fix(stats): flush throttled daily mileage projections

go/vehicle-gateway/cmd/stat-writer/main_test.go

@@ -105,20 +105,21 @@ func TestProcessStatMessageRecordsMetrics(t *testing.T) {
 			ProjectionsWritten:             1,
 			ProjectionsSkippedThrottled:    2,
 		}, cacheStats: stats.CacheStats{
-			LastTotalMileageEntries: 300,
-			LastSourceSeenEntries:   3,
-			LastProjectionEntries:   280,
-			BaselineEntries:         295,
-			MaxEntries:              1000000,
-			LastCleanupAt:           time.Unix(1782918600, 0),
-			LastCleanupTotalMileage: 11,
-			LastCleanupSourceSeen:   1,
-			LastCleanupProjection:   9,
-			LastCleanupBaseline:     10,
-			TotalMileageEvictions:   4,
-			SourceSeenEvictions:     1,
-			ProjectionEvictions:     2,
-			BaselineEvictions:       3,
+			LastTotalMileageEntries:  300,
+			LastSourceSeenEntries:    3,
+			LastProjectionEntries:    280,
+			PendingProjectionEntries: 12,
+			BaselineEntries:          295,
+			MaxEntries:               1000000,
+			LastCleanupAt:            time.Unix(1782918600, 0),
+			LastCleanupTotalMileage:  11,
+			LastCleanupSourceSeen:    1,
+			LastCleanupProjection:    9,
+			LastCleanupBaseline:      10,
+			TotalMileageEvictions:    4,
+			SourceSeenEvictions:      1,
+			ProjectionEvictions:      2,
+			BaselineEvictions:        3,
 		}},
 		&contextCheckingStatCommitter{},
 		kafka.Message{Topic: "vehicle.fields.go.jt808.v1", Partition: 4, Offset: 30, HighWaterMark: 41, Value: payload},
@@ -150,6 +151,7 @@ func TestProcessStatMessageRecordsMetrics(t *testing.T) {
 		`vehicle_stat_cache_entries{cache="last_total_mileage"} 300`,
 		`vehicle_stat_cache_entries{cache="source_seen"} 3`,
 		`vehicle_stat_cache_entries{cache="projection"} 280`,
+		`vehicle_stat_pending_projection_entries 12`,
 		`vehicle_stat_cache_entries{cache="baseline"} 295`,
 		`vehicle_stat_cache_max_entries{cache="last_total_mileage"} 1000000`,
 		`vehicle_stat_cache_max_entries{cache="source_seen"} 1000000`,
@@ -177,6 +179,52 @@ func TestProcessStatMessageRecordsMetrics(t *testing.T) {
 	}
 }
 
+func TestFlushPendingProjectionsRecordsEventualProjectionMetrics(t *testing.T) {
+	registry := metrics.NewRegistry()
+	flusher := &recordingPendingProjectionFlusher{
+		result: stats.ProjectionFlushResult{Attempted: 3, Written: 3},
+	}
+	readyBefore := time.Date(2026, 7, 19, 15, 4, 45, 0, time.Local)
+
+	flushPendingProjections(context.Background(), discardStatLogger{}, registry, flusher, readyBefore)
+
+	if flusher.calls != 1 || !flusher.readyBefore.Equal(readyBefore) {
+		t.Fatalf("flusher calls=%d readyBefore=%s, want one call at %s", flusher.calls, flusher.readyBefore, readyBefore)
+	}
+	text := registry.Render()
+	for _, want := range []string{
+		`vehicle_stat_pending_projections_total{status="attempted"} 3`,
+		`vehicle_stat_pending_projections_total{status="written"} 3`,
+		`vehicle_stat_last_pending_projection_unix_seconds{status="written"} `,
+	} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("pending projection metrics missing %s:\n%s", want, text)
+		}
+	}
+}
+
+func TestFlushPendingProjectionsRetainsErrorMetricForRetry(t *testing.T) {
+	registry := metrics.NewRegistry()
+	flusher := &recordingPendingProjectionFlusher{
+		result: stats.ProjectionFlushResult{Attempted: 3, Written: 1, Failed: 2},
+		err:    errors.New("temporary projection failure"),
+	}
+
+	flushPendingProjections(context.Background(), discardStatLogger{}, registry, flusher, time.Time{})
+
+	text := registry.Render()
+	for _, want := range []string{
+		`vehicle_stat_pending_projections_total{status="attempted"} 3`,
+		`vehicle_stat_pending_projections_total{status="written"} 1`,
+		`vehicle_stat_pending_projections_total{status="error"} 2`,
+		`vehicle_stat_last_pending_projection_unix_seconds{status="error"} `,
+	} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("pending projection error metrics missing %s:\n%s", want, text)
+		}
+	}
+}
+
 func TestRecordStatWriteE2EDurationSkipsMissingReceivedAt(t *testing.T) {
 	registry := metrics.NewRegistry()
 
@@ -1232,6 +1280,19 @@ type discardStatLogger struct{}
 func (discardStatLogger) Error(string, ...any) {}
 func (discardStatLogger) Warn(string, ...any)  {}
 
+type recordingPendingProjectionFlusher struct {
+	result      stats.ProjectionFlushResult
+	err         error
+	calls       int
+	readyBefore time.Time
+}
+
+func (f *recordingPendingProjectionFlusher) FlushPendingProjections(_ context.Context, readyBefore time.Time) (stats.ProjectionFlushResult, error) {
+	f.calls++
+	f.readyBefore = readyBefore
+	return f.result, f.err
+}
+
 var errTestStatAppend = errors.New("test stat append failed")
 
 func committedOffsets(messages []kafka.Message) []int64 {