diff --git a/frontend/src/adapters/http/frames.ts b/frontend/src/adapters/http/frames.ts
index e61cef9..d63e8e2 100644
--- a/frontend/src/adapters/http/frames.ts
+++ b/frontend/src/adapters/http/frames.ts
@@ -94,7 +94,7 @@ export interface ServerFrame {
   payload: Record<string, unknown>;
 }
 
-/** Payload of a `terminal.attached` acknowledgement. */
+/** Payload of a `terminal.attached` acknowledgement (B5, `server.rs`). */
 export interface AttachedPayload {
   session: {
     sessionId: string;
@@ -104,8 +104,15 @@ export interface AttachedPayload {
     cols: number;
   };
   nextSeq: number;
+  /**
+   * Bounded scrollback replayed at (re)attach. B5 sends a single entry (`seq:0`)
+   * carrying all retained bytes, or an empty array when there is nothing to
+   * replay.
+   */
   scrollback: { seq: number; bytesBase64: string }[];
   gap: boolean;
+  /** Lifecycle status carried on the ack (B5 sends `"running"`). */
+  status?: string;
   /** Conversation id minted by an `agent.launch` (mirrors `assignedConversationId`). */
   assignedConversationId?: string;
 }
@@ -117,6 +124,16 @@ export interface OutputPayload {
   bytesBase64: string;
 }
 
+/**
+ * Payload of a `terminal.status` frame (B5). `status` is a lifecycle transition
+ * (`"exited"` on close); `exitCode` is present for `"exited"` (may be `null`).
+ */
+export interface StatusPayload {
+  sessionId: string;
+  status: string;
+  exitCode?: number | null;
+}
+
 /** Payload of a `chat.output` frame (structured assistant stream). */
 export interface ChatOutputPayload {
   sessionId: string;
diff --git a/frontend/src/adapters/http/streamGateways.ts b/frontend/src/adapters/http/streamGateways.ts
index 3966980..61ecd13 100644
--- a/frontend/src/adapters/http/streamGateways.ts
+++ b/frontend/src/adapters/http/streamGateways.ts
@@ -93,12 +93,11 @@ export function makeWsTerminalHandle(
     detach(): void {
       // Stop delivering output locally and tell the server the view is gone. The
       // backend PTY keeps running (detach ≠ close), matching the Tauri handle.
-      ws.removeOutputSink(sessionId);
-      void ws.sendFireAndForget("terminal.detach", { sessionId });
+      // Untracking also disables reconnection re-attach for this session.
+      void ws.detachTerminal(sessionId);
     },
     async close(): Promise<void> {
-      ws.removeOutputSink(sessionId);
-      await ws.send("terminal.close", { sessionId });
+      await ws.closeTerminalSession(sessionId);
     },
   };
 }
@@ -137,37 +136,33 @@ export class HttpTerminalGateway implements TerminalGateway {
     options: OpenTerminalOptions,
     onData: (bytes: Uint8Array) => void,
   ): Promise<TerminalHandle> {
-    const ack = await this.ws.send("terminal.open", {
-      projectId: undefined, // TODO(F3/B5): the port lacks projectId; confirm contract.
-      nodeId: options.nodeId ?? null,
+    // B5: `terminal.open` carries no projectId; `cwd` is a server-validated path.
+    // A fresh open has empty scrollback (the view does not repaint on open).
+    const res = await this.ws.openTerminal({
       cwd: options.cwd,
       rows: options.rows,
       cols: options.cols,
+      nodeId: options.nodeId ?? null,
+      onData,
     });
-    const payload = ack.payload as unknown as AttachedPayload;
-    const sessionId = payload.session.sessionId;
-    this.ws.setOutputSink(sessionId, onData);
-    const scrollback = attachedToScrollback(payload);
-    if (scrollback.length > 0) onData(scrollback);
-    return makeWsTerminalHandle(sessionId, this.ws);
+    return makeWsTerminalHandle(res.sessionId, this.ws);
   }
 
   async reattach(
     sessionId: string,
     onData: (bytes: Uint8Array) => void,
   ): Promise<ReattachResult> {
-    const ack = await this.ws.send("terminal.attach", { sessionId, lastSeq: null });
-    const payload = ack.payload as unknown as AttachedPayload;
-    this.ws.setOutputSink(sessionId, onData);
+    // The view repaints the returned scrollback itself (TerminalView contract);
+    // the client does not also push it through `onData` on the initial attach.
+    const res = await this.ws.attachTerminal({ sessionId, onData });
     return {
-      handle: makeWsTerminalHandle(sessionId, this.ws),
-      scrollback: attachedToScrollback(payload),
+      handle: makeWsTerminalHandle(res.sessionId, this.ws),
+      scrollback: res.scrollback,
     };
   }
 
   async closeTerminal(sessionId: string): Promise<void> {
-    this.ws.removeOutputSink(sessionId);
-    await this.ws.send("terminal.close", { sessionId });
+    await this.ws.closeTerminalSession(sessionId);
   }
 }
 
