diff --git a/frontend/src/adapters/http/httpInvoker.test.ts b/frontend/src/adapters/http/httpInvoker.test.ts
index 141eedc..dcbbe59 100644
--- a/frontend/src/adapters/http/httpInvoker.test.ts
+++ b/frontend/src/adapters/http/httpInvoker.test.ts
@@ -77,6 +77,29 @@ describe("HttpInvoker", () => {
     });
   });
 
+  it("fires onUnauthorized on a 401 (and still throws)", async () => {
+    const { fetchImpl } = fakeFetch(
+      { code: "UNAUTHENTICATED", message: "no session" },
+      { ok: false, status: 401 },
+    );
+    const onUnauthorized = vi.fn();
+    const http = new HttpInvoker({ baseUrl: "https://host", fetchImpl, onUnauthorized });
+
+    await expect(http.invoke("list_projects")).rejects.toMatchObject({
+      code: "UNAUTHENTICATED",
+    });
+    expect(onUnauthorized).toHaveBeenCalledOnce();
+  });
+
+  it("does not fire onUnauthorized on a non-401 error", async () => {
+    const { fetchImpl } = fakeFetch({ code: "NOT_FOUND", message: "x" }, { ok: false, status: 404 });
+    const onUnauthorized = vi.fn();
+    const http = new HttpInvoker({ baseUrl: "https://host", fetchImpl, onUnauthorized });
+
+    await expect(http.invoke("open_project", { projectId: "x" })).rejects.toBeTruthy();
+    expect(onUnauthorized).not.toHaveBeenCalled();
+  });
+
   it("wraps a network failure in a TRANSPORT_ERROR GatewayError", async () => {
     const fetchImpl: FetchLike = async () => {
       throw new Error("boom");
diff --git a/frontend/src/adapters/http/httpInvoker.ts b/frontend/src/adapters/http/httpInvoker.ts
index 162d869..9db8ec1 100644
--- a/frontend/src/adapters/http/httpInvoker.ts
+++ b/frontend/src/adapters/http/httpInvoker.ts
@@ -30,6 +30,8 @@ export type FetchLike = (
     headers?: Record<string, string>;
     body?: string;
     signal?: AbortSignal;
+    /** Cookie policy — F2 uses `same-origin` so the session cookie rides along. */
+    credentials?: "same-origin" | "include" | "omit";
   },
 ) => Promise<{
   ok: boolean;
@@ -47,6 +49,12 @@ export interface HttpInvokerConfig {
   token?: string;
   /** Injected fetch (defaults to global `fetch`). */
   fetchImpl?: FetchLike;
+  /**
+   * Called when the backend answers `401` (the session cookie is missing or
+   * expired). F2 wires this to the web session so the app routes back to the
+   * pairing screen. The `GatewayError` is still thrown to the caller.
+   */
+  onUnauthorized?: () => void;
 }
 
 /** Builds a {@link GatewayError} from an arbitrary thrown/parsed value. */
@@ -71,10 +79,12 @@ export class HttpInvoker {
   private readonly baseUrl: string;
   private readonly token?: string;
   private readonly fetchImpl: FetchLike;
+  private readonly onUnauthorized?: () => void;
 
   constructor(config: HttpInvokerConfig) {
     this.baseUrl = config.baseUrl.replace(/\/+$/, "");
     this.token = config.token;
+    this.onUnauthorized = config.onUnauthorized;
     // `globalThis.fetch` exists in the browser (and jsdom); the cast narrows it
     // to the minimal shape used here.
     this.fetchImpl =
@@ -98,6 +108,9 @@ export class HttpInvoker {
         method: "POST",
         headers,
         body: JSON.stringify({ command, args }),
+        // Same-origin so the HttpOnly session cookie is sent automatically
+        // (ticket #13: no secret in the URL/headers from JS).
+        credentials: "same-origin",
       });
     } catch (networkError) {
       const err: GatewayError = {
@@ -108,6 +121,9 @@ export class HttpInvoker {
     }
 
     if (!res.ok) {
+      // A 401 means the session cookie is missing/expired: signal the app to
+      // route back to pairing (the error is still thrown to the caller).
