diff --git a/src/adapters/http/client.js b/src/adapters/http/client.js
new file mode 100644
index 0000000..a7a0e63
--- /dev/null
+++ b/src/adapters/http/client.js
@@ -0,0 +1,438 @@
+import { systemClock } from "../../application/ports/clock-port.js";
+import { getApiOperation } from "../../contracts/api-operations.js";
+import { retryDelay, shouldRetry } from "./retry-policy.js";
+
+const noAuthSession =
+  /** @type {import("../../application/ports/auth-session-port.js").AuthSessionPort} */ ({
+  getState: () => /** @type {"unauthenticated"} */ ("unauthenticated"),
+  attach: async (request) => request,
+  recover: async () => /** @type {"no-session"} */ ("no-session"),
+  onUnauthenticated: () => {},
+});
+
+/**
+ * @typedef {{
+ *   kind: string,
+ *   code: string,
+ *   retryable: boolean,
+ *   operationId: string,
+ *   attemptCount: number,
+ *   httpStatus?: number,
+ *   requestId?: string,
+ *   traceId?: string,
+ *   retryAfterMs?: number,
+ *   userMessageKey: string,
+ *   action: string
+ * }} HttpFailure
+ */
+
+/**
+ * @typedef {{ ok: true, value: unknown, meta: Record<string, string> } |
+ * { ok: false, error: HttpFailure }} HttpResult
+ */
+
+/**
+ * @typedef {{
+ *   code?: string,
+ *   httpStatus?: number,
+ *   requestId?: string,
+ *   traceId?: string,
+ *   retryAfterMs?: number
+ * }} FailureDetails
+ */
+
+/**
+ * @param {{
+ *   baseUrl: string,
+ *   fetcher?: typeof fetch,
+ *   authSession?: import("../../application/ports/auth-session-port.js").AuthSessionPort,
+ *   clock?: import("../../application/ports/clock-port.js").ClockPort,
+ *   random?: () => number,
+ *   validatePayload?: (schemaId: string, value: unknown) =>
+ *     { success: true, data: unknown } | { success: false },
+ *   idempotencyKeyFactory?: () => string
+ * }} dependencies
+ */
+export function createHttpClient(dependencies) {
+  const fetcher = dependencies.fetcher ?? fetch;
+  const authSession = dependencies.authSession ?? noAuthSession;
+  const clock = dependencies.clock ?? systemClock;
+  const random = dependencies.random ?? Math.random;
+  const validatePayload =
+    dependencies.validatePayload ??
+    ((_schemaId, value) => ({ success: /** @type {true} */ (true), data: value }));
+  const idempotencyKeyFactory =
+    dependencies.idempotencyKeyFactory ?? (() => crypto.randomUUID());
+
+  /**
+   * @param {string} operationId
+   * @param {{
+   *   body?: unknown,
+   *   routeId?: string,
+   *   signal?: AbortSignal,
+   *   idempotencyKey?: string
+   * }} [input]
+   */
+  async function execute(operationId, input = {}) {
+    const operation = getApiOperation(operationId);
+    const logicalIdempotencyKey =
+      operation.idempotency === "keyed"
+        ? input.idempotencyKey ?? idempotencyKeyFactory()
+        : undefined;
+    let retryCount = 0;
+    let recoveryUsed = false;
+
+    while (true) {
+      const attempt = retryCount;
+      /** @type {HttpResult} */
+      const outcome = await performAttempt({
+        operation,
+        input,
+        attempt,
+        idempotencyKey: logicalIdempotencyKey,
+      });
+
+      if (outcome.ok) return outcome;
+
+      if (outcome.error.httpStatus === 401 && !recoveryUsed) {
+        recoveryUsed = true;
+        const recovered = await recoverSession(authSession, operation, outcome.error);
+        if (!recovered.ok) return recovered;
+        if (operation.idempotency === "none") {
+          return {
+            ok: false,
+            error: {
+              ...outcome.error,
+              retryable: false,
+              action: "retry",
+            },
+          };
+        }
+        continue;