diff --git a/frontend/src/adapters/http/terminalGateway.test.ts b/frontend/src/adapters/http/terminalGateway.test.ts
new file mode 100644
index 0000000..c7449bc
--- /dev/null
+++ b/frontend/src/adapters/http/terminalGateway.test.ts
@@ -0,0 +1,144 @@
+/**
+ * F3 — the WS terminal gateway + handle round-trip against the B5 frame contract:
+ * open→attached (empty scrollback), attach→attached (scrollback returned for the
+ * view to repaint, not double-pushed), input/resize emit conforming frames,
+ * detach ≠ close, and `terminal.output` bytes are base64-decoded into the sink.
+ */
+import { describe, it, expect, vi } from "vitest";
+
+import { HttpTerminalGateway } from "./streamGateways";
+import { WsLiveClient, type WebSocketLike } from "./wsLiveClient";
+import { bytesToBase64 } from "./frames";
+
+class FakeSocket implements WebSocketLike {
+  sent: string[] = [];
+  onopen: (() => void) | null = null;
+  onmessage: ((event: { data: string }) => void) | null = null;
+  onerror: ((event: unknown) => void) | null = null;
+  onclose: (() => void) | null = null;
+  send(data: string): void {
+    this.sent.push(data);
+  }
+  close(): void {
+    this.onclose?.();
+  }
+  receive(frame: unknown): void {
+    this.onmessage?.({ data: JSON.stringify(frame) });
+  }
+}
+
+/** Client whose socket auto-opens on the next microtask. */
+function client(): { ws: WsLiveClient; sockets: FakeSocket[] } {
+  const sockets: FakeSocket[] = [];
+  const ws = new WsLiveClient({
+    wsUrl: "wss://host",
+    socketFactory: () => {
+      const s = new FakeSocket();
+      sockets.push(s);
+      queueMicrotask(() => s.onopen?.());
+      return s;
+    },
+  });
+  return { ws, sockets };
+}
+
+/** Awaits the frame the client just sent, then replies with `reply(id)`. */
+async function replyToLast(
+  socket: FakeSocket,
+  index: number,
+  reply: (id: string) => unknown,
+): Promise<Record<string, unknown>> {
+  await vi.waitFor(() => expect(socket.sent.length).toBeGreaterThan(index));
+  const sent = JSON.parse(socket.sent[index]);
+  socket.receive(reply(sent.id));
+  return sent;
+}
+
+function attachedAck(id: string, sessionId: string, scrollbackBytes?: Uint8Array) {
+  return {
+    kind: "terminal.attached",
+    replyTo: id,
+    payload: {
+      session: { sessionId, rows: 30, cols: 120 },
+      scrollback: scrollbackBytes
+        ? [{ seq: 0, bytesBase64: bytesToBase64(scrollbackBytes) }]
+        : [],
+      nextSeq: scrollbackBytes ? 1 : 0,
+      status: "running",
+      gap: false,
+    },
+  };
+}
+
+describe("HttpTerminalGateway round-trip (B5 frames)", () => {
+  it("open → attached with empty scrollback; output is decoded into the sink", async () => {
+    const { ws, sockets } = client();
+    const gw = new HttpTerminalGateway(ws);
+    const chunks: Uint8Array[] = [];
+
+    const handlePromise = gw.openTerminal({ cwd: "/srv/app", rows: 30, cols: 120 }, (b) =>
+      chunks.push(b),
+    );
+    const sent = await replyToLast(sockets[0], 0, (id) => attachedAck(id, "s1"));
+    const handle = await handlePromise;
+
+    // Conforming open frame (no projectId; cwd is server-validated).
+    expect(sent.kind).toBe("terminal.open");
+    expect(sent.payload).toMatchObject({ cwd: "/srv/app", rows: 30, cols: 120 });
+    expect(handle.sessionId).toBe("s1");
+    // No scrollback pushed on a fresh open.
+    expect(chunks).toHaveLength(0);
+
+    // A terminal.output frame is base64-decoded and written to the sink.
+    sockets[0].receive({
+      kind: "terminal.output",
+      payload: { sessionId: "s1", seq: 1, bytesBase64: bytesToBase64(new Uint8Array([104, 105])) },
+    });
+    expect(chunks).toEqual([new Uint8Array([104, 105])]);
+  });
+
+  it("attach → attached returns the scrollback for the view (not double-pushed)", async () => {
+    const { ws, sockets } = client();
+    const gw = new HttpTerminalGateway(ws);
+    const chunks: Uint8Array[] = [];
+    const scroll = new Uint8Array([65, 66, 67]);
+
+    const resPromise = gw.reattach("s7", (b) => chunks.push(b));
+    const sent = await replyToLast(sockets[0], 0, (id) => attachedAck(id, "s7", scroll));
+    const res = await resPromise;
+
+    expect(sent.kind).toBe("terminal.attach");
+    expect(sent.payload).toMatchObject({ sessionId: "s7" });
+    // Scrollback is returned for TerminalView to repaint…
