feat(09-01): add Engine with parallel fanout and ExampleSource

- Engine.Register/List/SweepAll with ants pool fanout
- ExampleSource emits two deterministic findings (SourceType=recon:example)
- Tests cover Register/List idempotency, SweepAll aggregation, empty-registry,
  and Enabled() filtering

pkg/recon/engine_test.go

@@ -0,0 +1,57 @@
+package recon
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRegisterList(t *testing.T) {
+	e := NewEngine()
+	require.Empty(t, e.List())
+
+	e.Register(ExampleSource{})
+	require.Equal(t, []string{"example"}, e.List())
+
+	// Re-registering the same name is idempotent.
+	e.Register(ExampleSource{})
+	require.Equal(t, []string{"example"}, e.List())
+}
+
+func TestSweepAll(t *testing.T) {
+	e := NewEngine()
+	e.Register(ExampleSource{})
+
+	findings, err := e.SweepAll(context.Background(), Config{Query: "ignored"})
+	require.NoError(t, err)
+	require.Len(t, findings, 2, "ExampleSource should emit exactly 2 deterministic findings")
+
+	for _, f := range findings {
+		require.Equal(t, "recon:example", f.SourceType)
+		require.NotEmpty(t, f.ProviderName)
+		require.NotEmpty(t, f.KeyMasked)
+		require.NotEmpty(t, f.Source)
+	}
+}
+
+func TestSweepAll_NoSources(t *testing.T) {
+	e := NewEngine()
+	findings, err := e.SweepAll(context.Background(), Config{})
+	require.NoError(t, err)
+	require.Nil(t, findings)
+}
+
+// disabledSource tests that Enabled() filtering works.
+type disabledSource struct{ ExampleSource }
+
+func (disabledSource) Name() string          { return "disabled" }
+func (disabledSource) Enabled(Config) bool   { return false }
+
+func TestSweepAll_FiltersDisabled(t *testing.T) {
+	e := NewEngine()
+	e.Register(disabledSource{})
+	findings, err := e.SweepAll(context.Background(), Config{})
+	require.NoError(t, err)
+	require.Empty(t, findings)
+}