diff --git a/internal/bus/bus.go b/internal/bus/bus.go
new file mode 100644
index 0000000..db04f20
--- /dev/null
+++ b/internal/bus/bus.go
@@ -0,0 +1,124 @@
+// Package bus provides an in-process publish/subscribe event bus. It is the
+// asynchronous communication channel mandated by the Cyrene architecture:
+// synchronous calls go through interfaces and dependency injection, while
+// asynchronous events and agent-to-agent messages flow through this bus. The
+// API is deliberately NATS-like so the bus can later be swapped for an
+// out-of-process NATS deployment (or another transport) without changing call
+// sites; see DevDocs/00-overview.md and DevDocs/02-development-constraints.md.
+//
+// # Matching
+//
+// Both subjects and subscription patterns are dot-separated token strings.
+// Two wildcards are supported:
+//
+//   - "*" matches exactly one non-empty token. For example "runtime.*.start"
+//     matches "runtime.loop.start" but not "runtime.loop".
+//   - ">" matches one or more trailing tokens and may only appear as the last
+//     token (NATS semantics). For example "runtime.>" matches
+//     "runtime.loop.start" but not "runtime".
+//
+// A pattern with no wildcard matches only an identical subject.
+//
+// # Delivery semantics
+//
+// Publish fans out asynchronously and never waits for a handler to finish.
+// Each subscription is served by a single worker goroutine reading from a
+// bounded per-subscription channel, which serializes handler execution for
+// that subscription and bounds its memory. When the buffer is full the event
+// is dropped and counted (see busImpl.Dropped) instead of blocking the
+// publisher; that trade-off is what keeps Publish non-blocking and is the
+// documented cost of an unbounded producer.
+//
+// Handler errors are ignored by this M0 core; consumers that need them should
+// capture and log them at the call site. A panic raised by a handler is
+// recovered so a misbehaving subscriber cannot take down the bus or starve
+// other subscribers.
+package bus
+
+import (
+	"context"
+	"errors"
+)
+
+// Event is a single published message.
+type Event struct {
+	// Subject is the token string the message was published to.
+	Subject string
+	// Payload is the arbitrary value associated with the event.
+	Payload any
+}
+
+// Handler processes a delivered Event. It runs on the subscription's own
+// worker goroutine, so invocations for the same subscription are serialized.
+// A non-nil error is ignored by the M0 core (see the package comment).
+type Handler func(ctx context.Context, e Event) error
+
+// Bus is the in-process publish/subscribe contract. Keep this interface
+// narrow so an alternate transport (for example NATS) can satisfy it without
+// changing consumers, and so it is trivial to mock in tests.
+type Bus interface {
+	// Publish asynchronously fans an event out to every subscription whose
+	// pattern matches subject. It never blocks waiting for a handler to run;
+	// when a subscription's buffer is full the event is dropped for that
+	// subscription and counted. It returns ErrClosed if the bus is closed and
+	// a wrapped error if subject is invalid or ctx is canceled.
+	Publish(ctx context.Context, subject string, payload any) error
+	// Subscribe registers h for events whose subject matches pattern and
+	// returns an unsubscribe function that removes the registration. When ctx
+	// is canceled the registration is removed automatically. It returns
+	// ErrClosed if the bus is already closed.
+	Subscribe(ctx context.Context, pattern string, h Handler) (unsubscribe func(), err error)
+	// Close is idempotent and safe to call concurrently. It prevents further
+	// Publish/Subscribe calls, unsubscribes every registration, cancels the
+	// handlers' contexts, and stops every worker. It returns nil.
+	Close() error
+}
+
+// Sentinel errors returned by the bus. Use errors.Is to test for them.
+var (
+	// ErrClosed is returned when publishing to or subscribing on a closed bus.
+	ErrClosed = errors.New("bus: closed")
+	// ErrInvalidArgument is returned when a subject is empty, a pattern is
+	// malformed, or a handler is nil.
+	ErrInvalidArgument = errors.New("bus: invalid argument")
+)
+
+// defaultQueueSize is the per-subscription event buffer used when no option
+// overrides it.
+const defaultQueueSize = 64
+
+// config carries the resolved construction options.
+type config struct {
+	queueSize int
+}
+
+// Option customizes a bus built by New. Options are applied in order before
+// the bus starts accepting traffic.
