Fix CI: resolve mypy type errors in config.py and server.py

- config.py: Add default empty string to os.getenv calls used with Path()
- server.py: Add Optional[] to threshold, min_val, max_val parameters
- server.py: Add _decay_engine type hint to HebbianMindDatabase.__init__
- server.py: Add Dict type annotation to by_category variable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: For-Sunny

src/hebbian_mind/config.py

@@ -82,7 +82,7 @@ class Config:
     RAM_DISK_ENABLED: bool = os.getenv("HEBBIAN_MIND_RAM_DISK", "false").lower() == "true"
     RAM_DATA_DIR: Optional[Path] = (
         (
-            Path(os.getenv("HEBBIAN_MIND_RAM_DIR"))
+            Path(os.getenv("HEBBIAN_MIND_RAM_DIR", ""))
             if os.getenv("HEBBIAN_MIND_RAM_DIR")
             else _get_default_ram_dir()
         )
@@ -99,7 +99,7 @@ class Config:
     # PRECOG concept extractor integration (optional)
     PRECOG_ENABLED: bool = os.getenv("HEBBIAN_MIND_PRECOG_ENABLED", "false").lower() == "true"
     PRECOG_PATH: Optional[Path] = (
-        Path(os.getenv("HEBBIAN_MIND_PRECOG_PATH"))
+        Path(os.getenv("HEBBIAN_MIND_PRECOG_PATH", ""))
         if os.getenv("HEBBIAN_MIND_PRECOG_PATH")
         else None
     )

src/hebbian_mind/server.py

@@ -95,6 +95,7 @@ def __init__(self):
         self._in_transaction = False
         self._coactivation_count = 0
         self._lock = threading.RLock()  # Serialize all DB access across threads
+        self._decay_engine: Optional[HebbianDecayEngine] = None
 
         self._init_connections()
         self._init_schema()
@@ -500,7 +501,7 @@ def get_node_by_name(self, name: str) -> Optional[Dict]:
         row = cursor.fetchone()
         return dict(row) if row else None
 
-    def analyze_content(self, content: str, threshold: float = None) -> List[Dict]:
+    def analyze_content(self, content: str, threshold: Optional[float] = None) -> List[Dict]:
         """Analyze content and return activated nodes.
 
         Enhanced with PRECOG ConceptExtractor (optional):
@@ -1124,7 +1125,9 @@ def _validate_string(value: Any, name: str, max_length: int = 100000) -> str:
     return value
 
 
-def _validate_number(value: Any, name: str, min_val: float = None, max_val: float = None) -> float:
+def _validate_number(
+    value: Any, name: str, min_val: Optional[float] = None, max_val: Optional[float] = None
+) -> float:
     """Validate and return a numeric parameter."""
     if not isinstance(value, (int, float)):
         raise ValueError(f"{name} must be a number, got {type(value).__name__}")
@@ -1420,7 +1423,7 @@ async def call_tool(name: str, arguments: Dict) -> List[types.TextContent]:
             if category:
                 nodes = [n for n in nodes if n["category"] == category]
 
-            by_category = {}
+            by_category: Dict[str, List[Dict[str, Any]]] = {}
             for node in nodes:
                 cat = node["category"]
                 if cat not in by_category: