fix(session_search): coerce limit to int to prevent TypeError with non-int values (#10522)

Models (especially open-source like qwen3.5-plus) may send non-int values
for the limit parameter — None (JSON null), string, or even a type object.
This caused TypeError: '<=' not supported between instances of 'int' and
'type' when the value reached min()/comparison operations.

Changes:
- Add defensive int coercion at session_search() entry with fallback to 3
- Clamp limit to [1, 5] range (was only capped at 5, not floored)
- Add tests for None, type object, string, negative, and zero limit values

Reported by community user ludoSifu via Discord.

tools/session_search_tool.py

@@ -310,7 +310,15 @@ def session_search(
     if db is None:
         return tool_error("Session database not available.", success=False)
 
-    limit = min(limit, 5)  # Cap at 5 sessions to avoid excessive LLM calls
+    # Defensive: models (especially open-source) may send non-int limit values
+    # (None when JSON null, string "int", or even a type object).  Coerce to a
+    # safe integer before any arithmetic/comparison to prevent TypeError.
+    if not isinstance(limit, int):
+        try:
+            limit = int(limit)
+        except (TypeError, ValueError):
+            limit = 3
+    limit = max(1, min(limit, 5))  # Clamp to [1, 5]
 
     # Recent sessions mode: when query is empty, return metadata for recent sessions.
     # No LLM calls — just DB queries for titles, previews, timestamps.