Guards API

Send-time checkpoints: a condition about the person, checked at the moment an email is about to go out, and what to do when it's true.

Method & path	What it does
`GET /api/v1/guards`	Every guard in evaluation order, what each is holding, plus the condition vocabulary this install knows.
`POST /api/v1/guards`	Create one.
`GET /api/v1/guards/:id`	One guard.
`PATCH /api/v1/guards/:id`	Update it.
`DELETE /api/v1/guards/:id`	Delete it, releasing whatever it held.
`POST /api/v1/guards/:id/toggle`	Body: `enabled`. Turning one off releases its holds.

POST /api/v1/guards
{ "name": "Members skip pitches",
  "action": "skip",
  "scope_kind": "label",
  "scope_value": "pitch",
  "enabled": true,
  "condition": { "type": "has_tag", "tag": "member" } }

Note: action is read from the request body specifically, because action is also Rails' own routing parameter. Send it as JSON and it works as written.

Actions, in escalating order

Action	What happens to this send
`pause`	Held, and it waits. Releases by itself when the condition stops being true.
`skip`	Dropped, and the person carries on to whatever comes next.
`cancel_sequence`	Their whole run through that sequence ends.
`exit_flow`	Their run through the flow ends.

Scopes

`scope_kind`	Covers
`all`	Every email. `scope_value` is ignored and cleared.
`label`	Emails carrying that label.
`flow`	Emails scheduled by that flow (by key).
`sequence`	Emails from that sequence (by id).
`broadcast`	That broadcast's sends (by id).

The built-in suppression guard

Unsubscribed → drop. Always on, not deletable, and toggle refuses it with 422. It's the standing guarantee the entire provider seam rests on: the local database is the suppression authority, checked before every send, whatever the provider does or doesn't do on its side. A guard you can switch off wouldn't be that.

Conditions

The same vocabulary as flow branches and segments — the flow schema lists every type and operator. GET /api/v1/guards returns the install's own fields, tags, products and segments alongside, so a condition can be written without guessing at names.