curriculum-project-hub/docs/adr/0028-member-group-management-and-resolution.md

# ADR 0028: Member Group Management And Resolution

## Status

Accepted.

## Context

ADR-0020 fixed `Organization` as the tenant root and ADR-0019 pinned the
principal-set permission model. The file library (《文件库-接口契约.md》) computes
effective permission over two principal kinds — `USER` and `GROUP` — and consumes
the group side through a single read-only port, `GroupResolver`
(`resolveMemberGroupIds(userId) → groupIds[]`, contract C2/G2).

The contract's v0.1 proposal framed the Group system as a *separate HTTP service*
owned by another team, consumed read-only. In practice the schema now carries the
group tables directly in the hub database (`MemberGroup`, `MemberGroupMembership`,
`MemberGroupClosure` — a global, unlimited-depth, closure-backed hierarchy), and
the product requirement is to build **group management in the backend admin**, not
to integrate a foreign service. Until this ADR, nothing read or wrote those tables:
the live `GroupResolver` was a transitional implementation reading flat hub `Team`
membership, and the admin "Group 管理" panel actually managed `Team`.

This ADR settles the semantics needed to make the `MemberGroup` tables the real,
in-hub group system.

## Decision

### Group system is in-hub, not a foreign service

`MemberGroup` is the platform's global member-group principal. It lives in the hub
database and is managed through the `/database` backend. The contract's "separate
service" framing was an unfrozen v0.1 proposal; the implementation aligns to the
tables that were actually built. The `GroupResolver` port stays — an external
`HUB_GROUP_SERVICE_URL` HTTP implementation remains a supported override — but the
default implementation reads the in-hub `MemberGroup` closure.

### Authority: website administrator only

Group create/delete and member add/remove are restricted to the **website
administrator**, defined (consistently with the rest of the file library, D19/C4
adaptation) as an `OWNER`/`ADMIN` of the silo Organization (`isWebsiteAdmin` in
`filelib/guards.ts`). ADR-0023's `PlatformIdentity` is the future "true" platform
control plane; the file library uniformly uses org OWNER/ADMIN today and this
feature stays consistent with that. Reading groups for the authorization selector
(`/groups/search`) is **not** admin-gated — picking a group to grant is a Manage
holder's ability, not an administrator's.

### Resolution semantics (the crux)

`resolveMemberGroupIds(user)` returns the user's **active direct groups ∪ the
active ancestors of those groups**, deduplicated (the closure's depth-0 self row
makes each direct group its own ancestor). This is the single query the permission
engine relies on; equivalently: a grant placed on group G applies to members of G
and of every descendant of G (requirement 3.2 — permission flows down the tree, so
resolution collects up the tree). It is computed **live, never cached** (contract
D4/G4): a membership change is visible on the very next protected request.

MemberGroup is global (no `organizationId`), so resolution is not org-scoped.

### Soft delete via `archivedAt`, cascading the subtree

Delete is soft: `MemberGroup.archivedAt` is a tag. Deleting a group
cascade-soft-deletes its **whole subtree** (walk `MemberGroupClosure` where
`ancestorId = G`, stamp `archivedAt` on each active descendant) — an application
operation, not a DB constraint. Closure and membership rows are **retained**;
resolution and listing filter by `archivedAt`, so an archived group and everything
under it stop contributing to permission at once.

### Closure maintenance

The closure is maintained on **create**: insert `(G, G, 0)`, then for a parent `P`
insert `(a.ancestorId, G, a.depth + 1)` for every `a` in
`closure where descendantId = P`. v1 does **not** support reparenting a group
(moving it under a new parent). The schema reserves reparent (closure rebuild plus
the cycle guard "reject a new parent inside the moved subtree"); it is a follow-on.

### Rename and description edits are in scope; reparent stays out

A group's `name` and `description` are mutable by the website administrator
(`PATCH /database/api/groups/:id`, audited as `group.update`). This is deliberately
separated from reparent: renaming touches **no** closure row and cannot create a
cycle, so it carries none of the invariant risk that keeps reparent out of v1. The
endpoint therefore **rejects** a `parentId` field outright rather than ignoring it,
so a future reparent cannot arrive silently through this route. Passing an empty
`description` clears it; omitting a field leaves it unchanged.

### Restore is deliberately asymmetric with delete

Archived groups stay visible to the administrator (`GET
/database/api/groups?includeArchived=1` returns them carrying `archivedAt`; the
console tags and greys them) and can be restored (`POST
/database/api/groups/:id/restore`, audited as `group.restore`).

Restore is **not** the mirror image of delete. Delete cascades down the whole
subtree; restore un-archives **the group plus every archived ancestor of it, and
nothing below it**:

- Restoring the ancestor chain is **mandatory**, not a convenience. An active group
  whose parent is archived has no path in the tree, and the `depth` derivation
  (closure row count) presumes "an active group's ancestors are active" — the
  invariant that cascade-delete establishes. Restoring a node alone would break it.
- The subtree is deliberately **left archived**. A group's descendants may have been
  archived for reasons of their own, and one click should not silently re-grant
  permission across a whole historical branch. Descendants remain visible in their
  archived state and are each restored explicitly.

Restore takes effect immediately, like every other membership change (D4/G4): the
group resumes contributing permission on the next resolution.

An archived group is **readable but not writable**. Its membership rows are never
revoked by archiving, so `listMembers` succeeds on an archived group — the console
must be able to show *who was in it* before deciding whether to restore it. Every
mutation, by contrast, still requires an active group (`requireActiveGroup` → 404):
rename, child creation, and member add/remove all reject. The group is inert for
permission purposes and frozen for editing, but not hidden and not forgotten.

### Member picker reads global users, admin-only

`GET /database/api/users/search` backs the "add member" picker: it matches `User`
by display name or Feishu open id and is gated to the website administrator, the
same authority that may add members. It widens no existing capability — adding a
member already accepts **any** global user (`resolveUser` does not require an org
membership), so the endpoint only replaces blind id entry with search. It is
deliberately **not** opened to the non-admin authorization-selector audience that
`/groups/search` serves: choosing a group to grant is a Manage-holder action,
whereas enumerating people is not. `excludeGroupId` filters out the target group's
active members so the picker cannot surface a candidate that must 409.

### Audit is written in-hub

The contract (C3 §6.3) originally deferred group actions to the foreign Group
service's own audit. With the group system in-hub, group mutations are audited
through the existing file-library sink (`filelib/audit.ts`, same-transaction
`AuditEntry`) under the silo Organization — `MemberGroup` has no `organizationId`,
so the audit row is attributed to the silo org. New actions: `group.create`,
`group.update`, `group.delete`, `group.restore`, `group.member_add`,
`group.member_remove`; new audit object type `group`.

## Consequences

- The default `GroupResolver` becomes the in-hub `MemberGroup` closure reader.
  `createTeamGroupResolver` is retained but deprecated (no longer wired); existing
  flat-Team group grants no longer resolve for the file library.
- Group grants take effect in real time through the existing `effectiveRole`
  reducer (P6) with no change to the permission algebra — only the set of group ids
  fed to it changes.
- v1 omits reparent; the closure invariants above must hold whenever reparent is
  added later (rebuild descendants' ancestor rows, reject cycles).
- Group management is an admin-only surface; the authorization selector is not.
- Numeric limits (max depth, max members) and a hard-delete/restore path remain
  follow-on operational decisions; they must not weaken the archived-filter,
  admin-authority, or live-resolution invariants fixed here.