+type Option func(*config)
+
+// WithQueueSize sets the per-subscription event buffer size. Buffers bound how
+// many undelivered events a subscription may hold before events begin to be
+// dropped. Non-positive values are ignored and the default is kept.
+func WithQueueSize(n int) Option {
+	return func(c *config) {
+		if n > 0 {
+			c.queueSize = n
+		}
+	}
+}
+
+// New builds a bus with the supplied options. The returned *busImpl
+// implements Bus and also exposes busImpl.Dropped for observability.
+func New(opts ...Option) *busImpl {
+	cfg := config{queueSize: defaultQueueSize}
+	for _, opt := range opts {
+		opt(&cfg)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	return &busImpl{
+		queueSize: cfg.queueSize,
+		subs:      make(map[uint64]*subscription),
+		ctx:       ctx,
+		cancel:    cancel,
+	}
+}
diff --git a/internal/bus/bus_test.go b/internal/bus/bus_test.go
new file mode 100644
index 0000000..c0cca52
--- /dev/null
+++ b/internal/bus/bus_test.go
@@ -0,0 +1,454 @@
+package bus
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+)
+
+// recvWithTimeout blocks until a value is delivered or the deadline passes,
+// failing the test on timeout. It makes delivery assertions deterministic
+// instead of relying on a bare sleep.
+func recvWithTimeout[T any](t *testing.T, ch <-chan T, timeout time.Duration) T {
+	t.Helper()
+	select {
+	case v := <-ch:
+		return v
+	case <-time.After(timeout):
+		t.Fatalf("timed out waiting for a delivery after %v", timeout)
+		var zero T
+		return zero
+	}
+}
+
+// assertNoRecv fails if a value arrives on ch within d. It is used for the
+// negative cases where the registration is already gone, so nothing is ever
+// enqueued and the channel stays empty.
+func assertNoRecv[T any](t *testing.T, ch <-chan T, d time.Duration) {
+	t.Helper()
+	select {
+	case v := <-ch:
+		t.Fatalf("unexpected delivery: %v", v)
+	case <-time.After(d):
+	}
+}
+
+// waitSubs polls the registry until it holds exactly want subscriptions, with a
+// deadline, so context-cancellation behavior can be asserted deterministically.
+func waitSubs(t *testing.T, b *busImpl, want int) {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		b.mu.RLock()
+		got := len(b.subs)
+		b.mu.RUnlock()
+		if got == want {
+			return
+		}
+		if time.Now().After(deadline) {
+			t.Fatalf("subscriber count = %d, want %d", got, want)
+		}
+		time.Sleep(time.Millisecond)
+	}
+}
+
+func TestMatch_Rules(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		pattern string
+		subject string
+		want    bool
+	}{
+		{name: "exact match", pattern: "runtime.loop.start", subject: "runtime.loop.start", want: true},
+		{name: "exact mismatch", pattern: "runtime.loop.start", subject: "runtime.loop.stop", want: false},
+		{name: "exact subject has more tokens", pattern: "runtime.loop", subject: "runtime.loop.start", want: false},
+		{name: "exact subject has fewer tokens", pattern: "runtime.loop.start", subject: "runtime", want: false},
+		{name: "gt matches nested", pattern: "runtime.>", subject: "runtime.loop.start", want: true},
+		{name: "gt matches one child", pattern: "runtime.>", subject: "runtime.loop", want: true},
+		{name: "gt does not match parent", pattern: "runtime.>", subject: "runtime", want: false},
+		{name: "gt alone matches nested", pattern: ">", subject: "runtime.loop.start", want: true},
+		{name: "gt alone matches single", pattern: ">", subject: "runtime", want: true},
+		{name: "star matches one token", pattern: "runtime.*.start", subject: "runtime.loop.start", want: true},
+		{name: "star rejects extra token", pattern: "runtime.*.start", subject: "runtime.loop.x.start", want: false},
+		{name: "star rejects value mismatch", pattern: "runtime.*.start", subject: "runtime.loop.stop", want: false},
+		{name: "star alone matches single", pattern: "*", subject: "runtime", want: true},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if got := match(tt.pattern, tt.subject); got != tt.want {
+				t.Errorf("match(%q, %q) = %v, want %v", tt.pattern, tt.subject, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestPublish_ExactMatch(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 4)
+
+	if _, err := b.Subscribe(context.Background(), "runtime.loop.start", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "runtime.loop.start", "hit"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	if p := recvWithTimeout(t, got, 2*time.Second); p != "hit" {
+		t.Fatalf("payload = %v, want hit", p)
+	}
+
+	if err := b.Publish(context.Background(), "runtime.loop.stop", "miss"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestPublish_GTailWildcard(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 4)
+
+	if _, err := b.Subscribe(context.Background(), "runtime.>", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	for _, subject := range []string{"runtime.loop.start", "runtime.loop", "runtime.loop.a.b"} {
+		if err := b.Publish(context.Background(), subject, subject); err != nil {
+			t.Fatalf("Publish(%q): %v", subject, err)
+		}
+		if p := recvWithTimeout(t, got, 2*time.Second); p != subject {
+			t.Fatalf("payload = %v, want %q", p, subject)
+		}
+	}
+
+	// "runtime.>" must not match the exact "runtime", and a different root
+	// must not match at all.
