ADR-0039: The Console Can Light the Stand for Every Source, Until It Is Switched Back

Context

The stand is lit for records only (ADR-0028): NP_DARK_SOURCES=itunes,spotify makes nowplayd give those sources’ covers the look dark, and lightd draws it as a dark stand. That is right for the room and stays the default.

It is in the way when working on the stand itself. Trying an effect, tuning lightd’s colors or watching how a cover comes out needs music on demand, and iTunes or Spotify is the music that can be put on from a chair. Today that means changing a setting in nowplayd’s environment and restarting it, and remembering to change it back.

The console is where a person already looks at the stand. It only looks (ADR-0018), and that record says controls would be a decision of their own: they change what the console’s account may publish, and who may reach the page. It also says a page with no login is “not acceptable for a page with controls”. This record is that decision for one control.

Options considered

Leave it a setting. Edit NP_DARK_SOURCES and restart nowplayd. Nothing new, and nothing a person can change without a shell on the Pi.

A command, like the screen’s (ADR-0020). The console publishes “all sources” once; nowplayd holds it in memory. A restart of nowplayd forgets it, and the console cannot know what nowplayd holds without being told something back.

The console keeps the state and tells nowplayd. The console would hold something nobody else can read, and one that restarts would have to be asked again. It is a page, not a store.

lightd decides, lighting a dark look anyway while switched. lightd would know that dark means a source, which is what ADR-0009 and ADR-0028 keep from it.

A retained setting on the broker, read by nowplayd. The broker already keeps what must outlive a restart (scenes, presence, the current track). One retained message is the state; whoever writes it last decides; nowplayd and the console both read it, so the page shows what is in force rather than what it last sent.

Decision

The stand’s sources are a retained setting on the broker, which the console can change and nowplayd obeys. It stays as set until it is set again.

• The topic is eds/nowplaying/stand, retained, holding {"v":1,"sources":"records"} or {"v":1,"sources":"all"}. A word, not a boolean, so a third choice is a new word and not a second flag.
• records is ADR-0028: the sources in NP_DARK_SOURCES get the look dark. all treats that list as empty: every source’s cover lights the stand from its colors, and from an album’s own look (ADR-0019). Nothing else in nowplayd changes: arbitration, the beacon’s hold, idle and standby are as they were.
• No message, an empty one, a wrong version or a word nowplayd does not know is records, and nowplayd logs the last three. The default needs nothing on the broker.
• It applies at once. When the setting changes, nowplayd publishes the current cover’s look again, so a track already playing lights or darkens then, not at the next track.
• The console shows it and switches it. It subscribes to the topic and draws the setting in force beside the stand: “Stand: records” or “Stand: all sources”, the second marked so it is not missed. The switch publishes the other word, retained.
• It stays on until it is switched off. No timer and no reset at the next record. A setting for working on the stand that turned itself off would turn off mid-work; one that is left on is plain on the page that shows the stand.
• It is a setting, not a command. Commands (ADR-0020) are never retained, because a pause replayed later is wrong. A setting is retained because a setting forgotten is wrong. The two do not share topics.
• The console’s account may publish this one topic besides its presence, and nowplayd’s may read it. Both are changed in the tenant’s main.tf and in images/backend/files/accounts.conf, as one list kept in two places.
• The page’s one route that changes anything is POST /api/stand, with a JSON body. It refuses any other content type, and a request whose Origin is not the console’s own, so another site open in the same browser cannot switch it. It publishes, and answers with what it published; the page shows the setting when the broker echoes it back, not before.
• There is no login. Anyone who can open the console can switch it. The console is reached only from the site’s trusted networks and the home network, and this control changes which covers light a strip of LEDs and nothing else: no playback, no volume, nothing that leaves the house. ADR-0018’s “not acceptable for a page with controls” was written for controls in general; this is accepted for this one. A control that does more is a new decision, and that question comes back with it.

Consequences

• The stand can be worked on with iTunes or Spotify from a browser, and the room put back from the same place.
• Left on, the stand lights for iTunes in an empty room, as it did before ADR-0028. The console says so; nothing else does.
• The console is no longer only a reader. Its account can publish one topic, and its server has a route that is not GET. CLAUDE.md, the console’s README and ADR-0018’s “it only looks” are qualified to “it looks, and switches the stand’s sources”.
• NP_DARK_SOURCES remains and still says which sources are dark when the setting is records. Changing which sources those are is still a setting and a restart.
• The setting outlives everything but the broker’s store. A broker that loses its retained messages (a new card) is back to records, which is the safe way to forget.
• A nowplayd from before this ignores the topic, and the console’s switch does nothing visible. They are deployed together.
• lightd, the firmware and the cover screen do not change. lightd is sent covers and looks as it always was; it does not know there is a setting.

What would settle it

Tested in nowplayd’s contract and publisher (the setting’s words, an unknown one, the look said again on a change and only then, a record and an empty room left alone) and in the console (the setting read and defaulting to records; the route refusing another origin, no origin, a form, an unknown word and anything but POST, and absent with no way to the bus).

On the development broker, 2026-10-19, with nowplayd (NP_DARK_SOURCES=itunes) and the console running and an iTunes track playing: the look was dark; POST /api/stand all made it the cover’s own look within a second, and the console’s picture said all; records made it dark again. Restarted five times while all, nowplayd published the cover’s own look each time and never dark. The first try did publish dark for a moment, because the retained track and the retained setting arrive together and were taken in either order; nowplayd now takes a waiting setting before a decision.

A Pi already running has its accounts already made, so eds-backend-setup now compares each account’s grants with the list and makes it again, with the password it has, when they differ.

Not yet shown:

• iTunes playing, switched to all from the console: the stand lights from its cover within a few seconds, without the next track.
• Switched back to records: the stand goes dark, and the screen and the console still show the cover.
• nowplayd restarted while all: still all.
• A record played while all: lit as before.