fix: classify landed file mutations with diagnostics

tests/agent/test_tool_result_classification.py

@@ -0,0 +1,30 @@
+"""Tests for shared tool result classification helpers."""
+
+import json
+
+from agent.tool_result_classification import file_mutation_result_landed
+
+
+def test_write_file_with_nested_lint_error_counts_as_landed():
+    result = json.dumps({
+        "bytes_written": 12,
+        "lint": {"status": "error", "output": "SyntaxError: invalid syntax"},
+    })
+
+    assert file_mutation_result_landed("write_file", result) is True
+
+
+def test_patch_with_nested_lsp_diagnostics_counts_as_landed():
+    result = json.dumps({
+        "success": True,
+        "diff": "--- a/tmp.py\n+++ b/tmp.py\n",
+        "lsp_diagnostics": "<diagnostics>ERROR [1:1] type mismatch</diagnostics>",
+    })
+
+    assert file_mutation_result_landed("patch", result) is True
+
+
+def test_top_level_file_mutation_error_does_not_count_as_landed():
+    result = json.dumps({"success": True, "error": "post-write verification failed"})
+
+    assert file_mutation_result_landed("patch", result) is False