per-chat-config

name	per-chat-config
description	Add a per-chat configurable knob (spam_threshold, report_hour, captcha_difficulty) — migration → ChatConfig struct → API DTO → transactional update endpoint.

Per-Chat Config (Vixen server)

Read first:

• server/docs/database.md — chat_config schema.
• server/docs/config.md — knob registry.
• server/docs/rules/api-routes.md — endpoint conventions.
• server/docs/rules/migrations.md — schema bump rules.

Steps

1. Migration: ALTER TABLE chat_config ADD COLUMN {name} {type} NOT NULL DEFAULT ... plus matching .down.sql. If the column is NOT NULL and existing rows must take a non-default value, backfill with an UPDATE in the same migration.
2. Update ChatConfig in server/src/models/chat_config.rs and DTO in server/src/api/dto.rs.
3. Expose PATCH /api/v1/chats/{chat_id}/config in server/src/api/routes_config.rs. Validate the moderator's chat scope server-side — don't trust the JWT's chat_ids claim alone.
4. Inside the handler:

let mut tx = state.pool.begin().await?;
let cfg: ChatConfig = sqlx::query_as!(ChatConfig,
    "SELECT * FROM chat_config WHERE chat_id = $1 FOR UPDATE", chat_id)
    .fetch_one(&mut *tx).await?;
sqlx::query!("UPDATE chat_config SET {name} = $1 WHERE chat_id = $2", value, chat_id)
    .execute(&mut *tx).await?;
tx.commit().await?;

5. If cache-dependent (e.g., spam_weights cached in Moka), invalidate by chat_id key after commit.
6. Update server/docs/database.md (schema row) and server/docs/config.md (knob table).

Gotchas

• Transaction is not optional. Concurrent moderator changes race otherwise — read-modify-write outside a transaction loses writes.
• Server-side moderator check is mandatory. chat_id in the path is attacker-controlled; the JWT only proves the user is some moderator somewhere.
• NOT NULL + existing rows requires a DEFAULT in the ALTER or a backfill UPDATE in the same migration.
• Validate value range (spam_threshold ∈ 0..=100, report_hour ∈ 0..=23) before UPDATE. Return AppError::BadRequest with a useful message.
• Cache invalidation is manual. Document in server/docs/config.md which knobs are cached and which aren't.
• Telegram IDs i64. chat_id BIGINT everywhere.

Verification

• cargo sqlx prepare --check.
• cargo test config_update — happy path + concurrent-write test.

Related

• add-migration — schema-bump conventions.
• add-api-route — middleware stack and OpenAPI.
• transaction-discipline — FOR UPDATE patterns.