ProdDash/docs/MODULE-GUIDE.md

# ProdDash Module Guide

How to build, install and test a ProdDash module. Everything a module author
needs is on this page — you never have to read the shell's source.

A **module** is one kind of dashboard tile: the live transcript, the
Now/Next display, a clock. Users add any number of tiles of your module to
their own dashboards, move and resize them, and give each tile its own
per-tile settings. Your module renders inside the tile and talks to the
outside world only through the small API the shell hands it.

## Rules every module follows

These are not style preferences — the admin page, the installer and the
people running the booth depend on them.

1. **All settings live in the ProdDash admin page.** Server-wide settings go
   in `configSchema`, per-tile settings in `instanceSchema`. Never a separate
   setup page, wizard, config file the operator edits by hand, or environment
   variable.
2. **Dependencies ship inside the module folder.** Zero dependencies is the
   norm (the shell has none). Anything you genuinely need is vendored into
   the module — or fetched by your own `init()` on first start, with the
   admin health line saying what is happening. No `npm install`, no
   installer, no "run this first".
3. **Everything the module does runs inside the module.** No helper scripts,
   companion programs, daemons or services the operator has to start next to
   ProdDash. If your feature needs a listener, a decoder or a worker, your
   server entry owns it: start it in `init()`, stop it in `stop()`, report
   it in `health()`. A child process the module itself spawns and supervises
   is fine; a program someone launches by hand is not.
4. **Declare the ProdDash version you need** (`"proddash": ">=1.1.0"` in the
   manifest) and **bump your own `version`** whenever you change the module.
   The admin page refuses to install a module whose requirement the running
   shell doesn't meet, and it offers updates by comparing versions.

## The shape of a module

A module is one folder dropped into `modules/`:

```
modules/<id>/
├── module.json      manifest (required)
├── client.js        ES module, client entry (required)
├── server.js        server entry (optional — only if you need server code)
└── ... assets       (css, images…) served statically at /modules/<id>/
```

**Installation is exactly this:** in the admin page, open **Available
modules** and press **Install** — the module is downloaded from the ProdDash
repo into the server's data directory (`<data dir>/modules/<id>/`) and starts
immediately. Developing locally? Drop the folder into `modules/` (bundled
with the checkout) or into the data directory's `modules/` and restart. No
shell code changes, ever. Modules bundled with a checkout and modules
installed from the admin page live side by side; when both have the same id
the newer version runs. **Uninstall** in the admin page removes an installed
module's files (a bundled one is hidden instead, since its folder belongs to
the app); its settings are kept for a later reinstall.

## module.json

```json
{
  "id": "my-module",
  "name": "My Module",
  "version": "1.0.0",
  "proddash": ">=1.1.0",
  "description": "One line shown in the Add-tile picker and the admin page",
  "permissions": [
    { "kind": "microphone", "reason": "Why this module needs it, in one line" }
  ],
  "client": "client.js",
  "server": "server.js",
  "style": "style.css",
  "minSize": { "w": 2, "h": 2 },
  "defaultSize": { "w": 4, "h": 3 },
  "configSchema": {
    "upstreamUrl": { "type": "string", "label": "Upstream URL", "default": "http://10.0.0.5:1234" },
    "apiKey":      { "type": "password", "label": "API key", "default": "" }
  },
  "instanceSchema": {
    "channel": { "type": "string", "label": "Channel filter", "default": "" }
  }
}
```

| Field | Required | Meaning |
| --- | --- | --- |
| `id` | yes | Must equal the folder name. Lowercase, dashes. |
| `name` | yes | Human name shown on the tile header and in menus. |
| `version` | yes | Your module's version (`x.y.z`). Bump it on every change — the admin page offers updates when the repo's copy is newer than the installed one. |
| `proddash` | yes | The ProdDash versions this module works with: `">=1.1.0"`, `"^1.1.0"`, `">=1.1.0 <2.0.0"`, or `"*"`. A module whose requirement the running shell doesn't meet is listed in the admin page but never loaded, and can't be installed from the catalog. |
| `description` | no | Shown in the admin page / picker. |
| `permissions` | no | What macOS must allow before this module can work — see **Permissions macOS has to grant**. Ignored by the shell; read by the macOS launcher. |
| `provides` | no | Capabilities other modules can consume — `["timers"]` today. Forwarded in `/api/modules` so a consumer can find you. See **Working with other modules**. |
| `client` | yes | Client entry file, loaded as an ES module. |
| `server` | no | Server entry file (CommonJS), loaded with `require()`. |
| `style` | no | A stylesheet the shell injects once per module. |
| `minSize`, `defaultSize` | no | Tile size in grid cells (12 columns wide; rows are ~72 px). Defaults: min 1×1, default 4×3. |
| `configSchema` | no | **Admin config** — server-wide settings (URLs, ports, keys) edited once at `/admin` for everyone. |
| `instanceSchema` | no | **Per-tile settings** — chosen in each tile's gear menu and stored with that browser's layout (filters, text sizes, display options). They apply as they are changed, so keep them to display choices. |
| `tiles` | no | Fixed multi-tile list for client-only modules; server modules export a dynamic `tiles()` instead. See **Presenting multiple tiles**. |