+    expect(res.scrollback).toEqual(scroll);
+    // …and NOT also pushed through onData (no double paint on the initial attach).
+    expect(chunks).toHaveLength(0);
+  });
+
+  it("input and resize emit conforming frames; detach ≠ close", async () => {
+    const { ws, sockets } = client();
+    const gw = new HttpTerminalGateway(ws);
+
+    const handlePromise = gw.openTerminal({ cwd: "/srv", rows: 24, cols: 80 }, () => {});
+    await replyToLast(sockets[0], 0, (id) => attachedAck(id, "s1"));
+    const handle = await handlePromise;
+    const base = sockets[0].sent.length;
+
+    await handle.write(new Uint8Array([13]));
+    await handle.resize(40, 140);
+
+    const input = JSON.parse(sockets[0].sent[base]);
+    expect(input.kind).toBe("terminal.input");
+    expect(input.payload).toEqual({ sessionId: "s1", bytesBase64: bytesToBase64(new Uint8Array([13])) });
+
+    const resize = JSON.parse(sockets[0].sent[base + 1]);
+    expect(resize.kind).toBe("terminal.resize");
+    expect(resize.payload).toEqual({ sessionId: "s1", rows: 40, cols: 140 });
+
+    // detach keeps the PTY alive (terminal.detach); close kills it (terminal.close).
+    handle.detach();
+    await vi.waitFor(() =>
+      expect(JSON.parse(sockets[0].sent[base + 2]).kind).toBe("terminal.detach"),
+    );
+  });
+});
diff --git a/frontend/src/adapters/http/wsLiveClient.ts b/frontend/src/adapters/http/wsLiveClient.ts
index 21e9d70..a5e5f07 100644
--- a/frontend/src/adapters/http/wsLiveClient.ts
+++ b/frontend/src/adapters/http/wsLiveClient.ts
@@ -1,28 +1,45 @@
 /**
- * WebSocket live client skeleton for the web transport — ticket #13, lot F1.
+ * WebSocket live client for the web transport — ticket #13, lot F3 (finalised
+ * from the F1 skeleton).
  *
- * Owns a single WS connection to `{wsUrl}/ws/live` and multiplexes over it, per
- * the B0 draft: PTY output, structured chat output and the low-frequency domain
- * event stream (`event.domain`, replacing Tauri `listen("domain://event")`).
+ * Owns a single WS connection to `{wsUrl}/ws/live` (authenticated by the session
+ * cookie at the upgrade — same-origin, no URL secret) and multiplexes over it,
+ * aligned on the **B5 frozen frame contract** (`crates/app-tauri/src/server.rs`):
  *
- * **F1 scope = skeleton.** The connection, frame envelope, request/reply
- * correlation by `id`, and the per-session output routing are implemented and
- * unit-testable (inject a fake WebSocket factory). What is deliberately deferred
- * to **F3/B5** (when a server exists — B3/B4): reconnection/backpressure, exact
- * `open`/`launch` reply shape, sequence-gap replay policy, and the full xterm
- * round-trip. Those are marked `TODO(F3/B5)`.
+ *  - client→server: `terminal.open` `{cwd,rows,cols}`, `terminal.attach`
+ *    `{sessionId,rows?,cols?,lastSeq?}`, `terminal.input` `{sessionId,bytesBase64}`,
+ *    `terminal.resize` `{sessionId,rows,cols}`, `terminal.detach` `{sessionId}`,
+ *    `terminal.close` `{sessionId}`, `ping`.
+ *  - server→client: `terminal.attached` (ack: `{session,scrollback,nextSeq,status,
+ *    gap,assignedConversationId}`), `terminal.output` `{sessionId,seq,bytesBase64}`,
+ *    `terminal.status` `{sessionId,status,exitCode}`, `error`, `pong`, plus the
+ *    low-frequency `event.domain` stream (domain events).
  *
- * Lives in `src/adapters/**`; touches no `@tauri-apps/api`.
+ * F3 additions over F1: a **connection state machine** (connecting / connected /
+ * reconnecting / closed) with automatic reconnection + re-attach and bounded
+ * scrollback repaint, and per-session **status routing** (`exited`). The terminal
+ * lifecycle is owned here so a browser reload / network drop transparently
+ * re-attaches the surviving server-side PTY. Multi-tab "last attach wins" is
+ * silent on the wire (the evicted attachment simply stops receiving output — see
+ * the F3 report), so there is nothing to crash on; the socket-close path handles
+ * disconnection uniformly.
+ *
+ * Lives in `src/adapters/**`; touches no `@tauri-apps/api`. The port
+ * (`TerminalGateway`/`TerminalHandle`) and `TerminalView` are unchanged; the UI
+ * indication of connection state is written into xterm through the session's own
+ * output sink (a notice line), so no component needs to know about this client.
  */
 