+      }
+
+      if (!shouldRetry(operation, outcome.error, retryCount)) {
+        return outcome;
+      }
+
+      const delay = retryDelay(outcome.error, retryCount, random, clock.now());
+      retryCount += 1;
+
+      try {
+        await clock.sleep(delay, input.signal);
+      } catch {
+        return {
+          ok: false,
+          error: failure("REQUEST_ABORTED", operationId, retryCount, {
+            code: "REQUEST_ABORTED",
+          }),
+        };
+      }
+    }
+  }
+
+  /**
+   * @param {{
+   *   operation: ReturnType<typeof getApiOperation>,
+   *   input: { body?: unknown, routeId?: string, signal?: AbortSignal },
+   *   attempt: number,
+   *   idempotencyKey?: string
+   * }} context
+   * @returns {Promise<HttpResult>}
+   */
+  async function performAttempt(context) {
+    const { operation, input, attempt, idempotencyKey } = context;
+    const controller = new AbortController();
+    let timedOut = false;
+    const timeout = setTimeout(() => {
+      timedOut = true;
+      controller.abort("timeout");
+    }, operation.timeoutMs);
+    const onExternalAbort = () => controller.abort(input.signal?.reason);
+    input.signal?.addEventListener("abort", onExternalAbort, { once: true });
+
+    const headers = new Headers({ Accept: "application/json" });
+    if (input.body !== undefined) headers.set("Content-Type", "application/json");
+    if (idempotencyKey) headers.set("Idempotency-Key", idempotencyKey);
+
+    let request = new Request(new URL(operation.path, dependencies.baseUrl), {
+      method: operation.method,
+      headers,
+      body: input.body === undefined ? undefined : JSON.stringify(input.body),
+      signal: controller.signal,
+    });
+
+    try {
+      if (operation.auth === "external-session") {
+        try {
+          request = await authSession.attach(request);
+        } catch {
+          return {
+            ok: false,
+            error: failure("AUTH_INTEGRATION_FAILURE", operation.operationId, attempt, {
+              code: "AUTH_ATTACH_FAILED",
+            }),
+          };
+        }
+      }
+
+      const response = await fetcher(request);
+      return await parseResponse(response, operation, attempt, validatePayload);
+    } catch {
+      if (timedOut) {
+        return {
+          ok: false,
+          error: failure("REQUEST_TIMEOUT", operation.operationId, attempt, {
+            code: "REQUEST_TIMEOUT",
+          }),
+        };
+      }
+      if (controller.signal.aborted || input.signal?.aborted) {
+        const externalReason = input.signal?.reason;
+        if (externalReason === "timeout") {
+          return {
+            ok: false,
+            error: failure("REQUEST_TIMEOUT", operation.operationId, attempt, {
+              code: "REQUEST_TIMEOUT",
+            }),
+          };
+        }
+        if (
+          externalReason !== undefined &&
+          !["navigation", "user", "superseded"].includes(String(externalReason))
+        ) {
+          return {
+            ok: false,
+            error: failure("UNKNOWN_FAILURE", operation.operationId, attempt, {
+              code: "EXTERNAL_ABORT_UNRESOLVED",
+            }),
+          };
+        }
+        return {
+          ok: false,
+          error: failure("REQUEST_ABORTED", operation.operationId, attempt, {
+            code: "REQUEST_ABORTED",
+          }),
+        };
+      }
+      return {
+        ok: false,
+        error: failure("NETWORK_UNREACHABLE", operation.operationId, attempt, {
+          code: "NETWORK_UNREACHABLE",
+        }),
+      };
+    } finally {
+      clearTimeout(timeout);
