ccusage Profile

Nearly all runtime cost lives in the Rust binary. references/rust.md covers
release builds, the branch-vs-main worktree setup, deterministic measurement,
JSON parity, and reproducing the CI performance comment.

Two habits carry across every profiling session here:

• Measure end-to-end on real logs before trusting a profile. The wins in this
  repository came from timing the real CLI over real Claude data; a
  microbenchmark answers an isolated question without predicting a CLI win.
• Re-verify daily, weekly, monthly, session, and blocks JSON after
  touching aggregation order, and record in the commit message any hotspot that
  was measured and deliberately left alone.

Node Paths

apps/ccusage/src/cli.js resolves and spawns the platform binary, so the
JavaScript side is a startup-latency question rather than a throughput one — a
profile of it covers launcher startup, not the work the binary does:

LOG_LEVEL=0 node --cpu-prof --cpu-prof-dir /tmp/ccusage-profiles apps/ccusage/src/cli.js daily --offline --json

Nothing else here runs on node. The tools under nix/tools/ are built with
bunCli/bunNodeModules and run under Bun; scripts in apps/ccusage/scripts/
carry nix shell shebangs that pick nushell, babashka, or bun. Time those
scripts directly and profile with their own runtime's tooling rather than
NODE_OPTIONS.

Point --cpu-prof-dir outside the worktree — nothing here ignores a profiles/
directory.