lightwalletd: adaptive reorg-lag tip + non-blocking startup coinsupply

Adaptive-lag: advertise a tip that trails the real tip by a reorg-rate-driven
lag (GetLatestBlock/GetLightdInfo) so wallets anchor shielded spends at a
settled height during reorg churn. Configurable via
-adaptive-lag/-lag-min/-lag-max/-lag-window; monitor_lwd.sh runs
-lag-min 4 -lag-max 12 -lag-window 30.

Startup coinsupply: the informational startup coinsupply RPC (result used only
for a log line) blocked the gRPC bind for minutes on a node whose supply index
is cold, keeping the lite endpoint down on every restart while it also starved
the block-cache ingestor. Run it in a goroutine so the bind is never blocked;
clients still get coinsupply on demand via the GetCoinsupply RPC.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

common/common.go

@@ -95,14 +95,46 @@ func GetCoinsupply(rpcClient *rpcclient.Client) (string, string, int, int, int,
 		return "", "", -1, -1, -1, -1, errors.Wrap(err, "error reading JSON response")
 	}
 
-	result := f.(map[string]interface{})["result"].(string)
-	coin := f.(map[string]interface{})["coin"].(string)
-	height := f.(map[string]interface{})["height"].(float64)
-	supply := f.(map[string]interface{})["supply"].(float64)
-	zfunds := f.(map[string]interface{})["zfunds"].(float64)
-	total := f.(map[string]interface{})["total"].(float64)
+	coinsupply, ok := f.(map[string]interface{})
+	if !ok {
+		return "", "", -1, -1, -1, -1, errors.New("unexpected coinsupply response format")
+	}
 
-	return result, coin, int(height), int(supply), int(zfunds), int(total), nil
+	getStringField := func(key string) string {
+		value, ok := coinsupply[key]
+		if !ok || value == nil {
+			return ""
+		}
+
+		if strValue, ok := value.(string); ok {
+			return strValue
+		}
+
+		return fmt.Sprintf("%v", value)
+	}
+
+	getNumberField := func(key string) int {
+		value, ok := coinsupply[key]
+		if !ok || value == nil {
+			return 0
+		}
+
+		number, ok := value.(float64)
+		if !ok {
+			return 0
+		}
+
+		return int(number)
+	}
+
+	result := getStringField("result")
+	coin := getStringField("coin")
+	height := getNumberField("height")
+	supply := getNumberField("supply")
+	zfunds := getNumberField("zfunds")
+	total := getNumberField("total")
+
+	return result, coin, height, supply, zfunds, total, nil
 }
 
 func getBlockFromRPC(rpcClient *rpcclient.Client, height int) (*walletrpc.CompactBlock, error) {
@@ -225,6 +257,13 @@ func BlockIngestor(rpcClient *rpcclient.Client, cache *BlockCache, log *logrus.E
 }
 
 func GetBlock(rpcClient *rpcclient.Client, cache *BlockCache, height int) (*walletrpc.CompactBlock, error) {
+	// Don't serve blocks above the advertised (lag-adjusted) tip, so wallets can
+	// neither sync nor anchor shielded spends into the unstable reorg zone.
+	if !cache.HeightAllowed(height) {
+		return nil, errors.New(
+			fmt.Sprintf("Block %d is above the advertised tip (reorg-lag protection)", height))
+	}
+
 	// First, check the cache to see if we have the block
 	block := cache.Get(height)
 	if block != nil {