+      input.signal?.removeEventListener("abort", onExternalAbort);
+    }
+  }
+
+  return Object.freeze({ execute });
+}
+
+/**
+ * @param {Response} response
+ * @param {import("../../contracts/api-operations.js").ApiOperation} operation
+ * @param {number} attempt
+ * @param {(schemaId: string, value: unknown) =>
+ *   { success: true, data: unknown } | { success: false }} validatePayload
+ * @returns {Promise<HttpResult>}
+ */
+async function parseResponse(response, operation, attempt, validatePayload) {
+  const contentType = response.headers.get("content-type") ?? "";
+  if (!contentType.toLowerCase().includes("application/json")) {
+    return {
+      ok: false,
+      error: failure("CONTENT_TYPE_MISMATCH", operation.operationId, attempt, {
+        code: "CONTENT_TYPE_MISMATCH",
+        httpStatus: response.status,
+      }),
+    };
+  }
+
+  let envelope;
+  try {
+    envelope = await response.json();
+  } catch {
+    return {
+      ok: false,
+      error: failure("MALFORMED_JSON", operation.operationId, attempt, {
+        code: "MALFORMED_JSON",
+        httpStatus: response.status,
+      }),
+    };
+  }
+
+  if (!envelope || typeof envelope !== "object") {
+    return {
+      ok: false,
+      error: failure("ENVELOPE_MISMATCH", operation.operationId, attempt, {
+        code: "ENVELOPE_MISMATCH",
+        httpStatus: response.status,
+      }),
+    };
+  }
+
+  const envelopeRecord = /** @type {Record<string, unknown>} */ (envelope);
+  if (typeof envelopeRecord.success !== "boolean") {
+    return {
+      ok: false,
+      error: failure("ENVELOPE_MISMATCH", operation.operationId, attempt, {
+        code: "ENVELOPE_MISMATCH",
+        httpStatus: response.status,
+      }),
+    };
+  }
+
+  if (response.ok && envelopeRecord.success === true && "data" in envelopeRecord) {
+    const payload = validatePayload(operation.responseSchema, envelopeRecord.data);
+    if (!payload.success) {
+      return {
+        ok: false,
+        error: failure("SCHEMA_MISMATCH", operation.operationId, attempt, {
+          code: "SCHEMA_MISMATCH",
+          httpStatus: response.status,
+        }),
+      };
+    }
+
+    return {
+      ok: true,
+      value: structuredClone(payload.data),
+      meta: safeMeta(envelopeRecord.meta),
+    };
+  }
+
+  const kind = statusKind(response.status);
+  const retryAfter = response.headers.get("retry-after");
+  return {
+    ok: false,
+    error: failure(kind, operation.operationId, attempt, {
+      code: safeBackendCode(envelope),
+      httpStatus: response.status,
+      requestId: safeMeta(envelopeRecord.meta).requestId,
+      traceId: safeMeta(envelopeRecord.meta).traceId,
+      retryAfterMs:
+        response.status === 429 && retryAfter
+          ? parseRetryAfterHeader(retryAfter)
+          : undefined,
+    }),
+  };
+}
+
+/**
+ * @param {import("../../application/ports/auth-session-port.js").AuthSessionPort} authSession
+ * @param {import("../../contracts/api-operations.js").ApiOperation} operation
+ * @param {HttpFailure} originalFailure
+ * @returns {Promise<{ok: true} | {ok: false, error: HttpFailure}>}
+ */
+async function recoverSession(authSession, operation, originalFailure) {
+  try {
+    const result = await authSession.recover();
+    if (result === "restored") return { ok: true };
+    if (result === "no-session") {
+      authSession.onUnauthenticated();
+      return {
+        ok: false,
+        error: failure("AUTH_REQUIRED", operation.operationId, originalFailure.attemptCount, {
+          code: "AUTH_REQUIRED",
+          httpStatus: 401,
+        }),
+      };
+    }
+  } catch {
+    // Normalized below.
