diff --git a/src/web/events/event-dependencies.ts b/src/web/events/event-dependencies.ts
new file mode 100644
index 0000000..97c8429
--- /dev/null
+++ b/src/web/events/event-dependencies.ts
@@ -0,0 +1,35 @@
+export interface EventClock {
+  now(): Date;
+}
+
+export interface EventIdGenerator {
+  next(occurredAt: Date): string;
+}
+
+/** The subset of Winston's logger contract used by the event hub. */
+export interface EventHubLogger {
+  warn(message: string, metadata?: Record<string, unknown>): unknown;
+}
+
+export const systemEventClock: EventClock = {
+  now: () => new Date(),
+};
+
+/**
+ * Generates lexically sortable IDs and remains monotonic if the wall clock
+ * moves backwards. The per-process sequence disambiguates events in one ms.
+ */
+export class MonotonicEventIdGenerator implements EventIdGenerator {
+  private lastTimestamp = 0;
+  private sequence = 0;
+
+  next(occurredAt: Date): string {
+    const timestamp = Math.max(occurredAt.getTime(), this.lastTimestamp);
+    this.sequence = timestamp === this.lastTimestamp ? this.sequence + 1 : 0;
+    this.lastTimestamp = timestamp;
+
+    return `${timestamp.toString().padStart(13, '0')}-${this.sequence
+      .toString()
+      .padStart(6, '0')}`;
+  }
+}
diff --git a/src/web/events/event-types.ts b/src/web/events/event-types.ts
new file mode 100644
index 0000000..e8c6da1
--- /dev/null
+++ b/src/web/events/event-types.ts
@@ -0,0 +1,101 @@
+export type BotRuntimeStatus = 'starting' | 'running' | 'stopping' | 'stopped';
+
+export type ConversationStatus =
+  | 'new'
+  | 'awaiting-reply'
+  | 'replied'
+  | 'closed';
+
+export type SyncKind = 'media' | 'messages' | 'conversations' | 'full';
+
+export type RedditSessionStatus =
+  | 'unknown'
+  | 'authenticating'
+  | 'authenticated'
+  | 'expired'
+  | 'logged-out'
+  | 'error';
+
+export interface RealtimeEventMap {
+  'bot.status.changed': {
+    status: BotRuntimeStatus;
+    dryRun: boolean;
+    reason?: string;
+  };
+  'message.sent': {
+    messageId: string;
+    recipient: string;
+    conversationId?: string;
+  };
+  'message.failed': {
+    recipient: string;
+    reason: string;
+    messageId?: string;
+    conversationId?: string;
+    code?: string;
+    retryable?: boolean;
+  };
+  'conversation.updated': {
+    conversationId: string;
+    status: ConversationStatus;
+    unreadCount?: number;
+  };
+  'reply.received': {
+    conversationId: string;
+    replyId: string;
+    sender: string;
+    preview?: string;
+  };
+  'sync.started': {
+    syncId: string;
+    kind: SyncKind;
+  };
+  'sync.progress': {
+    syncId: string;
+    kind: SyncKind;
+    completed: number;
+    total?: number;
+    message?: string;
+  };
+  'sync.completed': {
+    syncId: string;
+    kind: SyncKind;
+    processed: number;
+  };
+  'sync.failed': {
+    syncId: string;
+    kind: SyncKind;
+    reason: string;
+    code?: string;
+  };
+  'rate-limit.changed': {
+    limited: boolean;
+    remaining?: number;
+    resetsAt?: string;
+    reason?: string;
+  };
+  'reddit.session.changed': {
+    status: RedditSessionStatus;
+    username?: string;
+    reason?: string;
+  };
+  'log.created': {
+    level: 'debug' | 'info' | 'warn' | 'error';
+    message: string;
+    data?: unknown;
+  };
+}
+
+export type RealtimeEventType = keyof RealtimeEventMap;
+
+/** A distributive type so the default is a discriminated union. */
+export type RealtimeEvent<
+  TType extends RealtimeEventType = RealtimeEventType,
+> = TType extends RealtimeEventType
+  ? Readonly<{
+      id: string;
+      occurredAt: string;
+      type: TType;
+      payload: Readonly<RealtimeEventMap[TType]>;
+    }>
+  : never;
diff --git a/src/web/events/index.ts b/src/web/events/index.ts
new file mode 100644
index 0000000..c41cc1e
--- /dev/null
+++ b/src/web/events/index.ts
@@ -0,0 +1,23 @@
+export {
+  MonotonicEventIdGenerator,
+  systemEventClock,
+  type EventClock,
+  type EventHubLogger,
+  type EventIdGenerator,
+} from './event-dependencies.js';
+export {
