social-app/backend/AGENTS.md

# Backend Domain Rules

This file governs `backend/**` only. Keep it minimal, enforceable, and non-duplicative.

## Scope & Precedence

- Inherits root `AGENTS.md` and workspace runtime rules.
- If rules conflict, apply the stricter one.
- Keep backend-only constraints here; do not duplicate root routing logic.

## Runtime & Commands

- Python commands must use `uv` (`uv run`, `uv add`).
- Backend startup/shutdown must use `./infra/scripts/app.sh`.
- Check runtime logs from `./logs/*.log`.

## Code Quality Baseline

- Do not bypass lint/type gates (`ruff`, `basedpyright`).
- Use project logging (`core.logging`), never `print()` in runtime code.
- HTTP errors must follow RFC 7807 (`application/problem+json`).

## HTTP Error Contract (Must)

- Backend must construct error payload using RFC7807 fields plus stable extension fields: `code` and optional `params`.
- `code` must be machine-readable `UPPER_SNAKE_CASE`; do not use free-text `detail` as the only contract.
- Error code registry source of truth: `docs/protocols/common/http-error-codes.md`.
- Any create/modify/deprecate of error codes must update `docs/protocols/common/http-error-codes.md` in the same change.
- Keep response media type as `application/problem+json`.
- Long-term layering target: HTTP transport details stay in routers/global handlers; service/repository/dependencies should raise domain errors (`ApiProblemError` or domain-specific exceptions), not `HTTPException`.
- When refactoring existing code, prefer replacing `HTTPException` in service/repository/dependencies with `ApiProblemError` while preserving status/code semantics.

## Configuration & Secrets

- Read env only through `core.config.settings` (`Settings` / `config`).
- Do not use `os.getenv`/manual env parsing in backend runtime.
- Never hardcode keys/tokens/passwords.

## Architecture Rules

- Use `schema -> repository -> service` layering.
- Repository: CRUD + query composition only; no auth decisions, no transaction boundary.
- Service: authz + business logic + transaction boundary.
- `owner_id` must come from verified JWT (`sub`), never from client payload.

## Schema & Contract Rules

- Schema-first for new/changed data contracts.
- Strong typing required at boundaries (Pydantic/dataclass); avoid weak untyped payload contracts.
- Protocol/data contract changes must stay aligned with `docs/protocols/`.

## Database Rules

- Supabase Auth is identity source; backend enforces business authorization.
- Use service-role DB access only in backend.
- Soft delete uses `deleted_at`; reads must exclude deleted records by default.
- Alembic is the only schema migration source of truth.
- Database migrations use `./infra/scripts/dev-migrate.sh`:
  - `migrate` - run migrations only
  - `init-data` - seed data only
  - `bootstrap` - migrate + init-data

## Agent Runtime & Tools

- AG-UI protocol is mandatory for agent loop behavior.
- `ToolAgentOutput.result` is the canonical tool result field.
- Tool results must be machine-oriented and include IDs/outcomes needed for chaining.

## Tool Schema Rules for Small Models (e.g., qwen3.5-flash)

- Prefer `operations: list[OperationModel]` over parallel arrays.
- Validate tool args with strict Pydantic models (`extra="forbid"`).
- Keep payloads JSON-native (objects/lists), shallow, and deterministic.
- Make action-specific required fields explicit and fail with structured errors.
- Return per-item outcomes (`success/failed`, identifiers, partial status) for self-correction.
- Avoid broad entry-point coercion fallbacks; fix schema/prompt alignment first.
- Do not pass provider request fields with `None` values (avoid upstream 400 blocking tool calls).

## Testing

- Follow TDD for feature/bugfix work when practical.
- Prioritize regression tests for changed logic/contracts.
- Real DB tests must use `settings.test.*`; never hardcode test credentials.