Publish harness and TUI open-source

initial sync from the monorepo

crates/common/xai-circuit-breaker/src/window.rs

@@ -0,0 +1,76 @@
+//! Bounded sliding window over `(timestamp, is_failure)` samples.
+
+use std::collections::VecDeque;
+use std::time::{Duration, Instant};
+
+/// Safety cap on sliding window entries to bound memory under sustained
+/// high load (e.g. 10K req/s * 60s window would otherwise reach 600K
+/// entries).
+pub(crate) const MAX_WINDOW_ENTRIES: usize = 10_000;
+
+pub(crate) struct SlidingWindow {
+    entries: VecDeque<(Instant, bool)>,
+    /// Incremental count of `is_failure = true` entries currently in
+    /// `entries`. Maintained on push/pop so `error_rate()` is O(1)
+    /// instead of O(n) — avoids a per-request hot-path scan under
+    /// the breaker mutex.
+    failures: usize,
+}
+
+impl SlidingWindow {
+    pub(crate) fn new() -> Self {
+        Self {
+            entries: VecDeque::new(),
+            failures: 0,
+        }
+    }
+
+    pub(crate) fn push(&mut self, is_failure: bool, at: Instant) {
+        if self.entries.len() >= MAX_WINDOW_ENTRIES
+            && let Some((_, was_failure)) = self.entries.pop_front()
+            && was_failure
+        {
+            self.failures -= 1;
+        }
+        self.entries.push_back((at, is_failure));
+        if is_failure {
+            self.failures += 1;
+        }
+    }
+
+    pub(crate) fn evict(&mut self, window: Duration, now: Instant) {
+        let Some(cutoff) = now.checked_sub(window) else {
+            return;
+        };
+        while let Some(&(ts, was_failure)) = self.entries.front() {
+            if ts < cutoff {
+                self.entries.pop_front();
+                if was_failure {
+                    self.failures -= 1;
+                }
+            } else {
+                break;
+            }
+        }
+    }
+
+    pub(crate) fn error_rate(&self) -> f64 {
+        if self.entries.is_empty() {
+            return 0.0;
+        }
+        self.failures as f64 / self.entries.len() as f64
+    }
+
+    pub(crate) fn sample_count(&self) -> usize {
+        self.entries.len()
+    }
+
+    pub(crate) fn clear(&mut self) {
+        self.entries.clear();
+        self.failures = 0;
+    }
+}
+
+#[cfg(test)]
+#[path = "window_tests.rs"]
+mod tests;