feat(09-02): add LimiterRegistry with per-source rate limiters and jitter

- NewLimiterRegistry + For(name, rate, burst) idempotent lookup
- Wait blocks on token then applies 100ms-1s jitter when stealth
- Per-source isolation (RECON-INFRA-05), ctx cancellation honored
- Tests: isolation, idempotency, ctx cancel, jitter range, no-jitter

pkg/recon/limiter.go

@@ -0,0 +1,64 @@
+// Package recon provides the OSINT/recon framework: per-source rate limiting,
+// stealth controls, robots.txt compliance, and parallel sweep orchestration.
+package recon
+
+import (
+	"context"
+	"math/rand"
+	"sync"
+	"time"
+
+	"golang.org/x/time/rate"
+)
+
+// LimiterRegistry holds one *rate.Limiter per source name.
+//
+// RECON-INFRA-05: each source owns its own limiter — no centralization.
+// Lookups are idempotent: the same name always returns the same *rate.Limiter
+// pointer, guaranteeing that token state persists across calls for a source.
+type LimiterRegistry struct {
+	mu       sync.Mutex
+	limiters map[string]*rate.Limiter
+}
+
+// NewLimiterRegistry constructs an empty registry.
+func NewLimiterRegistry() *LimiterRegistry {
+	return &LimiterRegistry{limiters: make(map[string]*rate.Limiter)}
+}
+
+// For returns the limiter for name, creating it with (r, burst) on first call.
+// Repeat calls with the same name return the same *rate.Limiter pointer,
+// regardless of subsequent (r, burst) arguments — the first registration wins.
+func (lr *LimiterRegistry) For(name string, r rate.Limit, burst int) *rate.Limiter {
+	lr.mu.Lock()
+	defer lr.mu.Unlock()
+	if l, ok := lr.limiters[name]; ok {
+		return l
+	}
+	l := rate.NewLimiter(r, burst)
+	lr.limiters[name] = l
+	return l
+}
+
+// Wait blocks until the source's token is available. If stealth is true,
+// an additional random jitter between 100ms and 1s is applied after the token
+// acquisition to evade fingerprint-based detection (RECON-INFRA-06 partial —
+// fully wired with the stealth package in 09-03).
+//
+// Context cancellation is honored both during the underlying limiter.Wait and
+// during the jitter sleep; ctx.Err() is returned promptly in either case.
+func (lr *LimiterRegistry) Wait(ctx context.Context, name string, r rate.Limit, burst int, stealth bool) error {
+	l := lr.For(name, r, burst)
+	if err := l.Wait(ctx); err != nil {
+		return err
+	}
+	if stealth {
+		jitter := time.Duration(100+rand.Intn(900)) * time.Millisecond
+		select {
+		case <-time.After(jitter):
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+	return nil
+}

pkg/recon/limiter_test.go

@@ -0,0 +1,61 @@
+package recon
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/time/rate"
+)
+
+func TestLimiterPerSourceIsolation(t *testing.T) {
+	r := NewLimiterRegistry()
+	a := r.For("a", 10, 1)
+	b := r.For("b", 10, 1)
+	require.NotNil(t, a)
+	require.NotNil(t, b)
+	require.NotSame(t, a, b, "different source names must yield distinct limiters")
+}
+
+func TestLimiterIdempotent(t *testing.T) {
+	r := NewLimiterRegistry()
+	a1 := r.For("a", 10, 1)
+	a2 := r.For("a", 10, 1)
+	require.Same(t, a1, a2, "repeat calls with same name must return same *rate.Limiter")
+}
+
+func TestWaitRespectsContext(t *testing.T) {
+	r := NewLimiterRegistry()
+	// Prime limiter with a very slow rate so Wait would block
+	_ = r.For("slow", rate.Limit(0.001), 1)
+	// Consume the single burst token so the next Wait actually blocks
+	l := r.For("slow", rate.Limit(0.001), 1)
+	require.True(t, l.Allow())
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // pre-cancelled
+
+	err := r.Wait(ctx, "slow", rate.Limit(0.001), 1, false)
+	require.Error(t, err)
+}
+
+func TestJitterRange(t *testing.T) {
+	r := NewLimiterRegistry()
+	// High rate so only jitter meaningfully contributes
+	start := time.Now()
+	err := r.Wait(context.Background(), "fast", rate.Limit(1000), 100, true)
+	elapsed := time.Since(start)
+	require.NoError(t, err)
+	require.GreaterOrEqual(t, elapsed, 90*time.Millisecond, "jitter should be >= 100ms (with slack)")
+	require.LessOrEqual(t, elapsed, 1200*time.Millisecond, "jitter should be <= 1s (with slack)")
+}
+
+func TestJitterDisabled(t *testing.T) {
+	r := NewLimiterRegistry()
+	start := time.Now()
+	err := r.Wait(context.Background(), "fast2", rate.Limit(1000), 100, false)
+	elapsed := time.Since(start)
+	require.NoError(t, err)
+	require.Less(t, elapsed, 50*time.Millisecond, "no jitter when stealth=false")
+}