+  }
+
+  return {
+    ok: false,
+    error: failure(
+      "AUTH_INTEGRATION_FAILURE",
+      operation.operationId,
+      originalFailure.attemptCount,
+      { code: "AUTH_RECOVERY_FAILED" },
+    ),
+  };
+}
+
+/**
+ * @param {string} kind
+ * @param {string} operationId
+ * @param {number} attempt
+ * @param {FailureDetails} [details]
+ * @returns {HttpFailure}
+ */
+function failure(kind, operationId, attempt, details = {}) {
+  const retryable = new Set([
+    "NETWORK_UNREACHABLE",
+    "REQUEST_TIMEOUT",
+    "RATE_LIMITED",
+    "SERVER_FAILURE",
+  ]).has(kind);
+  const action =
+    kind === "AUTH_REQUIRED"
+      ? "reauth"
+      : retryable
+        ? "retry"
+        : kind === "REQUEST_ABORTED"
+          ? "none"
+          : "contact-support";
+
+  return Object.freeze({
+    kind,
+    code: details.code ?? kind,
+    retryable,
+    operationId,
+    attemptCount: attempt + 1,
+    ...(details.httpStatus === undefined ? {} : { httpStatus: details.httpStatus }),
+    ...(details.requestId ? { requestId: details.requestId } : {}),
+    ...(details.traceId ? { traceId: details.traceId } : {}),
+    ...(details.retryAfterMs === undefined
+      ? {}
+      : { retryAfterMs: details.retryAfterMs }),
+    userMessageKey: `error.${kind.toLowerCase()}`,
+    action,
+  });
+}
+
+/** @param {number} status */
+function statusKind(status) {
+  if (status === 401) return "AUTH_REQUIRED";
+  if (status === 403) return "FORBIDDEN";
+  if (status === 404) return "NOT_FOUND";
+  if (status === 409) return "CONFLICT";
+  if (status === 422) return "VALIDATION_REJECTED";
+  if (status === 429) return "RATE_LIMITED";
+  if (status >= 500) return "SERVER_FAILURE";
+  if (status >= 400) return "UNKNOWN_CLIENT_FAILURE";
+  return "ENVELOPE_MISMATCH";
+}
+
+/** @param {unknown} envelope */
+function safeBackendCode(envelope) {
+  if (!envelope || typeof envelope !== "object") return "HTTP_FAILURE";
+  const error = /** @type {Record<string, unknown>} */ (envelope).error;
+  if (!error || typeof error !== "object") return "HTTP_FAILURE";
+  const code = /** @type {Record<string, unknown>} */ (error).code;
+  return typeof code === "string" ? code : "HTTP_FAILURE";
+}
+
+/** @param {unknown} meta @returns {Record<string, string>} */
+function safeMeta(meta) {
+  if (!meta || typeof meta !== "object") return {};
+  const metaRecord = /** @type {Record<string, unknown>} */ (meta);
+  return {
+    ...(typeof metaRecord.requestId === "string"
+      ? { requestId: metaRecord.requestId }
+      : {}),
+    ...(typeof metaRecord.traceId === "string" ? { traceId: metaRecord.traceId } : {}),
+  };
+}
+
+/** @param {string} value */
+function parseRetryAfterHeader(value) {
+  const seconds = Number(value);
+  if (Number.isFinite(seconds) && seconds >= 0) return seconds * 1_000;
+  const timestamp = Date.parse(value);
+  return Number.isFinite(timestamp) ? Math.max(0, timestamp - Date.now()) : undefined;
+}
diff --git a/src/adapters/http/retry-policy.js b/src/adapters/http/retry-policy.js
new file mode 100644
index 0000000..ecf787e
--- /dev/null
+++ b/src/adapters/http/retry-policy.js
@@ -0,0 +1,79 @@
+const retryKinds = new Set([
+  "NETWORK_UNREACHABLE",
+  "REQUEST_TIMEOUT",
+  "RATE_LIMITED",
+  "SERVER_FAILURE",
+]);
+
+/**
+ * @param {number} retryIndex
+ * @param {() => number} [random]
+ * @param {number} [baseDelayMs]
+ * @param {number} [maxDelayMs]
+ */
+export function calculateBackoff(
+  retryIndex,
+  random = Math.random,
+  baseDelayMs = 250,
+  maxDelayMs = 2_000,
+) {
+  return Math.min(maxDelayMs, baseDelayMs * 2 ** retryIndex) * random();
+}
+
+/** @param {string | null | undefined} value @param {number} [now] */
+export function parseRetryAfter(value, now = Date.now()) {
