Preserve discarded patch context

src/lai_automation/git.py

@@ -115,6 +115,13 @@ class GitWorkspace:
             deleted += int(remove) if remove.isdigit() else 0
         return ChangeSummary(tuple(files), added, deleted)
 
+    def diff(self, limit: int = 12_000) -> str:
+        output = self._git("diff", "--no-ext-diff", "--unified=3").stdout
+        if len(output) <= limit:
+            return output
+        half = limit // 2
+        return output[:half] + "\n...[diff middle omitted]...\n" + output[-half:]
+
     def commit(self, report_id: int) -> str:
         self._git("add", "--all")
         self._git("commit", "-m", f"Fix failure report #{report_id}")

src/lai_automation/worker.py

@@ -120,6 +120,7 @@ class AutomationWorker:
                         report.id,
                         attempt,
                     )
+                    discarded_diff = workspace.diff()
                     workspace.restore_checkpoint(valid_checkpoint)
                     restored_state = (
                         "The last syntax-valid changes were restored. Correct them without recreating "
@@ -131,7 +132,8 @@ class AutomationWorker:
                         report,
                         RuntimeError(
                             f"{exception}\n{restored_state} Make smaller edits and run php -l on each "
-                            "changed PHP file."
+                            "changed PHP file. Reconstruct the intended application fix from this discarded "
+                            f"patch excerpt, correcting its syntax:\n{discarded_diff}"
                         ),
                     )
                     continue

tests/test_git.py

@@ -83,4 +83,25 @@ def test_checkpoint_restores_last_valid_changes(tmp_path) -> None:
     workspace.restore_checkpoint(checkpoint)
 
     assert tracked.read_text() == "<?php\nreturn ['valid'];\n"
-    assert added.exists()
+    assert added.exists()
+
+
+def test_diff_returns_discarded_patch_excerpt(tmp_path) -> None:
+    workspace = GitWorkspace(settings(workspace_root=tmp_path), 5)
+    workspace.path.mkdir()
+    subprocess.run(["git", "init"], cwd=workspace.path, check=True, capture_output=True)
+    tracked = workspace.path / "service.php"
+    tracked.write_text("<?php\nreturn 'old';\n")
+    subprocess.run(["git", "add", "."], cwd=workspace.path, check=True)
+    subprocess.run(
+        ["git", "-c", "user.email=test@example.invalid", "-c", "user.name=Test", "commit", "-m", "base"],
+        cwd=workspace.path,
+        check=True,
+        capture_output=True,
+    )
+    tracked.write_text("<?php\nreturn 'new';\n")
+
+    patch = workspace.diff()
+
+    assert "-return 'old';" in patch
+    assert "+return 'new';" in patch

tests/test_worker.py

@@ -158,6 +158,7 @@ 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.diff.return_value = "--- app/Service.php\n+++ app/Service.php\n+intended fix"
     workspace.checkpoint.return_value = "valid-checkpoint"
     workspace.commit.return_value = "commit-id"
 
@@ -167,6 +168,7 @@ 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]
+    assert "intended fix" in worker.agent.run.call_args_list[1].args[1]
     workspace.restore_checkpoint.assert_called_once_with(None)
     worker._run_tests.assert_called_once()
 
@@ -207,6 +209,7 @@ def test_malformed_retry_restores_last_syntax_valid_attempt() -> None:
         Mock(returncode=0, stdout="No syntax errors", stderr=""),
         Mock(returncode=0, stdout="No syntax errors", stderr=""),
     ]
+    workspace.diff.return_value = "--- app/Service.php\n+++ app/Service.php\n+application repair"
     workspace.checkpoint.side_effect = ["checkpoint-1", "checkpoint-3"]
     workspace.commit.return_value = "commit-id"
 
@@ -216,6 +219,7 @@ def test_malformed_retry_restores_last_syntax_valid_attempt() -> None:
     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 "application repair" in worker.agent.run.call_args_list[2].args[1]
     assert worker._run_tests.call_count == 2