fix(metrics): update hints

readme.hints.md

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+# SmartProxy Development Hints
+
+## Byte Tracking and Metrics
+
+### Double Counting Issue (Fixed)
+
+**Problem**: Initial data chunks were being counted twice in the byte tracking:
+1. Once when stored in `pendingData` in `setupDirectConnection()`
+2. Again when the data flowed through bidirectional forwarding
+
+**Solution**: Removed the byte counting when storing initial chunks. Bytes are now only counted when they actually flow through the `setupBidirectionalForwarding()` callbacks.
+
+### HttpProxy Metrics (Fixed)
+
+**Problem**: HttpProxy forwarding was updating connection record byte counts but not calling `metricsCollector.recordBytes()`, resulting in missing throughput data.
+
+**Solution**: Added `metricsCollector.recordBytes()` calls to the HttpProxy bidirectional forwarding callbacks.
+
+### Metrics Architecture
+
+The metrics system has three layers:
+1. **Connection Records** (`record.bytesReceived/bytesSent`): Track total bytes per connection
+2. **ThroughputTracker**: Accumulates bytes between samples for rate calculations (bytes/second)
+3. **connectionByteTrackers**: Track bytes per connection with timestamps for per-route/IP metrics
+
+Total byte counts come from connection records only, preventing double counting.
+
+## Connection Cleanup
+
+### Zombie Connection Detection
+
+The connection manager performs comprehensive zombie detection every 10 seconds:
+- **Full zombies**: Both incoming and outgoing sockets destroyed but connection not cleaned up
+- **Half zombies**: One socket destroyed, grace period expired (5 minutes for TLS, 30 seconds for non-TLS)
+- **Stuck connections**: Data received but none sent back after threshold (5 minutes for TLS, 60 seconds for non-TLS)
+
+### Cleanup Queue
+
+Connections are cleaned up through a batched queue system:
+- Batch size: 100 connections
+- Processing triggered immediately when batch size reached
+- Otherwise processed after 100ms delay
+- Prevents overwhelming the system during mass disconnections
+
+## Keep-Alive Handling
+
+Keep-alive connections receive special treatment based on `keepAliveTreatment` setting:
+- **standard**: Normal timeout applies
+- **extended**: Timeout multiplied by `keepAliveInactivityMultiplier` (default 6x)
+- **immortal**: No timeout, connections persist indefinitely
+
+## PROXY Protocol
+
+The system supports both receiving and sending PROXY protocol:
+- **Receiving**: Automatically detected from trusted proxy IPs (configured in `proxyIPs`)
+- **Sending**: Enabled per-route or globally via `sendProxyProtocol` setting
+- Real client IP is preserved and used for all connection tracking and security checks