Add silent-exception lint gate and annotate justified sites

.pre-commit-config.yaml

@@ -30,6 +30,12 @@ repos:
         language: system
         types: [python]
         pass_filenames: false
+      - id: silent-exceptions
+        name: silent exception lint
+        entry: uv run python scripts/lint_silent_exceptions.py
+        language: system
+        types: [python]
+        pass_filenames: false
 
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v5.0.0

changelog.d/+silent-exception-lint.added.md

@@ -0,0 +1 @@
+Add silent-exception lint gate and `# silent: <reason>` annotations to prevent unlogged exception swallowing

scripts/lint_silent_exceptions.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+"""Lint for silent exception swallowing patterns that ruff S110 misses.
+
+Checks production code (src/) for:
+1. contextlib.suppress(Exception) without a ``# silent:`` justification
+2. ``except ...: continue`` without logging or a ``# silent:`` comment
+
+Exit code 0 = clean, 1 = violations found.
+"""
+
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+_SUPPRESS_RE = re.compile(r"contextlib\.suppress\(\s*Exception\s*\)")
+_SILENT_TAG = re.compile(r"#\s*silent:")
+
+SRC = Path("src")
+
+
+def _check_file(path: Path) -> list[str]:
+    violations: list[str] = []
+    lines = path.read_text().splitlines()
+
+    for i, line in enumerate(lines, 1):
+        # Pattern 1: contextlib.suppress(Exception) without justification
+        if _SUPPRESS_RE.search(line) and not _SILENT_TAG.search(line):
+            violations.append(
+                f"{path}:{i}: contextlib.suppress(Exception) without '# silent: <reason>'"
+            )
+
+        # Pattern 2: bare except-continue (no logging on same or next line)
+        stripped = line.strip()
+        if stripped in ("continue", "continue  # noqa"):
+            # Walk back to find enclosing except
+            for j in range(i - 2, max(i - 5, -1), -1):
+                prev = lines[j].strip() if 0 <= j < len(lines) else ""
+                if prev.startswith("except"):
+                    # Check if there's logging between except and continue
+                    block = "\n".join(lines[j : i - 1])
+                    if "log" not in block and "warn" not in block and "# silent:" not in block:
+                        violations.append(
+                            f"{path}:{i}: except-continue without logging or '# silent: <reason>'"
+                        )
+                    break
+
+    return violations
+
+
+def main() -> int:
+    if not SRC.exists():
+        return 0
+
+    violations: list[str] = []
+    for path in sorted(SRC.rglob("*.py")):
+        violations.extend(_check_file(path))
+
+    for v in violations:
+        print(v, file=sys.stderr)
+
+    if violations:
+        print(
+            f"\n{len(violations)} silent-exception violation(s). "
+            "Add '# silent: <reason>' to justify, or add logging.",
+            file=sys.stderr,
+        )
+    return 1 if violations else 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

src/milo/_compat.py

@@ -126,7 +126,7 @@ def _loop() -> None:
             try:
                 cur = os.get_terminal_size()
             except OSError:
-                continue
+                continue  # silent: terminal may be detached
             if cur != prev:
                 prev = cur
                 callback(cur.columns, cur.lines)

src/milo/app.py

@@ -357,13 +357,13 @@ def _on_state_change() -> None:
             # Each cleanup step is individually guarded so a failure in one
             # does not prevent the rest from running.
             if tick_thread is not None:
-                with contextlib.suppress(Exception):
+                with contextlib.suppress(Exception):  # silent: teardown must not propagate
                     stop_tick.set()
-            with contextlib.suppress(Exception):
+            with contextlib.suppress(Exception):  # silent: teardown must not propagate
                 renderer.stop()
-            with contextlib.suppress(Exception):
+            with contextlib.suppress(Exception):  # silent: teardown must not propagate
                 stop_resize()
-            with contextlib.suppress(Exception):
+            with contextlib.suppress(Exception):  # silent: teardown must not propagate
                 store.shutdown()
 
         final_state = store.state

src/milo/config.py

@@ -289,7 +289,7 @@ def _load_file(filepath: str) -> dict[str, Any]:
             )
             raise ImportError(msg) from e
         with open(path) as f:
-            return yaml.safe_load(f) or {}
+            return yaml.safe_load(f) or {}  # empty YAML returns None; default to {}
 
     if suffix == ".json":
         import json

src/milo/dev.py

@@ -72,7 +72,7 @@ def _check_changes(self) -> list[Path]:
                 try:
                     mtime = p.stat().st_mtime
                 except OSError:
-                    continue
+                    continue  # silent: file may vanish between is_file and stat
                 if p in self._mtimes:
                     if mtime > self._mtimes[p]:
                         changed.append(p)

src/milo/gateway.py

@@ -183,7 +183,7 @@ def _run_gateway() -> None:
                 request = json.loads(line)
             except json.JSONDecodeError:
                 _write_error(None, -32700, "Parse error")
-                continue
+                continue  # silent: error already sent via JSON-RPC
 
             req_id = request.get("id")
             method = request.get("method", "")

src/milo/mcp.py

@@ -160,7 +160,7 @@ def run_mcp_server(cli: CLI) -> None:
             request = json.loads(line)
         except json.JSONDecodeError:
             _write_error(None, -32700, "Parse error")
-            continue
+            continue  # silent: error already sent via JSON-RPC
 
         req_id = request.get("id")
         method = request.get("method", "")

src/milo/registry.py

@@ -166,7 +166,7 @@ def _health_check_entry(name: str, info: dict[str, Any]) -> HealthResult:
                         stale=stale,
                     )
             except json.JSONDecodeError:
-                continue
+                continue  # silent: skip malformed lines; falls through to unreachable
 
         return HealthResult(
             name=name,