v0.4.0

Added

• New std/tcp@v1 and std/udp@v1 actions: raw TCP/UDP probes — connect (TCP),
  send an optional payload (send / send_base64), optionally read a response
  and assert a substring (expect), all with per-request timing. Latency feeds
  the same metrics as HTTP, so percentiles are comparable across transports.
• Config files gain a before: block: setup steps that run once before the
  load (not per iteration). Each step's outputs is exposed to test steps under
  the config namespace — ${{ config.<name>.<field> }} — for building a
  reusable value (e.g. a token or connection profile). A failing setup step
  aborts the run before any VU starts.
• Config files gain a variables: block: static values exposed to steps as
  ${{ vars.<key> }}.
• Steps accept uses: as an alias for use:.
• New std/file-read@v1 action: read a file once into a process-wide cache
  (revalidated by mtime/size) and reference its content from later steps via
  ${{ name.content }} — text or base64 encoding.
• New std/file-write@v1 action: write (or append) content to a file —
  e.g. persist ${{ resp.body }} to disk; base64 content is decoded before
  writing.
• std/http@v1 output now includes response headers (lowercase names),
  and ${{ ... }} paths descend nested objects — chain requests on response
  headers: headers: { x-session: "${{ r1.headers.x-session }}" }.
• std/http@v1 can send multipart/form-data: a multipart: array of
  parts — text fields (value) and file uploads (file, with optional
  filename/content_type). Mutually exclusive with body; the boundary
  header is set automatically.

Changed

• Release notes are now written by hand in UPCOMING.md instead of being a
  bare commit diff; the release workflow publishes and then resets the file.
• Steps without ${{ ... }} placeholders skip the interpolation pass
  entirely — no per-iteration deep clone of the with: block on the hot
  path. The ${{ ... }} variable syntax is now fully documented in the
  YAML reference.
• The native engine tracks request durations in a fixed-size HDR histogram
  (~tens of KB) instead of storing every sample: long soak runs no longer
  grow memory 8 bytes per request (a 30-hour run at 10k RPS previously
  needed ~26 GB at the final summary). Quantiles are now within ≤1% of the
  exact value — invisible at the precision the summary prints.
• The step engine exposes an ActionHandler registration seam
  (register_action) so downstream builds can add custom pro/* actions
  without forking; built-in std/* actions pay no lookup cost for it.

Full Changelog: v0.3.0...v0.4.0