adding DB Error in Observability

OBSERVABILITY_FIX_NOTES.md

@@ -0,0 +1,17 @@
+# Observability severity patch
+
+- Central `severity_policy.py` classifies explicit MCP failures, guardrail blocks, judge rejections, RAG failures and memory/cache errors.
+- `Telemetry.event()` accepts `level` and `status_message` and preserves WARNING/ERROR events as individual observations in compact mode.
+- `Telemetry.span()` handle supports `set_status(level, message)`; failed MCP results mark their span ERROR without raising exceptions.
+- Long-term-memory read/write failures emit telemetry while preserving existing fallback behavior.
+- Guardrail blocked and negative judge evaluation emit WARNING when these helper methods are invoked.
+- Normal cache misses and empty RAG results are not automatically failures.
+
+## Scope / limitations
+- Existing call sites must invoke `GuardrailTelemetry.blocked` for guardrail blocking events; this patch does not rewrite every pipeline call site.
+- Redis cache currently has no injected Telemetry instance, so its existing logger errors are not yet Langfuse observations. A separate dependency-injection change is required to cover that path safely.
+- RAG database connection errors that are caught by external KBDB integrations without emitting a telemetry event cannot be classified automatically.
+- No live Langfuse ingestion test was possible in this environment. Verify both compact and verbose modes against your server.
+
+## Validation
+`PYTHONPATH=libs/agent_framework/src python -m pytest -q tests/test_observability_severity_policy.py`