-import type { DomainEvent } from "@/domain";
+import type { DomainEvent, Unsubscribe } from "@/domain";
 import {
   base64ToBytes,
   bytesToBase64,
+  type AttachedPayload,
   type ClientFrame,
   type ClientFrameKind,
   type OutputPayload,
   type ServerFrame,
+  type StatusPayload,
 } from "./frames";
 
 /** Minimal WebSocket surface used here; injectable so tests pass a fake. */
@@ -38,14 +55,48 @@ export interface WebSocketLike {
 /** Factory building a {@link WebSocketLike} for a URL (defaults to global WS). */
 export type WebSocketFactory = (url: string) => WebSocketLike;
 
+/** Injectable deferred-call primitives (defaults to global timers). */
+export type SetTimeoutLike = (fn: () => void, ms: number) => unknown;
+export type ClearTimeoutLike = (handle: unknown) => void;
+
+/** UI-facing connection state of the live socket. */
+export type ConnectionState = "connecting" | "connected" | "reconnecting" | "closed";
+
 /** Configuration for the live client. */
 export interface WsLiveClientConfig {
   /** Base WS URL, e.g. `wss://host:port`. No trailing slash. */
   wsUrl: string;
-  /** Bearer token (ticket #13 auth). B0 note: prefer header/cookie over URL. */
+  /** Bearer token (dev/tests only). Prod auth is the session cookie at upgrade. */
   token?: string;
   /** Injected WebSocket factory (defaults to `new WebSocket(url)`). */
   socketFactory?: WebSocketFactory;
+  /** Base reconnect delay in ms (exponential backoff, capped). Default 500. */
+  reconnectBaseMs?: number;
+  /** Max reconnect delay in ms. Default 10000. */
+  reconnectMaxMs?: number;
+  /** Injected `setTimeout` (tests drive reconnection deterministically). */
+  setTimeoutImpl?: SetTimeoutLike;
+  /** Injected `clearTimeout`. */
+  clearTimeoutImpl?: ClearTimeoutLike;
+}
+
+/** A live terminal subscription tracked for output routing + reconnection replay. */
+interface TerminalSubscription {
+  /** Delivers raw PTY bytes (and adapter notices) to the xterm view. */
+  onData: (bytes: Uint8Array) => void;
+  /** Optional lifecycle callback (`exited`), for tests / future UI. */
+  onStatus?: (status: string, exitCode?: number | null) => void;
+  /** Last output sequence seen — sent as `lastSeq` when re-attaching. */
+  lastSeq: number;
+}
+
+/** Result of opening/attaching a terminal over the WS. */
+export interface TerminalAttachResult {
+  sessionId: string;
+  /** Bounded scrollback bytes to repaint (empty on a fresh open). */
+  scrollback: Uint8Array;
+  assignedConversationId?: string;
+  status?: string;
 }
 
 let frameCounter = 0;
@@ -55,20 +106,50 @@ function nextFrameId(): string {
   return `c${frameCounter}`;
 }
 
+const encoder = new TextEncoder();
+/** Encodes a human notice line to bytes for writing into xterm. */
+function notice(text: string): Uint8Array {
+  return encoder.encode(`\r\n\x1b[2m[${text}]\x1b[0m\r\n`);
+}
+
+/** Concatenates an attached-frame scrollback list into a single byte buffer. */
+function scrollbackBytes(payload: AttachedPayload): Uint8Array {
+  const chunks = payload.scrollback.map((c) => base64ToBytes(c.bytesBase64));
+  const total = chunks.reduce((n, c) => n + c.length, 0);
+  const out = new Uint8Array(total);
+  let offset = 0;
+  for (const c of chunks) {
+    out.set(c, offset);
+    offset += c.length;
+  }
+  return out;
+}
+
 /**
- * Manages the single live WebSocket. Callers subscribe an output sink per PTY
- * session and a single domain-event handler; the client routes inbound frames.
+ * Manages the single live WebSocket, the connection state machine, and the live
+ * terminal sessions (so reconnection re-attaches them transparently).
  */
 export class WsLiveClient {
   private readonly wsUrl: string;
   private readonly token?: string;
   private readonly socketFactory: WebSocketFactory;
+  private readonly reconnectBaseMs: number;
+  private readonly reconnectMaxMs: number;
+  private readonly setTimeoutImpl: SetTimeoutLike;
+  private readonly clearTimeoutImpl: ClearTimeoutLike;
 
   private socket: WebSocketLike | null = null;
   private opening: Promise<void> | null = null;
+  private disposed = false;
+  private everConnected = false;
+  private connState: ConnectionState = "connecting";
+  private reconnectAttempt = 0;
+  private reconnectHandle: unknown = null;
 
-  /** Per-session PTY output sinks (sessionId → onData). */
+  /** Per-session PTY output sinks (sessionId → onData). Low-level routing map. */
   private readonly outputSinks = new Map<string, (bytes: Uint8Array) => void>();
+  /** Live terminal subscriptions tracked for reconnection replay + status. */
+  private readonly terminals = new Map<string, TerminalSubscription>();
   /** Pending command acknowledgements, keyed by client frame id. */
   private readonly pending = new Map<
     string,
@@ -76,6 +157,8 @@ export class WsLiveClient {
   >();
   /** The single domain-event handler (set by the system gateway). */
   private domainEventHandler: ((event: DomainEvent) => void) | null = null;
+  /** Connection-state listeners (UI / tests). */
+  private readonly connListeners = new Set<(state: ConnectionState) => void>();
 
   constructor(config: WsLiveClientConfig) {
     this.wsUrl = config.wsUrl.replace(/\/+$/, "");
@@ -83,65 +166,248 @@ export class WsLiveClient {
     this.socketFactory =
       config.socketFactory ??
       ((url: string) => new WebSocket(url) as unknown as WebSocketLike);
+    this.reconnectBaseMs = config.reconnectBaseMs ?? 500;
+    this.reconnectMaxMs = config.reconnectMaxMs ?? 10000;
+    this.setTimeoutImpl =
+      config.setTimeoutImpl ?? ((fn, ms) => setTimeout(fn, ms));
+    this.clearTimeoutImpl =
+      config.clearTimeoutImpl ?? ((h) => clearTimeout(h as ReturnType<typeof setTimeout>));
   }
 
