feat: async/parallel execution with configurable concurrency

Parallelize LLM calls across minibatches to reduce wall-clock time.
All domain ports (LLMPort, JudgePort, ProposerPort) are now async.
Adapter implementations wrap synchronous DSPy calls with asyncio.to_thread.
Judge calls run in parallel within a batch using asyncio.gather + semaphore.
Evaluator parallelizes minibatch execution with configurable concurrency.
Evolution loop and use case are fully async. Proposer stays sequential.
Added --max-concurrency CLI flag and max_concurrency YAML config field.
Added async_retry_with_backoff for async error handling.
All 139 unit tests pass.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/unit/test_error_handling.py

@@ -1,7 +1,7 @@
 """Unit tests for error handling: retry, circuit breaker, per-call isolation."""
 from __future__ import annotations
 
-from unittest.mock import MagicMock, patch
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 
@@ -96,7 +96,8 @@ def _make_eval_result(scores, feedbacks=None):
 
 
 class TestCircuitBreaker:
-    def test_trips_on_consecutive_failures(self):
+    @pytest.mark.asyncio
+    async def test_trips_on_consecutive_failures(self):
         """Loop stops when consecutive failures reach the threshold."""
         initial_eval = _make_eval_result([0.3, 0.4])
         evaluator = MagicMock()
@@ -109,8 +110,9 @@ class TestCircuitBreaker:
                 return initial_eval  # seed eval succeeds
             raise RuntimeError("LLM down")
 
-        evaluator.evaluate.side_effect = _evaluate
+        evaluator.evaluate = AsyncMock(side_effect=_evaluate)
         proposer = MagicMock()
+        proposer.propose = AsyncMock()
         bootstrap = MagicMock(spec=SyntheticBootstrap)
 
         loop = EvolutionLoop(
@@ -123,7 +125,7 @@ class TestCircuitBreaker:
             error_strategy="skip",
         )
         with patch.object(loop, "_log"):
-            state = loop.run(
+            state = await loop.run(
                 Prompt("test"),
                 [SyntheticExample("in", id=0), SyntheticExample("in2", id=1)],
                 "task",
@@ -135,7 +137,8 @@ class TestCircuitBreaker:
         assert len(cb_events) == 1
         assert state.iteration < 10  # stopped early
 
-    def test_abort_raises_on_first_error(self):
+    @pytest.mark.asyncio
+    async def test_abort_raises_on_first_error(self):
         """With error_strategy=abort, the first error raises immediately."""
         initial_eval = _make_eval_result([0.3, 0.4])
         evaluator = MagicMock()
@@ -148,8 +151,9 @@ class TestCircuitBreaker:
                 return initial_eval
             raise RuntimeError("LLM down")
 
-        evaluator.evaluate.side_effect = _evaluate
+        evaluator.evaluate = AsyncMock(side_effect=_evaluate)
         proposer = MagicMock()
+        proposer.propose = AsyncMock()
         bootstrap = MagicMock(spec=SyntheticBootstrap)
 
         loop = EvolutionLoop(
@@ -163,13 +167,14 @@ class TestCircuitBreaker:
         )
         with patch.object(loop, "_log"):
             with pytest.raises(RuntimeError, match="LLM down"):
-                loop.run(
+                await loop.run(
                     Prompt("test"),
                     [SyntheticExample("in", id=0), SyntheticExample("in2", id=1)],
                     "task",
                 )
 
-    def test_resets_on_success(self):
+    @pytest.mark.asyncio
+    async def test_resets_on_success(self):
         """Consecutive failure counter resets after a successful iteration."""
         initial_eval = _make_eval_result([0.3, 0.4])
         good_eval = _make_eval_result([0.8, 0.9])
@@ -194,9 +199,9 @@ class TestCircuitBreaker:
                 return initial_eval  # current eval
             return good_eval  # new eval
 
-        evaluator.evaluate.side_effect = _evaluate
+        evaluator.evaluate = AsyncMock(side_effect=_evaluate)
         proposer = MagicMock()
-        proposer.propose.return_value = Prompt("better prompt")
+        proposer.propose = AsyncMock(return_value=Prompt("better prompt"))
         bootstrap = MagicMock(spec=SyntheticBootstrap)
         bootstrap.sample_minibatch.return_value = [
             SyntheticExample(f"in{i}", id=i) for i in range(2)
@@ -212,7 +217,7 @@ class TestCircuitBreaker:
             error_strategy="skip",
         )
         with patch.object(loop, "_log"):
-            state = loop.run(
+            state = await loop.run(
                 Prompt("test"),
                 [SyntheticExample("in", id=0), SyntheticExample("in2", id=1)],
                 "task",
@@ -230,23 +235,24 @@ class TestCircuitBreaker:
 
 
 class TestPerCallIsolation:
-    def test_evaluator_isolates_execution_failure(self):
+    @pytest.mark.asyncio
+    async def test_evaluator_isolates_execution_failure(self):
         """A failing execution produces a sentinel output, not a crash."""
         executor = MagicMock()
-        executor.execute.side_effect = [
+        executor.execute = AsyncMock(side_effect=[
             "good output",
             RuntimeError("API error"),
             "another good output",
-        ]
+        ])
         judge = MagicMock()
-        judge.judge_batch.return_value = [
+        judge.judge_batch = AsyncMock(return_value=[
             (0.8, "good"),
             (0.0, "[judge error]"),
             (0.7, "ok"),
-        ]
+        ])
 
         evaluator = PromptEvaluator(executor, judge)
-        result = evaluator.evaluate(
+        result = await evaluator.evaluate(
             Prompt("test"),
             [
                 SyntheticExample("in0", id=0),
@@ -261,7 +267,8 @@ class TestPerCallIsolation:
         assert "execution error" in result.trajectories[1].output_text
         assert result.scores[0] == 0.8  # other items unaffected
 
-    def test_judge_adapter_isolates_single_failure(self):
+    @pytest.mark.asyncio
+    async def test_judge_adapter_isolates_single_failure(self):
         """DSPyJudgeAdapter returns sentinel for a failed item, not crash."""
         from prometheus.infrastructure.judge_adapter import DSPyJudgeAdapter
 
@@ -269,6 +276,7 @@ class TestPerCallIsolation:
         adapter._lm = MagicMock()
         adapter._max_retries = 1
         adapter._retry_delay_base = 0
+        adapter._semaphore = __import__("asyncio").Semaphore(5)
 
         # Mock _judge to fail on first call, succeed on second
         call_count = 0
@@ -289,9 +297,10 @@ class TestPerCallIsolation:
 
         with patch("prometheus.infrastructure.judge_adapter.dspy.context"):
             with patch(
-                "prometheus.infrastructure.retry.time.sleep"
+                "prometheus.infrastructure.retry.asyncio.sleep",
+                new=AsyncMock(),
             ):
-                results = adapter.judge_batch(
+                results = await adapter.judge_batch(
                     "task", [("input1", "output1"), ("input2", "output2")]
                 )