+  type BotRuntimeStatus,
+  type ConversationStatus,
+  type RealtimeEvent,
+  type RealtimeEventMap,
+  type RealtimeEventType,
+  type RedditSessionStatus,
+  type SyncKind,
+} from './event-types.js';
+export {
+  RealtimeEventHub,
+  type RealtimeEventHubOptions,
+  type RealtimeEventListener,
+  type RealtimeEventSubscription,
+  type SubscribeOptions,
+} from './realtime-event-hub.js';
diff --git a/src/web/events/realtime-event-hub.ts b/src/web/events/realtime-event-hub.ts
new file mode 100644
index 0000000..89462fb
--- /dev/null
+++ b/src/web/events/realtime-event-hub.ts
@@ -0,0 +1,222 @@
+import {
+  MonotonicEventIdGenerator,
+  systemEventClock,
+  type EventClock,
+  type EventHubLogger,
+  type EventIdGenerator,
+} from './event-dependencies.js';
+import {
+  type RealtimeEvent,
+  type RealtimeEventMap,
+  type RealtimeEventType,
+} from './event-types.js';
+import { ReplayBuffer, type Sequenced } from './replay-buffer.js';
+
+export type RealtimeEventListener = (event: RealtimeEvent) => void;
+
+export interface SubscribeOptions {
+  /** Value from the SSE `Last-Event-ID` request header. */
+  lastEventId?: string;
+}
+
+export interface RealtimeEventSubscription {
+  readonly closed: boolean;
+  unsubscribe(): void;
+}
+
+export interface RealtimeEventHubOptions {
+  capacity: number;
+  clock?: EventClock;
+  idGenerator?: EventIdGenerator;
+  logger?: EventHubLogger;
+}
+
+interface SubscriberState {
+  listener: RealtimeEventListener;
+  closed: boolean;
+  replaying: boolean;
+  lastDeliveredSequence: number;
+  queued: Sequenced<RealtimeEvent>[];
+}
+
+class HubSubscription implements RealtimeEventSubscription {
+  constructor(
+    private readonly state: SubscriberState,
+    private readonly remove: () => void,
+  ) {}
+
+  get closed(): boolean {
+    return this.state.closed;
+  }
+
+  unsubscribe(): void {
+    if (this.state.closed) {
+      return;
+    }
+    this.state.closed = true;
+    this.remove();
+  }
+}
+export class RealtimeEventHub {
+  private readonly buffer: ReplayBuffer<RealtimeEvent>;
+  private readonly clock: EventClock;
+  private readonly idGenerator: EventIdGenerator;
+  private readonly logger?: EventHubLogger;
+  private readonly subscribers = new Set<SubscriberState>();
+  private readonly dispatchQueue: Sequenced<RealtimeEvent>[] = [];
+  private sequence = 0;
+  private dispatching = false;
+  private isClosed = false;
+
+  constructor(options: RealtimeEventHubOptions) {
+    this.buffer = new ReplayBuffer(options.capacity);
+    this.clock = options.clock ?? systemEventClock;
+    this.idGenerator = options.idGenerator ?? new MonotonicEventIdGenerator();
+    this.logger = options.logger;
+  }
+
+  get closed(): boolean {
+    return this.isClosed;
+  }
+
+  publish<TType extends RealtimeEventType>(
+    type: TType,
+    payload: RealtimeEventMap[TType],
+  ): RealtimeEvent<TType> {
+    this.assertOpen();
+    const occurredAt = this.clock.now();
+    if (Number.isNaN(occurredAt.getTime())) {
+      throw new RangeError('clock returned an invalid date');
+    }
+
+    const id = this.idGenerator.next(occurredAt);
+    if (id.length === 0) {
+      throw new Error('idGenerator returned an empty event ID');
+    }
+
+    const event = Object.freeze({
+      id,
+      occurredAt: occurredAt.toISOString(),
+      type,
+      payload: Object.freeze({ ...payload }),
+    }) as RealtimeEvent<TType>;
+    const sequenced: Sequenced<RealtimeEvent> = {
+      sequence: ++this.sequence,
+      value: event,
+    };
+    this.buffer.push(sequenced);
+    this.dispatchQueue.push(sequenced);
+    this.drainDispatchQueue();
+    return event;
+  }
+
+  subscribe(
+    listener: RealtimeEventListener,
+    options: SubscribeOptions = {},
+  ): RealtimeEventSubscription {
+    this.assertOpen();
+    const state: SubscriberState = {
+      listener,
+      closed: false,
+      replaying: true,
+      lastDeliveredSequence: 0,
+      queued: [],
+    };
+    this.subscribers.add(state);
