[ariwired]

Closes #1

Required to close this issue

This PR closes #1 only when every item below is checked. Items stay unchecked until the command was actually run.

Tasks

• Create the backend/ directory. Evidence: backend/ in the file tree of this PR.
• Configure Python dependency management. Evidence: backend/pyproject.toml and backend/uv.lock.
• Create the visual_graph package. Evidence: backend/src/visual_graph/ with api, domain, spatial, graph and vision subpackages.
• Create the application entry point. Evidence: create_app() in main.py, the visual-graph console script and __main__.py.
• Create the initial test structure. Evidence: backend/tests/ with unit, api and integration folders.
• Configure basic development dependencies. Evidence: dev group in pyproject.toml (pytest, pytest-cov, Hypothesis, httpx, Ruff, mypy).
• Verify that the application can be imported and executed locally. Evidence: outputs in the Evidence section below.

Acceptance criteria

Criterion	Verified by
The backend can be installed locally	uv sync
The visual_graph package can be imported successfully	uv run python -c "import visual_graph"
A basic application entry point exists	uv run visual-graph, then GET /health/live returns {"status":"ok"}
The test directory is recognized by the test runner	uv run pytest collects and passes the tests
Dependencies are reproducible from the project configuration	uv sync --locked passes and the Backend CI check is green

Evidence

Install:

Import:

Tests:
<paste the uv run pytest --cov=visual_graph output>

Lint and types:

Entry point:
<paste the curl response from http://127.0.0.1:8000/health/live>

CI: see the Backend CI check on this PR.

What changed

• Python backend under backend/ using a src layout, managed with uv and a committed uv.lock
• App factory create_app() with the first endpoint, GET /health/live
• Settings loaded from the environment with pydantic-settings
• Tests organized as unit, api and integration, with the integration and inference markers excluded by default
• Backend CI workflow running Ruff, mypy and pytest on changes to backend/

Design notes

• The app is created by a factory, not at import time, so tests can import the module without required settings. Uvicorn runs it with the factory option.
• The domain and spatial packages are reserved as pure Python, with no FastAPI, Neo4j or torch imports, to keep the geometric engine testable in isolation.
• Neo4j, image handling and the detector are not included. Each is added by the issue that needs it.

Out of scope

Neo4j connection, /health/ready, domain models, object detection and the frontend.