Make the resolver pure DNS: JSON access log on stdout instead of a log store

The resolver kept its own query-log store (a bbolt ring, a live ring with SSE
fanout, rolling per-domain counters and dashboard time-series) for the console.
In a multi-node deployment each pod held a different slice of that, so every
view disagreed with itself, and the cost sat on the query path. Charts belong
in Grafana and log search in the log collector, so the store is gone.

internal/accesslog writes one JSON line per notable query to stdout. The default
is what was blocked and what failed (blocked, redirected, SERVFAIL, dropped,
refused); log_cached and sample_rate add ordinary answers for a debugging
session. Lines go through a bounded buffer to a single writer goroutine and are
dropped, and counted in fancydns_access_log_dropped_total, when the stream
cannot keep up, so a stalled log pipe can never stall a query. The config key is
access_log (the old qlog block is ignored, like any unknown key).

The metrics gain what the dashboard used to compute: fancydns_group_queries_total
by ACL group and outcome and fancydns_responses_total by RCODE. Removed with the
store: /api/dashboard, /api/logs, /api/logs/stream, /api/logs/clear,
/api/cache/top, the series rings, and the cache's per-name hit table, which took
a mutex and built a string on every cache hit.

Tests that read the old log now read the access-log lines; the contract test
drops the removed endpoints. The web console still calls them and is changed in
the next commit.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/cache/manager.go

@@ -2,7 +2,6 @@ package cache
 
 import (
 	"math"
-	"sort"
 	"strconv"
 	"sync"
 	"sync/atomic"
@@ -61,9 +60,6 @@ type Manager struct {
 	// It is set once at wiring time via SetPrefetcher.
 	prefetchFn atomic.Pointer[prefetcher]
 
-	// top holds a rolling per-domain hit counter for the "top cached" UI.
-	top *topDomains
-
 	// Blocked counts blocklist hits served from the matcher, kept here so the
 	// dashboard can show block volume without a second counter package.
 	blockedSince atomic.Uint64
@@ -87,7 +83,6 @@ func NewManager(opt Options, store *Store) *Manager {
 		opt:   opt,
 		now:   opt.Now,
 		store: store,
-		top:   newTopDomains(5000),
 	}
 	// Applied after construction rather than through NewLRU so the LRU keeps
 	// its two-argument signature; a 0 budget means unbounded.
@@ -143,7 +138,6 @@ func (m *Manager) Get(k Key) Result {
 		m.lru.Delete(k)
 		return Result{Kind: Miss}
 	}
-	m.top.observe(k, e)
 	res := Result{
 		Kind:        kind,
 		Msg:         msg,
@@ -289,7 +283,6 @@ func (m *Manager) putWire(k Key, wire []byte, ttl uint32, origin, upstream strin
 	copy(buf, wire)
 	// Record the insert too, not just the hits: a name queried once must show
 	// up in "top cached names", and a miss-only workload has no hits to count.
-	m.top.observe(k, &Entry{TTL: ttl, CreatedAt: now})
 	// Key bytes, the wire body and the entry struct: account for all three so
 	// the LRU budget reflects real memory.
 	e := &Entry{
@@ -414,7 +407,6 @@ func (m *Manager) Delete(k Key) { m.lru.Delete(k) }
 // snapshot so a restart does not resurrect it.
 func (m *Manager) Flush() {
 	m.lru.Flush()
-	m.top.reset()
 	if m.store != nil {
 		_ = m.store.Truncate()
 	}
@@ -454,11 +446,6 @@ func (m *Manager) Resize(size, shards int) {
 // Options returns the manager's current options.
 func (m *Manager) Options() Options { return m.opt }
 
-// TopEntries returns the hottest names in the cache for the UI.
-func (m *Manager) TopEntries(limit int) []TopEntry {
-	return m.top.top(limit)
-}
-
 // Stats is the JSON-friendly cache snapshot.
 type Stats struct {
 	Enabled     bool      `json:"enabled"`
@@ -540,93 +527,3 @@ func HumanBytes(n int64) string {
 		return neg + strconv.FormatFloat(float64(n)/(1024*1024*1024), 'f', 2, 64) + " GiB"
 	}
 }
-
-// topDomains is a bounded, periodic top-N counter. It uses a compact
-// min-heap-free approach: a plain map plus periodic pruning, which is far
-// cheaper than maintaining a sorted structure on every query.
-type topDomains struct {
-	mu     sync.Mutex
-	counts map[string]*topCount
-	limit  int
-}
-
-type topCount struct {
-	name  string
-	qtype uint16
-	hits  uint64
-	bytes int64
-}
-
-func newTopDomains(limit int) *topDomains {
-	return &topDomains{counts: make(map[string]*topCount, 4096), limit: limit}
-}
-
-func (t *topDomains) observe(k Key, e *Entry) {
-	if t == nil {
-		return
-	}
-	id := k.Name + "|" + strconv.Itoa(int(k.Type))
-	t.mu.Lock()
-	c, ok := t.counts[id]
-	if !ok {
-		if len(t.counts) > t.limit*2 {
-			t.pruneLocked()
-		}
-		c = &topCount{name: k.Name, qtype: k.Type}
-		t.counts[id] = c
-	}
-	c.hits++
-	c.bytes += int64(len(e.Wire))
-	t.mu.Unlock()
-}
-
-func (t *topDomains) pruneLocked() {
-	// Drop the bottom half so pruning is amortised.
-	type kv struct {
-		id string
-		c  *topCount
-	}
-	all := make([]kv, 0, len(t.counts))
-	for id, c := range t.counts {
-		all = append(all, kv{id, c})
-	}
-	sort.Slice(all, func(i, j int) bool { return all[i].c.hits < all[j].c.hits })
-	keep := len(all) / 2
-	for _, e := range all[keep:] {
-		delete(t.counts, e.id)
-	}
-}
-
-func (t *topDomains) reset() {
-	t.mu.Lock()
-	t.counts = make(map[string]*topCount, 4096)
-	t.mu.Unlock()
-}
-
-// TopEntry is one row of the "top cached names" table.
-type TopEntry struct {
-	Name  string `json:"name"`
-	Type  uint16 `json:"qtype"`
-	Hits  uint64 `json:"hits"`
-	Bytes int64  `json:"bytes"`
-}
-
-func (t *topDomains) top(limit int) []TopEntry {
-	if t == nil {
-		return nil
-	}
-	if limit <= 0 || limit > 500 {
-		limit = 50
-	}
-	t.mu.Lock()
-	out := make([]TopEntry, 0, limit)
-	for _, c := range t.counts {
-		out = append(out, TopEntry{Name: c.name, Type: c.qtype, Hits: c.hits, Bytes: c.bytes})
-	}
-	t.mu.Unlock()
-	sort.Slice(out, func(i, j int) bool { return out[i].Hits > out[j].Hits })
-	if len(out) > limit {
-		out = out[:limit]
-	}
-	return out
-}