+    const subscription = new HubSubscription(state, () => {
+      this.subscribers.delete(state);
+      state.queued = [];
+    });
+
+    for (const event of this.buffer.after(options.lastEventId)) {
+      this.deliver(state, event);
+      if (state.closed) {
+        return subscription;
+      }
+    }
+
+    state.replaying = false;
+    const queued = state.queued;
+    state.queued = [];
+    for (const event of queued) {
+      this.deliver(state, event);
+      if (state.closed) {
+        break;
+      }
+    }
+    return subscription;
+  }
+
+  recent(limit = this.buffer.capacity): readonly RealtimeEvent[] {
+    if (!Number.isInteger(limit) || limit < 0) {
+      throw new RangeError('limit must be a non-negative integer');
+    }
+    return limit === 0 ? [] : this.buffer.recent(limit);
+  }
+
+  close(): void {
+    if (this.isClosed) {
+      return;
+    }
+    this.isClosed = true;
+    for (const state of this.subscribers) {
+      state.closed = true;
+      state.queued = [];
+    }
+    this.subscribers.clear();
+    this.dispatchQueue.length = 0;
+    this.buffer.clear();
+  }
+
+  private drainDispatchQueue(): void {
+    if (this.dispatching) {
+      return;
+    }
+    this.dispatching = true;
+    try {
+      let next: Sequenced<RealtimeEvent> | undefined;
+      while ((next = this.dispatchQueue.shift()) !== undefined) {
+        for (const state of [...this.subscribers]) {
+          if (state.replaying) {
+            state.queued.push(next);
+          } else {
+            this.deliver(state, next);
+          }
+        }
+      }
+    } finally {
+      this.dispatching = false;
+    }
+  }
+
+  private deliver(
+    state: SubscriberState,
+    event: Sequenced<RealtimeEvent>,
+  ): void {
+    if (state.closed || event.sequence <= state.lastDeliveredSequence) {
+      return;
+    }
+    state.lastDeliveredSequence = event.sequence;
+    try {
+      state.listener(event.value);
+    } catch (error: unknown) {
+      state.closed = true;
+      state.queued = [];
+      this.subscribers.delete(state);
+      try {
+        this.logger?.warn(
+          'Realtime event subscriber failed; subscription closed',
+          { eventId: event.value.id, error },
+        );
+      } catch {
+        // A diagnostic logger must not break event delivery to healthy clients.
+      }
+    }
+  }
+
+  private assertOpen(): void {
+    if (this.isClosed) {
+      throw new Error('RealtimeEventHub is closed');
+    }
+  }
+}
diff --git a/src/web/events/replay-buffer.ts b/src/web/events/replay-buffer.ts
new file mode 100644
index 0000000..fadedf4
--- /dev/null
+++ b/src/web/events/replay-buffer.ts
@@ -0,0 +1,42 @@
+export interface Sequenced<TValue> {
+  readonly sequence: number;
+  readonly value: TValue;
+}
+
+export class ReplayBuffer<TValue extends { readonly id: string }> {
+  private values: Sequenced<TValue>[] = [];
+
+  constructor(readonly capacity: number) {
+    if (!Number.isInteger(capacity) || capacity <= 0) {
+      throw new RangeError('capacity must be a positive integer');
+    }
+  }
+
+  push(value: Sequenced<TValue>): void {
+    this.values.push(value);
+    if (this.values.length > this.capacity) {
+      this.values.shift();
+    }
+  }
+
+  after(lastEventId?: string): readonly Sequenced<TValue>[] {
+    if (lastEventId === undefined || lastEventId.length === 0) {
+      return [...this.values];
+    }
+
+    const matchingIndex = this.values.findIndex(
+      ({ value }) => value.id === lastEventId,
+    );
+    return matchingIndex === -1
+      ? [...this.values]
+      : this.values.slice(matchingIndex + 1);
+  }
+
+  recent(limit: number): readonly TValue[] {
+    return this.values.slice(-limit).map(({ value }) => value);
+  }
+
+  clear(): void {
+    this.values = [];
+  }
+}
diff --git a/tests/web/events/realtime-event-hub.test.ts b/tests/web/events/realtime-event-hub.test.ts
new file mode 100644
index 0000000..2080bf7
--- /dev/null
+++ b/tests/web/events/realtime-event-hub.test.ts
@@ -0,0 +1,256 @@