Both schemas map field names to specs:

```
{ "type": "string" | "number" | "boolean" | "switch" | "select" | "color" | "password" | "endpoint",
  "label": "Shown next to the field",
  "default": <value>,
  "group": "Section heading",                         // optional; see below
  "showWhen": "<other boolean/switch key>",           // optional; see below
  "help": "One line shown under the control",         // optional, admin config only
  "options": [ { "value": "a", "label": "A", "group": "Optgroup" }, … ],  // "select" only
  "optionsRoute": "/devices",                         // "select" only, admin config only
  "optionsDependsOn": "<other key>"                   // with optionsRoute; see below
}
```

`boolean` and `switch` are the same true/false value. In a tile's gear popover
both render as a switch; in the admin page `switch` is the toggle and
`boolean` the plainer checkbox (use `switch` for a feature on/off that other
fields depend on). **Label a switch with the noun of what it turns on** —
"Seconds", "Top bar", "Section headers" — never "Show seconds": on means
shown or enabled, off means hidden or disabled, and the label shouldn't say
so twice.
`color` renders a swatch picker and stores a `#rrggbb` string (give it a hex
default; the tile applies it as a CSS custom property — see `pco-plan`).

`group` gathers consecutive fields under a labeled subsection in the admin
page, so a module with several distinct concerns (e.g. a ProPresenter
connection and an LTC audio input) reads as clearly separated blocks. Fields
with no `group` render loose, before/after the grouped ones in schema order.

A manifest-level `configGroups` map can dress a group up further, keyed by
the group name:

```json
"configGroups": {
  "Planning Center credentials": { "collapsed": "whenSet", "help": "Where to get a token…" },
  "Show / hide":                 { "collapsed": true, "columns": 3 }
}
```

- `collapsed`: `true` (starts folded), `false` (starts open but can fold),
  or `"whenSet"` — folded once the group already holds values (a saved
  password, or anything other than the schema default), open while it is
  still empty. Omit it and the group is a plain, always-open block.
- `columns`: 2–4 lays the group's fields out in a grid — the way to keep a
  long checklist of booleans compact.
- `help`: guidance for the whole group. The admin page shows it as an
  ⓘ beside the group title (click or hover to read), so a group can carry a
  paragraph without pushing its fields down the page. Say where a value comes
  from, not what a field is.
- `toggle`: the key of a `switch` field in this group. It renders in the
  group's title row, at the right, as the group's on/off; the rest of the group
  dims while it is off, and the field is not repeated in the body. This is how
  an integration is disabled without unmounting the module — ProPresenter
  timers, say, on a Sunday when ProPresenter isn't running.

`help` on a field puts one line of guidance under its control — allowed
placeholders, where a value comes from. Keep labels short and put the
explanation there.

`group` and `help` work on `instanceSchema` fields too, and a manifest
`instanceGroups` map plays the `configGroups` role for the tile's gear
popover (`collapsed: true | false`, `columns`, `help`). That is how a module
with a long show/hide checklist keeps the popover usable — see `pco-plan`.
Display choices belong there, per tile; admin config is for connections.

`showWhen: "<key>"` hides a field until the boolean/`switch` field named
`<key>` is on — e.g. the audio device and channel appear only once the LTC
listener switch is enabled. The hidden field still keeps its stored value.

A `select` whose choices are only knowable at runtime (audio devices, serial
ports, discovered sources) sets `optionsRoute` instead of — or as a fallback
refresh of — static `options`: the admin page GETs
`/api/modules/<id><optionsRoute>` and expects `{ "options": [ { "value",
"label" }, … ] }` from one of the module's own server routes. The saved value
stays selectable even when the route is down or the option has vanished. (See
`propresenter-timers`' "Audio device" for a worked example.)

