No way to reply to a calendar invitation

[adriendesportes]

No way to reply to a calendar invitation

What's missing

hey can read an attendance status but never write one. hey event list --json returns
attendances[].status (needs_action, accepted, tentative, declined) and
manage_attendance, yet there is no command to answer an invitation.

Checked against main:

• .surface has no rsvp, attend, accept, decline, tentative or going entry.
  hey event is add, day, delete, edit, list, week, and none of their flags
  touches attendance status.
• outbound_replies and ical_event appear nowhere in the repository.
• The same two strings are absent from hey-sdk's openapi.json, whose Attendance
  schema is read-only (id, email_address, name, status).
• The calendar TUI reads Attendances only to render the guest list; it offers no reply
  action either.

To avoid a likely misreading: hey event add --invite / hey event edit --invite do write
attendance, through calendar_event[attendance_email_addresses][], but that is inviting
other people to your own event. It is not answering an invitation addressed to you. The
two are unrelated, and only the first is covered today.

Why a command on the event will not work

An invitation you have not answered has no calendar event at all. I checked this on a real
account: invitations sitting in the Imbox unanswered (including recurring ones) appear in
no calendar, on no date, while every answered one is present with
attendances[].status = accepted. HEY creates the event as part of replying.

So there is no event id to address, and hey event rsvp <event-id> cannot be the shape.
The invitation exists only as an email entry, so the command has to be addressed to the
thread.

What the web app does

Clicking Yes on an invitation submits this form:

POST /entries/{entry_id}/ical_events/{ical_event_id}/outbound_replies
Content-Type: application/x-www-form-urlencoded

calendar_event_outbound_reply[sender_email_address]=you@hey.com
calendar_event_outbound_reply[status]=accepted        # or tentative, or declined
calendar_event_outbound_reply[calendar_id]=3357

It answers with a 302. The name is apt: one request does two things, filing the event on
the chosen calendar and sending the iCalendar REPLY to the organizer. The form's own label
says "Add to calendar and reply…", and it becomes "Change your reply…" once an event
exists — though that wording is not a reliable indicator of whether you have answered, so
a command should not key on it.

entry_id is already reachable: it is the entry id from hey thread read <topic-id> --json.

The one wrinkle

ical_event_id is only available from the HTML turbo-frame:

GET /entries/{entry_id}/ical_events

GET /entries/{entry_id}/ical_events.json returns 406, and so does the same path with
Accept: application/json. The id has to be parsed out of the markup, next to the
outbound_replies form action. internal/htmlutil looks like the precedent for that, but
I would rather ask than guess: is there a JSON route I have not found, or would parsing the
frame be acceptable here?

Proposed shape

hey thread rsvp <thread-id> --yes | --no | --maybe [--calendar <id>]

Addressed to the thread, since no event exists yet. --calendar defaults to the option the
frame marks selected. Changing an existing reply could later take an event id, but that
seems worth keeping out of a first change.

Happy to send a PR along these lines if the approach and the command name suit you.