+      if (res.status === 401) this.onUnauthorized?.();
       // Preserve the backend `ErrorDto` when present; fall back to the status.
       let parsed: unknown;
       try {
diff --git a/frontend/src/adapters/http/index.ts b/frontend/src/adapters/http/index.ts
index b3a7d9b..98c8070 100644
--- a/frontend/src/adapters/http/index.ts
+++ b/frontend/src/adapters/http/index.ts
@@ -18,6 +18,7 @@ import type { Gateways } from "@/ports";
 import { LocalStorageUiPreferencesGateway } from "../uiPreferences";
 import { HttpInvoker } from "./httpInvoker";
 import { WsLiveClient } from "./wsLiveClient";
+import { getWebSession } from "./webSession";
 import {
   HttpConversationGateway,
   HttpEmbedderGateway,
@@ -77,7 +78,13 @@ function resolveEndpoints(config: HttpWsGatewaysConfig): {
  */
 export function createHttpWsGateways(config: HttpWsGatewaysConfig = {}): Gateways {
   const { baseUrl, wsUrl } = resolveEndpoints(config);
-  const http = new HttpInvoker({ baseUrl, token: config.token });
+  // Route 401s back to the pairing screen via the shared web session (F2).
+  const session = getWebSession();
+  const http = new HttpInvoker({
+    baseUrl,
+    token: config.token,
+    onUnauthorized: () => session.notifyUnauthorized(),
+  });
   const ws = new WsLiveClient({ wsUrl, token: config.token });
 
   return {
@@ -108,3 +115,4 @@ export function createHttpWsGateways(config: HttpWsGatewaysConfig = {}): Gateway
 
 export { HttpInvoker } from "./httpInvoker";
 export { WsLiveClient } from "./wsLiveClient";
+export { WebSession, getWebSession, setWebSessionForTests } from "./webSession";
diff --git a/frontend/src/adapters/http/webSession.test.ts b/frontend/src/adapters/http/webSession.test.ts
new file mode 100644
index 0000000..afef6d2
--- /dev/null
+++ b/frontend/src/adapters/http/webSession.test.ts
@@ -0,0 +1,92 @@
+/**
+ * F2 — the web session: pairing handshake (success marks the flag; wrong code
+ * rejects with a clear message), and the 401 → unauthorized transition that
+ * clears the flag and notifies subscribers.
+ */
+import { describe, it, expect, vi } from "vitest";
+
+import type { FetchLike } from "./httpInvoker";
+import { WebSession, type FlagStore } from "./webSession";
+
+function memStore(): FlagStore {
+  const map = new Map<string, string>();
+  return {
+    getItem: (k) => map.get(k) ?? null,
+    setItem: (k, v) => void map.set(k, v),
+    removeItem: (k) => void map.delete(k),
+  };
+}
+
+function fetchReturning(status: number, body: unknown): {
+  fetchImpl: FetchLike;
+  calls: { url: string; init: unknown }[];
+} {
+  const calls: { url: string; init: unknown }[] = [];
+  const fetchImpl: FetchLike = async (url, init) => {
+    calls.push({ url, init });
+    return {
+      ok: status >= 200 && status < 300,
+      status,
+      json: async () => body,
+      text: async () => JSON.stringify(body),
+    };
+  };
+  return { fetchImpl, calls };
+}
+
+describe("WebSession pairing", () => {
+  it("POSTs the code to /api/pair and marks the flag on success", async () => {
+    const store = memStore();
+    const { fetchImpl, calls } = fetchReturning(200, { ok: true });
+    const session = new WebSession({ baseUrl: "https://host/", fetchImpl, store });
+
+    expect(session.isPaired()).toBe(false);
+    await session.pair("4821-93");
+
+    expect(session.isPaired()).toBe(true);
+    expect(calls[0].url).toBe("https://host/api/pair");
+    expect(JSON.parse((calls[0].init as { body: string }).body)).toEqual({ code: "4821-93" });
+  });
+
+  it("rejects a wrong code with a clear message and stays unpaired", async () => {
+    const store = memStore();
+    const { fetchImpl } = fetchReturning(401, { code: "INVALID", message: "bad code" });
+    const session = new WebSession({ baseUrl: "https://host", fetchImpl, store });
+
+    await expect(session.pair("nope")).rejects.toMatchObject({ code: "INVALID_PAIRING_CODE" });
+    expect(session.isPaired()).toBe(false);
+  });
+
+  it("falls back to a default message when the server sends no body", async () => {
+    const { fetchImpl } = fetchReturning(403, undefined);
+    const session = new WebSession({ baseUrl: "https://host", fetchImpl, store: memStore() });
+
+    await expect(session.pair("x")).rejects.toMatchObject({
+      code: "INVALID_PAIRING_CODE",
+      message: "Code d'appairage invalide.",
+    });
+  });
+});
+
+describe("WebSession unauthorized handling", () => {
+  it("clears the flag and notifies subscribers on notifyUnauthorized", () => {
+    const store = memStore();
+    const session = new WebSession({ baseUrl: "https://host", store });
+    session.markPaired();
+    const handler = vi.fn();
+    session.onUnauthorized(handler);
+
+    session.notifyUnauthorized();
+
+    expect(session.isPaired()).toBe(false);
+    expect(handler).toHaveBeenCalledOnce();
+  });
+
+  it("forget() clears the flag (best-effort local sign-out)", () => {
+    const store = memStore();
+    const session = new WebSession({ baseUrl: "https://host", store });
+    session.markPaired();
+    session.forget();
+    expect(session.isPaired()).toBe(false);
+  });
+});
diff --git a/frontend/src/adapters/http/webSession.ts b/frontend/src/adapters/http/webSession.ts
new file mode 100644
index 0000000..810e5f2
--- /dev/null
+++ b/frontend/src/adapters/http/webSession.ts
@@ -0,0 +1,175 @@
+/**
+ * Web client session (pairing + auth routing) — ticket #13, lot F2.
