feat(routing): pass-rate fetcher with TTL cache

HTTP client that calls GET /pass-rate?skill=X&window=Y on the brain pod.
Caches *float64 results (including nil) per-skill for the configured TTL
(default 60s). On non-200 or network error returns (nil, err) so the
upstream router can fall through to default-to-local.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/routing/passrate_test.go

@@ -0,0 +1,73 @@
+package routing_test
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/mathiasbq/supervisor/internal/routing"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFetcherGetReturnsPassRate(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, http.MethodGet, r.Method)
+		assert.Equal(t, "/pass-rate", r.URL.Path)
+		assert.Equal(t, "tdd", r.URL.Query().Get("skill"))
+		assert.Equal(t, "7d", r.URL.Query().Get("window"))
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]any{"skill": "tdd", "pass_rate": 0.94})
+	}))
+	defer srv.Close()
+
+	f := routing.NewFetcher(srv.URL, "7d", time.Minute)
+	pr, err := f.Get(context.Background(), "tdd")
+	require.NoError(t, err)
+	require.NotNil(t, pr)
+	assert.InDelta(t, 0.94, *pr, 1e-9)
+}
+
+func TestFetcherGetReturnsNilWhenNoData(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(map[string]any{"skill": "novel", "pass_rate": nil})
+	}))
+	defer srv.Close()
+
+	f := routing.NewFetcher(srv.URL, "7d", time.Minute)
+	pr, err := f.Get(context.Background(), "novel")
+	require.NoError(t, err)
+	assert.Nil(t, pr)
+}
+
+func TestFetcherCachesWithinTTL(t *testing.T) {
+	var calls int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		atomic.AddInt32(&calls, 1)
+		_ = json.NewEncoder(w).Encode(map[string]any{"pass_rate": 0.5})
+	}))
+	defer srv.Close()
+
+	f := routing.NewFetcher(srv.URL, "7d", time.Minute)
+	for i := 0; i < 5; i++ {
+		_, err := f.Get(context.Background(), "tdd")
+		require.NoError(t, err)
+	}
+	assert.Equal(t, int32(1), atomic.LoadInt32(&calls), "should hit upstream once and serve four times from cache")
+}
+
+func TestFetcherSurfacesUpstreamError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.Error(w, "boom", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+
+	f := routing.NewFetcher(srv.URL, "7d", time.Minute)
+	pr, err := f.Get(context.Background(), "tdd")
+	require.Error(t, err)
+	assert.Nil(t, pr)
+}