Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/client-api.md`:
- Around line 2335-2356: The docs for sysMsgData are incomplete and should be
updated to match the runtime payloads exposed by model.MembersAdded and the
member_* shapes. Expand the members_added table to include the missing channels
([ChannelRef][]) and addedUsersCount fields, and add a shared named SysMsgUser
schema for the user object so member_removed and member_left reference it
instead of an inline compound type. Also add JSON examples for members_added,
member_removed, and member_left so clients can parse each payload shape
correctly.

In `@history-service/internal/cassrepo/messages_by_room_integration_test.go`:
- Around line 351-373: The round-trip test for `GetMessagesBefore` only covers
populated `MembersAdded` slices, so it does not verify the empty-array
serialization behavior. Extend `messages_by_room_integration_test.go` by adding
a case around `model.MembersAdded` that uses an empty `Individuals` or `Orgs`
slice, then load it through `repo.GetMessagesBefore` and assert the decoded
slice is non-nil and has length 0. Keep the existing
`model.MessageTypeMembersAdded` and `json.Unmarshal` checks so the test locks
down the schema change for empty collections too.

In `@room-worker/handler_test.go`:
- Around line 4173-4193: The test for publishChannelSysMessages currently only
checks that MessageTypeMembersAdded is not emitted, so it can still pass if
nothing is published at all. Update
TestHandler_PublishChannelSysMessages_EmptySkipsMembersAdded to also assert that
a room_created event is emitted by publishChannelSysMessages for the create-room
path, using the existing published slice and model.MessageEvent checks alongside
the current members_added negative assertion.
- Around line 4116-4171: The tests for publishChannelSysMessages only verify the
populated side of model.MembersAdded and miss the empty-slice contract, so add
assertions in the existing create-room cases to check that users-only publishes
a non-nil empty Orgs slice and orgs-only publishes a non-nil empty Individuals
slice. Use the existing TestHandler_PublishChannelSysMessages_UsersOnly and
TestHandler_PublishChannelSysMessages_OrgsOnly cases, and validate the
unmarshaled payload fields in the same spot where payload.Individuals is already
checked, so regressions to null or omitted empty collections are caught.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@room-worker/handler_test.go`:
- Around line 4107-4156: The add-members sys-msg test in
TestHandler_ProcessAddMembers_RequesterExcludedFromSysMsg should also verify the
empty Orgs contract. Extend the payload assertions after unmarshalling
model.MembersAdded to check that payload.Orgs is non-nil and empty, matching the
same nonNil serialization behavior already covered in the
PublishChannelSysMessages tests. This keeps the processAddMembers path aligned
with the existing members_added payload contract alongside Individuals and
Channels.
- Around line 4252-4275: The test in
TestHandler_PublishChannelSysMessages_OrgsOnly hard-codes the added users count,
which leaves the emitted sysmsg payload field unverified. Replace the fixed
value passed into publishChannelSysMessages with a scenario-derived count, or
add an assertion on payload.AddedUsersCount after unmarshalling the MembersAdded
payload, so the test checks the actual value written by
Handler.publishChannelSysMessages.

---

Nitpick comments:
In `@room-worker/handler_test.go`:
- Around line 4032-4306: The add-member and channel sys-message tests repeat the
same controller/store/published-handler setup, so extract that boilerplate into
a shared helper like the existing create-room test helper. Add a helper near
these tests that builds the gomock controller, NewMockSubscriptionStore,
published slice, and Handler with the common siteID/keyStore/keySender wiring,
then update the affected tests to use it so future add/remove-member cases stay
consistent and easier to maintain.