Hass Declarative

HA Declarative Entity Management

All HA automations, scenes, and scripts are defined in Nix under modules/services/hass/_domains/. A post-deploy sweep service removes anything not in the declared set.

Architecture

_lib.nix                       ← shared helpers (ensureEnabled)
_domains/                      ← domain files (Nix modules)
  ambient.nix                  ← lighting schedules, plant lights
  aranet.nix                   ← CO2 monitoring
  conversation.nix             ← voice intents
  lighting.nix                 ← adaptive lighting, AL sleep mode
  modes.nix                    ← DND, guest mode, everything_off script
  sleep/default.nix            ← bedtime flow, wake detection, 8Sleep sync
  tv.nix                       ← TV idle timer, sleep timer
  vacation.nix                 ← presence-based vacation mode

sweep-unmanaged.nix            ← extracts declared IDs at build time
sweep-unmanaged.py             ← runtime: removes orphans via WS API
_tests/eval-automations.nix    ← structural assertions (flake check)

Entity Identity

How HA maps Nix config → entity registry:

Scene slugs: HA lowercases the name and replaces spaces/hyphens with underscores. Keep names ASCII-alphanumeric + spaces to avoid slug surprises.

Adding Entities

Automation

Add to the automation = lib.mkAfter (ensureEnabled [...]) list in the appropriate domain file. Every automation must have a unique id field — the sweep service uses it.

Always wrap with ensureEnabled (from _lib.nix) — it injects initial_state = true so automations re-enable on HA restart. Without it, HA silently persists "off" state from the entity registry and automations stay disabled forever. The eval test catches missing wrappers at build time.

{ lib, ... }:
let
  inherit (import ../_lib.nix) ensureEnabled;
in {
  services.home-assistant.config.automation = lib.mkAfter (ensureEnabled [
    {
      alias = "Human-Readable Name";
      id = "unique_snake_case_id";
      description = "What it does";
      trigger = { platform = "time"; at = "22:00:00"; };
      condition = [];
      action = [{ action = "scene.turn_on"; target.entity_id = "scene.foo"; }];
    }
  ]);
}

Individual automations can override with initial_state = false if ever needed (the // merge gives right-hand precedence), but we never want this in practice.

Scene

Add to scene = lib.mkAfter [...]. Scenes use name as their identity.

{
  name = "My Scene";
  icon = "mdi:icon-name";
  entities = {
    "light.some_light" = "on";
    "switch.some_switch" = "off";
  };
}

Script

Add to script = lib.mkAfter {...} (attrset, not list). The attribute key becomes the entity_id.

my_script_key = {
  alias = "Human Name";
  icon = "mdi:icon";
  sequence = [{ action = "light.turn_off"; target.entity_id = "light.foo"; }];
};

Or directly on config: script.my_key = {...}; (as in modes.nix).

Removing Entities

1. Delete from the domain .nix file
2. Deploy (hey nuc)
3. hass-sweep-unmanaged service auto-removes the orphan from HA's entity registry

No manual cleanup needed. Check sweep results:

hey nuc-service hass-sweep-unmanaged
ssh nuc "sudo journalctl -u hass-sweep-unmanaged --no-pager -n 30"

Sweep Service

sweep-unmanaged.nix creates a systemd oneshot that runs after HA starts.

Build time: Evaluates NixOS config to extract:

• automation_ids — from haConfig.automation[].id
• scene_entity_ids — from haConfig.scene[].name → scene.<slug>
• script_entity_ids — from haConfig.script keys → script.<key>

Writes these to a JSON manifest in the Nix store.

Runtime (sweep-unmanaged.py):

1. Waits for HA to be ready (120s timeout)
2. Connects via WebSocket, authenticates with agent-automation JWT
3. Lists all entity registry entries
4. For each automation.* / scene.* / script.* not in the manifest:
   • Checks platform to avoid removing integration-created entities
   • Removes from entity registry via config/entity_registry/remove
5. Wipes UI YAML files (automations.yaml, scenes.yaml, scripts.yaml)

Platform filtering (safety):

• Automations: only removes platform = "automation" (YAML-sourced)
• Scenes: only removes platform = "homeassistant" (YAML-sourced)
• Scripts: only removes platform = "script" (YAML-sourced)
• Integration-created entities (Ecobee scenes, etc.) are never touched

Eval Test Assertions

_tests/eval-automations.nix runs as nix flake check and pre-commit hook. Tests structural properties:

• Every automation has initial_state = true — catches missing ensureEnabled wrappers
• Required automations/scenes exist
• Time guards present on wake detection (the "4:47 AM fix")
• Good Morning has presence-aware conditions
• Winding Down resets awake booleans

Add assertions when adding automations with critical invariants.

initial_state enforcement

The initial_state assertion is global — it iterates all automations in the final merged config. No per-automation opt-in needed. If you add an automation anywhere without ensureEnabled, the build fails:

automation 'My Thing' missing initial_state = true (use ensureEnabled from _lib.nix)

Why this matters: HA's initial_state defaults to "restore from entity registry." If an automation was ever toggled off in the UI (or the registry entry drifts), it stays off across restarts — silently. With configWritable = false, the UI toggle is especially dangerous since there's no way to re-enable it without redeploying. ensureEnabled + the eval assertion make this class of bug impossible.

Debugging

# Check what the sweep would do (dry-run)
ssh nuc "sudo systemctl cat hass-sweep-unmanaged"  # see ExecStart paths
ssh nuc "sudo /path/to/python3 /path/to/sweep-unmanaged.py /path/to/manifest.json --dry-run"

# View the build-time manifest
nix eval --json '.#nixosConfigurations.nuc.config.services.home-assistant.config.automation' 2>/dev/null | python3 -c "import json,sys; print([a['id'] for a in json.load(sys.stdin) if a.get('id')])"

# Run eval assertions locally
nix build '.#checks.x86_64-linux.ha-automation-assertions' --dry-run

References