+ *
+ * The real authentication material is a session cookie set by the server at
+ * pairing (`POST /api/pair {code}` → `Set-Cookie: … HttpOnly; Secure;
+ * SameSite=Strict`). Because it is **HttpOnly** the browser sends it
+ * automatically on same-origin requests but JS can never read it. So this module
+ * keeps only a lightweight, JS-visible **"paired" flag** (in `localStorage`) to
+ * decide which screen to render — never the secret itself.
+ *
+ * On a `401` from any `/api/invoke`, the {@link HttpInvoker} calls
+ * {@link WebSession.notifyUnauthorized}, which clears the flag and notifies
+ * subscribers so the app routes back to the pairing screen. "Forget" is a
+ * best-effort local clear (server-side cookie revocation is B8).
+ *
+ * Lives in `src/adapters/**`; touches no `@tauri-apps/api`.
+ */
+
+import type { GatewayError, Unsubscribe } from "@/domain";
+import type { FetchLike } from "./httpInvoker";
+
+const PAIRED_FLAG_KEY = "idea.web.paired";
+
+/** Minimal `localStorage`-like surface, injectable for tests. */
+export interface FlagStore {
+  getItem(key: string): string | null;
+  setItem(key: string, value: string): void;
+  removeItem(key: string): void;
+}
+
+/** Configuration for a {@link WebSession}. */
+export interface WebSessionConfig {
+  /** Backend base URL (no trailing slash). Defaults to the page origin. */
+  baseUrl?: string;
+  /** Injected fetch (defaults to global `fetch`, with same-origin credentials). */
+  fetchImpl?: FetchLike;
+  /** Injected flag store (defaults to `window.localStorage`, else in-memory). */
+  store?: FlagStore;
+}
+
+/** In-memory fallback when `localStorage` is unavailable (SSR/tests). */
+function memoryStore(): FlagStore {
+  const map = new Map<string, string>();
+  return {
+    getItem: (k) => map.get(k) ?? null,
+    setItem: (k, v) => void map.set(k, v),
+    removeItem: (k) => void map.delete(k),
+  };
+}
+
+function defaultStore(): FlagStore {
+  try {
+    if (typeof window !== "undefined" && window.localStorage) {
+      return window.localStorage;
+    }
+  } catch {
+    /* access can throw in a sandboxed iframe; fall through */
+  }
+  return memoryStore();
+}
+
+function defaultBaseUrl(): string {
+  return typeof window !== "undefined" && window.location
+    ? window.location.origin
+    : "http://localhost";
+}
+
+/**
+ * The web session state machine. One instance is shared between the pairing UI
+ * and the HTTP invoker (via the module singleton below).
