test(channels): pin stdlib-style logging across src (#1531)

After #1533, the napcat follow-up and #1529, no logger call in src passes a
'{}' message with arguments and none calls loguru's .opt(). An AST scan now
fails on either, with a probe proving the scan sees both forms.

agent/tests/test_channel_stdlib_logging.py

@@ -8,8 +8,11 @@ before anything is logged.
 
 from __future__ import annotations
 
+import ast
 import asyncio
 import logging
+import re
+from pathlib import Path
 from types import SimpleNamespace
 
 import pytest
@@ -34,3 +37,35 @@ def test_signal_safe_handle_logs_and_swallows(caplog) -> None:
     assert "Error in receive: boom" in record.getMessage()
     assert "100%" in record.getMessage()
     assert record.exc_info is not None
+
+
+_SRC = Path(__file__).resolve().parents[1] / "src"
+_BRACE_PLACEHOLDER = re.compile(r"\{(?:![rs])?(?::[^{}]*)?\}")
+_LOG_METHODS = {"debug", "info", "warning", "warn", "error", "exception", "critical"}
+
+
+def _loguru_style_calls(path: Path) -> list[str]:
+    found = []
+    for node in ast.walk(ast.parse(path.read_text(encoding="utf-8"))):
+        if not (isinstance(node, ast.Call) and isinstance(node.func, ast.Attribute)):
+            continue
+        if node.func.attr == "opt":
+            found.append(f"{path.name}:{node.lineno} .opt()")
+        elif node.func.attr in _LOG_METHODS and len(node.args) > 1:
+            first = node.args[0]
+            if isinstance(first, ast.Constant) and isinstance(first.value, str) and _BRACE_PLACEHOLDER.search(first.value):
+                found.append(f"{path.name}:{node.lineno} {first.value!r}")
+    return found
+
+
+def test_no_loguru_style_logging_anywhere_in_src() -> None:
+    """The whole tree logs through stdlib (#1533, its napcat follow-up, #1529)."""
+    offenders = [hit for path in sorted(_SRC.rglob("*.py")) for hit in _loguru_style_calls(path)]
+    assert not offenders, offenders
+
+
+def test_the_scan_sees_a_loguru_style_call(tmp_path: Path) -> None:
+    """Guard the guard: an empty scan would pass vacuously."""
+    probe = tmp_path / "probe.py"
+    probe.write_text('logger.info("sent {} to {}", a, b)\nlogger.opt(exception=True).error("x")\n', encoding="utf-8")
+    assert len(_loguru_style_calls(probe)) == 2