+	if err := b.Publish(context.Background(), "runtime", "miss-root"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	if err := b.Publish(context.Background(), "other.x", "miss-other"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestPublish_StarWildcard(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 4)
+
+	if _, err := b.Subscribe(context.Background(), "runtime.*.start", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "runtime.loop.start", "hit"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	if p := recvWithTimeout(t, got, 2*time.Second); p != "hit" {
+		t.Fatalf("payload = %v, want hit", p)
+	}
+
+	for _, subject := range []string{"runtime.loop.x.start", "runtime.loop.stop", "runtime.loop"} {
+		if err := b.Publish(context.Background(), subject, "miss"); err != nil {
+			t.Fatalf("Publish(%q): %v", subject, err)
+		}
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestSubscribe_UnsubscribeStopsDelivery(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 2)
+
+	unsub, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "a.b", "first"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	if p := recvWithTimeout(t, got, 2*time.Second); p != "first" {
+		t.Fatalf("payload = %v, want first", p)
+	}
+
+	unsub()
+	if err := b.Publish(context.Background(), "a.b", "second"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestPublish_NonBlockingSlowHandler(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+
+	started := make(chan struct{})
+	release := make(chan struct{})
+	var once sync.Once
+	handler := func(ctx context.Context, e Event) error {
+		once.Do(func() { close(started) })
+		<-release
+		return nil
+	}
+	if _, err := b.Subscribe(context.Background(), "slow", handler); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "slow", "payload"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+
+	// The handler started and is still blocked on release. Because Publish has
+	// already returned, it did not wait for the handler to finish.
+	select {
+	case <-started:
+	case <-time.After(2 * time.Second):
+		t.Fatal("handler did not start")
+	}
+	select {
+	case <-release:
+		t.Fatal("handler finished before release was closed")
+	case <-time.After(50 * time.Millisecond):
+	}
+	close(release)
+}
+
+func TestBus_CloseStopsDelivery(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 1)
+
+	if _, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "a.b", "before-close"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	if p := recvWithTimeout(t, got, 2*time.Second); p != "before-close" {
+		t.Fatalf("payload = %v, want before-close", p)
+	}
+
+	if err := b.Close(); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+	if err := b.Publish(context.Background(), "a.b", "after-close"); !errors.Is(err, ErrClosed) {
+		t.Fatalf("Publish after Close error = %v, want ErrClosed", err)
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestPublish_InvalidSubject(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+
+	for _, subject := range []string{"", ".a", "a.", "a..b"} {
+		err := b.Publish(context.Background(), subject, "x")
+		if !errors.Is(err, ErrInvalidArgument) {
+			t.Errorf("Publish(%q) error = %v, want ErrInvalidArgument", subject, err)
+		}
+	}
+}
+
+func TestSubscribe_InvalidPattern(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+
+	for _, pattern := range []string{"", ".a", "a.", "a..b", "a.>.b"} {
+		_, err := b.Subscribe(context.Background(), pattern, func(ctx context.Context, e Event) error { return nil })
+		if !errors.Is(err, ErrInvalidArgument) {
+			t.Errorf("Subscribe(%q) error = %v, want ErrInvalidArgument", pattern, err)
+		}
+	}
+}
+
+func TestSubscribe_NilHandler(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+
+	_, err := b.Subscribe(context.Background(), "a.b", nil)
+	if !errors.Is(err, ErrInvalidArgument) {