An option may carry a `group`: options sharing one render under a single
`<optgroup>`, so a tree (Planning Center folders, device classes) is
browsable inside the select. `optionsDependsOn: "<key>"` makes the admin
page fetch the options with that other field's current value appended as a
query parameter (`?<key>=<value>`), now and again whenever it changes — e.g.
a plan list that follows the chosen service type. (Both in `pco-plan`.)

`password` fields are admin-config only in practice: their values are stored
in the server's `modules.json` (in the per-machine data directory, see the
README), handed to your *server* entry, and **never sent to browsers** — not in `/api/modules`, and never echoed back into the admin
form. Anything upstream that needs the secret must go through your server
routes.

### Connection settings: use `endpoint`

Anything that points at a device or service on the network — ProPresenter,
ProdCom, a camera, a mixer — must be **one `endpoint` field**, so every
module's connection is entered the same way. The admin page renders an
endpoint as a single "Host / IP : Port" control; the value is stored and
handed to your server as an object:

```json
"propresenter": {
  "type": "endpoint",
  "label": "ProPresenter",
  "default": { "host": "", "port": 1025 }
}
```

```js
// in your server entry
const { host, port } = config.propresenter;
const base = `http://${host}:${port}`;
```

Do **not** split host and port into separate `string`/`number` fields, and
do **not** ask for a full `http://…` URL unless the setting genuinely is a
web address where protocol or path matter (a page to embed, a webhook).
Endpoints belong in admin config, not per-tile settings — connections are
server-wide by design.

Admin config lives in `modules.json` inside the server's data directory
(written by the admin page — your module never touches that file, and it
survives updates of the app folder). Per-tile settings live inside each
browser's layout.

### Permissions macOS has to grant

Some things a module does need the operating system's permission, not just
configuration: reading an audio input, reaching gear on the local network.
macOS grants those to the **application that owns the process**, which for
ProdDash is the macOS launcher (`launcher/macos`) — the server is its child,
so the prompts are asked, and remembered, in ProdDash's name. A server
started over SSH or from a bare launchd job has no such owner, and the
permission is silently absent rather than refused: an LTC input reads as
endless zeroes, a local host simply never answers.

Declare what you need, and why, so the launcher's Permissions tab can list
it and ask for it before a service rather than during one:

```json
"permissions": [
  { "kind": "microphone",    "reason": "Decoding SMPTE LTC timecode from an audio input on this machine" },
  { "kind": "local-network", "reason": "Reaching ProPresenter on this network" }
]
```

| `kind` | When to declare it |
| --- | --- |
| `microphone` | The module reads an audio input (`ltc-capture` and anything like it). |
| `local-network` | The module talks to gear on this building's network. Not needed for services out on the internet — Planning Center, say. |

`reason` is one line, shown to the operator as-is when they hover the
permission; modules giving the same reason are listed together. A bare `"permissions": ["microphone"]` works when
the standing explanation is enough. A `kind` the launcher doesn't manage is
still listed, so nothing goes unmentioned — the shell itself ignores the key
entirely, and other platforms ignore it too.

## Client entry (`client.js`)

An ES module whose **default export is a factory**. The shell calls it once
per tile:

```js
export default function create({ root, moduleApi }) {
  return {
    start() {},            // begin rendering / connecting
    stop() {},             // tear down EVERYTHING (timers, streams, observers)
    onResize(w, h) {},     // optional; tile was resized (w, h in grid cells)
    onConfigChange(cfg) {} // optional; admin config was saved
  };
}
```

- `root` — the tile's body element. **The module owns everything inside it
  and must never touch DOM outside it.**
- All four methods are optional, but a module without `stop()` will leak
  timers when its tile is removed. `stop()` must leave nothing running.

