MQTT: honor mqttRetainState for button press events

[dbochicchio]

Summary

Button press MQTT publishes (publishButton) were always sent with retained=false, so the "Last Press" timestamp sensor in Home Assistant went back to unknown after any MQTT reconnect (WiFi blip, app/HA restart), even though no button was actually pressed. This made it hard to detect real presses via state-change automations.

New setting: "Retain published state"

• Location: Settings → MQTT section, right below "Home Assistant auto-discovery".
• Preference key: mqttRetainState (SP_MQTT_RETAIN_STATE), default on.
• This preference already existed and was read internally (shouldRetainState()) for sensors/relays/dimmer, but had no UI toggle — it was only settable via the HTTP /settings API. It's now visible and editable from the on-device Settings screen too.
• Hint text: "Keep sensor, relay and button state on the broker so it survives a reconnect. Momentary events (switch press/release) are never retained regardless of this setting."

Code change

• MQTTServer.publishButton now respects shouldRetainState() instead of hardcoding retained=false. When enabled, the broker replays the last button payload on resubscribe, restoring the correct last-press timestamp. HA's MQTT event entity already discards replayed retained messages on its own, so this doesn't cause a duplicate/false event to fire.

Files changed

• app/src/main/java/me/rapierxbox/shellyelevatev2/mqtt/MQTTServer.java
• app/src/main/java/me/rapierxbox/shellyelevatev2/SettingsFragment.kt
• app/src/main/res/layout/settings_fragment.xml
• app/src/main/res/values/strings.xml

[Copilot]

Copilot review overview

🟡 Changes recommended

Disabling retention must also clear previously retained button payloads.

Review effort: Lite
Findings: 1

Open (1)

• Disabling retention does not clear existing retained button payloads · New

What changed in this PR

Adds a visible MQTT retention setting and applies it to button publications so Home Assistant can restore last-press timestamps after reconnects.

Changes:

• Adds and binds the “Retain published state” setting.
• Adds labels and explanatory hint text.
• Applies the retention preference to button MQTT messages.
• Disabling retention does not currently clear previously retained button payloads.

File	Summary
app/​src/​main/​res/​values/​strings.xml	Adds setting labels and hint text.
app/​src/​main/​res/​layout/​settings_fragment.xml	Adds the MQTT retention switch and hint.
app/​src/​main/​java/​me/​rapierxbox/​shellyelevatev2/​SettingsFragment.kt	Registers and binds the retention setting.
app/​src/​main/​java/​me/​rapierxbox/​shellyelevatev2/​mqtt/​MQTTServer.java	Applies retention to button publications.

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[Copilot]

Implemented in eaaec23: when retain is toggled from true to false, MQTT now clears retained button payloads (including power and tracked button-topic variants) before the next state sync so stale retained button events are removed.

[Copilot]

Expanded the retained-payload cleanup to cover every retained state topic published under this device’s MQTT namespace, while preserving availability and discovery topics. The change is in commit eaaec23.