Agonara membership

Program membership is participation in a program — being a Student or a
Program Curator of it. Every role's glossary names membership as something
governed outside its own workspace: it is shared, and owned by none of the
roles. This skill is the role-neutral view of that lifecycle.

Assumes `agonara-api-access` for the instance
URL, login, the agonara_session cookie, the X-Agonara-CSRF header on
mutations, and the accepted/rejected/fault envelope. This skill does not
repeat those mechanics.

The shared vocabulary

• Participation kind — student or program_curator. An identity may hold
  either (or neither) in a given program.
• Membership status — active, left, or removed.
• Invitation status — pending, accepted, declined, or revoked.

Read participation

• Your own memberships — GET /program-memberships/me. The programs the
  current identity participates in, with their kind and status.
• Effective participation —
  GET /programs/{programId}/participation/{participationKind} where
  participationKind is student or program_curator. Reads whether
  participation is in effect for the current identity, or for another identity
  via an optional identityId query parameter (reading another identity's
  participation needs the authority the API enforces — honor a rejected
  reason instead of inferring it).
• Membership history — GET /programs/{programId}/membership-events
  (paged via limit/cursor). The audit trail of membership changes;
  available to an Admin or that program's Program Curator.

Your invitations

• List — GET /program-invitations/me, optionally filtered by status
  (pending/accepted/declined/revoked). These are invitations addressed
  to the current Student identity.
• Accept — POST /program-invitations/{invitationId}/acceptance.
• Decline — POST /program-invitations/{invitationId}/decline.

Both actions are mutations: send the session cookie and X-Agonara-CSRF. They
act only on an invitation addressed to you and only while it is pending —
otherwise expect a rejected reason such as invitation_not_found or
invitation_not_pending.

What membership is not

Keep these out of this skill — they belong to a role skill and lean on this
shared model:

• Not curation, and not learning/corpus state. Membership says who
  participates; it says nothing about program content, accepted corpus, checks,
  attempts, or learner progress. Those are a separate concern with their own
  routes.
• Not invitation issuance or participant management — creating, listing, or
  revoking a program's invitations, listing participants, or removing a Student
  belongs to the curator skill.
• Not joining or leaving — a Student joining/leaving a self-join program, or
  a Curator leaving one, belongs to the student / curator skills.
• Not recovery — Admin-only exceptional membership recovery or revocation
  belongs to the admin skill.

If a task is one of these, this skill's job is to recognize it and hand off,
not to perform it.