FASTLY_TRACE_ID
A UUID generated by Fastly for each session. This is often a useful value to include in log messages, and also to send to upstream servers as an additional custom HTTP header, allowing for straightforward correlation of which WebAssembly session processed a request to requests later processed by an origin server. If a session is used to process multiple downstream requests, then you may wish to use the per-request UUID associated with each individual request handle instead of this environment variable.