### moduleApi

| Member | What it is |
| --- | --- |
| `id` | Your module id. |
| `instanceId` | Unique per tile — two tiles of the same module get different ids. Handy for keying anything per-tile. |
| `variant` | For multi-tile modules: the id of the tile-list entry this tile was added as, `''` otherwise (see **Presenting multiple tiles**). |
| `config` | Admin (server-wide) config, read-only, always current. Password fields are absent — they never reach the client. |
| `instanceSettings` | This tile's settings: your `instanceSchema` defaults overlaid with whatever this tile has saved. Read it fresh whenever you render — don't cache it. |
| `saveInstanceSettings(patch)` | Merge `patch` into this tile's settings and persist them with the layout. No restart happens — you made the change, you already know. Use it for state the user sets *inside* your tile (a toggled filter, a chosen tab). |
| `fetch(path, opts)` | `fetch` scoped to your server routes: `fetch('/state')` hits `/api/modules/<id>/state`. |
| `sse(path, handlers)` | An `EventSource` scoped the same way, **with auto-reconnect** (see below). Returns a handle with `close()`. |
| `setStatus(state, msg)` | Drives the tile's status dot: `'ok'`, `'connecting'` or `'error'`, plus a hover message. Call it honestly — during a live service the dot is how an operator spots a dead feed. |
| `header.addButton(…)` | Put a small button in the tile's own title bar (see below). |
| `header.addMenu(…)` | Put a dropdown menu button there (see below). |

### Title-bar controls

Modules don't build their own toolbars — actions live in the tile's title
bar, next to the shell's gear/close buttons:

```js
const btn = moduleApi.header.addButton({
  icon: '<svg …>…</svg>',   // inline SVG string, and/or
  label: 'A+',              // short text
  title: 'Larger text',     // hover tooltip
  onClick() { … },
});
btn.classList.add('active'); // toggle styling for on/off buttons

const menu = moduleApi.header.addMenu({
  label: 'Channels ▾',
  title: 'Choose visible channels',
  build(menuEl) {
    // called on every open with an emptied menu element — fill it with
    // buttons (give them your scoped classes; the container is styled and
    // fixed-positioned by the shell, so the tile's overflow can't clip it)
  },
});
menu.setLabel('Channels (2/4) ▾'); // update the button text any time
```

Everything you add is removed automatically when your instance stops, so a
remount never duplicates controls. Keep them compact (icon buttons, short
labels): the title bar is 32 px tall and shared with the tile's name.

One more thing to know: the user can hide the whole title bar with the
small notch on its bottom edge (a clean-view mode for wall displays). Your
controls disappear with it, so nothing essential — status, reconnects,
live data — may exist *only* as a header control.

`sse(path, handlers)` handlers:

```js
const stream = moduleApi.sse('/stream', {
  open(e)    {},                 // (re)connected
  error(e)   {},                 // connection lost — say so via setStatus
  message(e) {},                 // unnamed "data:" events
  events: { state(e) {} },       // named events by name
});
// later: stream.close()
```

Browsers' `EventSource` retries transient drops itself but gives up for good
when a retry gets a completed non-SSE response — which is what a proxy's 502
looks like while the upstream is down. The shell's `sse()` recreates closed
streams on a 3-second timer until they work again, so **reconnect logic is
free**: handle `open` (refresh/backfill your state; you may have missed
events) and `error` (report degraded status), and you're resilient. Streams
you forget to close are force-closed when the tile unmounts — but close your
own in `stop()` anyway.

### Lifecycle you must expect

- **Any number of instances.** Two transcript tiles with different filters
  is a feature. Keep all state inside `create()`'s closure — no module-level
  mutable state in `client.js`.
- **Remounts are routine.** Gear settings apply as the user changes them —
  there is no Apply button — so each change calls `stop()` and starts a fresh
  instance (typing is debounced, and an unchanged value remounts nothing).
  Starting cheaply matters: hold connections and timers in the closure and
  tear them down in `stop()`. When admin config changes, the shell calls your
  `onConfigChange(cfg)` if you export one, otherwise it remounts you. Either
  way you must come back cleanly.
- **The tile can be removed at any moment.** `stop()` is your only notice.

### Rules for the client

1. **Never touch DOM outside `root`. Never define global CSS.** Scope every
   rule in your stylesheet with the attribute the shell puts on your tiles:

   ```css
   [data-module="my-module"] .my-thing { … }
   ```

   (Shadow DOM works too, if you prefer full isolation.)

2. **Style with the shell's CSS variables — no hardcoded colors.** The
   palette: `--bg` (page), `--panel` (tile), `--border`, `--text`,
   `--muted`, `--accent`, `--accent-text` (text that sits on the accent —
   dark on most themes, white where the accent is deep), `--danger`,
   `--warn`. Derive tints with
   `color-mix(in srgb, var(--accent) 20%, transparent)`. This is what makes
   every module look native — and what makes the dashboard's **themes**
   (Admin → Theme) reach into every tile: a theme swaps those variables and
   nothing else. A colour a tile is configured with (a `color` instance
   setting, applied as a custom property on the tile) is set closer than the
   theme and wins over it, by design.

