | undefined>;
+
+export interface HalResource {
+  _type: string;
+  id?: number;
+  _links?: HalLinks;
+  _embedded?: Record<string, unknown>;
+  [key: string]: unknown;
+}
+
+export interface HalCollection<T = HalResource> extends HalResource {
+  _type: "Collection" | "WorkPackageCollection" | string;
+  total: number;
+  count: number;
+  pageSize: number;
+  offset: number;
+  _embedded: {
+    elements: T[];
+    [key: string]: unknown;
+  };
+}
+
+export interface OpenProjectApiErrorPayload {
+  _type?: string;
+  errorIdentifier?: string;
+  message?: string;
+  errors?: Record<string, unknown> | unknown[];
+}
+
+// =============================================================================
+// Normalized Domain Models (Token-Efficient LLM Representations)
+// =============================================================================
+
+export interface PaginatedResult<T> {
+  items: T[];
+  total: number;
+  count: number;
+  pageSize: number;
+  offset: number;
+}
+
+export interface ProjectSummary {
+  id: number;
+  identifier: string;
+  name: string;
+  active: boolean;
+  public: boolean;
+  description?: string;
+  createdAt?: string;
+  updatedAt?: string;
+}
+
+export interface ProjectDetail extends ProjectSummary {
+  parentId?: number | null;
+  parentName?: string | null;
+  status?: string | null;
+  statusExplanation?: string | null;
+}
+
+export interface WorkPackageSummary {
+  id: number;
+  subject: string;
+  type: string;
+  typeId?: number;
+  status: string;
+  statusId?: number;
+  priority?: string;
+  priorityId?: number;
+  project: string;
+  projectId?: number;
+  author?: string;
+  authorId?: number;
+  assignee?: string;
+  assigneeId?: number;
+  startDate?: string | null;
+  dueDate?: string | null;
+  estimatedTime?: string | null;
+  spentTime?: string | null;
+  percentageDone?: number | null;
+  createdAt?: string;
+  updatedAt?: string;
+}
+
+export interface WorkPackageDetail extends WorkPackageSummary {
+  description?: string;
+  parent?: { id: number; subject?: string } | null;
+  children?: Array<{ id: number; subject?: string }>;
+  lockVersion: number;
+  customFields?: Record<string, unknown>;
+}
+
+export interface QuerySummary {
+  id: number;
+  name: string;
+  public: boolean;
+  starred?: boolean;
+  projectId?: number | null;
+  projectName?: string | null;
+}
+
+export interface QueryDetail extends QuerySummary {
+  columns: string[];
+  sortBy?: Array<{ attribute: string; direction: "asc" | "desc" }>;
+  filters: Array<{ field: string; operator: string; values: string[] }>;
+  resultsHref?: string;
+}
+
+export interface StatusItem {
+  id: number;
+  name: string;
+  isClosed: boolean;
+  isDefault?: boolean;
+  color?: string;
+}
+
+export interface TypeItem {
+  id: number;
+  name: string;
+  isMilestone: boolean;
+  isDefault?: boolean;
+  color?: string;
+}
+
+export interface PriorityItem {
+  id: number;
+  name: string;
+  isActive: boolean;
+  isDefault?: boolean;
+  color?: string;
+}
+
+export interface UserItem {
+  id: number;
+  name: string;
+  login?: string;
+  email?: string;
+  admin?: boolean;
+  status?: string;
+}
+
+// =============================================================================
+// Filter Criteria Interfaces
+// =============================================================================
+
+export type FilterOperator =
+  | "="
+  | "!"
