fix(config): add default catch-all decision to enable PII detection for all requests

This fixes the E2E PII detection test failures (0% detection rate) by ensuring
PII detection is always enabled, even when no specific decision matches.

Previously, requests with model='MoM' (used by E2E tests) did not match any
decision criteria, causing decisionName to be empty. This triggered the check:
  if decisionName == '' { return false } // PII detection disabled

The fix adds a catch-all default_decision with:
- priority: 1 (lowest - matches only if nothing else does)
- type: 'always' (matches any request)
- pii_types_allowed: [] (blocks ALL PII for safety)

This ensures the 100 E2E PII test cases will be blocked correctly.

Fixes vllm-project#647 E2E test failures

Signed-off-by: Yossi Ovadia <[email protected]>

Author: yossiovadia

config/testing/config.e2e.yaml

@@ -359,6 +359,24 @@ decisions:
           enabled: true
           pii_types_allowed: ["EMAIL_ADDRESS", "PERSON", "GPE", "PHONE_NUMBER", "US_SSN", "CREDIT_CARD"]
 
+  # Default catch-all decision for unmatched requests (E2E PII test fix)
+  # This ensures PII detection is always enabled, even when no specific decision matches
+  - name: "default_decision"
+    description: "Default catch-all decision - blocks all PII for safety"
+    priority: 1  # Lowest priority - only matches if nothing else does
+    rules:
+      operator: "OR"
+      conditions:
+        - type: "always"  # Always matches as fallback
+    modelRefs:
+      - model: "Model-B"
+        use_reasoning: false
+    plugins:
+      - type: "pii"
+        configuration:
+          enabled: true
+          pii_types_allowed: []  # Block ALL PII - empty list means nothing allowed
+
 default_model: "Model-A"
 
 # API Configuration