fix(memory): skills template None value causes empty content

- skills.yaml: use |default(0, true) to handle None values in Jinja2
  template (default() only replaces undefined, not None)
- content.py: log and raise on template rendering failure instead of
  silently swallowing the exception (results in empty content)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: chenjw

openviking/prompts/templates/memory/skills.yaml

@@ -7,7 +7,7 @@ enabled: true
 content_template: |
   Skill: {{ skill_name }}
   
-  - Success rate: {{ ((success_count|default(0) / (total_executions|default(1) if total_executions|default(0) > 0 else 1)) * 100)|round|int }}% ({{ success_count|default(0) }}/{{ total_executions|default(0) }})
+  - Success rate: {{ ((success_count|default(0, true) / (total_executions|default(1, true) if total_executions|default(0, true) > 0 else 1)) * 100)|round|int }}% ({{ success_count|default(0, true) }}/{{ total_executions|default(0, true) }})
   - Best for: {{ best_for|default('N/A') }}
   - Recommended flow: {{ recommended_flow|default('N/A') }}
   - Key dependencies: {{ key_dependencies|default('N/A') }}

openviking/session/memory/utils/content.py

@@ -76,9 +76,11 @@ def serialize_with_metadata(
 
             jinja_template = env.from_string(content_template)
             content = jinja_template.render(**template_vars).strip()
-        except Exception:
-            # If template rendering fails, use content as-is
-            pass
+        except Exception as e:
+            from openviking.telemetry import tracer
+
+            tracer.error(f"Template rendering failed, skipping write: {e}")
+            raise
 
     # Clean metadata - remove None values and memory_type
     clean_metadata = {k: v for k, v in metadata.items() if v is not None and k != "memory_type"}