+  if (!value) return null;
+
+  const seconds = Number(value);
+  if (Number.isFinite(seconds)) {
+    return seconds < 0 ? null : seconds * 1_000;
+  }
+
+  const timestamp = Date.parse(value);
+  if (!Number.isFinite(timestamp)) return null;
+  return Math.max(0, timestamp - now);
+}
+
+/**
+ * @param {{ idempotency: "safe" | "keyed" | "none" }} operation
+ * @param {{ kind: string, retryAfterMs?: number, httpStatus?: number }} failure
+ * @param {number} retryCount
+ * @param {number} [maxRetries]
+ */
+export function shouldRetry(operation, failure, retryCount, maxRetries = 2) {
+  if (retryCount >= maxRetries) return false;
+  if (!retryKinds.has(failure.kind)) return false;
+  if (
+    failure.kind === "SERVER_FAILURE" &&
+    failure.httpStatus !== undefined &&
+    ![502, 503, 504].includes(failure.httpStatus)
+  ) {
+    return false;
+  }
+  if (
+    failure.kind === "RATE_LIMITED" &&
+    typeof failure.retryAfterMs === "number" &&
+    failure.retryAfterMs > 30_000
+  ) {
+    return false;
+  }
+  return operation.idempotency === "safe" || operation.idempotency === "keyed";
+}
+
+/**
+ * @param {{ kind: string, retryAfterMs?: number, retryAfter?: string }} failure
+ * @param {number} retryIndex
+ * @param {() => number} [random]
+ * @param {number} [now]
+ */
+export function retryDelay(failure, retryIndex, random = Math.random, now = Date.now()) {
+  const localBackoff = calculateBackoff(retryIndex, random);
+  if (failure.kind !== "RATE_LIMITED") return localBackoff;
+
+  const retryAfterMs =
+    typeof failure.retryAfterMs === "number"
+      ? failure.retryAfterMs
+      : parseRetryAfter(failure.retryAfter, now);
+
+  return retryAfterMs === null ? localBackoff : Math.max(localBackoff, retryAfterMs);
+}
diff --git a/src/contracts/api-operations.js b/src/contracts/api-operations.js
new file mode 100644
index 0000000..08c6558
--- /dev/null
+++ b/src/contracts/api-operations.js
@@ -0,0 +1,51 @@
+/**
+ * @typedef {{
+ *   method: string,
+ *   path: string,
+ *   operationId: string,
+ *   auth: "none" | "external-session",
+ *   timeoutMs: number,
+ *   idempotency: "safe" | "keyed" | "none",
+ *   requestSchema: string,
+ *   responseSchema: string,
+ *   owner: string
+ * }} ApiOperation
+ */
+
+/** @param {ApiOperation} definition */
+const operation = (definition) => Object.freeze(definition);
+
+export const API_OPERATIONS = Object.freeze({
+  LIST_SAMPLE_RESOURCES: operation({
+    method: "GET",
+    path: "/api/sample/resources",
+    operationId: "LIST_SAMPLE_RESOURCES",
+    auth: "external-session",
+    timeoutMs: 10_000,
+    idempotency: "safe",
+    requestSchema: "SampleResourceListQuery",
+    responseSchema: "SampleResourceListPayload",
+    owner: "feature-sample-feature-slice-contract-fixture",
+  }),
+  CREATE_SAMPLE_RESOURCE: operation({
+    method: "POST",
+    path: "/api/sample/resources",
+    operationId: "CREATE_SAMPLE_RESOURCE",
+    auth: "external-session",
+    timeoutMs: 10_000,
+    idempotency: "keyed",
+    requestSchema: "CreateSampleResourceCommand",
+    responseSchema: "SampleResourcePayload",
+    owner: "feature-sample-feature-slice-contract-fixture",
+  }),
+});
+
+/** @param {string} operationId */
+export function getApiOperation(operationId) {
+  const registry = /** @type {Record<string, ApiOperation>} */ (API_OPERATIONS);
+  const selected = registry[operationId];
+  if (!selected) {
+    throw new Error(`Unregistered API operation: ${operationId}`);
+  }
+  return selected;
+}
diff --git a/tests/integration/http-client.test.js b/tests/integration/http-client.test.js
new file mode 100644
index 0000000..28c1dd0
--- /dev/null
+++ b/tests/integration/http-client.test.js
@@ -0,0 +1,71 @@