+  | "!="
+  | "~"
+  | "!~"
+  | ">="
+  | "<="
+  | "o" // open
+  | "c" // closed
+  | "*" // any / all
+  | "t" // today
+  | "w" // this week
+  | "nd" // next days
+  | string;
+
+export interface FilterElement {
+  [property: string]: {
+    operator: FilterOperator;
+    values: string[];
+  };
+}
+
+export interface WorkPackageFilterParams {
+  projectId?: number | string;
+  status?: "open" | "closed" | string | number;
+  typeId?: number | string;
+  assigneeId?: number | string;
+  authorId?: number | string;
+  priorityId?: number | string;
+  subject?: string;
+  customFilters?: FilterElement[];
+}
diff --git a/src/config/index.ts b/src/config/index.ts
new file mode 100644
index 0000000..0c1125d
--- /dev/null
+++ b/src/config/index.ts
@@ -0,0 +1,43 @@
+import { z } from "zod";
+
+/**
+ * Zod schema for OpenProject MCP server configuration.
+ */
+export const configSchema = z.object({
+  baseUrl: z
+    .string({ required_error: "OPENPROJECT_BASE_URL is required" })
+    .url("OPENPROJECT_BASE_URL must be a valid URL")
+    .transform((val) => val.replace(/\/+$/, "")),
+  apiKey: z
+    .string({ required_error: "OPENPROJECT_API_KEY is required" })
+    .min(1, "OPENPROJECT_API_KEY must not be empty"),
+  readOnly: z.boolean().default(false),
+});
+
+export type AppConfig = z.infer<typeof configSchema>;
+
+/**
+ * Parses and validates configuration from environment variables and CLI arguments.
+ *
+ * @param env - Environment variable map (defaults to process.env)
+ * @param argv - CLI arguments array (defaults to process.argv)
+ * @returns Validated AppConfig object
+ */
+export function parseConfig(
+  env: Record<string, string | undefined> = process.env,
+  argv: string[] = process.argv
+): AppConfig {
+  const isReadOnlyArg = argv.includes("--read-only");
+  const readOnlyEnv = env.OPENPROJECT_READ_ONLY?.trim().toLowerCase();
+  const isReadOnly =
+    isReadOnlyArg ||
+    readOnlyEnv === "true" ||
+    readOnlyEnv === "1" ||
+    readOnlyEnv === "yes";
+
+  return configSchema.parse({
+    baseUrl: env.OPENPROJECT_BASE_URL,
+    apiKey: env.OPENPROJECT_API_KEY,
+    readOnly: isReadOnly,
+  });
+}
diff --git a/src/context.ts b/src/context.ts
new file mode 100644
index 0000000..064d1aa
--- /dev/null
+++ b/src/context.ts
@@ -0,0 +1,50 @@
+
+/**
+ * Request Context and AsyncLocalStorage Scoping for Multi-User Safety.
+ */
+
+import { AsyncLocalStorage } from "node:async_hooks";
+import type { OpenProjectClient } from "./client/api-client.ts";
+
+export interface RequestContext {
+  client: OpenProjectClient;
+  isReadOnly: boolean;
+  sessionId?: string;
+  userId?: string;
+}
+
+const asyncLocalStorage = new AsyncLocalStorage<RequestContext>();
+
+/**
+ * Retrieves the current request context for the active asynchronous execution chain.
+ * Throws an error if called outside of a runWithContext() scope.
+ */
+export function getRequestContext(): RequestContext {
+  const context = asyncLocalStorage.getStore();
+  if (!context) {
+    throw new Error(
+      "No active RequestContext found. Operations must be executed within runWithContext()."
+    );
+  }
+  return context;
+}
+
+/**
+ * Attempts to retrieve the current request context, returning undefined if outside scope.
+ */
+export function tryGetRequestContext(): RequestContext | undefined {
+  return asyncLocalStorage.getStore();
+}
+
+/**
+ * Executes a function within the scope of a specific RequestContext.
