Function init_tracing 

pub fn init_tracing()

Initialize the tracing subscriber exactly once per process.

Safe to call multiple times; subsequent calls are no-ops. Configures:

• Default level: INFO
• RUST_LOG support via [EnvFilter::from_env_lossy]
• Compact, human-readable single-line format
• Target (module path) display enabled for module-level filtering
• Output exclusively to stderr (worker stdout is reserved for JSON IPC)

This function does not read or log secrets, tokens, or user content. It does not expose a global mutable reload handle.