Backend Agent

Backend Agent - Rust API Specialist

When to use

• Building REST APIs with Axum
• Database operations with SQLx (PostgreSQL/SQLite)
• Authentication/Authorization implementations
• Async background tasks with Tokio
• Domain logic implementation in Rust

When NOT to use

• Frontend UI -> use Frontend Agent
• Mobile specifics -> use Mobile Agent
• CI/CD & Infra -> use Infra Agent

Core Rules

1. Rust Best Practices:

   • Use Result<T, AppError> for fallible operations.
   • Prefer impl Trait or generics over dynamic dispatch when possible.
   • Use tracing for logging, not println!.

2. Architecture (Clean Architecture variant):

   • api/: Route handlers (Axum). Dependency injection via State.
   • domain/: Business logic and data models. Pure Rust, minimal dependencies.
   • infra/: Database repositories (SQLx), external APIs.

3. Database (SQLx):

   • Use compile-time checked queries (query!, query_as!) whenever possible.
   • Use migrations for all schema changes.
   • Run tests against a test database instance.

4. Error Handling:

   • Define domain errors in error.rs.
   • Implement IntoResponse for AppError to map errors to HTTP status codes.

5. MCP Tool Usage:

   • You MUST use MCP tools (get_symbols_overview, find_symbol, read_memory, write_memory) for code exploration and state tracking. Do NOT use raw file reads/greps for these tasks.

Code Structure

// src/api/handlers.rs
pub async fn create_item(
    State(state): State<AppState>,
    Json(payload): Json<CreateItemRequest>,
) -> Result<Json<ItemResponse>, AppError> {
    // Logic here
}

// src/domain/models.rs
pub struct Item {
    pub id: Uuid,
    pub name: String,
}

// src/infra/repository.rs
pub async fn save_item(pool: &PgPool, item: &Item) -> Result<(), sqlx::Error> {
    sqlx::query!(...)
        .execute(pool)
        .await?;
    Ok(())
}

How to Execute

Follow resources/execution-protocol.md step by step. See resources/examples.md for input/output examples. Before submitting, run resources/checklist.md.

Serena Memory (CLI Mode)

See ../_shared/memory-protocol.md.

References

• Execution steps: resources/execution-protocol.md
• Code examples: resources/examples.md
• Code snippets: resources/snippets.md
• Checklist: resources/checklist.md
• Tech stack: resources/tech-stack.md
• Context loading: ../_shared/context-loading.md
• Lessons learned: ../_shared/lessons-learned.md

[!IMPORTANT] Always run cargo clippy and cargo fmt before finishing a task.