+ *
+ * @param context - Request context holding the isolated OpenProject client and options
+ * @param fn - Asynchronous or synchronous callback to execute
+ */
+export function runWithContext<T>(
+  context: RequestContext,
+  fn: () => T
+): T {
+  return asyncLocalStorage.run(context, fn);
+}
diff --git a/tests/client.test.ts b/tests/client.test.ts
new file mode 100644
index 0000000..7a78e6d
--- /dev/null
+++ b/tests/client.test.ts
@@ -0,0 +1,608 @@
+import { describe, expect, test } from "bun:test";
+import { parseConfig } from "../src/config/index.ts";
+import {
+  getRequestContext,
+  runWithContext,
+  tryGetRequestContext,
+  type RequestContext,
+} from "../src/context.ts";
+import {
+  OpenProjectClient,
+  OpenProjectAuthenticationError,
+  OpenProjectForbiddenError,
+  OpenProjectNotFoundError,
+  OpenProjectConflictError,
+  OpenProjectValidationError,
+  OpenProjectRateLimitError,
+  OpenProjectServerError,
+} from "../src/client/api-client.ts";
+import {
+  FilterBuilder,
+  buildWorkPackageFilters,
+  serializeFilters,
+} from "../src/client/filter-builder.ts";
+import {
+  extractIdFromHref,
+  resolveLink,
+  extractRawText,
+  normalizeProjectSummary,
+  normalizeProject,
+  normalizeWorkPackageSummary,
+  normalizeWorkPackage,
+  normalizeQuerySummary,
+  normalizeQuery,
+  normalizeStatus,
+  normalizeType,
+  normalizePriority,
+  normalizeUser,
+  unpackCollection,
+  unpackHalResource,
+} from "../src/client/hal-parser.ts";
+import type { HalCollection, HalResource } from "../src/client/types.ts";
+
+// =============================================================================
+// 1. Configuration Parsing & Validation
+// =============================================================================
+
+describe("Configuration Parser", () => {
+  test("parses valid configuration and trims trailing slashes", () => {
+    const config = parseConfig(
+      {
+        OPENPROJECT_BASE_URL: "http://localhost:8080///",
+        OPENPROJECT_API_KEY: "valid-test-key-12345",
+      },
+      []
+    );
+
+    expect(config.baseUrl).toBe("http://localhost:8080");
+    expect(config.apiKey).toBe("valid-test-key-12345");
+    expect(config.readOnly).toBe(false);
+  });
+
+  test("enables readOnly mode from env OPENPROJECT_READ_ONLY", () => {
+    const config = parseConfig(
+      {
+        OPENPROJECT_BASE_URL: "http://localhost:8080",
+        OPENPROJECT_API_KEY: "secret",
+        OPENPROJECT_READ_ONLY: "true",
+      },
+      []
+    );
+    expect(config.readOnly).toBe(true);
+  });
+
+  test("enables readOnly mode from --read-only argv flag", () => {
+    const config = parseConfig(
+      {
+        OPENPROJECT_BASE_URL: "http://localhost:8080",
+        OPENPROJECT_API_KEY: "secret",
+      },
+      ["node", "index.js", "--read-only"]
+    );
+    expect(config.readOnly).toBe(true);
+  });
+
+  test("throws error when OPENPROJECT_BASE_URL is invalid", () => {
+    expect(() =>
+      parseConfig({
+        OPENPROJECT_BASE_URL: "not-a-valid-url",
+        OPENPROJECT_API_KEY: "secret",
+      })
+    ).toThrow();
+  });
+
+  test("throws error when OPENPROJECT_API_KEY is missing or empty", () => {
+    expect(() =>
+      parseConfig({
+        OPENPROJECT_BASE_URL: "http://localhost:8080",
+        OPENPROJECT_API_KEY: "",
+      })
+    ).toThrow();
+  });
+});
+
+// =============================================================================
+// 2. Request Scoping & AsyncLocalStorage
+// =============================================================================
+
+describe("RequestContext Scoping", () => {
+  test("throws when getRequestContext() is called outside runWithContext", () => {
+    expect(() => getRequestContext()).toThrow(/No active RequestContext found/);
+    expect(tryGetRequestContext()).toBeUndefined();