+import { describe, expect, expectTypeOf, it, vi } from 'vitest';
+import {
+  MonotonicEventIdGenerator,
+  RealtimeEventHub,
+  type RealtimeEvent,
+  type RealtimeEventMap,
+} from '../../../src/web/events/index.js';
+
+function createDependencies() {
+  let timestamp = Date.parse('2026-08-08T12:00:00.000Z');
+  let sequence = 0;
+
+  return {
+    clock: {
+      now: () => new Date(timestamp++),
+    },
+    idGenerator: {
+      next: () => `event-${++sequence}`,
+    },
+  };
+}
+
+describe('RealtimeEventHub', () => {
+  it('creates typed envelopes with stable IDs and timestamps', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      ...createDependencies(),
+    });
+
+    const event = hub.publish('bot.status.changed', {
+      status: 'running',
+      dryRun: false,
+    });
+
+    expect(event).toStrictEqual({
+      id: 'event-1',
+      occurredAt: '2026-08-08T12:00:00.000Z',
+      type: 'bot.status.changed',
+      payload: { status: 'running', dryRun: false },
+    });
+    expectTypeOf(event).toEqualTypeOf<
+      RealtimeEvent<'bot.status.changed'>
+    >();
+  });
+
+  it('supports every event family through the event map', () => {
+    expectTypeOf<keyof RealtimeEventMap>().toEqualTypeOf<
+      | 'bot.status.changed'
+      | 'message.sent'
+      | 'message.failed'
+      | 'conversation.updated'
+      | 'reply.received'
+      | 'sync.started'
+      | 'sync.progress'
+      | 'sync.completed'
+      | 'sync.failed'
+      | 'rate-limit.changed'
+      | 'reddit.session.changed'
+      | 'log.created'
+    >();
+  });
+
+  it('fans out live events and stops delivery after unsubscribe', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      ...createDependencies(),
+    });
+    const listener = vi.fn();
+    const subscription = hub.subscribe(listener);
+
+    hub.publish('message.sent', {
+      messageId: 'message-1',
+      recipient: 'redditor',
+    });
+    subscription.unsubscribe();
+    subscription.unsubscribe();
+    hub.publish('conversation.updated', {
+      conversationId: 'conversation-1',
+      status: 'awaiting-reply',
+    });
+
+    expect(listener).toHaveBeenCalledTimes(1);
+    expect(listener.mock.calls[0]?.[0]).toMatchObject({
+      id: 'event-1',
+      type: 'message.sent',
+    });
+    expect(subscription.closed).toBe(true);
+  });
+
+  it('retains only the configured replay capacity', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 2,
+      ...createDependencies(),
+    });
+
+    hub.publish('log.created', { level: 'info', message: 'one' });
+    hub.publish('log.created', { level: 'info', message: 'two' });
+    hub.publish('log.created', { level: 'info', message: 'three' });
+
+    expect(hub.recent()).toEqual([
+      expect.objectContaining({ id: 'event-2' }),
+      expect.objectContaining({ id: 'event-3' }),
+    ]);
+    expect(hub.recent(1)).toEqual([
+      expect.objectContaining({ id: 'event-3' }),
+    ]);
+  });
+
+  it('resumes strictly after Last-Event-ID and replays the available window for an unknown ID', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 3,
+      ...createDependencies(),
+    });
+    hub.publish('log.created', { level: 'info', message: 'one' });
+    hub.publish('log.created', { level: 'info', message: 'two' });
+    hub.publish('log.created', { level: 'info', message: 'three' });
+
+    const resumed = vi.fn();
+    hub.subscribe(resumed, { lastEventId: 'event-1' });
+    expect(resumed.mock.calls.map(([event]) => event.id)).toEqual([
+      'event-2',
+      'event-3',
+    ]);
+
+    const boundedHub = new RealtimeEventHub({
+      capacity: 2,
+      ...createDependencies(),
+    });
+    boundedHub.publish('log.created', { level: 'info', message: 'evicted' });
+    boundedHub.publish('log.created', { level: 'info', message: 'available one' });
+    boundedHub.publish('log.created', { level: 'info', message: 'available two' });
+    const stale = vi.fn();
+    boundedHub.subscribe(stale, { lastEventId: 'event-1' });
+    expect(stale.mock.calls.map(([event]) => event.id)).toEqual([
