refactor: audit-driven hygiene pass across modules and infra

Concurrency
- lolschedule: serialize subscriber Get→mutate→Put via state.subscribersMu;
  the single-slot list was previously losing writes under concurrent
  /lolschedule_subscribe.
- trading: PriceClient memoises its default *http.Client so /trade_stats
  reuses TLS connections across held tickers.

Observability
- server/log_middleware: defer the req log line and recover panics so a
  panicking cron handler still emits the structured req entry CloudWatch
  filters on for 5xx alerting.
- server/router (cron): inner recover with cron-name context captures the
  panicking job before the middleware's safety net does.
- telegram/webhook: rune-safe truncation in dispatch logs — Vietnamese,
  Korean, and emoji previews no longer ship as garbled bytes.
- lolschedule/api_client: same rune-safe fix for error-body log truncation.
- telegram/webhook: gate the post-recover WriteHeader(200) so a panicking
  handler that already touched w doesn't trigger superfluous-WriteHeader.

Correctness
- twentyq: clearGame error during solved-relaunch is logged instead of
  silently swallowed (was a permanent deadlock vector on KV failure).
- misc /mstats: KV read failure replies "Could not load stats. Try again
  later." to the user instead of returning into the dispatcher; matches the
  pattern other modules use.
- migrate_cf_data trading-audit-dump: surface f.Close error so a truncated
  JSONL never passes silently as a complete audit dump.

Operator ergonomics
- migrate_cf_data (all 4 subcommands): signal.NotifyContext for SIGINT /
  SIGTERM. Ctrl-C mid-Scan now propagates cleanly instead of leaving a
  half-converted DynamoDB table.
- ai/ratelimit: doc the Lambda-recycle memory bound to match keylock.Map
  so a future reviewer doesn't re-flag the unbounded map.

I/O-changing (user-approved)
- lolschedule daily push auto-prunes subscribers whose Telegram error
  matches a terminal marker (blocked / deactivated / chat gone). Transient
  errors keep the chat on the list. Subscribe message updated to mention
  the auto-cleanup.
- twentyq seed pool grown 50 → 178; repeat-collision threshold moves from
  ~9 plays to ~17 (birthday paradox).
- util /info flipped Public → Protected — chat/thread/sender IDs are no
  longer enumerable by every group member.
- cmd/server WriteTimeout 6min → 75s (cron 60s + 15s slack). No-op on
  Lambda; matters only for local non-Lambda runs.
- webhook + cron rejection paths drop response bodies (no fingerprintable
  text for internet scanners hitting the public Function URL). Status
  codes preserved for CloudWatch metrics; structured log lines carry the
  rejection reason for operator triage.

Tests added: TestTruncateRunes, TestRunDailyPush_PrunesDeadSubscribers,
TestIsTerminalSendError, TestInfo_DeniedToNonOwner,
TestInfo_DeniedToChannelMessageNoFrom, plus owner-allowed counterparts.

internal/modules/util/handlers_test.go

@@ -28,8 +28,9 @@ func installUtil(t *testing.T, ownerID int64) *testutil.RecordingBot {
 	return rb
 }
 
-func TestInfo_PrivateChat(t *testing.T) {
-	rb := installUtil(t, 0)
+func TestInfo_PrivateChat_OwnerAllowed(t *testing.T) {
+	// /info is Protected — sender must be the bot owner to get a reply.
+	rb := installUtil(t, 42)
 	rb.Bot.ProcessUpdate(context.Background(), testutil.NewPrivateMessage(42, "/info"))
 
 	got := rb.LastSent().Text()
@@ -40,8 +41,8 @@ func TestInfo_PrivateChat(t *testing.T) {
 	}
 }
 
-func TestInfo_GroupChat(t *testing.T) {
-	rb := installUtil(t, 0)
+func TestInfo_GroupChat_OwnerAllowed(t *testing.T) {
+	rb := installUtil(t, 7)
 	rb.Bot.ProcessUpdate(context.Background(), testutil.NewGroupMessage(-100, 7, "/info"))
 
 	got := rb.LastSent().Text()
@@ -52,13 +53,22 @@ func TestInfo_GroupChat(t *testing.T) {
 	}
 }
 
-func TestInfo_ChannelMessageNoFrom(t *testing.T) {
+func TestInfo_DeniedToNonOwner(t *testing.T) {
+	// Non-admin sender → Protected denies silently (no reply, no leak of
+	// the command's existence).
+	rb := installUtil(t, 999)
+	rb.Bot.ProcessUpdate(context.Background(), testutil.NewGroupMessage(-100, 7, "/info"))
+	if calls := rb.Sent(); len(calls) != 0 {
+		t.Errorf("non-owner /info replied: %+v", calls)
+	}
+}
+
+func TestInfo_DeniedToChannelMessageNoFrom(t *testing.T) {
+	// Channel posts have no From. Protected denies (no sender to check).
 	rb := installUtil(t, 0)
 	rb.Bot.ProcessUpdate(context.Background(), testutil.NewChannelMessage(-200, "/info"))
-
-	got := rb.LastSent().Text()
-	if !strings.Contains(got, "sender id: n/a") {
-		t.Errorf("info channel reply missing 'sender id: n/a'; got %q", got)
+	if calls := rb.Sent(); len(calls) != 0 {
+		t.Errorf("channel-post /info replied: %+v", calls)
 	}
 }
 

internal/modules/util/info.go

@@ -15,8 +15,13 @@ import (
 // IDs, with "n/a" fallbacks. Used to debug bot routing in groups + topics.
 func infoCommand() modules.Command {
 	return modules.Command{
-		Name:        "info",
-		Visibility:  modules.VisibilityPublic,
+		Name: "info",
+		// Protected (not Public) because the response exposes internal
+		// routing IDs — chat id, thread id, sender id. Useful for admins
+		// debugging group/topic routing; not something every group member
+		// should be able to enumerate. Non-admins see no response at all
+		// (Visibility denies are silent — see dispatcher.go:31).
+		Visibility:  modules.VisibilityProtected,
 		Description: "Show chat id, thread id, and sender id (debug helper)",
 		Handler: func(ctx context.Context, b *bot.Bot, update *models.Update) error {
 			msg := update.Message