+  });
+
+  test("provides isolated context inside runWithContext", async () => {
+    const clientA = new OpenProjectClient({
+      baseUrl: "http://host-a",
+      apiKey: "key-a",
+    });
+    const contextA: RequestContext = {
+      client: clientA,
+      isReadOnly: false,
+      userId: "user-a",
+    };
+
+    await runWithContext(contextA, async () => {
+      const activeCtx = getRequestContext();
+      expect(activeCtx.userId).toBe("user-a");
+      expect(activeCtx.client.baseUrl).toBe("http://host-a");
+      expect(activeCtx.isReadOnly).toBe(false);
+    });
+  });
+
+  test("maintains isolated context across concurrent asynchronous tasks", async () => {
+    const client1 = new OpenProjectClient({
+      baseUrl: "http://localhost:8080",
+      apiKey: "key-user-1",
+    });
+    const client2 = new OpenProjectClient({
+      baseUrl: "http://localhost:8080",
+      apiKey: "key-user-2",
+    });
+
+    const ctx1: RequestContext = { client: client1, isReadOnly: false, userId: "user-1" };
+    const ctx2: RequestContext = { client: client2, isReadOnly: true, userId: "user-2" };
+
+    const task1 = runWithContext(ctx1, async () => {
+      await new Promise((resolve) => setTimeout(resolve, 15));
+      const current = getRequestContext();
+      expect(current.userId).toBe("user-1");
+      expect(current.isReadOnly).toBe(false);
+      return current.userId;
+    });
+
+    const task2 = runWithContext(ctx2, async () => {
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      const current = getRequestContext();
+      expect(current.userId).toBe("user-2");
+      expect(current.isReadOnly).toBe(true);
+      return current.userId;
+    });
+
+    const results = await Promise.all([task1, task2]);
+    expect(results).toEqual(["user-1", "user-2"]);
+  });
+});
+
+// =============================================================================
+// 3. Filter Builder
+// =============================================================================
+
+describe("FilterBuilder", () => {
+  test("builds individual filters correctly", () => {
+    const builder = new FilterBuilder();
+    builder.project(12).status("open").type(3);
+
+    const filters = builder.build();
+    expect(filters).toEqual([
+      { project: { operator: "=", values: ["12"] } },
+      { status: { operator: "o", values: [] } },
+      { type: { operator: "=", values: ["3"] } },
+    ]);
+  });
+
+  test("handles closed and specific status IDs", () => {
+    const builderClosed = new FilterBuilder().status("closed");
+    expect(builderClosed.build()).toEqual([
+      { status: { operator: "c", values: [] } },
+    ]);
+
+    const builderSpecific = new FilterBuilder().status("7");
+    expect(builderSpecific.build()).toEqual([
+      { status: { operator: "=", values: ["7"] } },
+    ]);
+  });
+
+  test("builds full query from WorkPackageFilterParams", () => {
+    const filters = buildWorkPackageFilters({
+      projectId: "mcp-test-project",
+      status: "open",
+      assigneeId: "me",
+      priorityId: 2,
+      subject: "bug in auth",
+    });
+
+    expect(filters).toEqual([
+      { project: { operator: "=", values: ["mcp-test-project"] } },
+      { status: { operator: "o", values: [] } },
+      { assignee: { operator: "=", values: ["me"] } },
+      { priority: { operator: "=", values: ["2"] } },
+      { subject: { operator: "~", values: ["bug in auth"] } },
+    ]);
+
+    const serialized = serializeFilters(filters);
+    expect(typeof serialized).toBe("string");
+    expect(JSON.parse(serialized)).toEqual(filters);
+  });
+});
+
+// =============================================================================
+// 4. HAL Parser & Normalizers
+// =============================================================================
+