-  /** Registers the domain-event handler (replaces any previous one). */
+  // -------------------------------------------------------------------------
+  // Connection state
+  // -------------------------------------------------------------------------
+
+  /** Current connection state. */
+  getConnectionState(): ConnectionState {
+    return this.connState;
+  }
+
+  /** Subscribes to connection-state transitions (returns an unsubscribe). */
+  onConnectionStateChange(listener: (state: ConnectionState) => void): Unsubscribe {
+    this.connListeners.add(listener);
+    return () => this.connListeners.delete(listener);
+  }
+
+  private setConnState(state: ConnectionState): void {
+    if (this.connState === state) return;
+    this.connState = state;
+    for (const listener of this.connListeners) listener(state);
+  }
+
+  // -------------------------------------------------------------------------
+  // Domain events (system gateway)
+  // -------------------------------------------------------------------------
+
   setDomainEventHandler(handler: (event: DomainEvent) => void): void {
     this.domainEventHandler = handler;
   }
-
-  /** Clears the domain-event handler. */
   clearDomainEventHandler(): void {
     this.domainEventHandler = null;
   }
 
-  /** Registers a per-session PTY output sink. */
+  // -------------------------------------------------------------------------
+  // Low-level output sink map (used by the agent gateway too)
+  // -------------------------------------------------------------------------
+
   setOutputSink(sessionId: string, onData: (bytes: Uint8Array) => void): void {
     this.outputSinks.set(sessionId, onData);
   }
-
-  /** Drops a per-session PTY output sink (view detached). */
   removeOutputSink(sessionId: string): void {
     this.outputSinks.delete(sessionId);
   }
 
+  // -------------------------------------------------------------------------
+  // Connection lifecycle
+  // -------------------------------------------------------------------------
+
   /** Ensures the socket is connected, connecting on first use. */
   async ensureConnected(): Promise<void> {
     if (this.socket) return;
     if (this.opening) return this.opening;
+    return this.connect();
+  }
 
+  private connect(): Promise<void> {
+    this.setConnState(this.everConnected ? "reconnecting" : "connecting");
     this.opening = new Promise<void>((resolve, reject) => {
-      // B0 auth note: token should ride an `Authorization` header / secure
-      // cookie at upgrade, NOT a URL secret. Browsers can't set WS upgrade
-      // headers, so the token placement is a contract point to confirm (see the
-      // F1 report). The query below is only a placeholder for the skeleton.
+      // Prod: the session cookie rides the upgrade (same-origin). The optional
+      // token is a dev/test convenience only (never a prod secret in the URL).
       const url = this.token
         ? `${this.wsUrl}/ws/live?token=${encodeURIComponent(this.token)}`
         : `${this.wsUrl}/ws/live`;
       const socket = this.socketFactory(url);
       socket.onopen = () => {
         this.socket = socket;
+        this.opening = null;
+        this.everConnected = true;
+        this.reconnectAttempt = 0;
+        this.setConnState("connected");
         resolve();
       };
       socket.onerror = (event) => {
         this.opening = null;
         reject(event);
       };
-      socket.onclose = () => {
-        // TODO(F3/B5): reconnection + re-attach of live sessions. For F1 we drop
-        // the socket so a later call reconnects fresh.
-        this.socket = null;
-        this.rejectAllPending({ code: "WS_CLOSED", message: "socket closed" });
-      };
+      socket.onclose = () => this.handleSocketClosed();
       socket.onmessage = (event) => this.handleMessage(event.data);
     });
     return this.opening;
   }
 
