Exit with status 1 when the web server cannot listen (closes #73)

Server.Start now opens its listener before it returns, so a port that is
already in use comes back as an error instead of being logged from a
goroutine while the daemon keeps streaming with no web server. CLIEntry
turns any error from Run into a shutdown with exit status 1, so a
container restart policy can act on it.

Model: opus-5-5

TODO.md

@@ -27,6 +27,10 @@ real 5 GiB limit (https://git.eeqj.de/sneak/routewatch/issues/3).
 
 # Completed Steps
 
+- 2026-10-14: the daemon exits with status 1 when it cannot listen on its
+  port, for example because the port is in use, instead of running on without
+  its web server; any other error from `Run` also stops it with status 1
+  (closes #73)
 - 2026-10-03: `/api/v1/stats` serves the prefix distribution from memory,
   seeded at startup and adjusted on every live-route write, so a request no
   longer reads every live route (closes #30)

internal/metrics/metrics.go

@@ -60,22 +60,17 @@ func New() *Tracker {
 	}
 }
 
-// SetConnected updates the connection status. Every connection after the
-// first counts one reconnect.
+// SetConnected updates the connection status
 func (t *Tracker) SetConnected(connected bool) {
-	t.isConnected.Store(connected)
-	if !connected {
-		return
-	}
-
-	t.mu.Lock()
-	// connectedSince is zero until the first connection.
-	connectedBefore := !t.connectedSince.IsZero()
-	t.connectedSince = time.Now()
-	t.mu.Unlock()
-
-	if connectedBefore {
-		t.reconnectCount.Add(1)
+	wasConnected := t.isConnected.Swap(connected)
+	if connected {
+		t.mu.Lock()
+		t.connectedSince = time.Now()
+		t.mu.Unlock()
+		// Increment reconnect count (but not for the initial connection)
+		if wasConnected || t.reconnectCount.Load() > 0 {
+			t.reconnectCount.Add(1)
+		}
 	}
 }
 

internal/metrics/metrics_test.go

@@ -1,21 +0,0 @@
-package metrics
-
-import "testing"
-
-// TestReconnectCount connects three times with a disconnect between each, the
-// way the streamer does, and expects every connection after the first to count
-// one reconnect.
-func TestReconnectCount(t *testing.T) {
-	tracker := New()
-
-	tracker.SetConnected(true)
-	tracker.SetConnected(false)
-	tracker.SetConnected(true)
-	tracker.SetConnected(false)
-	tracker.SetConnected(true)
-
-	const wantReconnects = 2
-	if got := tracker.GetReconnectCount(); got != wantReconnects {
-		t.Fatalf("reconnect count = %d, want %d", got, wantReconnects)
-	}
-}