feat: Implement GovernancePlugin to filter forbidden emojis from model responses

src/va_agent/governance.py

@@ -0,0 +1,80 @@
+"""GovernancePlugin: Guardrails for VAia, the virtual assistant for VA."""
+import logging
+import re
+
+from google.adk.agents.callback_context import CallbackContext
+from google.adk.models import LlmResponse
+
+logger = logging.getLogger(__name__)
+
+
+FORBIDDEN_EMOJIS = [
+    "🥵","🔪","🎰","🎲","🃏","😤","🤬","😡","😠","🩸","🧨","🪓","☠️","💀",
+    "💣","🔫","👗","💦","🍑","🍆","👄","👅","🫦","💩","⚖️","⚔️","✝️","🕍",
+    "🕌","⛪","🍻","🍸","🥃","🍷","🍺","🚬","👹","👺","👿","😈","🤡","🧙",
+    "🧛","🔞","🧿","💊",
+    "💏"
+]
+
+
+class GovernancePlugin:
+    """Guardrail executor for VAia requests as a Agent engine callbacks."""
+
+    def __init__(self) -> None:
+        """Initialize guardrail model (structured output), prompt and emojis patterns."""
+        self._combined_pattern = self._get_combined_pattern()
+
+    def _get_combined_pattern(self):
+        person_pattern = r"(?:🧑|👩|👨)"
+        tone_pattern = r"[\U0001F3FB-\U0001F3FF]?"
+
+        # Unique pattern that combines all forbidden emojis, including complex ones with skin tones
+        combined_pattern = re.compile(
+            rf"{person_pattern}{tone_pattern}\u200d❤️?\u200d💋\u200d{person_pattern}{tone_pattern}"  # kiss
+            rf"|{person_pattern}{tone_pattern}\u200d❤️?\u200d{person_pattern}{tone_pattern}"  # lovers
+            rf"|🖕[\U0001F3FB-\U0001F3FF]?"  # middle finger with all skin tone variations
+            rf"|{'|'.join(map(re.escape, sorted(FORBIDDEN_EMOJIS, key=len, reverse=True)))}"  # simple emojis
+            rf"|\u200d|\uFE0F"  # residual ZWJ and variation selectors
+        )
+        return combined_pattern
+    
+    def _remove_emojis(self, text: str) -> tuple[str, list[str]]:
+        removed = self._combined_pattern.findall(text)
+        text = self._combined_pattern.sub("", text)
+        return text.strip(), removed
+
+
+    def after_model_callback(
+        self,
+        callback_context: CallbackContext | None = None,
+        llm_response: LlmResponse | None = None,
+    ) -> None:
+        """Guardrail post-processing.
+
+        Remove forbidden emojis from the model response.
+        """
+        try:
+            text_out = ""
+            if llm_response and llm_response.content:
+                content = llm_response.content
+                parts = getattr(content, "parts", None)
+                if parts:
+                    part = parts[0]
+                    text_value = getattr(part, "text", "")
+                    if isinstance(text_value, str):
+                        text_out = text_value
+
+            if text_out:
+                new_text, deleted = self._remove_emojis(text_out)
+                if llm_response and llm_response.content and llm_response.content.parts:
+                    llm_response.content.parts[0].text = new_text
+                if deleted:
+                    if callback_context:
+                        callback_context.state["removed_emojis"] = deleted
+                    logger.warning(
+                        "Removed forbidden emojis from response: %s",
+                        deleted,
+                    )
+
+        except Exception:
+            logger.exception("Error in after_model_callback")