2. Constraints

Technical constraints

Constraint	Background
PyMammotion is the only mower protocol implementation	The Mammotion protocol is unofficial; a firmware update can break features at any time. Pin the version and update firmware only after community feedback.
Bluetooth is the default link	WLAN control is announced but not available. Bluetooth runs through an ESP32 bridge that connects outbound to the Device-Gateway.
Python 3.13	One language for services, PyMammotion (requires 3.13 or newer) and Home Assistant. See ADR 0010.
PostgreSQL only	No SQLite (see ADR 0006).
Only portable open components	PostgreSQL, S3-compatible storage, OIDC, NATS. No provider-specific cloud services.
Images for amd64 and arm64	Mini PC, Raspberry Pi 5 and cloud.

Organizational constraints

Constraint	Background
Licensing	AGPL-3.0 for services and apps, Apache-2.0 for libraries (ADR 0005).
Language	All code, comments, commits and documentation are English; UI is German by default plus English.
Process	One task at a time, each with tests and README; definition of done includes docs and ADRs.
Terms of use	Uncritical for personal use; review before redistribution or commercial use.

Conventions

• Twelve-factor style: configuration and secrets only via environment variables or secret files, never in images.
• Stateless services, structured logs on stdout, health/readiness/liveness endpoints, graceful shutdown.
• Database migrations (Alembic) run as a separate step before start and stay backward compatible.
• Contracts only evolve backward compatibly; events are never reinterpreted, new versions are added instead.

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