+      'event-2',
+      'event-3',
+    ]);
+  });
+
+  it('preserves order and prevents duplicate delivery when publish occurs during replay', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      ...createDependencies(),
+    });
+    hub.publish('log.created', { level: 'info', message: 'one' });
+    hub.publish('log.created', { level: 'info', message: 'two' });
+    const received: string[] = [];
+
+    hub.subscribe((event) => {
+      received.push(event.id);
+      if (event.id === 'event-1') {
+        hub.publish('log.created', { level: 'info', message: 'during replay' });
+      }
+    });
+
+    expect(received).toEqual(['event-1', 'event-2', 'event-3']);
+  });
+
+  it('keeps every subscriber in order across re-entrant publishes', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      ...createDependencies(),
+    });
+    const firstReceived: string[] = [];
+    const secondReceived: string[] = [];
+    hub.subscribe((event) => {
+      firstReceived.push(event.id);
+      if (event.id === 'event-1') {
+        hub.publish('log.created', { level: 'info', message: 'nested' });
+      }
+    });
+    hub.subscribe((event) => secondReceived.push(event.id));
+
+    hub.publish('log.created', { level: 'info', message: 'outer' });
+
+    expect(firstReceived).toEqual(['event-1', 'event-2']);
+    expect(secondReceived).toEqual(['event-1', 'event-2']);
+  });
+
+  it('isolates failed subscribers and reports failures through an injected logger', () => {
+    const logger = { warn: vi.fn() };
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      logger,
+      ...createDependencies(),
+    });
+    const healthyListener = vi.fn();
+    const failedSubscription = hub.subscribe(() => {
+      throw new Error('client disconnected');
+    });
+    hub.subscribe(healthyListener);
+
+    hub.publish('reddit.session.changed', { status: 'authenticated' });
+    hub.publish('reddit.session.changed', { status: 'expired' });
+
+    expect(failedSubscription.closed).toBe(true);
+    expect(healthyListener).toHaveBeenCalledTimes(2);
+    expect(logger.warn).toHaveBeenCalledOnce();
+    expect(logger.warn).toHaveBeenCalledWith(
+      'Realtime event subscriber failed; subscription closed',
+      expect.objectContaining({ eventId: 'event-1', error: expect.any(Error) }),
+    );
+  });
+
+  it('closes all subscriptions cleanly and rejects use after close', () => {
+    const hub = new RealtimeEventHub({
+      capacity: 10,
+      ...createDependencies(),
+    });
+    const first = hub.subscribe(vi.fn());
+    const second = hub.subscribe(vi.fn());
+
+    hub.close();
+    hub.close();
+
+    expect(first.closed).toBe(true);
+    expect(second.closed).toBe(true);
+    expect(hub.closed).toBe(true);
+    expect(() =>
+      hub.publish('sync.started', { syncId: 'sync-1', kind: 'media' }),
+    ).toThrow('RealtimeEventHub is closed');
+    expect(() => hub.subscribe(vi.fn())).toThrow(
+      'RealtimeEventHub is closed',
+    );
+  });
+
+  it('validates construction and recent limits', () => {
+    expect(
+      () =>
+        new RealtimeEventHub({
+          capacity: 0,
+          ...createDependencies(),
+        }),
+    ).toThrow('capacity must be a positive integer');
+
+    const hub = new RealtimeEventHub({
+      capacity: 1,
+      ...createDependencies(),
+    });
+    expect(() => hub.recent(-1)).toThrow(
+      'limit must be a non-negative integer',
+    );
+  });
+});
+
+describe('MonotonicEventIdGenerator', () => {
+  it('generates unique sortable IDs when timestamps repeat or move backwards', () => {
+    const generator = new MonotonicEventIdGenerator();
+    const first = generator.next(new Date('2026-08-08T12:00:00.001Z'));
+    const second = generator.next(new Date('2026-08-08T12:00:00.001Z'));
+    const third = generator.next(new Date('2026-08-08T12:00:00.000Z'));
+
+    expect(new Set([first, second, third])).toHaveLength(3);
+    expect([first, second, third]).toEqual([...[first, second, third]].sort());
+  });
+});