Phase 3: rooms, local only

Implements PLAN.md Phase 3: the roomserver, the room half of storage, the
Client-Server room endpoints and the admin room endpoints. A client can now
create a room, invite, join, leave, kick, ban, send messages and state,
redact, name a room with an alias and find one in the public directory.
Nothing talks to another server; every operation that would need to is
refused with a message that says so rather than a bare M_FORBIDDEN.

roomserver: one input pipeline every event goes through, whatever sent it —
validate, authorise, resolve, persist, emit. The rules are not
reimplemented here; internal/matrix is pure library code and this is what
connects it to a database and to a room's history. The Client-Server
handlers do no authorisation of their own, deliberately: whether Alice may
kick Bob is a question about the room's power levels, and the one place
that is answered correctly is the authorisation rules inside the pipeline.

A mutex per room serialises writers. Two events racing into one room would
each read the same forward extremities, both become one, and fork the room
for no reason — which would then need state resolution to put back
together. State resolution is wired in anyway for the multi-extremity
case. It is unreachable from outside in this phase, and the alternative is
a pipeline that authorises against one arbitrary branch of a fork without
saying so.

Room versions 3 to 12 all work and are each tested end to end. Version 12
earns that coverage: its room ID is the create event's own ID, its create
event carries no room_id, and the create event is excluded from every other
event's auth_events — so the state auth.Check is given is the event's
auth_events plus the create event, which that version identifies by room ID
rather than citing.

createRoom sends the spec's events in the spec's order, each authorised
against what the ones before it produced. A failure part-way leaves an
incomplete room, which is the lesser evil: the alternative is holding every
event of a new room in memory and writing them in one transaction, making
the pipeline that authorises them a special case. The one failure a second
client can cause at any time, an alias clash, takes the room row back out.

Redactions stay two decisions, as the spec keeps them. The rules let almost
any redaction into the room; whether it applies to its target is a separate
test, run inside the same transaction as the redaction itself so that a
client holding an event ID can always read the stripped event.

storage: events keyed by event ID rather than by a surrogate, since an
event ID appears in prev_events, auth_events, state snapshots and client
requests alike. Stream ordering comes from a counter row bumped inside the
write transaction, because a PostgreSQL sequence is explicitly not
transactional and a rolled-back write would leave a hole in the stream that
/sync would have to be taught to skip. State snapshots are stored per event
and deduplicated by content hash, so the table grows with state changes
rather than with traffic — and that is what makes "the state after a
forward extremity" answerable at all. The room's listing columns are
denormalised onto its row because the public directory orders every
published room by member count and pages the result, which cannot be done
by reading each room's state in turn.

Federation-disabled behaviour from PLAN.md section 3 is enforced here.
Restricted joins are the exception that works: the rule needs a signature
from the authorising user's server verified, and while federation is off
that server is always this one.

adminapi: room list and detail, purge, force-leave, and room and event
counters on the dashboard. clientapi gains its own rate-limit buckets for
createRoom and for joining, both of which write events rather than read
them.

Tested against the real event core and a real database rather than fakes:
what is under test is whether an event this server signs is one the
authorisation rules accept, and a fake of either would only prove that the
pipeline calls what the fake expects. The storage tests run against both
SQL drivers. docs/rooms.md describes the pipeline, the storage decisions
and the known gaps — chief among them that history visibility is
room-level rather than per-event, and that /sync still reports no rooms,
both of which belong with the event stream in Phase 4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/admin-api.md

@@ -101,6 +101,94 @@ the admin's own action, not a public sign-up. `username` is normalised
 (lower-cased) like any other localpart. A taken name is
 `400 M_USER_IN_USE`, an unusable one `400 M_INVALID_USERNAME`.
 
+### `GET /rooms`
+
+```
+GET /rooms?search=ops&limit=50&offset=0
+```
+
+Ordered by joined-member count, biggest first, then by room ID — the second
+key is not decoration, because paging an order that is not total can show
+the same room on two pages and skip another, and ties in member count are
+the common case. `search` matches a substring of the room ID, name, topic or
+canonical alias, case-insensitively.
+
+```json
+{
+  "rooms": [
+    {
+      "room_id": "!abc:warp.example",
+      "room_version": "11",
+      "creator": "@alice:warp.example",
+      "name": "Operations",
+      "topic": "Ops chat",
+      "canonical_alias": "#ops:warp.example",
+      "join_rule": "public",
+      "history_visibility": "shared",
+      "guest_access": "forbidden",
+      "published": true,
+      "joined_members": 12,
+      "created_at_ms": 1760000000000
+    }
+  ],
+  "total": 1,
+  "limit": 50,
+  "offset": 0
+}
+```
+
+Everything after `creator` is read from the room's current state and kept in
+the room's own row. That is denormalisation on purpose: this listing and the
+public room directory both order every room by member count and page the
+result, which cannot be done by reading each room's state in turn.
+
+### `GET /rooms/{roomID}`
+
+The list row plus the things only a count can answer.
+
+```json
+{
+  "room_id": "!abc:warp.example",
+  "members": 15,
+  "invited_members": 2,
+  "joined_members": 12,
+  "aliases": ["#ops:warp.example"],
+  "forward_extremities": ["$sPfXR..."]
+}
+```
+
+`members` counts every `m.room.member` event in the current state whatever
+the membership, because a room with one member and forty bans is not the
+same room as one with a single member. `forward_extremities` is where the
+room's DAG ends; there is normally exactly one, and more than one means the
+room has forked.
+
+### `DELETE /rooms/{roomID}`
+
+Purges the room: its events, its state, its aliases and its row. There is no
+undo and the members are not told — the only way to tell them would have
+been to add an event to a room that no longer exists.
+
+It is a `DELETE` on the room rather than a `POST` to an action because that
+is what it is, and because the method makes a panel's confirm dialog
+mandatory in a way a `POST` does not. Purging a room that is not there is
+`404`, not a silent success: an operator who sees an `OK` has to be able to
+believe the room was there.
+
+### `POST /rooms/{roomID}/force_leave`
+
+```json
+{"user_id": "@alice:warp.example"}
+```
+
+Makes a user leave without asking the room's rules whether they may. A user
+stuck in a room — one whose power levels are broken, or whose last moderator
+has gone — is what this exists for, and in such a room the rules are exactly
+what is in the way. It is still an ordinary membership event, signed and
+added to the room, so the other members see what happened.
+
+A user who is not in the room gets `403`: there is nothing to leave.
+
 ### `GET /stats`
 
 The dashboard payload.
@@ -114,13 +202,16 @@ The dashboard payload.
   "admins": 1,
   "deactivated": 0,
   "devices": 19,
+  "rooms": 4,
+  "published_rooms": 1,
+  "events": 312,
   "federation_enabled": false,
   "registration_enabled": false
 }
 ```
 
-Room and event counters join it in Phase 3, when there is something to
-count.
+The three room counters are zero on a server that started without a signing
+key, which has no roomserver and so no rooms.
 
 ## Errors
 
@@ -134,4 +225,11 @@ configuration is what refuses it.
 Phase 9 completes the admin API: deactivating users, resetting passwords,
 revoking devices, granting the admin flag, registration token management,
 the federation allow/deny list editor, server notices, media quotas and an
-audit log of admin actions. Rooms arrive with the roomserver in Phase 3.
+audit log of admin actions.
+
+The room endpoints will grow with it: a room's state and its recent events
+for an operator looking at a report, and a way to publish or withdraw a room
+from the directory without borrowing a member's token.
+
+A server started without a signing key has no roomserver, and the four room
+endpoints then answer `503` rather than failing on the first call.