+		t.Fatalf("Subscribe(nil) error = %v, want ErrInvalidArgument", err)
+	}
+}
+
+func TestBus_ClosedError(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	if err := b.Close(); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "a.b", "x"); !errors.Is(err, ErrClosed) {
+		t.Fatalf("Publish after Close error = %v, want ErrClosed", err)
+	}
+	if _, err := b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error { return nil }); !errors.Is(err, ErrClosed) {
+		t.Fatalf("Subscribe after Close error = %v, want ErrClosed", err)
+	}
+	if err := b.Close(); err != nil {
+		t.Fatalf("second Close error = %v, want nil", err)
+	}
+}
+
+func TestBus_DroppedCounter(t *testing.T) {
+	t.Parallel()
+
+	b := New(WithQueueSize(1))
+	defer b.Close()
+
+	started := make(chan struct{})
+	release := make(chan struct{})
+	var once sync.Once
+	if _, err := b.Subscribe(context.Background(), "d", func(ctx context.Context, e Event) error {
+		once.Do(func() { close(started) })
+		<-release
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	if err := b.Publish(context.Background(), "d", "first"); err != nil {
+		t.Fatalf("Publish first: %v", err)
+	}
+	select {
+	case <-started:
+	case <-time.After(2 * time.Second):
+		t.Fatal("handler did not start; worker failed to drain")
+	}
+
+	// The worker is now blocked in the handler, so it consumed "first" and the
+	// single-slot buffer is empty. The next enqueue fills it; the two after
+	// that find it full and are dropped.
+	for _, payload := range []string{"fill1", "fill2", "fill3"} {
+		if err := b.Publish(context.Background(), "d", payload); err != nil {
+			t.Fatalf("Publish %s: %v", payload, err)
+		}
+	}
+	if got := b.Dropped(); got != 2 {
+		t.Fatalf("Dropped() = %d, want 2", got)
+	}
+	close(release)
+}
+
+func TestSubscribe_ContextCancelAutoUnsub(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	defer b.Close()
+	got := make(chan any, 1)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	if _, err := b.Subscribe(ctx, "a.b", func(ctx context.Context, e Event) error {
+		got <- e.Payload
+		return nil
+	}); err != nil {
+		t.Fatalf("Subscribe: %v", err)
+	}
+
+	cancel()
+	waitSubs(t, b, 0)
+
+	if err := b.Publish(context.Background(), "a.b", "after-cancel"); err != nil {
+		t.Fatalf("Publish: %v", err)
+	}
+	assertNoRecv(t, got, 100*time.Millisecond)
+}
+
+func TestPublish_ConcurrentSafety(t *testing.T) {
+	t.Parallel()
+
+	b := New(WithQueueSize(8))
+	defer b.Close()
+
+	const workers = 8
+	const iterations = 200
+	var wg sync.WaitGroup
+	for w := 0; w < workers; w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := 0; i < iterations; i++ {
+				if i%3 == 0 {
+					unsub, err := b.Subscribe(context.Background(), "c", func(ctx context.Context, e Event) error {
+						return nil
+					})
+					if err == nil {
+						unsub()
+					}
+					continue
+				}
+				_ = b.Publish(context.Background(), "c", i)
+				_ = b.Publish(context.Background(), "c.x", i)
+			}
+		}()
+	}
+	wg.Wait()
+
+	if err := b.Close(); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+}
+
+func TestClose_Concurrent(t *testing.T) {
+	t.Parallel()
+
+	b := New()
+	var wg sync.WaitGroup
+	for i := 0; i < 8; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = b.Publish(context.Background(), "a.b", 1)
+			_, _ = b.Subscribe(context.Background(), "a.b", func(ctx context.Context, e Event) error { return nil })
+			_ = b.Close()
+		}()
+	}
+	wg.Wait()
+
+	if err := b.Close(); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+}
diff --git a/internal/bus/impl.go b/internal/bus/impl.go
new file mode 100644
index 0000000..339c36b
--- /dev/null
+++ b/internal/bus/impl.go
@@ -0,0 +1,192 @@
+package bus
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"sync/atomic"
+)
+
+// Compile-time assertion that *busImpl satisfies Bus.