+ */
+export class WebSession {
+  private readonly baseUrl: string;
+  private readonly fetchImpl: FetchLike;
+  private readonly store: FlagStore;
+  private readonly unauthorizedHandlers = new Set<() => void>();
+
+  constructor(config: WebSessionConfig = {}) {
+    this.baseUrl = (config.baseUrl ?? defaultBaseUrl()).replace(/\/+$/, "");
+    this.fetchImpl = config.fetchImpl ?? (globalThis.fetch as unknown as FetchLike);
+    this.store = config.store ?? defaultStore();
+  }
+
+  /** Whether the client believes it is paired (a session cookie should exist). */
+  isPaired(): boolean {
+    return this.store.getItem(PAIRED_FLAG_KEY) === "1";
+  }
+
+  /** Records the paired flag (called after a successful pair). */
+  markPaired(): void {
+    this.store.setItem(PAIRED_FLAG_KEY, "1");
+  }
+
+  /** Best-effort local sign-out: clears the flag (server revocation is B8). */
+  forget(): void {
+    this.store.removeItem(PAIRED_FLAG_KEY);
+  }
+
+  /**
+   * Performs the pairing handshake: `POST /api/pair {code}`. On success the
+   * server sets the session cookie and this records the paired flag. A wrong code
+   * rejects with a {@link GatewayError} carrying a clear message.
+   */
+  async pair(code: string): Promise<void> {
+    let res: Awaited<ReturnType<FetchLike>>;
+    try {
+      res = await this.fetchImpl(`${this.baseUrl}/api/pair`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ code }),
+      });
+    } catch (networkError) {
+      const err: GatewayError = {
+        code: "TRANSPORT_ERROR",
+        message: `Impossible de joindre le serveur : ${String(networkError)}`,
+      };
+      throw err;
+    }
+
+    if (!res.ok) {
+      let parsed: unknown;
+      try {
+        parsed = await res.json();
+      } catch {
+        parsed = undefined;
+      }
+      const message =
+        parsed && typeof parsed === "object" && "message" in parsed
+          ? String((parsed as GatewayError).message)
+          : res.status === 401 || res.status === 403
+            ? "Code d'appairage invalide."
+            : `Échec de l'appairage (HTTP ${res.status}).`;
+      const err: GatewayError = {
+        code: res.status === 401 || res.status === 403 ? "INVALID_PAIRING_CODE" : "PAIRING_FAILED",
+        message,
+      };
+      throw err;
+    }
+
+    // Cookie is now set by the server (HttpOnly — not read here); record the flag.
+    this.markPaired();
+  }
+
+  /**
+   * Called by the HTTP invoker on a `401`: the session cookie is missing/expired.
+   * Clears the flag and notifies subscribers so the app returns to pairing.
+   */
+  notifyUnauthorized(): void {
+    this.forget();
+    for (const handler of this.unauthorizedHandlers) handler();
+  }
+
+  /** Subscribes to unauthorized transitions (returns an unsubscribe). */
+  onUnauthorized(handler: () => void): Unsubscribe {
+    this.unauthorizedHandlers.add(handler);
+    return () => this.unauthorizedHandlers.delete(handler);
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Module singleton (shared between the invoker and the pairing UI)
+// ---------------------------------------------------------------------------
+
+let singleton: WebSession | null = null;
+
+/** Returns the shared web session, creating it on first use. */
+export function getWebSession(): WebSession {
+  if (!singleton) singleton = new WebSession();
+  return singleton;
+}
+
+/** Overrides the singleton (tests). Pass `null` to reset to a fresh default. */
+export function setWebSessionForTests(session: WebSession | null): void {
+  singleton = session;
+}
diff --git a/frontend/src/app/main.tsx b/frontend/src/app/main.tsx
index c6819d7..3cb59f7 100644
--- a/frontend/src/app/main.tsx
+++ b/frontend/src/app/main.tsx
@@ -5,7 +5,8 @@ import ReactDOM from "react-dom/client";
 
 import { App } from "./App";
 import { ViewWindow, parseViewWindowParams } from "./ViewWindow";
-import { DIProvider } from "./di";
+import { WebApp } from "@/features/web";
+import { DIProvider, resolveTransport } from "./di";
 import "@/shared/styles/theme.css";
 
 const root = document.getElementById("root");
@@ -18,10 +19,17 @@ if (!root) {
 // follows the main window's focused project; otherwise the full app.
 const viewParams = parseViewWindowParams(window.location.search);
 
+// Ticket #13, F2: in web (HTTP) transport mode the browser client renders the
+// pairing-gated, read-only `WebApp`. Desktop (Tauri) is unchanged — it renders
+// the full `App` (or a detached view window). Detached windows are desktop-only.
+const isWeb = resolveTransport() === "http";
+
 ReactDOM.createRoot(root).render(
   <React.StrictMode>
     <DIProvider>
-      {viewParams ? (
+      {isWeb ? (
+        <WebApp />
+      ) : viewParams ? (
         <ViewWindow panel={viewParams.panel} />
       ) : (
         <App />
diff --git a/frontend/src/features/web/PairingScreen.tsx b/frontend/src/features/web/PairingScreen.tsx
new file mode 100644
index 0000000..04e0685
--- /dev/null
+++ b/frontend/src/features/web/PairingScreen.tsx
@@ -0,0 +1,96 @@
+/**
+ * Web pairing screen — ticket #13, lot F2.
