ingest: add configurable MQTT write timeout (MQTT_WRITE_TIMEOUT_SECONDS)

Bounds PINGREQ/SUBSCRIBE writes so a stalled write through the Cloudflare
WebSocket proxy can't hang the client. Default 0 (paho's existing no-timeout
behavior); wired through docker-compose. Recommended ~20s when behind a
buffering reverse proxy.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -64,6 +64,7 @@ services:
       - MQTT_STALE_AFTER_SECONDS=${MQTT_STALE_AFTER_SECONDS:-300}
       - MQTT_KEEPALIVE_SECONDS=${MQTT_KEEPALIVE_SECONDS:-30}
       - MQTT_PING_TIMEOUT_SECONDS=${MQTT_PING_TIMEOUT_SECONDS:-20}
+      - MQTT_WRITE_TIMEOUT_SECONDS=${MQTT_WRITE_TIMEOUT_SECONDS:-0}
       - MESHCORE_BATCH_FLUSH_SECONDS=${MESHCORE_BATCH_FLUSH_SECONDS:-10}
       - MESHCORE_BATCH_MAX_ROWS=${MESHCORE_BATCH_MAX_ROWS:-5000}
       - MESHCORE_BATCH_BUFFER=${MESHCORE_BATCH_BUFFER:-50000}

ingest/internal/ingestcommon/ingest.go

@@ -154,6 +154,10 @@ func (d *Daemon) connectToBroker(broker MQTTBrokerConfig, idx int, maxRetries in
 		// proxy's buffering/jitter; 10s was tight and produced false
 		// "pingresp not received" disconnects. Configurable for tuning.
 		opts.SetPingTimeout(time.Duration(GetEnvIntOrDefault("MQTT_PING_TIMEOUT_SECONDS", 20)) * time.Second)
+		// Bound writes (PINGREQ/SUBSCRIBE) so a stalled write through the
+		// Cloudflare WebSocket proxy can't hang the client. 0 (paho default)
+		// disables it; set MQTT_WRITE_TIMEOUT_SECONDS to enable.
+		opts.SetWriteTimeout(time.Duration(GetEnvIntOrDefault("MQTT_WRITE_TIMEOUT_SECONDS", 0)) * time.Second)
 		// Start a fresh session on every (re)connect and resubscribe explicitly in
 		// the OnConnect handler below. This avoids depending on broker-side session
 		// persistence — which is exactly what left the client connected-but-