Preserve valid agent retry progress

tests/test_worker.py

@@ -139,6 +139,7 @@ def test_php_syntax_failure_discards_attempt_before_full_validation() -> None:
         Mock(returncode=0, stdout="No syntax errors", stderr=""),
         Mock(returncode=0, stdout="No syntax errors", stderr=""),
     ]
+    workspace.checkpoint.return_value = "valid-checkpoint"
     workspace.commit.return_value = "commit-id"
 
     with patch("lai_automation.worker.GitWorkspace", return_value=workspace):
@@ -147,10 +148,58 @@ def test_php_syntax_failure_discards_attempt_before_full_validation() -> None:
     assert worker.agent.run.call_count == 2
     assert "unexpected token" in worker.agent.run.call_args_list[1].args[1]
     assert "clean repository" in worker.agent.run.call_args_list[1].args[1]
-    workspace.discard_changes.assert_called_once()
+    workspace.restore_checkpoint.assert_called_once_with(None)
     worker._run_tests.assert_called_once()
 
 
+def test_malformed_retry_restores_last_syntax_valid_attempt() -> None:
+    report = FailureReport(
+        id=56,
+        chat_message_id=1,
+        source="user_feedback",
+        category="incorrect_answer",
+        user_feedback="Wrong hours",
+        feedback_type="wrong_result",
+        expected_behavior="Use time registration",
+        prompt="Hours in April",
+        response="0 hours",
+        sql_query="SELECT 0",
+        error_message=None,
+        context={},
+    )
+    config = settings(mode="pr", dry_run=False, gitea_token="token", max_agent_attempts=3)
+    worker = AutomationWorker(config)
+    worker.reports = Mock()
+    worker.reports.claim_next.return_value = report
+    worker.agent = Mock()
+    worker.agent.run.side_effect = ["valid but failing", "broken retry", "corrected retry"]
+    worker.gitea = Mock()
+    worker._run_tests = Mock(side_effect=[RuntimeError("Expected hour rule"), []])
+    workspace = Mock()
+    workspace.path = Path("/tmp/nonexistent-workspace")
+    workspace.branch = "ai/failure-56"
+    workspace.summary.return_value = ChangeSummary(
+        ("config/erp_semantics.php", "tests/Unit/FixTest.php"), 20, 2
+    )
+    workspace.run_args.side_effect = [
+        Mock(returncode=0, stdout="No syntax errors", stderr=""),
+        Mock(returncode=0, stdout="No syntax errors", stderr=""),
+        Mock(returncode=255, stdout="Parse error", stderr="unexpected token"),
+        Mock(returncode=0, stdout="No syntax errors", stderr=""),
+        Mock(returncode=0, stdout="No syntax errors", stderr=""),
+    ]
+    workspace.checkpoint.side_effect = ["checkpoint-1", "checkpoint-3"]
+    workspace.commit.return_value = "commit-id"
+
+    with patch("lai_automation.worker.GitWorkspace", return_value=workspace):
+        assert worker.run_once()
+
+    assert worker.agent.run.call_count == 3
+    workspace.restore_checkpoint.assert_called_once_with("checkpoint-1")
+    assert "last syntax-valid changes were restored" in worker.agent.run.call_args_list[2].args[1]
+    assert worker._run_tests.call_count == 2
+
+
 def test_failed_validation_gets_one_correction_before_pr() -> None:
     report = FailureReport(
         id=13,