+var _ Bus = (*busImpl)(nil)
+
+// busImpl is the default in-process Bus implementation. It is safe for
+// concurrent use.
+type busImpl struct {
+	queueSize int
+	mu        sync.RWMutex
+	subs      map[uint64]*subscription
+	nextID    atomic.Uint64
+	dropped   atomic.Uint64
+	closed    atomic.Bool
+	ctx       context.Context
+	cancel    context.CancelFunc
+	closeOnce sync.Once
+}
+
+// Dropped returns the total number of events dropped because a subscription's
+// buffer was full. It is useful for observing backpressure on the bus.
+func (b *busImpl) Dropped() uint64 {
+	return b.dropped.Load()
+}
+
+// subscription is one registered handler plus its bounded queue and the single
+// worker goroutine that drains it.
+type subscription struct {
+	id      uint64
+	pattern string
+	handler Handler
+	events  chan Event
+	done    chan struct{}
+	ctx     context.Context
+	cancel  context.CancelFunc
+	once    sync.Once
+}
+
+// stop idempotently cancels the handler context and signals the worker to
+// exit. It is safe to call more than once and from more than one goroutine.
+func (s *subscription) stop() {
+	s.once.Do(func() {
+		s.cancel()
+		close(s.done)
+	})
+}
+
+// Publish fans an event out to every matching subscription without waiting for
+// any handler. It holds the read lock across the fan-out so a concurrent
+// Close cannot stop a worker mid-broadcast. Events that cannot be queued
+// because a subscription buffer is full are dropped and counted.
+func (b *busImpl) Publish(ctx context.Context, subject string, payload any) error {
+	if err := validateSubject(subject); err != nil {
+		return err
+	}
+	if err := ctx.Err(); err != nil {
+		return fmt.Errorf("bus: publish %q: %w", subject, err)
+	}
+
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	if b.closed.Load() {
+		return fmt.Errorf("bus is closed: %w", ErrClosed)
+	}
+
+	ev := Event{Subject: subject, Payload: payload}
+	for _, sub := range b.subs {
+		if !match(sub.pattern, subject) {
+			continue
+		}
+		if err := ctx.Err(); err != nil {
+			return fmt.Errorf("bus: publish %q: %w", subject, err)
+		}
+		select {
+		case sub.events <- ev:
+		default:
+			b.dropped.Add(1)
+		}
+	}
+	return nil
+}
+
+// Subscribe registers a handler and returns an unsubscribe function. The
+// registration is removed automatically when the caller's context is canceled.
+func (b *busImpl) Subscribe(ctx context.Context, pattern string, h Handler) (func(), error) {
+	if err := validatePattern(pattern); err != nil {
+		return nil, err
+	}
+	if h == nil {
+		return nil, fmt.Errorf("bus: handler must not be nil: %w", ErrInvalidArgument)
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, fmt.Errorf("bus: subscribe %q: %w", pattern, err)
+	}
+
+	subCtx, subCancel := context.WithCancel(b.ctx)
+	sub := &subscription{
+		id:      b.nextID.Add(1),
+		pattern: pattern,
+		handler: h,
+		events:  make(chan Event, b.queueSize),
+		done:    make(chan struct{}),
+		ctx:     subCtx,
+		cancel:  subCancel,
+	}
+
+	b.mu.Lock()
+	if b.closed.Load() {
+		b.mu.Unlock()
+		subCancel()
+		return nil, fmt.Errorf("bus is closed: %w", ErrClosed)
+	}
+	b.subs[sub.id] = sub
+	b.mu.Unlock()
+
+	b.startWorker(sub)
+
+	go func() {
+		select {
+		case <-ctx.Done():
+			b.removeSub(sub.id, sub)
+		case <-sub.done:
+			// Already removed; nothing to do.
+		}
+	}()
+
+	return func() { b.removeSub(sub.id, sub) }, nil
+}
+
+// Close is idempotent and safe to call concurrently. It marks the bus closed,
+// cancels every handler context, unsubscribes all registrations, and signals
+// every worker to stop. It does not wait for in-flight handlers, which instead
+// observe their canceled context.