3. **No external network calls from the client.** Browsers talk only to
   ProdDash. Anything upstream (your device, service, API) goes through your
   module's server routes — same reasoning as the reference apps: no CORS,
   no per-browser credentials, one place that owns the connection.

4. **Handle upstream loss.** Reconnect with backoff (or lean on `sse()`),
   and report honestly via `setStatus`. Tiles run unattended during live
   services; a module that silently freezes is worse than one that says
   it's down.

## Server entry (`server.js`)

Optional — only needed when your module talks to something upstream or keeps
server-side state. CommonJS, Node built-ins only (keep the zero-dependency
ethos; Node 18+ so global `fetch` is available). Exports either or both of:

```js
module.exports = {
  init({ config, log, shell }) {
    // Called on startup / re-init, BEFORE routes(). Start your upstream
    // connection here. Return a handle:
    return {
      stop() {},                                  // tear everything down
      health() { return { status: 'ok', message: '' }; }  // optional
    };
  },

  routes({ config, log, shell }) {
    // Route table, mounted under /api/modules/<id>/
    return {
      'GET /state':     (req, res) => { … },
      'GET /stream':    (req, res) => { … },      // SSE — see notes
      'POST /command':  (req, res) => { … },
      'GET /proxy/*':   (req, res) => { … },      // trailing /* = prefix route
      '* /anything/*':  (req, res) => { … },      // * method = any method
    };
  },
};
```

- `config` is your admin config: `configSchema` defaults overlaid with what
  the admin page saved — **including password fields**.
- `log(...)` prefixes output with your module id.
- `shell.port` is the port ProdDash is serving on — what you need to read
  another module's routes over loopback (`http://127.0.0.1:${shell.port}/api/
  modules/<id>/…`). Never guess it.
- Handlers get plain Node `(req, res)`. On a prefix route, `req.wildcard` is
  the matched remainder (leading `/` included) and `req.search` is the query
  string (with `?`, or `''`) — so a proxy rebuilds the upstream path as
  `req.wildcard + req.search`.
- Exact routes match the path exactly; prefix routes (`/x/*`) match `/x` and
  everything under it. First declared match wins.
- **Re-init instead of restart:** when the admin page saves your config, the
  shell calls your handle's `stop()`, then `init()` and `routes()` again
  with the new config. Keep module-level state inside `init()`'s closure (or
  reset it there) so a re-init starts clean. Disabling a module unmounts its
  routes entirely (clients get 404).
- `health()` feeds the admin page's status line — report your upstream's
  reachability (`status: 'ok' | 'connecting' | 'error'`), not just "running".
- A throw from `init()`/`routes()` marks the module as failed: the error
  shows in `/admin`, and API calls answer 502 until a config fix re-inits
  it. Validate config early so bad input fails loudly there.

### Presenting multiple tiles

By default a module is one entry in the ＋ Add-tile picker. A module can
instead present a **list of tiles** — one picker entry each, grouped under
the module's name. This is how a module whose content is naturally plural
works: one tile per ProPresenter timer, one tile per admin-configured page.

Export `tiles` from your server entry (sync or async):

```js
module.exports = {
  init({ config, log }) { … },
  routes({ config, log }) { … },

  tiles({ config, log }) {
    // e.g. derived from admin config, or discovered from your upstream
    return config.pages.map((page) => ({
      id: page.name,                    // stable id, stored with the tile
      name: page.name,                  // picker label AND the tile's title
      description: page.url,            // optional line under the label
      settings: { page: page.name },    // preset instance settings
      defaultSize: { w: 4, h: 3 },      // optional per-entry size overrides
      minSize: { w: 2, h: 2 },
    }));
  },
};
```

- `tiles()` runs on **every picker load**, so the list may be live data —
  keep it fast (answer from state you already hold; don't fetch upstream on
  demand). A throw or a hang (>2 s) falls back to the classic single entry,
  so a dead upstream can't break the picker.
- When the user adds an entry, its `settings` overlay your `instanceSchema`
  defaults in that tile's instance settings, the entry's `name` becomes the
  tile's title, and `moduleApi.variant` carries its `id`.
- The tile keeps its variant id and title even if the entry later vanishes
  from your list (a timer deleted in ProPresenter, a page removed in admin).
  **Your client decides what that means** — show a clear "no longer
  configured" state rather than erroring.
- A client-only module can declare a fixed list as a `tiles` array in
  `module.json` instead (same entry shape).
- An empty list (or no `tiles` at all) keeps today's behavior: one picker
  entry, no preset.