+describe("HAL Normalizer", () => {
+  test("extracts numeric IDs from URLs", () => {
+    expect(extractIdFromHref("/api/v3/projects/42")).toBe(42);
+    expect(extractIdFromHref("/api/v3/work_packages/123/relations")).toBe(123);
+    expect(extractIdFromHref(null)).toBeUndefined();
+    expect(extractIdFromHref("")).toBeUndefined();
+  });
+
+  test("resolves links and text fields", () => {
+    const link = { href: "/api/v3/types/5", title: "Bug" };
+    expect(resolveLink(link)).toEqual({ id: 5, title: "Bug", href: "/api/v3/types/5" });
+    expect(resolveLink(null)).toBeUndefined();
+
+    expect(extractRawText("plain string")).toBe("plain string");
+    expect(extractRawText({ raw: "raw markdown", html: "<p>html</p>" })).toBe("raw markdown");
+    expect(extractRawText({ html: "<p>html only</p>" })).toBe("<p>html only</p>");
+    expect(extractRawText(null)).toBe("");
+  });
+
+  test("normalizes Project HAL resource", () => {
+    const rawProject: HalResource = {
+      _type: "Project",
+      id: 4,
+      identifier: "test-proj",
+      name: "Test Project",
+      active: true,
+      public: false,
+      description: { raw: "Project description", html: "<p>Project description</p>" },
+      statusExplanation: { raw: "All green", html: "" },
+      _links: {
+        self: { href: "/api/v3/projects/4", title: "Test Project" },
+        parent: { href: "/api/v3/projects/1", title: "Parent Project" },
+        status: { href: "/api/v3/project_statuses/2", title: "ON TRACK" },
+      },
+    };
+
+    const detail = normalizeProject(rawProject);
+    expect(detail.id).toBe(4);
+    expect(detail.identifier).toBe("test-proj");
+    expect(detail.name).toBe("Test Project");
+    expect(detail.active).toBe(true);
+    expect(detail.public).toBe(false);
+    expect(detail.description).toBe("Project description");
+    expect(detail.parentId).toBe(1);
+    expect(detail.parentName).toBe("Parent Project");
+    expect(detail.status).toBe("ON TRACK");
+    expect(detail.statusExplanation).toBe("All green");
+  });
+
+  test("normalizes WorkPackage HAL resource", () => {
+    const rawWp: HalResource = {
+      _type: "WorkPackage",
+      id: 55,
+      subject: "Fix critical login loop",
+      startDate: "2026-09-01",
+      dueDate: "2026-09-10",
+      lockVersion: 3,
+      description: { raw: "Investigation needed." },
+      _links: {
+        self: { href: "/api/v3/work_packages/55" },
+        type: { href: "/api/v3/types/2", title: "Bug" },
+        status: { href: "/api/v3/statuses/1", title: "New" },
+        priority: { href: "/api/v3/priorities/8", title: "High" },
+        project: { href: "/api/v3/projects/4", title: "Test Project" },
+        author: { href: "/api/v3/users/1", title: "Admin User" },
+        assignee: { href: "/api/v3/users/2", title: "Developer" },
+        parent: { href: "/api/v3/work_packages/50", title: "Parent Task" },
+        children: [
+          { href: "/api/v3/work_packages/56", title: "Subtask 1" },
+          { href: "/api/v3/work_packages/57", title: "Subtask 2" },
+        ],
+      },
+    };
+
+    const detail = normalizeWorkPackage(rawWp);
+    expect(detail.id).toBe(55);
+    expect(detail.subject).toBe("Fix critical login loop");
+    expect(detail.type).toBe("Bug");
+    expect(detail.typeId).toBe(2);
+    expect(detail.status).toBe("New");
+    expect(detail.statusId).toBe(1);
+    expect(detail.priority).toBe("High");
+    expect(detail.priorityId).toBe(8);
+    expect(detail.project).toBe("Test Project");
+    expect(detail.projectId).toBe(4);
+    expect(detail.author).toBe("Admin User");
+    expect(detail.authorId).toBe(1);
+    expect(detail.assignee).toBe("Developer");
+    expect(detail.assigneeId).toBe(2);
+    expect(detail.parent).toEqual({ id: 50, subject: "Parent Task" });
