tracing

Structured logging framework, paired with tracing-subscriber for terminal output. Used instead of println! per CLAUDE.md's conventions (levels: trace/debug/info/warn/error). Chosen as the ecosystem standard, with a ready-made formatter.

main.rs's init_logging(debug: bool) installs the subscriber once, first thing in main. debug comes from the --debug CLI flag (extract_debug_flag), not an environment variable — CLAUDE.md prefers a flag/config.toml over env vars for per-run settings. With --debug, the filter is fixed to "info,trango=debug,word_analysis=debug"; otherwise RUST_LOG still works as a lower-level escape hatch, defaulting to info.

Pitfalls

• init_logging() must run before any tracing::*! calls, or events are dropped silently.
• The env-filter feature (needed for both --debug and RUST_LOG) isn't in tracing-subscriber's default features — enabled explicitly in crates/app/Cargo.toml.
• Plain RUST_LOG=debug also enables chatty dependency logs (winit especially) — scope it like --debug does, e.g. RUST_LOG=trango=debug,word_analysis=debug.