fix: validate project path key, avoid shared mutable default

bin/config.py

@@ -13,7 +13,9 @@ def load_config(path=CONFIG_PATH):
     if not cfg or 'projects' not in cfg or not cfg['projects']:
         raise ConfigError(f"'projects' list is required in {path}")
     for p in cfg['projects']:
-        p.setdefault('benchmarks', DEFAULTS['benchmarks'])
+        if not isinstance(p, dict) or 'path' not in p:
+            raise ConfigError(f"Each project must have a 'path' key, got: {p!r}")
+        p.setdefault('benchmarks', list(DEFAULTS['benchmarks']))
         p.setdefault('time_limit_minutes', DEFAULTS['time_limit_minutes'])
         p['path'] = os.path.expanduser(p['path'])
     cfg.setdefault('token_threshold', {'context_remaining_pct': 60, 'api_budget_usd': 5.0})

tests/test_config.py

@@ -23,6 +23,18 @@ def test_missing_projects_raises():
         load_config(name)
     os.unlink(name)
 
+def test_project_missing_path_raises():
+    data = {
+        'projects': [{'benchmarks': ['echo ok']}],  # no 'path' key
+        'token_threshold': {'context_remaining_pct': 60, 'api_budget_usd': 5.0}
+    }
+    with tempfile.NamedTemporaryFile('w', suffix='.yaml', delete=False) as f:
+        yaml.dump(data, f)
+        name = f.name
+    with pytest.raises(ConfigError):
+        load_config(name)
+    os.unlink(name)
+
 def test_expands_tilde_in_path():
     data = {
         'projects': [{'path': '~/.claude', 'benchmarks': [], 'time_limit_minutes': 5}],