+ *
+ * Shown by {@link WebApp} when the client is not paired. The user types the code
+ * the server printed at first launch; on submit we `POST /api/pair {code}` via
+ * the {@link WebSession}. On success the server sets the HttpOnly session cookie
+ * and we advance to the workspace; a wrong code shows a clear message.
+ *
+ * Transport-neutral at the component seam: it talks to the injected
+ * {@link WebSession}, never to `@tauri-apps/api` (the CI guard `no-direct-invoke`
+ * stays green). Pure web-only UI — desktop never mounts it.
+ */
+
+import { useState, type FormEvent } from "react";
+
+import type { GatewayError } from "@/domain";
+import { Button, Field, Input, Panel } from "@/shared";
+import type { WebSession } from "@/adapters/http";
+
+interface PairingScreenProps {
+  /** The shared web session performing the `POST /api/pair` handshake. */
+  session: WebSession;
+  /** Called once pairing succeeds (cookie set) so the app can advance. */
+  onPaired: () => void;
+}
+
+function describe(e: unknown): string {
+  if (e && typeof e === "object" && "message" in e) {
+    return String((e as GatewayError).message);
+  }
+  return String(e);
+}
+
+export function PairingScreen({ session, onPaired }: PairingScreenProps) {
+  const [code, setCode] = useState("");
+  const [error, setError] = useState<string | null>(null);
+  const [busy, setBusy] = useState(false);
+
+  async function submit(e: FormEvent): Promise<void> {
+    e.preventDefault();
+    const trimmed = code.trim();
+    if (!trimmed || busy) return;
+    setBusy(true);
+    setError(null);
+    try {
+      await session.pair(trimmed);
+      onPaired();
+    } catch (err) {
+      setError(describe(err));
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  return (
+    <div className="flex h-full items-center justify-center bg-canvas p-6">
+      <Panel className="w-full max-w-sm">
+        <form onSubmit={submit} className="flex flex-col gap-4">
+          <div className="flex flex-col gap-1">
+            <h1 className="text-lg font-semibold tracking-tight">Appairer cet appareil</h1>
+            <p className="text-sm text-muted">
+              Saisissez le code affiché par le serveur IdeA pour connecter ce
+              navigateur.
+            </p>
+          </div>
+
+          <Field label="Code d'appairage">
+            {({ id, describedBy }) => (
+              <Input
+                id={id}
+                aria-describedby={describedBy}
+                value={code}
+                onChange={(e) => setCode(e.target.value)}
+                placeholder="p. ex. 4821-93"
+                autoFocus
+                autoComplete="one-time-code"
+                disabled={busy}
+                invalid={!!error}
+              />
+            )}
+          </Field>
+
+          {error && (
+            <p role="alert" data-testid="pairing-error" className="text-sm text-danger">
+              {error}
+            </p>
+          )}
+
+          <Button type="submit" disabled={busy || code.trim().length === 0}>
+            {busy ? "Appairage…" : "Appairer"}
+          </Button>
+        </form>
+      </Panel>
+    </div>
+  );
+}
diff --git a/frontend/src/features/web/WebApp.test.tsx b/frontend/src/features/web/WebApp.test.tsx
new file mode 100644
index 0000000..7ae53ef
--- /dev/null
+++ b/frontend/src/features/web/WebApp.test.tsx
@@ -0,0 +1,120 @@
+/**
+ * F2 — the web client routing + pairing flow:
+ *  - not paired ⇒ pairing screen; wrong code ⇒ clear error, stays on pairing;
+ *  - successful pair ⇒ read-only workspace (project list + open + snapshot);
+ *  - a 401 (session.notifyUnauthorized) ⇒ back to pairing.