### Server-Sent Events from a module

For live data, expose a `/stream` route and let clients use
`moduleApi.sse('/stream', …)`:

```js
'GET /stream': (req, res) => {
  res.writeHead(200, {
    'Content-Type': 'text/event-stream; charset=utf-8',
    'Cache-Control': 'no-cache, no-transform',
    Connection: 'keep-alive',
  });
  res.write('retry: 3000\n\n');
  res.write(`event: state\ndata: ${JSON.stringify(latest)}\n\n`); // instant paint
  streams.add(res);
  req.on('close', () => streams.delete(res));
}
```

Broadcast only when the payload actually changed, send a `: ping\n\n`
comment every ~15 s so idle connections survive sleepy Wi-Fi, and wrap every
per-client `res.write` in try/catch (drop the client on failure). The
`propresenter-now-next` module is the reference implementation of this
pattern.

## Working with other modules

Modules don't import each other. When one needs what another knows, it reads
that module's **own server routes over loopback**, exactly as a browser would:
`http://127.0.0.1:${shell.port}/api/modules/<id>/…`. The PCO Plan module
follows ProPresenter this way — it reads `propresenter-now-next`'s `/stream`
rather than talking to ProPresenter a second time. A consumer must survive the
provider being disabled, uninstalled, or restarting mid-service (404s and
dropped connections are normal; retry with backoff and say so in `health()`).

### Offering timers to the Timers module

The Timers module shows timers from anywhere: ProPresenter, LTC, its own
clock, and any module that offers some. A module offers timers by:

1. Declaring it — `"provides": ["timers"]` in `module.json`. The shell
   forwards `provides` in `/api/modules`, which is how the Timers module finds
   providers without a list anyone maintains.
2. Serving `GET /timers` from its server routes, returning a snapshot:

```json
{
  "source": "pco-plan",
  "label": "PCO Plan",
  "updatedAt": 1757800000000,
  "timers": [
    {
      "id": "service",
      "label": "Service",
      "kind": "elapsed",
      "state": "running",
      "startedAt": 1757799000000,
      "elapsedMs": 1000000,
      "remainingMs": null,
      "targetMs": 4500000,
      "status": { "text": "Welcome & Announcements", "tone": "ok" },
      "detail": "Item 3 of 12"
    }
  ]
}
```

| Field | Meaning |
| --- | --- |
| `source`, `label` | Your module id, and the heading the Timers module puts over your timers. |
| `updatedAt` | ms since epoch when this snapshot was taken. Every duration below is *as of this instant*. |
| `id` | Stable within your module — the Timers module keys tile settings (shown/hidden, colours) on `source` + `id`. |
| `kind` | `elapsed` (counts up), `countdown` (counts down to zero), `clock` (a time of day; put the ISO time in `status.text`). |
| `state` | `running`, `paused`, `stopped` (finished; value frozen), `idle` (exists, hasn't started — a timer that will start at 11:00). |
| `startedAt` | ms epoch when it last started running; the consumer extrapolates from here, so a running timer never needs a fast poll. |
| `elapsedMs`, `remainingMs` | The values at `updatedAt`; `null` when not meaningful for the kind. |
| `targetMs` | Planned length (elapsed) or full length (countdown), or `null`. Lets the consumer colour overruns. |
| `status` | Optional one-liner the consumer shows beside the time — the current item, "ahead 1:20". `tone`: `ok`, `warn`, `danger`, `muted`. |
| `detail` | Optional second line. |

The consumer derives the displayed time locally from `startedAt`/`elapsedMs`
and its own clock, so a snapshot every couple of seconds is plenty — `/timers`
must be cheap to answer (serve from state you already hold; never call
upstream to answer it). Optionally also serve `GET /timers/stream` as SSE
(`event: timers`, `data:` the same object, on every change plus a heartbeat
comment every 15 s); the consumer uses the stream when it exists and polls
`/timers` otherwise. Only offer timers a production tech would want on a
wall — the Timers module lets them hide any of them per tile, but every entry
you add is a decision someone has to make.

## Complete minimal example

A working clock — copy-paste this as your starter. (A slightly fancier
version ships in `modules/clock/`.)