+  private handleSocketClosed(): void {
+    this.socket = null;
+    this.opening = null;
+    this.rejectAllPending({ code: "WS_CLOSED", message: "socket closed" });
+    if (this.disposed) {
+      this.setConnState("closed");
+      return;
+    }
+    // Only reconnect when there is a live terminal to re-attach; otherwise stay
+    // idle until the next explicit use.
+    if (this.terminals.size > 0) {
+      this.setConnState("reconnecting");
+      for (const sub of this.terminals.values()) sub.onData(notice("déconnecté — reconnexion…"));
+      this.scheduleReconnect();
+    } else {
+      this.setConnState("reconnecting");
+    }
+  }
+
+  private scheduleReconnect(): void {
+    if (this.disposed || this.reconnectHandle) return;
+    const delay = Math.min(
+      this.reconnectMaxMs,
+      this.reconnectBaseMs * 2 ** this.reconnectAttempt,
+    );
+    this.reconnectAttempt += 1;
+    this.reconnectHandle = this.setTimeoutImpl(() => {
+      this.reconnectHandle = null;
+      void this.reconnectNow();
+    }, delay);
+  }
+
+  private async reconnectNow(): Promise<void> {
+    if (this.disposed) return;
+    try {
+      await this.connect();
+      await this.reattachAll();
+    } catch {
+      // Still down: back off and retry (unless everything was detached/closed).
+      if (this.terminals.size > 0) this.scheduleReconnect();
+    }
+  }
+
+  /** Re-attaches every tracked terminal after a reconnect and repaints scrollback. */
+  private async reattachAll(): Promise<void> {
+    for (const [sessionId, sub] of this.terminals) {
+      try {
+        const ack = await this.send("terminal.attach", {
+          sessionId,
+          lastSeq: sub.lastSeq,
+        });
+        const payload = ack.payload as unknown as AttachedPayload;
+        sub.onData(notice("reconnecté"));
+        const bytes = scrollbackBytes(payload);
+        if (bytes.length > 0) sub.onData(bytes);
+        if (typeof payload.nextSeq === "number") {
+          sub.lastSeq = Math.max(0, payload.nextSeq - 1);
+        }
+      } catch {
+        // A single session failing to re-attach (e.g. server killed it) must not
+        // block the others; leave it tracked for the next reconnect cycle.
+      }
+    }
+  }
+
+  // -------------------------------------------------------------------------
+  // Terminal sessions (high-level; used by HttpTerminalGateway)
+  // -------------------------------------------------------------------------
+
+  /** Opens a fresh terminal (`terminal.open`) and starts tracking it. */
+  openTerminal(params: {
+    cwd: string;
+    rows: number;
+    cols: number;
+    nodeId?: string | null;
+    onData: (bytes: Uint8Array) => void;
+    onStatus?: (status: string, exitCode?: number | null) => void;
+  }): Promise<TerminalAttachResult> {
+    return this.attachInternal(
+      "terminal.open",
+      { cwd: params.cwd, rows: params.rows, cols: params.cols, nodeId: params.nodeId ?? null },
+      { onData: params.onData, onStatus: params.onStatus, lastSeq: 0 },
+    );
+  }
+
+  /** Re-attaches to an existing terminal (`terminal.attach`) and tracks it. */
+  attachTerminal(params: {
+    sessionId: string;
+    rows?: number;
+    cols?: number;
+    lastSeq?: number;
+    onData: (bytes: Uint8Array) => void;
+    onStatus?: (status: string, exitCode?: number | null) => void;
+  }): Promise<TerminalAttachResult> {
+    return this.attachInternal(
+      "terminal.attach",
+      {
+        sessionId: params.sessionId,
+        rows: params.rows,
+        cols: params.cols,
+        lastSeq: params.lastSeq ?? null,
+      },
+      { onData: params.onData, onStatus: params.onStatus, lastSeq: params.lastSeq ?? 0 },
+      params.sessionId,
+    );
+  }
+
+  private async attachInternal(
+    kind: ClientFrameKind,
+    payload: Record<string, unknown>,
+    sub: TerminalSubscription,
+    knownSessionId?: string,
+  ): Promise<TerminalAttachResult> {
+    const ack = await this.send(kind, payload);
+    const ap = ack.payload as unknown as AttachedPayload;
+    const sessionId = knownSessionId ?? ap.session.sessionId;
+    if (typeof ap.nextSeq === "number") sub.lastSeq = Math.max(0, ap.nextSeq - 1);
+    this.terminals.set(sessionId, sub);
+    // Route output to the subscription's onData (the low-level map is the single
+    // source of routing; lastSeq is tracked in handleMessage).
+    this.setOutputSink(sessionId, sub.onData);
+    return {
+      sessionId,
+      scrollback: scrollbackBytes(ap),
+      assignedConversationId: ap.assignedConversationId,
+      status: ap.status,
+    };
+  }
+
+  /** Detaches the view (server PTY keeps running): stop tracking + `terminal.detach`. */
+  async detachTerminal(sessionId: string): Promise<void> {
+    this.removeTerminal(sessionId);
+    await this.sendFireAndForget("terminal.detach", { sessionId });
+  }
+
+  /** Kills the PTY (`terminal.close`) and stops tracking. */
+  async closeTerminalSession(sessionId: string): Promise<void> {
+    this.removeTerminal(sessionId);
+    await this.send("terminal.close", { sessionId });
+  }
+
+  private removeTerminal(sessionId: string): void {
+    this.terminals.delete(sessionId);
+    this.outputSinks.delete(sessionId);
+  }
+
+  // -------------------------------------------------------------------------
+  // Frame I/O
+  // -------------------------------------------------------------------------
+
   /**
-   * Sends a client frame and resolves with its acknowledgement frame (the server
-   * frame whose `replyTo` equals this frame's `id`). Fire-and-forget frames
-   * (input/resize/detach) can ignore the returned promise.
+   * Sends a client frame and resolves with its acknowledgement (the server frame
+   * whose `replyTo` equals this frame's `id`).
    */
   async send(
     kind: ClientFrameKind,
@@ -150,8 +416,7 @@ export class WsLiveClient {
     await this.ensureConnected();
     const socket = this.socket;
     if (!socket) {
-      const err = { code: "WS_CLOSED", message: "socket not connected" };
-      throw err;
+      throw { code: "WS_CLOSED", message: "socket not connected" };
     }
     const id = nextFrameId();
     const frame: ClientFrame = { id, kind, payload };
@@ -180,12 +445,19 @@ export class WsLiveClient {
 