+ */
+import { describe, it, expect } from "vitest";
+import { act, fireEvent, render, screen, waitFor } from "@testing-library/react";
+
+import type { Gateways } from "@/ports";
+import { DIProvider } from "@/app/di";
+import { createMockGateways, MockWorkStateGateway } from "@/adapters/mock";
+import { WebSession } from "@/adapters/http";
+import type { FetchLike } from "@/adapters/http/httpInvoker";
+import type { FlagStore } from "@/adapters/http/webSession";
+import { WebApp } from "./WebApp";
+
+function memStore(): FlagStore {
+  const map = new Map<string, string>();
+  return {
+    getItem: (k) => map.get(k) ?? null,
+    setItem: (k, v) => void map.set(k, v),
+    removeItem: (k) => void map.delete(k),
+  };
+}
+
+const okFetch: FetchLike = async () => ({
+  ok: true,
+  status: 200,
+  json: async () => ({ ok: true }),
+  text: async () => "{}",
+});
+
+const rejectFetch: FetchLike = async () => ({
+  ok: false,
+  status: 401,
+  json: async () => ({ code: "INVALID", message: "bad" }),
+  text: async () => "{}",
+});
+
+/** Mock gateways seeded with one project + a work-state snapshot. */
+async function seededGateways(): Promise<Gateways> {
+  const gateways = createMockGateways();
+  const project = await gateways.project.createProject("Demo", "/srv/demo");
+  (gateways.workState as MockWorkStateGateway)._setProjectWorkState(project.id, {
+    agents: [
+      { agentId: "a1", name: "Archi", profileId: "p1", busy: { state: "idle" }, tickets: [] },
+    ],
+    conversations: [],
+  });
+  return gateways;
+}
+
+function renderWebApp(session: WebSession, gateways: Gateways) {
+  return render(
+    <DIProvider gateways={gateways}>
+      <WebApp session={session} />
+    </DIProvider>,
+  );
+}
+
+describe("WebApp pairing routing", () => {
+  it("shows the pairing screen when not paired", async () => {
+    const session = new WebSession({ baseUrl: "https://h", fetchImpl: okFetch, store: memStore() });
+    renderWebApp(session, await seededGateways());
+
+    expect(screen.getByText("Appairer cet appareil")).toBeTruthy();
+    expect(screen.queryByText("Projets")).toBeNull();
+  });
+
+  it("advances to the read-only workspace after a successful pair", async () => {
+    const session = new WebSession({ baseUrl: "https://h", fetchImpl: okFetch, store: memStore() });
+    renderWebApp(session, await seededGateways());
+
+    fireEvent.change(screen.getByLabelText("Code d'appairage"), { target: { value: "4821-93" } });
+    fireEvent.click(screen.getByRole("button", { name: "Appairer" }));
+
+    expect(await screen.findByText("Projets")).toBeTruthy();
+    expect(await screen.findByText("Demo")).toBeTruthy();
+    expect(session.isPaired()).toBe(true);
+  });
+
+  it("shows a clear error on a wrong code and stays on pairing", async () => {
+    const session = new WebSession({ baseUrl: "https://h", fetchImpl: rejectFetch, store: memStore() });
+    renderWebApp(session, await seededGateways());
+
+    fireEvent.change(screen.getByLabelText("Code d'appairage"), { target: { value: "nope" } });
+    fireEvent.click(screen.getByRole("button", { name: "Appairer" }));
+
+    expect(await screen.findByTestId("pairing-error")).toBeTruthy();
+    expect(screen.queryByText("Projets")).toBeNull();
+    expect(session.isPaired()).toBe(false);
+  });
+
+  it("opens a project read-only and renders the work-state snapshot", async () => {
+    const session = new WebSession({ baseUrl: "https://h", fetchImpl: okFetch, store: memStore() });
+    session.markPaired();
+    renderWebApp(session, await seededGateways());
+
+    // Workspace is shown directly (already paired); open the seeded project.
+    fireEvent.click(await screen.findByText("Demo"));
+
+    const snapshot = await screen.findByTestId("web-workstate");
+    expect(snapshot.textContent).toContain("Archi");
+    expect(snapshot.textContent).toContain("idle");
+  });
+
+  it("returns to pairing when the session reports unauthorized (401)", async () => {
+    const session = new WebSession({ baseUrl: "https://h", fetchImpl: okFetch, store: memStore() });
+    session.markPaired();
+    renderWebApp(session, await seededGateways());
+
+    expect(await screen.findByText("Projets")).toBeTruthy();
+
+    act(() => session.notifyUnauthorized());
+
+    await waitFor(() => expect(screen.getByText("Appairer cet appareil")).toBeTruthy());
+    expect(screen.queryByText("Projets")).toBeNull();
+  });
+});
diff --git a/frontend/src/features/web/WebApp.tsx b/frontend/src/features/web/WebApp.tsx
new file mode 100644
index 0000000..274f06d
--- /dev/null
+++ b/frontend/src/features/web/WebApp.tsx
@@ -0,0 +1,63 @@
+/**
+ * Web client root — ticket #13, lot F2. Mounted (instead of the desktop `App`)
+ * only when the HTTP transport is selected (`VITE_TRANSPORT="http"`).