`modules/hello-clock/module.json`

```json
{
  "id": "hello-clock",
  "name": "Hello Clock",
  "version": "1.0.0",
  "description": "Minimal example module",
  "client": "client.js",
  "style": "style.css",
  "minSize": { "w": 2, "h": 1 },
  "defaultSize": { "w": 3, "h": 2 },
  "instanceSchema": {
    "showSeconds": { "type": "boolean", "label": "Show seconds", "default": true }
  }
}
```

`modules/hello-clock/client.js`

```js
export default function create({ root, moduleApi }) {
  let timer = null;

  function tick() {
    const { showSeconds } = moduleApi.instanceSettings;
    root.querySelector('.hc-time').textContent = new Date().toLocaleTimeString(
      [], { hour: '2-digit', minute: '2-digit', ...(showSeconds ? { second: '2-digit' } : {}) }
    );
  }

  return {
    start() {
      root.innerHTML = '<div class="hc-time"></div>';
      tick();
      timer = setInterval(tick, 250);
      moduleApi.setStatus('ok', 'Ticking');
    },
    stop() {
      clearInterval(timer);
      root.innerHTML = '';
    },
  };
}
```

`modules/hello-clock/style.css`

```css
[data-module="hello-clock"] .hc-time {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2.4em;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: var(--text);
}
```

Drop the folder in `modules/`, restart ProdDash, and “Hello Clock” appears
in the Add-tile picker (new modules are enabled by default; `/admin` can
disable them).

## Testing your module

**Run it:**

```bash
node server.js        # from the repo root — prints the LAN URL
```

The server logs each module it mounts (or why it refused to). `/admin`
shows mount errors and your `health()` line; the browser console shows
client-side failures (a tile that fails to start says so in the tile).

**Poke the pieces directly:**

- `GET /api/modules` — what the shell sees (your manifest + non-secret config).
- `GET /api/modules/<id>/...` — your routes, `curl`-able. For SSE:
  `curl -N http://localhost:24500/api/modules/<id>/stream`.
- `GET /api/admin/state` — enabled flags, health, mount errors.

**Mock upstreams** (so you can develop without the real gear):

- ProdCom: `node tools/prodcom-mock.js` (port 24480) — channels, groups,
  history, and a live stream with in-progress speech. Point the
  transcript module's ProdCom URL at `http://127.0.0.1:24480`.
- ProPresenter: `node band-lineup-display/tmp/pp-mock.js 1599` — playlists
  and an advancing slide index (including the arrangement-repeat case).
  Point the Now/Next module at host `127.0.0.1`, port `1599`.
- ProPresenter timers: `node tools/pp-timers-mock.js 1600` — running,
  overrunning, stopped and elapsed timers plus an LTC timecode that
  periodically drops to no-signal (`--no-ltc` serves a ProPresenter without
  a timecode API). Also serves the stage-display websocket with an
  LTC-labeled layout field (`--stage-pwd`, `--no-ltc-field` exercise its
  failure paths). Point the Timers module at host `127.0.0.1`, port `1600`.
- Planning Center: `node tools/pco-mock.js` (port 24700) — folders, service
  types, plans (last week / today / next week), plan times and items with
  songs, keys and item notes, behind a Basic/Bearer auth check. Planning
  Center is a cloud API, so the module reads its base URL from the
  environment instead of admin config: run ProdDash with
  `PCO_PLAN_API_BASE=http://127.0.0.1:24700 node server.js`, enter any
  Application ID + Secret under PCO Plan in `/admin`, save, then pick
  "Sunday Service" from the Service type list. Its item titles match
  `pp-mock.js`, so running both mocks exercises the ProPresenter matching.

**The resilience checklist** — every module must pass this before it's done:

1. Add your tile, then **kill the upstream** (or the mock). The status dot
   must go red (with a useful hover message) and the tile must show a clear
   degraded state, not a freeze.
2. **Restart the upstream.** The tile must recover by itself — no reload,
   no clicking.
3. **Restart ProdDash itself** with the tile open. Same expectation.
4. Add **two tiles of your module** with different per-tile settings — both
   must work independently.
5. **Remove your tile**, then check the browser console and server log: no
   errors, no timers still firing, no streams still open.
6. Change your admin config in `/admin` while the tile is open — the tile
   must pick it up (via `onConfigChange` or the automatic remount).
7. Reload the page — the tile comes back with its settings intact.