hail CLI v0.21.0

Repo release 0.22.0 — this CLI release is cli-v0.21.0.

An agent-ready API surface: /v1 URLs, rate-limit headers on every response,
a fully described OpenAPI spec, and MCP capability discovery without auth.

Component versions cut alongside this release:
sdk-v0.15.1 (PyPI: hail-sdk==0.15.1), cli-v0.21.0 (Homebrew + GitHub Releases).

API versioning — /v1

• Every customer-facing route is now canonical under /v1/<resource>, and
  /v1 is the only mount in the OpenAPI schema. The legacy unprefixed paths
  still work but carry Deprecation: true plus a successor-version Link
  header and are excluded from the schema. See
  docs/public/versioning.md.
• The regenerated spec and Go CLI client talk to /v1.

Rate limiting

• Every customer response carries RateLimit-Limit / RateLimit-Remaining /
  RateLimit-Reset; exceeding the limit returns 429 with Retry-After.
  Documented in the OpenAPI spec. Three public, self-credentialed routes
  (Twilio webhook receivers, the RFC 8058 unsubscribe endpoint) are exempt so
  they don't share a bucket with anonymous internet traffic.

OpenAPI descriptions

• Every schema-visible operation and every transitively-referenced schema
  field (56 schemas) now has a real, accurate description.

MCP discovery

• initialize and tools/list succeed without a bearer token, so an agent
  can see what Hail offers before authenticating. Every other method still
  401s. A 64 KiB cap bounds the pre-auth body peek; a per-IP rate cap bounds
  anonymous session creation.

Voicebot

• The AI-disclosure line and first_message are spoken as one turn. They
  were two separate utterances with an awkward gap between them.

Email

• GET /email-domains reports default_from: null when the hail-mail
  address the org would mint is already claimed by another tenant. A pinned
  HAIL_MAIL_FROM is one address per deployment, so the first org to send
  takes it and every other org's send 409s — the preview promised an
  address the send path refuses.
• Every surface that mentions opens or clicks now says that open and click
  tracking only works for emails with an HTML body: a plain-text-only email
  still gets sent / delivered / bounce events, but never opened /
  clicked (the SES tracking pixel and link rewriting live in the HTML
  part). Stated in the API schema descriptions, MCP tool docstrings, SDK
  docstrings, CLI help, and docs/public/webhooks.md.
  The website console shows matching notes in the email drawer and the
  deliverability dashboard.

Docs

• Every docs page and every generated API reference page is also served as
  plain markdown: append .md to its URL. /docs/llms.txt indexes every
  guide and API operation; /docs/llms-full.txt concatenates everything
  into one file. The API markdown carries the same field descriptions as
  the HTML pages.
• Tagline refreshed everywhere to "Give your AI agent a voice, a real phone
  number, and an inbox."

Internal

• Deploy prunes images older than two weeks on the production VM after a
  successful rollout. Each deploy pulled :latest plus sha-<commit> for
  three services and removed nothing, until the disk filled and a deploy
  died mid-pull.
• Release tags: there is no umbrella v<X.Y.Z> tag any more. GoReleaser strips
  the cli- prefix, so that name already belongs to the CLI's release page; a
  hand-made one made cli-v0.20.0 publish its binaries onto a page whose tag
  pointed at older code. release-cli.yml now fails when the stripped tag
  already exists on another commit, and the runbook documents the rule.