+import { HttpResponse, http } from "msw";
+import { setupServer } from "msw/node";
+import { afterAll, afterEach, beforeAll, describe, expect, it } from "vitest";
+
+import { createHttpClient } from "../../src/adapters/http/client.js";
+
+let attempts = 0;
+const server = setupServer(
+  http.get("https://api.test/api/sample/resources", () => {
+    attempts += 1;
+    if (attempts < 3) {
+      return HttpResponse.json(
+        { success: false, error: { code: "TEMPORARY" } },
+        { status: 503 },
+      );
+    }
+    return HttpResponse.json({
+      success: true,
+      data: [{ id: "resource-1", name: "Example" }],
+      meta: { requestId: "request-1", traceId: "trace-1" },
+    });
+  }),
+);
+
+beforeAll(() => server.listen({ onUnhandledRequest: "error" }));
+afterEach(() => {
+  attempts = 0;
+  server.resetHandlers();
+});
+afterAll(() => server.close());
+
+const clock = {
+  now: () => 0,
+  sleep: async () => {},
+};
+
+describe("shared HTTP client", () => {
+  it("retries a safe request at most twice and returns validated data", async () => {
+    const client = createHttpClient({
+      baseUrl: "https://api.test",
+      clock,
+      random: () => 0,
+    });
+
+    await expect(
+      client.execute("LIST_SAMPLE_RESOURCES", { routeId: "SAMPLE_RESOURCE_LIST" }),
+    ).resolves.toMatchObject({
+      ok: true,
+      value: [{ id: "resource-1" }],
+      meta: { requestId: "request-1" },
+    });
+    expect(attempts).toBe(3);
+  });
+
+  it("rejects a non-JSON response without exposing its body", async () => {
+    server.use(
+      http.get(
+        "https://api.test/api/sample/resources",
+        () => new HttpResponse("<secret>raw body</secret>", { status: 502 }),
+      ),
+    );
+    const client = createHttpClient({ baseUrl: "https://api.test", clock });
+    const result = await client.execute("LIST_SAMPLE_RESOURCES");
+
+    expect(result).toMatchObject({
+      ok: false,
+      error: { kind: "CONTENT_TYPE_MISMATCH" },
+    });
+    expect(JSON.stringify(result)).not.toContain("raw body");
+  });
+});
diff --git a/tests/unit/retry-policy.test.js b/tests/unit/retry-policy.test.js
new file mode 100644
index 0000000..de7cd34
--- /dev/null
+++ b/tests/unit/retry-policy.test.js
@@ -0,0 +1,47 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  calculateBackoff,
+  parseRetryAfter,
+  retryDelay,
+  shouldRetry,
+} from "../../src/adapters/http/retry-policy.js";
+
+describe("HTTP retry policy", () => {
+  it("uses capped exponential full jitter", () => {
+    expect(calculateBackoff(0, () => 0.5)).toBe(125);
+    expect(calculateBackoff(8, () => 1)).toBe(2_000);
+  });
+
+  it("parses retry-after and chooses the longer bounded delay", () => {
+    expect(parseRetryAfter("2", 0)).toBe(2_000);
+    expect(retryDelay({ kind: "RATE_LIMITED", retryAfterMs: 500 }, 0, () => 0)).toBe(
+      500,
+    );
+  });
+
+  it("allows at most two retries for safe or keyed requests", () => {
+    const failure = { kind: "SERVER_FAILURE" };
+    expect(shouldRetry({ idempotency: "safe" }, failure, 0)).toBe(true);
+    expect(shouldRetry({ idempotency: "keyed" }, failure, 1)).toBe(true);
+    expect(shouldRetry({ idempotency: "safe" }, failure, 2)).toBe(false);
+    expect(shouldRetry({ idempotency: "none" }, failure, 0)).toBe(false);
+    expect(
+      shouldRetry(
+        { idempotency: "safe" },
+        { kind: "SERVER_FAILURE", httpStatus: 500 },
+        0,
+      ),
+    ).toBe(false);
+  });
+
+  it("does not automatically wait beyond 30 seconds", () => {
+    expect(
+      shouldRetry(
+        { idempotency: "safe" },
+        { kind: "RATE_LIMITED", retryAfterMs: 31_000 },
+        0,
+      ),
+    ).toBe(false);
+  });
+});