+    expect(detail.children).toEqual([
+      { id: 56, subject: "Subtask 1" },
+      { id: 57, subject: "Subtask 2" },
+    ]);
+    expect(detail.description).toBe("Investigation needed.");
+    expect(detail.lockVersion).toBe(3);
+  });
+
+  test("normalizes Query, Status, Type, Priority, and User", () => {
+    const rawQuery: HalResource = {
+      _type: "Query",
+      id: 10,
+      name: "My Tasks",
+      public: true,
+      starred: true,
+      filters: [
+        {
+          _links: {
+            filter: { title: "Status" },
+            operator: { title: "open" },
+          },
+          values: [],
+        },
+      ],
+      _links: {
+        self: { href: "/api/v3/queries/10" },
+        project: { href: "/api/v3/projects/4", title: "Test Project" },
+        columns: [
+          { href: "/api/v3/queries/columns/id", title: "ID" },
+          { href: "/api/v3/queries/columns/subject", title: "Subject" },
+        ],
+        sortBy: [{ href: "/api/v3/queries/sort_bys/id-desc", title: "ID (descending)" }],
+      },
+    };
+
+    const query = normalizeQuery(rawQuery);
+    expect(query.id).toBe(10);
+    expect(query.name).toBe("My Tasks");
+    expect(query.columns).toEqual(["ID", "Subject"]);
+    expect(query.sortBy).toEqual([{ attribute: "id", direction: "desc" }]);
+    expect(query.filters).toEqual([{ field: "Status", operator: "open", values: [] }]);
+
+    const status = normalizeStatus({ _type: "Status", id: 1, name: "New", isClosed: false });
+    expect(status).toEqual({ id: 1, name: "New", isClosed: false, isDefault: undefined, color: undefined });
+
+    const type = normalizeType({ _type: "Type", id: 2, name: "Bug", isMilestone: false });
+    expect(type).toEqual({ id: 2, name: "Bug", isMilestone: false, isDefault: undefined, color: undefined });
+
+    const priority = normalizePriority({ _type: "Priority", id: 8, name: "High", isActive: true });
+    expect(priority).toEqual({ id: 8, name: "High", isActive: true, isDefault: undefined, color: undefined });
+
+    const user = normalizeUser({ _type: "User", id: 4, name: "Admin", login: "admin", email: "a@b.com", admin: true });
+    expect(user).toEqual({ id: 4, name: "Admin", login: "admin", email: "a@b.com", admin: true, status: undefined });
+  });
+
+  test("unpacks collection with pagination metadata", () => {
+    const rawCollection: HalCollection = {
+      _type: "Collection",
+      total: 100,
+      count: 2,
+      pageSize: 2,
+      offset: 1,
+      _embedded: {
+        elements: [
+          { _type: "Status", id: 1, name: "New", isClosed: false },
+          { _type: "Status", id: 2, name: "Closed", isClosed: true },
+        ],
+      },
+    };
+
+    const unpacked = unpackCollection(rawCollection, normalizeStatus);
+    expect(unpacked.total).toBe(100);
+    expect(unpacked.count).toBe(2);
+    expect(unpacked.pageSize).toBe(2);
+    expect(unpacked.offset).toBe(1);
+    expect(unpacked.items.length).toBe(2);
+    expect(unpacked.items[0]?.name).toBe("New");
+    expect(unpacked.items[1]?.name).toBe("Closed");
+  });
+
+  test("unpackHalResource strips noisy operational links", () => {
+    const raw: HalResource = {
+      _type: "WorkPackage",
+      id: 1,
+      subject: "Test",
+      _links: {
+        self: { href: "/api/v3/work_packages/1" },
+        update: { href: "/api/v3/work_packages/1/form", method: "post" },
+        delete: { href: "/api/v3/work_packages/1", method: "delete" },
+        schema: { href: "/api/v3/work_packages/schemas/1" },
+        project: { href: "/api/v3/projects/4", title: "Project 4" },
+      },
+    };
+
+    const stripped = unpackHalResource(raw);
+    expect(stripped._type).toBe("WorkPackage");
+    expect(stripped.id).toBe(1);
+    expect(stripped.subject).toBe("Test");
+    expect(stripped.links).toEqual({
