From abecea768ea25ba298f705bdc012057656679d8b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 10 Jun 2026 15:57:19 +0000
Subject: [PATCH 1/3] Initial plan


From 0c8774a88806a1ce5601cb7652af5f013bde3ca9 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 10 Jun 2026 16:05:07 +0000
Subject: [PATCH 2/3] Fix Learner2D restore snapshot mutation in balancing asks

---
 adaptive/learner/learner2D.py            |  6 +++---
 adaptive/tests/test_balancing_learner.py | 14 +++++++++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/adaptive/learner/learner2D.py b/adaptive/learner/learner2D.py
index 125fc055..349b0992 100644
--- a/adaptive/learner/learner2D.py
+++ b/adaptive/learner/learner2D.py
@@ -4,7 +4,7 @@
 import warnings
 from collections import OrderedDict
 from collections.abc import Callable, Iterable
-from copy import copy
+from copy import copy, deepcopy
 from math import sqrt
 
 import cloudpickle
@@ -897,8 +897,8 @@ def __getstate__(self):
             cloudpickle.dumps(self.function),
             self.bounds,
             self.loss_per_triangle,
-            self._stack,
-            self._get_data(),
+            deepcopy(self._stack),
+            deepcopy(self._get_data()),
         )
 
     def __setstate__(self, state):
diff --git a/adaptive/tests/test_balancing_learner.py b/adaptive/tests/test_balancing_learner.py
index c50b2105..5f91506e 100644
--- a/adaptive/tests/test_balancing_learner.py
+++ b/adaptive/tests/test_balancing_learner.py
@@ -2,7 +2,7 @@
 
 import pytest
 
-from adaptive.learner import BalancingLearner, Learner1D
+from adaptive.learner import BalancingLearner, Learner1D, Learner2D
 from adaptive.runner import simple
 
 strategies = ["loss", "loss_improvements", "npoints", "cycle"]
@@ -51,6 +51,18 @@ def test_ask_0(strategy):
     assert len(points) == 0
 
 
+def test_ask_without_pending_restores_learner2d_state():
+    learner = Learner2D(lambda xy: xy[0] + xy[1], bounds=((-1, 1), (-1, 1)))
+    initial_stack = list(learner._stack.items())
+    initial_data = learner.data.copy()
+
+    balancing_learner = BalancingLearner([learner])
+    balancing_learner.ask(1, tell_pending=False)
+
+    assert list(learner._stack.items()) == initial_stack
+    assert learner.data == initial_data
+
+
 @pytest.mark.parametrize(
     "strategy, goal_type, goal",
     [

From 5654448ea85babd5731e34beb73c266f88672bfc Mon Sep 17 00:00:00 2001
From: Bas Nijholt <bas@nijho.lt>
Date: Wed, 10 Jun 2026 15:39:45 -0700
Subject: [PATCH 3/3] Use shallow copies instead of deepcopy in
 Learner2D.__getstate__

Key-level mutations (stack pops/inserts) are all that restore() needs to
roll back; values are never mutated in place. A deepcopy of the full
data dict would add O(npoints) allocation to every
ask(tell_pending=False) call and to pickling.
---
 adaptive/learner/learner2D.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/adaptive/learner/learner2D.py b/adaptive/learner/learner2D.py
index 349b0992..f7e1fc21 100644
--- a/adaptive/learner/learner2D.py
+++ b/adaptive/learner/learner2D.py
@@ -4,7 +4,7 @@
 import warnings
 from collections import OrderedDict
 from collections.abc import Callable, Iterable
-from copy import copy, deepcopy
+from copy import copy
 from math import sqrt
 
 import cloudpickle
@@ -897,8 +897,8 @@ def __getstate__(self):
             cloudpickle.dumps(self.function),
             self.bounds,
             self.loss_per_triangle,
-            deepcopy(self._stack),
-            deepcopy(self._get_data()),
+            self._stack.copy(),
+            self._get_data().copy(),
         )
 
     def __setstate__(self, state):