+ *
+ * Routes on the {@link WebSession} paired flag: not paired ⇒ {@link PairingScreen};
+ * paired ⇒ the read-only {@link WebWorkspace}. It subscribes to the session's
+ * `onUnauthorized` signal so a `401` from any `/api/invoke` (expired/missing
+ * cookie) drops back to pairing automatically. A best-effort "Se déconnecter"
+ * clears the local flag (server-side cookie revocation is B8).
+ */
+
+import { useEffect, useState } from "react";
+
+import { Button } from "@/shared";
+import { getWebSession, type WebSession } from "@/adapters/http";
+import { PairingScreen } from "./PairingScreen";
+import { WebWorkspace } from "./WebWorkspace";
+
+interface WebAppProps {
+  /** Injectable session (tests); defaults to the shared singleton. */
+  session?: WebSession;
+}
+
+export function WebApp({ session }: WebAppProps = {}) {
+  const webSession = session ?? getWebSession();
+  const [paired, setPaired] = useState(() => webSession.isPaired());
+
+  useEffect(() => {
+    // A 401 anywhere clears the flag and fires this: return to pairing.
+    return webSession.onUnauthorized(() => setPaired(false));
+  }, [webSession]);
+
+  function signOut(): void {
+    webSession.forget();
+    setPaired(false);
+  }
+
+  return (
+    <div className="flex h-full flex-col bg-canvas text-content">
+      <header className="flex shrink-0 items-center justify-between border-b border-border px-6 py-3">
+        <div className="flex items-baseline gap-2">
+          <h1 className="text-lg font-semibold tracking-tight">IdeA</h1>
+          <span className="rounded-md bg-raised px-1.5 py-0.5 text-[0.65rem] font-medium uppercase text-muted">
+            web
+          </span>
+        </div>
+        {paired && (
+          <Button variant="ghost" size="sm" onClick={signOut}>
+            Se déconnecter
+          </Button>
+        )}
+      </header>
+
+      <div className="flex flex-1 flex-col overflow-hidden">
+        {paired ? (
+          <WebWorkspace />
+        ) : (
+          <PairingScreen session={webSession} onPaired={() => setPaired(true)} />
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/features/web/WebWorkspace.tsx b/frontend/src/features/web/WebWorkspace.tsx
new file mode 100644
index 0000000..c376f1e
--- /dev/null
+++ b/frontend/src/features/web/WebWorkspace.tsx
@@ -0,0 +1,156 @@
+/**
+ * Read-only web workspace — ticket #13, lot F2 (first shippable increment).
+ *
+ * The minimal post-pairing surface: list the projects, open one **read-only**,
+ * and show a snapshot of its live/work state. No PTY (xterm over WS = F3), no
+ * mutation — every call goes through the existing transport-neutral gateways
+ * (`project`, `workState`) via DI, so no component touches `@tauri-apps/api`.
+ *
+ * It reuses the frozen read-model types (`ProjectWorkState`) and only calls the
+ * commands B4 puts on the read-only allowlist: `list_projects`, `open_project`,
+ * `get_project_work_state`. A deliberately small surface — the full IDE (layout,
+ * agents, terminals) is out of scope until the streaming lots.
+ */
+
+import { useCallback, useEffect, useState } from "react";
+
+import type { GatewayError, Project, ProjectWorkState } from "@/domain";
+import { useGateways } from "@/app/di";
+import { Button, Panel, Spinner } from "@/shared";
+
+function describe(e: unknown): string {
+  if (e && typeof e === "object" && "message" in e) {
+    return String((e as GatewayError).message);
+  }
+  return String(e);
+}
+
+export function WebWorkspace() {
+  const { project, workState } = useGateways();
+  const [projects, setProjects] = useState<Project[] | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const [openId, setOpenId] = useState<string | null>(null);
+  const [snapshot, setSnapshot] = useState<ProjectWorkState | null>(null);
+  const [loadingSnapshot, setLoadingSnapshot] = useState(false);
+
+  const refresh = useCallback(async () => {
+    setError(null);
+    try {
+      setProjects(await project.listProjects());
+    } catch (e) {
+      setError(describe(e));
+    }
+  }, [project]);
+
+  useEffect(() => {
+    void refresh();
+  }, [refresh]);
+
+  const openReadOnly = useCallback(
+    async (projectId: string) => {
+      setError(null);
+      setLoadingSnapshot(true);
+      setOpenId(projectId);
+      setSnapshot(null);
+      try {
+        // Read-only: open resolves the project server-side, then we read the
+        // live/work-state snapshot. No layout/agents/PTY are mounted.