+      project: { id: 4, title: "Project 4" },
+    });
+  });
+});
+
+// =============================================================================
+// 5. OpenProjectClient HTTP & Error Sanitization (Unit Tests with Mock Fetch)
+// =============================================================================
+
+describe("OpenProjectClient (Mocked Unit Tests)", () => {
+  test("injects Basic Auth header and JSON Accept headers", async () => {
+    let capturedHeaders: Headers | undefined;
+
+    const mockFetch = async (_url: string | URL | Request, init?: RequestInit): Promise<Response> => {
+      capturedHeaders = new Headers(init?.headers);
+      return new Response(JSON.stringify({ _type: "Project", id: 1, name: "P1" }), {
+        status: 200,
+        headers: { "Content-Type": "application/hal+json" },
+      });
+    };
+
+    const client = new OpenProjectClient({
+      baseUrl: "http://example.com",
+      apiKey: "super-secret-token",
+      fetchFn: mockFetch,
+    });
+
+    const result = await client.get<{ id: number }>("/api/v3/projects/1");
+    expect(result.id).toBe(1);
+    expect(capturedHeaders?.get("Authorization")).toBe(`Basic ${btoa("apikey:super-secret-token")}`);
+    expect(capturedHeaders?.get("Accept")).toContain("application/hal+json");
+  });
+
+  test("sanitizes API credentials from error messages", async () => {
+    const secretKey = "super-secret-key-xyz-999";
+    const mockFetch = async (): Promise<Response> => {
+      return new Response(
+        JSON.stringify({
+          _type: "Error",
+          errorIdentifier: "urn:openproject-org:api:v3:errors:Unauthenticated",
+          message: `Authentication failed for key ${secretKey} and header Basic ${btoa("apikey:" + secretKey)}`,
+        }),
+        { status: 401, headers: { "Content-Type": "application/json" } }
+      );
+    };
+
+    const client = new OpenProjectClient({
+      baseUrl: "http://example.com",
+      apiKey: secretKey,
+      fetchFn: mockFetch,
+    });
+
+    try {
+      await client.get("/api/v3/projects");
+      expect(true).toBe(false); // Should not reach
+    } catch (err) {
+      expect(err).toBeInstanceOf(OpenProjectAuthenticationError);
+      const msg = (err as Error).message;
+      expect(msg).not.toContain(secretKey);
+      expect(msg).toContain("[REDACTED_API_KEY]");
+      expect(msg).toContain("[REDACTED_AUTH]");
+    }
+  });
+
+  test("maps HTTP status codes to appropriate error classes", async () => {
+    const createMockClient = (status: number, body: unknown, headers?: Record<string, string>) => {
+      const mockFetch = async (): Promise<Response> => {
+        return new Response(JSON.stringify(body), {
+          status,
+          headers: { "Content-Type": "application/json", ...headers },
+        });
+      };
+      return new OpenProjectClient({
+        baseUrl: "http://example.com",
+        apiKey: "dummy-key",
+        fetchFn: mockFetch,
+      });
+    };
+
+    // 403 Forbidden
+    await expect(
+      createMockClient(403, { message: "No permission" }).get("/res")
+    ).rejects.toBeInstanceOf(OpenProjectForbiddenError);
+
+    // 404 Not Found
+    await expect(
+      createMockClient(404, { message: "Item not found" }).get("/res")
+    ).rejects.toBeInstanceOf(OpenProjectNotFoundError);
+
+    // 409 Conflict
+    await expect(
+      createMockClient(409, { message: "Lock version mismatch" }).get("/res")
+    ).rejects.toBeInstanceOf(OpenProjectConflictError);
+
+    // 422 Validation
+    await expect(
+      createMockClient(422, { message: "Invalid attribute" }).get("/res")
+    ).rejects.toBeInstanceOf(OpenProjectValidationError);
+
+    // 429 Rate Limit
+    try {
+      await createMockClient(429, { message: "Slow down" }, { "retry-after": "60" }).get("/res");
+      expect(true).toBe(false);
