v0.6.0

Added

• WebSocket support — six new built-in actions, free and open source like
  every std/* transport. Two styles:

  A one-shot session (std/ws@v1) connects, exchanges messages, and
  closes in one step — timed as a single latency sample:

  steps:
    - uses: std/ws@v1
      with:
        url: wss://stream.example.com/feed
        messages:
          - send: '{"op":"subscribe","channel":"trades","id":"sub-${seq}"}'
            until_json: { type: trade }
      check:
        message_matches: { type: trade }

  A live connection (std/ws-connect@v1 + ws-send / ws-recv /
  ws-ping / ws-close) stays open across steps within an iteration, so WS
  traffic interleaves with HTTP steps:

  steps:
    - uses: std/ws-connect@v1
      with: { url: "wss://stream.example.com/feed" }
      outputs: feed
    - uses: std/ws-send@v1
      with:
        id: "${{ feed.id }}"
        send: '{"op":"order","id":"ord-${seq}","px":${randf(1.05,1.15,5)}}'
        repeat: 100
        interval_ms: 50
    - uses: std/ws-recv@v1
      with: { id: "${{ feed.id }}", until_json: { type: fill } }
    - uses: std/ws-close@v1
      with: { id: "${{ feed.id }}" }

  Text and binary (base64) frames, subprotocols (graphql-ws, STOMP, …),
  wss:// with skipTLSVerify for staging, and connection profiles via
  connection: ${{ config.x }}. See examples/websocket.test.yaml and
  docs/core/actions.md.

• Dynamic message generator in the open engine: text payloads expand
  single-brace tokens per send — ${seq}, ${uuid}, ${now} / ${now_ms} /
  ${now_iso}, ${rand(a,b)}, ${randf(a,b,dp)}, ${choice(x|y|z)} — and
  repeat + interval_ms emit a stream of unique messages from one template.

• Message asserts in std/check@v1: message_contains,
  message_matches (JSON-subset), and messages_count_gte work over the
  messages list any protocol action exposes (WebSocket and FIX alike), with
  at-least-one-matches semantics; on: got.messages.0 addresses a single
  message by position.

• Custom histogram metrics: an action reporting an array of millisecond
  samples under its metrics key gets a full percentile summary line
  (avg/p(50)/p(90)/p(95)/p(99)/min/max count=N). The engine uses it for
  ws_msg_rtt — time from a send to the first reply matching your
  until-condition. Handshakes and one-shot sessions feed http_req_duration;
  waiting on server pushes deliberately does not.

Full Changelog: v0.5.0...v0.6.0