docs(device): document the per-feature setpoint step

Gladys now stores a nullable `step` on a device feature, so a setpoint
carries the resolution its physical device actually accepts instead of
inheriting a per-category default (air conditioning was pinned to whole
degrees, which units steppable by half a degree could not express).

Nothing to add to the SDK code — features are published verbatim — but
integrations have no way to discover the field without the typings and
the README:

- index.d.ts: `step?: number` on DeviceFeature, with its semantics
- README: a "Setpoint step" section (example, positive-number rule,
  fallback when omitted, gladys_version caveat)
- typings test: a setpoint feature literal carrying `step`

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: corentinallemandsouthwatts

README.md

@@ -604,6 +604,34 @@ changed.forEach(({ id, value }) => lastValues.set(id, value));
 await gladys.publishStates(changed.map(({ id, value }) => ({ device_feature_external_id: id, state: value })));
 ```
 
+### Setpoint step
+
+A setpoint feature (`DEVICE_FEATURE_TYPES.*.TARGET_TEMPERATURE`, `AIR_CONDITIONING.TARGET_TEMPERATURE`…) can declare
+the resolution its physical device actually accepts, with `step`. It drives the `+`/`-` buttons of the setpoint
+widget in the dashboard: a unit steppable by half a degree gets `step: 0.5`, one that only takes whole degrees
+`step: 1`.
+
+```js
+{
+  name: 'Target temperature',
+  external_id: ids.feature('target-temperature'),
+  category: DEVICE_FEATURE_CATEGORIES.AIR_CONDITIONING,
+  type: DEVICE_FEATURE_TYPES.AIR_CONDITIONING.TARGET_TEMPERATURE,
+  unit: DEVICE_FEATURE_UNITS.CELSIUS,
+  min: 16,
+  max: 31,
+  step: 0.5, // the unit accepts half degrees — Mitsubishi, Daikin…
+  read_only: false,
+  has_feedback: true,
+}
+```
+
+`step` must be a strictly positive number; publishing anything else is a `400`. It is optional: omit it and Gladys
+falls back to its per-category default (a whole degree for air conditioning, half a degree for a thermostat) —
+declare it only when you know what the device supports, rather than guessing 1. Requires a Gladys that carries the
+per-feature step (check the `gladys_version` range of your manifest); an older Gladys ignores the field and keeps
+its category default.
+
 ### Device constants
 
 The SDK exports the canonical category / type / unit strings understood by Gladys — a verbatim mirror of

index.d.ts

@@ -38,6 +38,12 @@ export interface DeviceFeature {
   unit?: string;
   min?: number;
   max?: number;
+  /**
+   * Resolution the physical device accepts for a setpoint, e.g. `0.5` for an
+   * air conditioner steppable by half a degree. Drives the +/- buttons of the
+   * setpoint widget; omit it to let Gladys pick its per-category default.
+   */
+  step?: number;
   read_only?: boolean;
   has_feedback?: boolean;
   keep_history?: boolean;

test/types/api.test-d.ts

@@ -108,6 +108,17 @@ const main = async (): Promise<void> => {
   await gladys.connect();
 
   const devices: Device[] = await gladys.getDevices();
+  const setpoint: DeviceFeature = {
+    name: 'Target temperature',
+    external_id: gladys.externalId('ac:target-temperature'),
+    category: DEVICE_FEATURE_CATEGORIES.AIR_CONDITIONING,
+    type: DEVICE_FEATURE_TYPES.AIR_CONDITIONING.TARGET_TEMPERATURE,
+    unit: DEVICE_FEATURE_UNITS.CELSIUS,
+    min: 16,
+    max: 31,
+    step: 0.5,
+  };
+  const setpointStep: number | undefined = setpoint.step;
   const config: IntegrationConfig = await gladys.getConfig();
   const status = await gladys.getStatus();
   const version: string = status.gladys_version;