+        await project.openProject(projectId);
+        setSnapshot(await workState.getProjectWorkState(projectId));
+      } catch (e) {
+        setError(describe(e));
+      } finally {
+        setLoadingSnapshot(false);
+      }
+    },
+    [project, workState],
+  );
+
+  return (
+    <div className="flex h-full flex-col gap-4 overflow-y-auto p-6">
+      <div className="flex items-center justify-between">
+        <h2 className="text-base font-semibold tracking-tight">Projets</h2>
+        <Button variant="ghost" size="sm" onClick={() => void refresh()}>
+          Rafraîchir
+        </Button>
+      </div>
+
+      {error && (
+        <Panel className="border-danger/40">
+          <p className="text-sm text-danger">{error}</p>
+        </Panel>
+      )}
+
+      {projects === null ? (
+        <span className="inline-flex items-center gap-1.5 text-sm text-muted">
+          <Spinner size={12} /> Chargement des projets…
+        </span>
+      ) : projects.length === 0 ? (
+        <p className="text-sm text-muted">Aucun projet.</p>
+      ) : (
+        <ul className="flex flex-col gap-2" data-testid="web-project-list">
+          {projects.map((p) => (
+            <li key={p.id}>
+              <button
+                type="button"
+                onClick={() => void openReadOnly(p.id)}
+                aria-pressed={openId === p.id}
+                className="flex w-full flex-col items-start rounded-md border border-border bg-raised px-3 py-2 text-left transition-colors hover:border-primary aria-pressed:border-primary"
+              >
+                <span className="text-sm font-medium text-content">{p.name}</span>
+                <span className="text-xs text-faint">{p.root}</span>
+              </button>
+            </li>
+          ))}
+        </ul>
+      )}
+
+      {openId && (
+        <Panel className="mt-2">
+          <div className="mb-2 flex items-center justify-between">
+            <h3 className="text-sm font-semibold">
+              État (lecture seule)
+              <span className="ml-2 rounded bg-canvas px-1.5 py-0.5 text-[0.6rem] uppercase text-muted">
+                read-only
+              </span>
+            </h3>
+            {loadingSnapshot && <Spinner size={12} />}
+          </div>
+          {snapshot ? (
+            <WorkStateSnapshot snapshot={snapshot} />
+          ) : loadingSnapshot ? (
+            <p className="text-xs text-muted">Chargement de l'état…</p>
+          ) : (
+            <p className="text-xs text-muted">Aucun état disponible.</p>
+          )}
+        </Panel>
+      )}
+    </div>
+  );
+}
+
+/** Pure render of the read-only work-state snapshot. */
+function WorkStateSnapshot({ snapshot }: { snapshot: ProjectWorkState }) {
+  if (snapshot.agents.length === 0) {
+    return <p className="text-xs text-muted">Aucun agent actif.</p>;
+  }
+  return (
+    <ul className="flex flex-col gap-1.5" data-testid="web-workstate">
+      {snapshot.agents.map((a) => (
+        <li key={a.agentId} className="flex items-center justify-between text-xs">
+          <span className="text-content">{a.name}</span>
+          <span className="flex items-center gap-2 text-faint">
+            <span>{a.live ? `live · ${a.live.kind}` : "offline"}</span>
+            <span
+              className={
+                a.busy.state === "busy" ? "text-warning" : "text-success"
+              }
+            >
+              {a.busy.state === "busy" ? "busy" : "idle"}
+            </span>
+          </span>
+        </li>
+      ))}
+    </ul>
+  );
+}
diff --git a/frontend/src/features/web/index.ts b/frontend/src/features/web/index.ts
new file mode 100644
index 0000000..c15e2c5
--- /dev/null
+++ b/frontend/src/features/web/index.ts
@@ -0,0 +1,8 @@
+/**
+ * Web client feature (ticket #13, lot F2) — the read-only browser surface used
+ * when the HTTP transport is selected. Public entry is {@link WebApp}.
+ */
+
+export { WebApp } from "./WebApp";
+export { PairingScreen } from "./PairingScreen";
+export { WebWorkspace } from "./WebWorkspace";