Live camera view in the app, and the green light that was lying about it

Two changes, and the second was found by verifying the first.

## Watching a camera from the app, in another building

Snapshots answer "is that camera working". They do not answer "what is
happening in my shop right now", which is what somebody who opens the app away
from the counter is asking. Head office's browser already had that answer -
LiveHub plus cameras.Live, where the shop PC asks outbound whether anybody is
watching and pushes JPEG frames for as long as somebody is - and the app could
not reach it.

cloud.CameraLive opens that feed and the app's own loopback relay re-emits it
as multipart MJPEG. That is the trick: frames arrive base64 over SSE, an <img>
cannot render that, and an <img> renders MJPEG natively - so a tile is an
ordinary <img> pointed at loopback whether the camera is in this room or
another city.

- Reconnecting happens in the relay, not the page. The server caps one push at
  five minutes, so doing it here means the <img> never sees the stream end.
- The headers are flushed before the first frame. Go writes them on the first
  body write, so without that the whole response waits for the shop PC to
  start pushing. Measured against production: 30 seconds and not even a
  Content-Type, which surfaces as the request timing out.
- One camera at a time. Watching makes a shop PC upload, so a grid that went
  live at once would put an estate's worth of cameras on the wire because
  somebody opened a page.
- live.mjpeg is behind the same per-run token as the engine routes, and a
  wrong token is a 404 that never reaches head office at all.
- CameraLive uses its own HTTP client: the shared one's 30s timeout covers the
  whole response and would sever a working view every thirty seconds - the
  trap that made the server set WriteTimeout to zero for its own SSE endpoint.

## A camera read "Connected" for 34 minutes after the shop PC went blind

Which is why the verification above looked like a failure: head office
registered the viewer and no frame ever came.

reportWith returns early when the engine is unreachable - correctly, it has
nothing to say - so the last state it sent stays in the database looking
current. Measured live: cam2 and entrance both reading Connected, in green,
with last_seen_at 34 minutes old, while the heartbeat from the same PC said
cameras_up 0 of 0. Two surfaces reading two stored fields and disagreeing.

false could not be the answer. It means "this camera is not connecting", which
sends an installer to check cabling on a camera that was working perfectly the
last time anybody could ask it. So there are four states and one function:

  connected       reported recently, and working
  not_connecting  reported recently, and the stream will not open
  waiting         no shop PC has ever reported this camera
  stale           reported once, and not lately

- Connected is CLEARED when stale or waiting. A stale true left in place stays
  available to every client reading the field directly, and leaves two fields
  on one object disagreeing - how the shops screen once came out labelled
  Working, in green, above "2 of 3 cameras not connecting".
- Computed in scanCamera, so every camera anybody reads passes through it. A
  state computed per handler is one a handler forgets, and this had already
  reached three screens.
- CameraStaleAfter is 5 minutes: five missed reports, not one. Same reasoning
  as three missed heartbeats - an indicator that cries wolf gets ignored.
- An unparseable last_seen_at is stale. It should be impossible, which is why
  it must not fall through to the state that says everything is fine.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj

desktop/app.go

@@ -82,6 +82,14 @@ func (a *App) startup(ctx context.Context) {
 	if err := a.proxy.start(a.local.Base, a.local.User, a.local.Password); err != nil {
 		log.Printf("camera relay unavailable, tiles will not load: %v", err)
 	}
+	// And the other direction: watching a camera in another building, through
+	// head office's relay. Enabled unconditionally rather than only when a
+	// session already exists, because signing in is a thing that happens
+	// while the app is open - and CameraLive refuses without a session
+	// anyway, so there is nothing to gate.
+	if err := a.proxy.watchRemote(a.cloud.CameraLive); err != nil {
+		log.Printf("remote camera view unavailable: %v", err)
+	}
 
 	// A saved session means a shop PC that rebooted overnight comes back
 	// working instead of waiting for someone to log in.
@@ -646,6 +654,7 @@ func (a *App) Cameras() ([]map[string]any, error) {
 			"id": c.ID, "camera_id": c.CameraID, "label": c.Label,
 			"site": c.Site, "enabled": c.Enabled,
 			"connected": c.Connected, "last_seen_at": c.LastSeenAt,
+			"state": c.State, "state_note": c.StateNote,
 			"snapshot": c.Snapshot, "snapshot_at": c.SnapshotAt,
 			// What the screen keys off to hide Edit, Test and Check: this
 			// camera is on a network this PC cannot reach.
@@ -719,6 +728,23 @@ func (a *App) StreamURL(cameraID string) string {
 	return fmt.Sprintf("http://%s/api/cameras/%s/stream.mjpeg", base, cameraID)
 }
 
+// RemoteStreamURL is the live view of a camera in another building.
+//
+// The picture comes from head office's relay - the shop PC pushes frames
+// outbound because nothing can reach in - and this app re-emits them as MJPEG
+// on its own loopback, so a tile is an ordinary <img> either way. A screen
+// therefore never has to know which building it is looking at.
+//
+// Empty when the relay is not running, and the caller shows the last snapshot
+// instead. There is no useful fallback URL: the head-office endpoint needs
+// this session's bearer, which an <img> cannot send.
+func (a *App) RemoteStreamURL(cameraID string) string {
+	if !a.cloud.LoggedIn() {
+		return ""
+	}
+	return a.proxy.urlFor(cameraID, "live.mjpeg")
+}
+
 // ------------------------------------------------------------------- live --
 
 type LiveSnapshot struct {