+    } catch (e) {
+      expect(e).toBeInstanceOf(OpenProjectRateLimitError);
+      expect((e as OpenProjectRateLimitError).retryAfter).toBe(60);
+    }
+
+    // 500 Server Error
+    await expect(
+      createMockClient(500, { message: "Server crashed" }).get("/res")
+    ).rejects.toBeInstanceOf(OpenProjectServerError);
+  });
+});
+
+// =============================================================================
+// 6. Live OpenProject Container Integration Tests
+// =============================================================================
+
+describe("OpenProject Live API Integration (Local Container)", () => {
+  const liveBaseUrl = process.env.OPENPROJECT_BASE_URL || "http://localhost:8080";
+  const liveApiKey = process.env.OPENPROJECT_API_KEY;
+
+  test("fetches projects and work packages against live instance", async () => {
+    if (!liveApiKey) {
+      console.warn("Skipping live container test: OPENPROJECT_API_KEY not set");
+      return;
+    }
+
+    const client = new OpenProjectClient({
+      baseUrl: liveBaseUrl,
+      apiKey: liveApiKey,
+    });
+
+    // 1. Fetch projects
+    const projectsHal = await client.get<HalCollection>("/api/v3/projects");
+    expect(projectsHal._type).toBe("Collection");
+    const unpackedProjects = unpackCollection(projectsHal, normalizeProjectSummary);
+    expect(unpackedProjects.items.length).toBeGreaterThan(0);
+
+    const testProj = unpackedProjects.items.find((p) => p.identifier === "mcp-test-project");
+    expect(testProj).toBeDefined();
+    expect(testProj?.name).toBe("MCP Test Project");
+
+    // 2. Fetch single project detail
+    const projectDetailHal = await client.get<HalResource>(`/api/v3/projects/${testProj!.id}`);
+    const projectDetail = normalizeProject(projectDetailHal);
+    expect(projectDetail.identifier).toBe("mcp-test-project");
+
+    // 3. Fetch work packages with open status filter
+    const openWpsHal = await client.get<HalCollection>("/api/v3/work_packages", {
+      filters: serializeFilters(buildWorkPackageFilters({ status: "open" })),
+    });
+    expect(["Collection", "WorkPackageCollection"]).toContain(openWpsHal._type);
+    const unpackedWps = unpackCollection(openWpsHal, normalizeWorkPackageSummary);
+    expect(unpackedWps.items.length).toBeGreaterThan(0);
+
+    // 4. Fetch taxonomies (statuses, types, priorities)
+    const statusesHal = await client.get<HalCollection>("/api/v3/statuses");
+    const statuses = unpackCollection(statusesHal, normalizeStatus);
+    expect(statuses.items.length).toBeGreaterThan(0);
+    expect(statuses.items.some((s) => s.name === "New")).toBe(true);
+
+    const typesHal = await client.get<HalCollection>("/api/v3/types");
+    const types = unpackCollection(typesHal, normalizeType);
+    expect(types.items.length).toBeGreaterThan(0);
+    expect(types.items.some((t) => t.name === "Task")).toBe(true);
+
+    const prioritiesHal = await client.get<HalCollection>("/api/v3/priorities");
+    const priorities = unpackCollection(prioritiesHal, normalizePriority);
+    expect(priorities.items.length).toBeGreaterThan(0);
+  });
+
+  test("live 401 authentication failure with invalid key", async () => {
+    const client = new OpenProjectClient({
+      baseUrl: liveBaseUrl,
+      apiKey: "definitely-invalid-key-9999",
+    });
+
+    await expect(client.get("/api/v3/projects")).rejects.toBeInstanceOf(
+      OpenProjectAuthenticationError
+    );
+  });
+
+  test("live 404 not found failure with non-existent project", async () => {
+    if (!liveApiKey) return;
+
+    const client = new OpenProjectClient({
+      baseUrl: liveBaseUrl,
+      apiKey: liveApiKey,
+    });
+
+    await expect(client.get("/api/v3/projects/9999999")).rejects.toBeInstanceOf(
+      OpenProjectNotFoundError
+    );
+  });
+});