Document test-race target and OpenTelemetry env vars

- Add make test-race to the Running Tests section in CONTRIBUTING.md
  with a Race Detection Tests subsection explaining its importance for
  concurrent server code
- Add OpenTelemetry / Tracing Variables section to
  docs/ENVIRONMENT_VARIABLES.md documenting OTEL_EXPORTER_OTLP_ENDPOINT
  and OTEL_SERVICE_NAME env vars

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lpcox

CONTRIBUTING.md

@@ -462,13 +462,28 @@ make test-integration
 # Run all tests (unit + integration)
 make test-all
 
+# Run unit tests with race detection
+make test-race
+
 # Run unit tests with coverage
 make coverage
 
 # Run specific package tests
 go test ./internal/server/...
 ```
 
+#### Race Detection Tests
+
+The MCP Gateway is a concurrent HTTP server, so race detection is especially
+important when modifying server, launcher, or guard code:
+
+```bash
+make test-race
+```
+
+This runs `go test -race` across all internal packages to catch data races in
+concurrent code paths.
+
 ### Writing Tests
 
 - Place tests in `*_test.go` files alongside the code

docs/ENVIRONMENT_VARIABLES.md

@@ -81,3 +81,12 @@ These environment variables configure guard policies (e.g., AllowOnly policies f
 | `MCP_GATEWAY_ALLOWONLY_SCOPE_OWNER` | AllowOnly owner scope value (sets default for `--allowonly-scope-owner`) | (disabled) |
 | `MCP_GATEWAY_ALLOWONLY_SCOPE_REPO` | AllowOnly repo name (requires owner) (sets default for `--allowonly-scope-repo`) | (disabled) |
 | `MCP_GATEWAY_ALLOWONLY_MIN_INTEGRITY` | AllowOnly integrity level: `none`, `unapproved`, `approved`, `merged` (sets default for `--allowonly-min-integrity`) | (disabled) |
+
+## OpenTelemetry / Tracing Variables
+
+These standard OpenTelemetry environment variables set defaults for the corresponding `--otlp-*` CLI flags:
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `OTEL_EXPORTER_OTLP_ENDPOINT` | OTLP HTTP endpoint for trace export (e.g., `http://localhost:4318`). Tracing is disabled when empty. Sets default for `--otlp-endpoint`. | (disabled) |
+| `OTEL_SERVICE_NAME` | Service name reported in traces. Sets default for `--otlp-service-name`. | `mcp-gateway` |