   /** Closes the socket and rejects everything pending. */
   dispose(): void {
+    this.disposed = true;
+    if (this.reconnectHandle) {
+      this.clearTimeoutImpl(this.reconnectHandle);
+      this.reconnectHandle = null;
+    }
     this.rejectAllPending({ code: "WS_CLOSED", message: "client disposed" });
     this.outputSinks.clear();
+    this.terminals.clear();
     this.domainEventHandler = null;
     this.socket?.close();
     this.socket = null;
     this.opening = null;
+    this.setConnState("closed");
   }
 
   private rejectAllPending(err: unknown): void {
@@ -198,20 +470,25 @@ export class WsLiveClient {
     try {
       frame = JSON.parse(data) as ServerFrame;
     } catch {
-      return; // Ignore malformed frames in the skeleton.
+      return; // Ignore malformed frames.
     }
 
     // Route unsolicited streams first (no replyTo).
     switch (frame.kind) {
       case "terminal.output": {
         const payload = frame.payload as unknown as OutputPayload;
+        const sub = this.terminals.get(payload.sessionId);
+        if (sub && typeof payload.seq === "number") sub.lastSeq = payload.seq;
         const sink = this.outputSinks.get(payload.sessionId);
-        // TODO(F3/B5): honour `seq` ordering + gap detection for precise replay.
         if (sink) sink(base64ToBytes(payload.bytesBase64));
         return;
       }
+      case "terminal.status": {
+        const payload = frame.payload as unknown as StatusPayload;
+        this.handleStatus(payload);
+        return;
+      }
       case "event.domain": {
-        // `payload` is a DomainEventDto (kind-tagged); forward as-is.
         this.domainEventHandler?.(frame.payload as unknown as DomainEvent);
         return;
       }
@@ -229,4 +506,25 @@ export class WsLiveClient {
       }
     }
   }
+
+  private handleStatus(payload: StatusPayload): void {
+    const sub = this.terminals.get(payload.sessionId);
+    if (!sub) return;
+    if (payload.status === "exited" || payload.status === "closed") {
+      const code = payload.exitCode;
+      sub.onData(
+        notice(
+          code === null || code === undefined
+            ? "session terminée"
+            : `session terminée (code ${code})`,
+        ),
+      );
+      sub.onStatus?.(payload.status, payload.exitCode);
+      // The PTY is gone: stop tracking so a later disconnect does not try to
+      // re-attach a dead session.
+      this.removeTerminal(payload.sessionId);
+    } else {
+      sub.onStatus?.(payload.status, payload.exitCode);
+    }
+  }
 }
diff --git a/frontend/src/adapters/http/wsLiveClientReconnect.test.ts b/frontend/src/adapters/http/wsLiveClientReconnect.test.ts
new file mode 100644
index 0000000..da057e7
--- /dev/null
+++ b/frontend/src/adapters/http/wsLiveClientReconnect.test.ts
@@ -0,0 +1,170 @@
+/**
+ * F3 — the WS live client connection state machine + reconnection:
+ *  - disconnected (socket close) ⇒ `reconnecting`, a notice is written to xterm;
+ *  - on reconnect, the tracked terminal is re-attached with its `lastSeq` and the
+ *    bounded scrollback is repainted; state returns to `connected`;
+ *  - a `terminal.status` `exited` frame notifies the session and stops tracking
+ *    (so a later disconnect does not try to re-attach a dead PTY).
+ */
+import { describe, it, expect, vi } from "vitest";
+
+import { WsLiveClient, type WebSocketLike, type ConnectionState } from "./wsLiveClient";
+import { bytesToBase64 } from "./frames";
+
+class FakeSocket implements WebSocketLike {
+  sent: string[] = [];
+  onopen: (() => void) | null = null;
+  onmessage: ((event: { data: string }) => void) | null = null;
+  onerror: ((event: unknown) => void) | null = null;
+  onclose: (() => void) | null = null;
+  send(data: string): void {
+    this.sent.push(data);
+  }
+  close(): void {
+    this.onclose?.();
+  }
+  receive(frame: unknown): void {
+    this.onmessage?.({ data: JSON.stringify(frame) });
+  }
+}
+
+function harness() {
+  const sockets: FakeSocket[] = [];
+  let timerFn: (() => void) | null = null;
+  const ws = new WsLiveClient({
+    wsUrl: "wss://host",
+    reconnectBaseMs: 1,
+    socketFactory: () => {
+      const s = new FakeSocket();
+      sockets.push(s);
+      queueMicrotask(() => s.onopen?.());
+      return s;
+    },
+    setTimeoutImpl: (fn) => {
+      timerFn = fn;
+      return 1;
+    },
+    clearTimeoutImpl: () => {
+      timerFn = null;
+    },
+  });
+  const states: ConnectionState[] = [];
