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🤖 ## Summary This PR fixes two ways the relay could report a channel change that did not fully happen. **1. Channel settings could be saved only in part, while the app was told that they all worked.** When an owner or admin changed a channel's settings (name, description, topic, public or private, message lifetime, archived or not, who can join), the relay saved the request first and then applied each setting with its own database write. If one write failed, the relay only logged the error. It skipped the remaining settings and still reported success. Sending the request again did nothing, because the relay saw it as already saved. Example: a switch from public to private could fail while the app showed success, and the channel stayed public. Now saving the request, applying every setting and saving the "settings changed" messages in the channel happen in one database transaction. Either all of it is saved or none of it is: - If anything fails, nothing is saved and the client gets an error. It can send the same request again. - A repeat of a request that already succeeded is reported as a duplicate and changes nothing. This is also true when the repeat arrives while the first copy is still being saved. - A request to restore a channel that is not archived, or to change an archived channel without restoring it, is refused and nothing is saved. Before, the relay saved the request and a "settings changed" message, and then the restore failed. - Live updates go out only after the save commits. These are: removing access for people who lose it, and pushing the new messages and channel info to clients. **2. A published member list could include someone who had just been removed.** For some channels the relay publishes a list of the channel's members. While it builds that list, it holds a per-channel membership lock. Kicks by a relay admin and the automatic kick after a deploy did not take that lock. A kick could commit after the list was read, so the published list still showed the removed member. Channel deletion also did not wait for the lock. Kicks, channel deletion and the automatic add when someone joins a Huddle (voice call) now all take the lock first. The published list then includes the change, or the change waits until the list is saved. ## Details - **One lock order for all channel settings writes.** Before, each writer took its own locks. Review kept finding writers that took them in a different order or forgot one. `lock_channel_for_settings_write` (`crates/buzz-db/src/store/channel.rs`) is now the only place that takes them. The order is: 1. the membership lock, only when the public/private setting or the "who can join" setting (`join_role`) changes. Without it, a member add could read the old rule while the change commits. 2. the message-lifetime (TTL) lock: exclusive for a lifetime change, shared otherwise. 3. the channel row (`FOR NO KEY UPDATE`). This does not block the key lock that a member insert takes. The row lock also orders two copies of the same request, so the second copy sees the first as already stored. - The function returns a `ChannelSettingsWriter`. The writer borrows the transaction that took the locks, so the compiler stops it from being used with another transaction or after commit. The settings writes (`update_channel_on`, `set_topic_on`, `set_purpose_on`, `set_archived_on`) require the writer. They refuse a change its locks do not cover. - `Db::apply_channel_metadata_event` stores the channel-edit event (kind:9002) and its mentions, applies the settings and stores the "settings changed" messages (kind:40099) in one transaction. The older single-purpose writes (`update_channel`, `set_topic`, `set_purpose`, `archive_channel`, `unarchive_channel`) use the same helpers and behave as before. - `ingest.rs` and `validate_admin_event`: channel edits no longer check archived/active state before the write. The transaction checks it after its duplicate check, under the row lock. A refusal there goes back to the client as `invalid:`. Channel edits have their own save path and skip the general post-save step. `handle_side_effects` refuses them, so no caller can go around the transaction. - `side_effects.rs`: `emit_system_message` is split into signing and sending. The messages are signed before the transaction and sent after it. All "settings changed" messages from one edit share one timestamp and come in a fixed order (topic, purpose, visibility, lifetime, archive). - A change to "who can join" (`join_role`) is applied in the same transaction and announced with its own `join_role_changed` message. - **Membership lock outside settings** (`relay_admin_actions.rs`, `channel_members.rs`, `audio/handler.rs`): both kick paths (`execute_kick_with_marker`, `deploy_kick_member`) take the membership lock before they remove the member. The marker kick still undoes the removal if its lease check fails after waiting. The Huddle join takes its locks through a new `ChannelMembershipLocks` token, and the auto-add is a method on that token, so it cannot run without the lock. `soft_delete_channel` takes the full settings lock order. - **Limit of the membership lock:** it covers member changes, public/private and "who can join" changes, and channel deletion. It does not cover archiving: archive writes and the cleanup of expired temporary channels do not take it. The cleanup keeps its single UPDATE. A comment in `channel.rs` explains why that is safe and why it must not be split into a read and a write. ### Related issue Follow-up to the review of #8143 (which added the "who can join" setting). That review found that channel edits could be applied in part. No separate issue. ### Testing New PostgreSQL tests in `crates/buzz-relay/src/handlers/edit_metadata_postgres_tests.rs`: - `failed_edit_stores_nothing`: a test trigger makes one write fail partway through the transaction. Nothing is stored or changed, on the first send or a resend. Without the trigger, the same signed request applies in full. - `resent_edit_is_a_duplicate`, `resent_archive_and_unarchive_are_duplicates`: a resend after success is a duplicate and adds nothing. - `resend_validated_after_the_first_commit_is_a_duplicate`: a resend validated after its first copy committed is a duplicate, with no second change and no second message. - `concurrent_copies_of_a_restore_apply_once`: two copies of one restore, held at the channel lock until both are waiting, apply once. The other copy is a duplicate. - `unarchive_of_an_active_channel_is_refused`, `join_role_edit_is_applied_and_announced`. Lock tests in buzz-db: each one holds a member list in progress and checks that the writer waits for it. They cover a "who can join" change (`channel_members.rs`), the deploy kick and the marker kick (`relay_admin_actions.rs`), and channel deletion (`channel.rs`). The kick and delete tests fail when the new locks are removed. These tests and the existing channel-edit tests in `group_state_postgres_tests` pass locally against a migrated PostgreSQL database. --------- Signed-off-by: Logan Johnson <loganj@squareup.com> Co-authored-by: Larry <627498bd4bd1f281a16431e3c6cce3b5c25b6692798c78672298aefbf2f8f8b5@buzz.block.builderlab.xyz>