fix: a batch put back on a full capture queue drops the oldest, counted

src/agentcompile/_capture.py

@@ -179,13 +179,22 @@ def _take(self) -> list[str]:
                 self.dropped += 1
                 continue
             if batch and size + len(line) > MAX_BATCH_BYTES:
-                with self._lock:  # the rest waits for the next batch, in order
-                    self._queue.extendleft(reversed(records[i:]))
+                self._put_back(records[i:])
                 break
             batch.append(line)
             size += len(line)
         return batch
 
+    def _put_back(self, rest: list[dict[str, Any]]) -> None:
+        """Calls taken for a batch that didn't fit, back at the front, in order. They are the
+        oldest: when newer calls filled the queue meanwhile, they are the ones dropped, and
+        counted (extendleft would evict the newest instead, silently)."""
+        with self._lock:
+            room = (self._queue.maxlen or len(rest)) - len(self._queue)
+            keep = rest[len(rest) - max(room, 0) :]
+            self.dropped += len(rest) - len(keep)
+            self._queue.extendleft(reversed(keep))
+
     def _send_batch(self) -> None:
         batch = self._take()
         if not batch:

tests/test_hardening.py

@@ -312,3 +312,14 @@ def test_wrapping_again_reuses_the_sender_and_keeps_one_destination(tmp_path: Pa
         )
     assert len(_capture._ALL) == 1
     assert len(_outcome._settings) == 1
+
+
+def test_putting_a_batch_back_on_a_full_queue_drops_the_oldest_counted() -> None:
+    import collections
+
+    capturer = _capture.Capturer(Settings("http://ac.test", "ack_acme.k", None, 1.0))
+    capturer._queue = collections.deque([{"id": n} for n in (4, 5, 6)], maxlen=4)
+    capturer._put_back([{"id": 2}, {"id": 3}])  # older calls, one free place
+    assert [r["id"] for r in capturer._queue] == [3, 4, 5, 6] and capturer.dropped == 1
+    capturer._put_back([{"id": 1}])  # no room: the oldest is the one dropped
+    assert [r["id"] for r in capturer._queue] == [3, 4, 5, 6] and capturer.dropped == 2