docs(env): document LPB_PAYLOAD_DEBUG in .env.example

Author: localpibox

.env.example

@@ -79,6 +79,13 @@ LPB_AGENT_BROWSER_IDLE_TIMEOUT_MS=300000
 #   0.20   → 262K context → 52.4K max tokens
 # LPB_MAX_TOKENS_CONTEXT_RATIO=0.06
 
+# Capture outgoing provider payloads (lemonade-pi-plugin) — ALL models.
+# 1 = the plugin logs one JSON line per request (tuned view for catalogued
+# models, raw view otherwise) to /tmp/pi-payload-capture.jsonl inside the
+# container. Used to verify exactly what goes over the wire.
+# See lemonade-pi-plugin/docs/qwen-thinking-mainstream-pi.md §5.0/§7.
+# LPB_PAYLOAD_DEBUG=1
+
 # SSH port for `lpb --ssh` (default: 2222)
 # LPB_SSH_PORT=2222