avoid repeated reading disk (#7369)

* avoid repeated reading disk

* checks both flush time AND read position advancement

* wait on cond

* fix reading

Gap detection and skipping to earliest memory time
Time-based reads that include events at boundary times for first reads (offset ≤ 0)
Aggregated subscriber wake-up via ListenersWaits signaling

* address comments

weed/util/log_buffer/log_buffer_queryability_test.go

@@ -236,3 +236,58 @@ func TestSchemaRegistryScenario(t *testing.T) {
 
 	t.Logf("Schema registry scenario test passed - schema value preserved: %d bytes", len(retrievedEntry.Data))
 }
+
+// TestTimeBasedFirstReadBeforeEarliest ensures starting slightly before earliest memory
+// does not force a disk resume and returns in-memory data (regression test)
+func TestTimeBasedFirstReadBeforeEarliest(t *testing.T) {
+	flushed := false
+	logBuffer := NewLogBuffer("local", 10*time.Minute,
+		func(logBuffer *LogBuffer, startTime, stopTime time.Time, buf []byte, minOffset, maxOffset int64) {
+			// keep in memory; we just want earliest time populated
+			_ = buf
+		},
+		func(startPosition MessagePosition, stopTsNs int64, eachLogEntryFn EachLogEntryFuncType) (MessagePosition, bool, error) {
+			// disk should not be consulted in this regression path
+			return startPosition, false, nil
+		},
+		func() {})
+
+	// Seed one entry so earliestTime is set
+	baseTs := time.Now().Add(-time.Second)
+	entry := &filer_pb.LogEntry{TsNs: baseTs.UnixNano(), Data: []byte("x"), Key: []byte("k"), Offset: 0}
+	logBuffer.AddLogEntryToBuffer(entry)
+	_ = flushed
+
+	// Start read 1ns before earliest memory, with offset sentinel (-2)
+	startPos := NewMessagePosition(baseTs.Add(-time.Nanosecond).UnixNano(), -2)
+	buf, _, err := logBuffer.ReadFromBuffer(startPos)
+	if err != nil {
+		t.Fatalf("ReadFromBuffer returned err: %v", err)
+	}
+	if buf == nil {
+		t.Fatalf("Expected in-memory data, got nil buffer")
+	}
+}
+
+// TestEarliestTimeExactRead ensures starting exactly at earliest time returns first entry (no skip)
+func TestEarliestTimeExactRead(t *testing.T) {
+	logBuffer := NewLogBuffer("local", 10*time.Minute,
+		func(logBuffer *LogBuffer, startTime, stopTime time.Time, buf []byte, minOffset, maxOffset int64) {},
+		func(startPosition MessagePosition, stopTsNs int64, eachLogEntryFn EachLogEntryFuncType) (MessagePosition, bool, error) {
+			return startPosition, false, nil
+		},
+		func() {})
+
+	ts := time.Now()
+	entry := &filer_pb.LogEntry{TsNs: ts.UnixNano(), Data: []byte("a"), Key: []byte("k"), Offset: 0}
+	logBuffer.AddLogEntryToBuffer(entry)
+
+	startPos := NewMessagePosition(ts.UnixNano(), -2)
+	buf, _, err := logBuffer.ReadFromBuffer(startPos)
+	if err != nil {
+		t.Fatalf("ReadFromBuffer err: %v", err)
+	}
+	if buf == nil || buf.Len() == 0 {
+		t.Fatalf("Expected data at earliest time, got nil/empty")
+	}
+}