diff --git a/src/reputation/historical_window.rs b/src/reputation/historical_window.rs
new file mode 100644
index 0000000..6076078
--- /dev/null
+++ b/src/reputation/historical_window.rs
@@ -0,0 +1,122 @@
+
+pub const WINDOW_SIZE: usize = 4096;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CircularWindow {
+    buffer: Vec<u64>,
+    write_ptr: usize,
+    entries_written: u64,
+}
+
+impl CircularWindow {
+    pub fn new() -> Self {
+        CircularWindow {
+            buffer: vec![0; WINDOW_SIZE],
+            write_ptr: 0,
+            entries_written: 0,
+        }
+    }
+
+    pub fn push_score(&mut self, score: u64) {
+        self.buffer[self.write_ptr] = score;
+        self.write_ptr = (self.write_ptr + 1) % WINDOW_SIZE;
+        self.entries_written += 1;
+    }
+
+    pub fn effective_entries(&self) -> Vec<u64> {
+        let effective_len = std::cmp::min(self.entries_written, WINDOW_SIZE as u64) as usize;
+        if effective_len == 0 {
+            return vec![];
+        }
+
+        if self.entries_written <= WINDOW_SIZE as u64 {
+            self.buffer[0..effective_len].to_vec()
+        } else {
+            let mut entries = Vec::with_capacity(WINDOW_SIZE);
+            entries.extend_from_slice(&self.buffer[self.write_ptr..]);
+            entries.extend_from_slice(&self.buffer[..self.write_ptr]);
+            entries
+        }
+    }
+
+    pub fn entry_count(&self) -> usize {
+        std::cmp::min(self.entries_written, WINDOW_SIZE as u64) as usize
+    }
+}
+
+impl Default for CircularWindow {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::reputation::compute_weighted_average;
+
+    #[test]
+    fn test_new_window_is_empty() {
+        let window = CircularWindow::new();
+        assert_eq!(window.entry_count(), 0);
+        assert!(window.effective_entries().is_empty());
+    }
+
+    #[test]
+    fn test_push_few_entries() {
+        let mut window = CircularWindow::new();
+        for i in 1..=100 {
+            window.push_score(i);
+        }
+        assert_eq!(window.entry_count(), 100);
+        let entries = window.effective_entries();
+        assert_eq!(entries.len(), 100);
+        for (idx, &entry) in entries.iter().enumerate() {
+            assert_eq!(entry, (idx + 1) as u64);
+        }
+    }
+
+    #[test]
+    fn test_push_full_window() {
+        let mut window = CircularWindow::new();
+        for i in 1..=WINDOW_SIZE {
+            window.push_score(i as u64);
+        }
+        assert_eq!(window.entry_count(), WINDOW_SIZE);
+        let entries = window.effective_entries();
+        assert_eq!(entries.len(), WINDOW_SIZE);
+        for (idx, &entry) in entries.iter().enumerate() {
+            assert_eq!(entry, (idx + 1) as u64);
+        }
+    }
+
+    #[test]
+    fn test_push_over_window() {
+        let mut window = CircularWindow::new();
+        for i in 1..=WINDOW_SIZE + 100 {
+            window.push_score(i as u64);
+        }
+        assert_eq!(window.entry_count(), WINDOW_SIZE);
+        let entries = window.effective_entries();
+        assert_eq!(entries.len(), WINDOW_SIZE);
+        for (idx, &entry) in entries.iter().enumerate() {
+            assert_eq!(entry, (idx + 101) as u64);
+        }
+    }
+
+    #[test]
+    fn test_compute_weighted_average_empty() {
+        let window = CircularWindow::new();
+        assert_eq!(compute_weighted_average(&window), 0);
+    }
+
+    #[test]
+    fn test_compute_weighted_average_few_entries() {
+        let mut window = CircularWindow::new();
+        for i in 1..=100 {
+            window.push_score(i);
+        }
+        // Sum 1..100 is 5050, average is 5050 / 100 = 50
+        assert_eq!(compute_weighted_average(&window), 50);
+    }
+}
diff --git a/src/reputation/mod.rs b/src/reputation/mod.rs
index fc98c04..6a8b686 100644
--- a/src/reputation/mod.rs
+++ b/src/reputation/mod.rs
@@ -1,11 +1,13 @@
 pub mod fixed_point;
+pub mod historical_window;
 pub mod score;
 pub mod score_engine;
 pub mod types;
 
+pub use historical_window::{CircularWindow, WINDOW_SIZE};
 pub use score_engine::{
-    apply_decay, decay_for_epochs, ema_update, reputation_weight, update_reputation,
-    MAX_DECAY_READOUT_ERROR,
+    apply_decay, compute_weighted_average, decay_for_epochs, ema_update, reputation_weight,
+    update_reputation, MAX_DECAY_READOUT_ERROR,
 };
 pub use types::{
     DecayFactor, EmaWeights, ReputationScore, TimeSinceLastUpdate, WindowSize, DEFAULT_DECAY_Q16,
diff --git a/src/reputation/score_engine.rs b/src/reputation/score_engine.rs
index 1ad03ca..159e38a 100644
--- a/src/reputation/score_engine.rs
+++ b/src/reputation/score_engine.rs
@@ -1,5 +1,18 @@
+use super::historical_window::CircularWindow;
 use super::types::{DecayFactor, EmaWeights, ReputationScore, TimeSinceLastUpdate, MAX_REPUTATION};
 
+/// Computes the weighted average of scores in a circular window, using only
+/// the actual number of valid entries written (not the full buffer size).
+pub fn compute_weighted_average(window: &CircularWindow) -> u64 {
+    let entries = window.effective_entries();
+    let count = entries.len();
+    if count == 0 {
+        return 0;
+    }
+    let sum: u64 = entries.iter().sum();
+    sum / count as u64
+}
+
 /// Updates a reputation score using a bounded exponential moving average.
 ///
 /// For gaps greater than or equal to the configured window, the historical