Optimize log buffer tail reads

app/log_buffer.py

@@ -2,6 +2,7 @@
 In-memory log buffer for AI engine output. Used to stream live logs to frontend.
 """
 from datetime import datetime
+from itertools import islice
 from typing import List, Literal
 from collections import deque
 
@@ -32,10 +33,9 @@ def clear() -> None:
 
 def get_logs(limit: int = 500) -> List[dict]:
     """Return last `limit` log entries, newest last."""
-    items = list(_buffer)
-    if limit and len(items) > limit:
-        items = items[-limit:]
-    return items
+    if not limit or limit >= len(_buffer):
+        return list(_buffer)
+    return list(reversed(list(islice(reversed(_buffer), limit))))
 
 
 def get_logs_response(running: bool) -> dict:

tests/test_log_buffer.py

@@ -0,0 +1,21 @@
+from app import log_buffer
+
+
+def test_get_logs_returns_tail_in_order():
+    log_buffer.clear()
+    for index in range(10):
+        log_buffer.emit("tick", f"message {index}")
+
+    logs = log_buffer.get_logs(limit=3)
+
+    assert [entry["message"] for entry in logs] == ["message 7", "message 8", "message 9"]
+
+
+def test_get_logs_zero_limit_preserves_existing_all_logs_behavior():
+    log_buffer.clear()
+    for index in range(3):
+        log_buffer.emit("tick", f"message {index}")
+
+    logs = log_buffer.get_logs(limit=0)
+
+    assert [entry["message"] for entry in logs] == ["message 0", "message 1", "message 2"]