@vltpkg/output

TODO

Tracing

@vltpkg/output/trace is a low overhead tracer for the install pipeline. It is off unless one of these is set, and when off every call returns after one boolean check.

• VLT_TRACE=<file> appends one JSON line per event to <file>. Every thread writes to the same file with the same wall clock, so worker events and main thread events sort onto one timeline by t.
• VLT_PHASES=1 prints one PHASES ... line to stderr at exit: the milliseconds between consecutive phase marks, the event loop delay percentiles (how long the main thread was busy with synchronous work while IO completions waited), and peak memory.

VLT_TRACE=trace.jsonl VLT_PHASES=1 vlt install
./scripts/trace-report.ts trace.jsonl --bucket=250

The report prints the phase timeline, what each span kind cost (manifest, request, extract, tarball:fetch, tarball:unpack, inflate, write), how many of each were in flight per time bucket, and for every phase how long each lane sat idle. An idle lane next to a busy one is a head-of-line stall.

Event kinds: phase (from mark()), <kind>:start/<kind>:end (from span(), paired by url, spec or name), request (the registry client's request events), lane (scheduler occupancy), rss (memory samples), build:level* (one BFS level of the ideal graph build), open and exit.