+  ws.onConnectionStateChange((s) => states.push(s));
+  return {
+    ws,
+    sockets,
+    states,
+    fireTimer: () => {
+      const fn = timerFn;
+      timerFn = null;
+      fn?.();
+    },
+    hasTimer: () => timerFn !== null,
+  };
+}
+
+function attachedAck(id: string, sessionId: string, nextSeq: number, scroll?: Uint8Array) {
+  return {
+    kind: "terminal.attached",
+    replyTo: id,
+    payload: {
+      session: { sessionId, rows: 30, cols: 120 },
+      scrollback: scroll ? [{ seq: 0, bytesBase64: bytesToBase64(scroll) }] : [],
+      nextSeq,
+      status: "running",
+      gap: false,
+    },
+  };
+}
+
+async function attach(
+  ws: WsLiveClient,
+  sockets: FakeSocket[],
+  sessionId: string,
+  onData: (b: Uint8Array) => void,
+  onStatus?: (s: string, c?: number | null) => void,
+): Promise<void> {
+  const p = ws.attachTerminal({ sessionId, onData, onStatus });
+  // The socket is created lazily by the factory inside ensureConnected.
+  await vi.waitFor(() => expect(sockets[0]?.sent.length ?? 0).toBeGreaterThan(0));
+  const sent = JSON.parse(sockets[0].sent[0]);
+  sockets[0].receive(attachedAck(sent.id, sessionId, 0));
+  await p;
+}
+
+const decode = (b: Uint8Array) => new TextDecoder().decode(b);
+
+describe("WsLiveClient connection state + reconnection", () => {
+  it("goes connecting → connected on the first attach", async () => {
+    const h = harness();
+    await attach(h.ws, h.sockets, "s1", () => {});
+    expect(h.ws.getConnectionState()).toBe("connected");
+    expect(h.states).toContain("connected");
+  });
+
+  it("on socket close it reconnects, re-attaches with lastSeq and repaints scrollback", async () => {
+    const h = harness();
+    const chunks: Uint8Array[] = [];
+    await attach(h.ws, h.sockets, "s1", (b) => chunks.push(b));
+
+    // Advance lastSeq via an output frame (seq 5).
+    h.sockets[0].receive({
+      kind: "terminal.output",
+      payload: { sessionId: "s1", seq: 5, bytesBase64: bytesToBase64(new Uint8Array([120])) },
+    });
+
+    // Drop the socket → reconnecting + a "déconnecté" notice.
+    h.sockets[0].close();
+    expect(h.ws.getConnectionState()).toBe("reconnecting");
+    expect(chunks.some((c) => decode(c).includes("déconnecté"))).toBe(true);
+    expect(h.hasTimer()).toBe(true);
+
+    // Fire the reconnect timer → a new socket opens and re-attaches.
+    h.fireTimer();
+    await vi.waitFor(() => expect(h.sockets.length).toBe(2));
+    await vi.waitFor(() => expect(h.sockets[1].sent.length).toBeGreaterThan(0));
+    const reattach = JSON.parse(h.sockets[1].sent[0]);
+    expect(reattach.kind).toBe("terminal.attach");
+    // lastSeq carries the last output seq seen (5) for precise replay.
+    expect(reattach.payload).toMatchObject({ sessionId: "s1", lastSeq: 5 });
+
+    // Server replies with fresh scrollback; the client repaints it + "reconnecté".
+    const scroll = new Uint8Array([82, 69]);
+    h.sockets[1].receive(attachedAck(reattach.id, "s1", 3, scroll));
+    await vi.waitFor(() => expect(h.ws.getConnectionState()).toBe("connected"));
+    // The repaint happens after the re-attach ack resolves (a microtask later).
+    await vi.waitFor(() =>
+      expect(chunks.some((c) => decode(c).includes("reconnecté"))).toBe(true),
+    );
+    expect(chunks.some((c) => c.length === 2 && c[0] === 82 && c[1] === 69)).toBe(true);
+  });
+
+  it("routes terminal.status exited to onStatus and stops tracking the session", async () => {
+    const h = harness();
+    const chunks: Uint8Array[] = [];
+    const onStatus = vi.fn();
+    await attach(h.ws, h.sockets, "s1", (b) => chunks.push(b), onStatus);
+
+    h.sockets[0].receive({
+      kind: "terminal.status",
+      payload: { sessionId: "s1", status: "exited", exitCode: 0 },
+    });
+
+    expect(onStatus).toHaveBeenCalledWith("exited", 0);
+    expect(chunks.some((c) => decode(c).includes("session terminée"))).toBe(true);
+
+    // Session untracked ⇒ a later socket close does not schedule a reconnect.
+    h.sockets[0].close();
+    expect(h.hasTimer()).toBe(false);
+  });
+
+  it("dispose() moves to closed and clears any pending reconnect", async () => {
+    const h = harness();
+    await attach(h.ws, h.sockets, "s1", () => {});
+    h.sockets[0].close();
+    expect(h.ws.getConnectionState()).toBe("reconnecting");
+    h.ws.dispose();
+    expect(h.ws.getConnectionState()).toBe("closed");
+    expect(h.hasTimer()).toBe(false);
+  });
+});