docs: clarify emit_tel stderr/stdout contract

Test PR to dogfood the codegraph-pr GitHub Action.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: anvanster

crates/codegraph-server/src/mcp/server.rs

@@ -11,6 +11,8 @@
 /// happen in the Rust binary — the JS wrapper handles PostHog ingestion.
 ///
 /// Silently dropped if serialization fails (never blocks the server).
+/// The wrapper parses these lines from stderr; stdout stays reserved for
+/// the JSON-RPC channel.
 fn emit_tel(value: serde_json::Value) {
     if let Ok(json) = serde_json::to_string(&value) {
         eprintln!("TEL: {json}");