+func (b *busImpl) Close() error {
+	b.closeOnce.Do(func() {
+		b.mu.Lock()
+		b.closed.Store(true)
+		b.cancel()
+		for _, sub := range b.subs {
+			sub.stop()
+		}
+		b.subs = make(map[uint64]*subscription)
+		b.mu.Unlock()
+	})
+	return nil
+}
+
+// startWorker launches the single goroutine that drains the subscription queue
+// and runs the handler for each event.
+func (b *busImpl) startWorker(sub *subscription) {
+	go func() {
+		for {
+			select {
+			case <-sub.done:
+				return
+			case ev := <-sub.events:
+				b.deliver(sub, ev)
+			}
+		}
+	}()
+}
+
+// deliver runs one handler invocation. It recovers panics so a misbehaving
+// subscriber cannot crash the bus, and it ignores the handler's returned error
+// (see the package comment).
+func (b *busImpl) deliver(sub *subscription, ev Event) {
+	defer func() {
+		_ = recover()
+	}()
+	_ = sub.handler(sub.ctx, ev)
+}
+
+// removeSub unsubscribes a registration exactly once. The events channel is
+// never closed by a sender, so a concurrent Publish cannot panic on a send;
+// this method only closes the done channel after the registration is gone.
+func (b *busImpl) removeSub(id uint64, sub *subscription) {
+	b.mu.Lock()
+	if _, ok := b.subs[id]; ok {
+		delete(b.subs, id)
+		b.mu.Unlock()
+		sub.stop()
+		return
+	}
+	b.mu.Unlock()
+}
diff --git a/internal/bus/match.go b/internal/bus/match.go
new file mode 100644
index 0000000..e51a4f7
--- /dev/null
+++ b/internal/bus/match.go
@@ -0,0 +1,63 @@
+package bus
+
+import (
+	"fmt"
+	"strings"
+)
+
+// match reports whether subject matches pattern using the wildcard rules
+// described in the package comment: "*" matches exactly one non-empty token,
+// ">" matches one or more trailing tokens and must be the last token, and any
+// other token matches an identical subject token. Callers must have validated
+// both inputs, so an empty token or a misplaced ">" never reaches here.
+func match(pattern, subject string) bool {
+	p := strings.Split(pattern, ".")
+	s := strings.Split(subject, ".")
+	i, j := 0, 0
+	for i < len(p) {
+		if p[i] == ">" {
+			// ">" is guaranteed to be the last token; it needs at least one
+			// remaining subject token.
+			return j < len(s)
+		}
+		if j >= len(s) {
+			return false
+		}
+		if p[i] != "*" && p[i] != s[j] {
+			return false
+		}
+		i++
+		j++
+	}
+	return j == len(s)
+}
+
+// validateSubject rejects an empty subject or one containing an empty token
+// (leading/trailing/repeated dots).
+func validateSubject(subject string) error {
+	if subject == "" {
+		return fmt.Errorf("bus: subject must not be empty: %w", ErrInvalidArgument)
+	}
+	if strings.HasPrefix(subject, ".") || strings.HasSuffix(subject, ".") || strings.Contains(subject, "..") {
+		return fmt.Errorf("bus: subject %q contains an empty token: %w", subject, ErrInvalidArgument)
+	}
+	return nil
+}
+
+// validatePattern rejects an empty pattern, one with an empty token, or one
+// where the ">" wildcard is not the final token.
+func validatePattern(pattern string) error {
+	if pattern == "" {
+		return fmt.Errorf("bus: pattern must not be empty: %w", ErrInvalidArgument)
+	}
+	if strings.HasPrefix(pattern, ".") || strings.HasSuffix(pattern, ".") || strings.Contains(pattern, "..") {
+		return fmt.Errorf("bus: pattern %q contains an empty token: %w", pattern, ErrInvalidArgument)
+	}
+	tokens := strings.Split(pattern, ".")
+	for i, tok := range tokens {
+		if tok == ">" && i != len(tokens)-1 {
+			return fmt.Errorf("bus: pattern %q: '>' wildcard must be the last token: %w", pattern, ErrInvalidArgument)
+		}
+	}
+	return nil
+}