feat(backend): adapt feed fetch interval to update frequencyHEADmain

Add per-feed fetch_interval_seconds (clamped to [1h, 24h]) that halves
on new articles and grows 1.5x when a fetch yields nothing, replacing
the fixed 1h schedule with the 10min cooldown filter. Scheduler tick
shortened to 30min so the 1h floor is honored with reasonable precision.

1 files changed, 30 insertions, 0 deletions

diff --git a/backend/cmd/serve_test.go b/backend/cmd/serve_test.go
new file mode 100644
index 0000000..82b7d53
--- /dev/null
+++ b/backend/cmd/serve_test.go
@@ -0,0 +1,30 @@
+package cmd
+
+import "testing"
+
+func TestNextFetchInterval(t *testing.T) {
+	tests := []struct {
+		name           string
+		current        int64
+		hadNewArticles bool
+		want           int64
+	}{
+		{"new articles halve from mid-range", 14400, true, 7200},
+		{"new articles halve from max", maxFetchIntervalSeconds, true, 43200},
+		{"new articles clamp at min when halving below", 3600, true, minFetchIntervalSeconds},
+		{"new articles clamp at min from slightly above", 4000, true, minFetchIntervalSeconds},
+		{"no articles grow by 1.5x from min", minFetchIntervalSeconds, false, 5400},
+		{"no articles grow by 1.5x from mid-range", 14400, false, 21600},
+		{"no articles clamp at max", maxFetchIntervalSeconds, false, maxFetchIntervalSeconds},
+		{"no articles clamp at max from slightly below", 60000, false, maxFetchIntervalSeconds},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := nextFetchInterval(tt.current, tt.hadNewArticles)
+			if got != tt.want {
+				t.Errorf("nextFetchInterval(%d, %v) = %d, want %d", tt.current, tt.hadNewArticles, got, tt.want)
+			}
+		})
+	}
+}