Add event-payload context resolver

src/activity_core/context_resolvers/__init__.py

@@ -1 +1,7 @@
-from activity_core.context_resolvers import kaizen, ops_inventory, repo_scoping, state_hub  # noqa: F401
+from activity_core.context_resolvers import (  # noqa: F401
+    event_payload,
+    kaizen,
+    ops_inventory,
+    repo_scoping,
+    state_hub,
+)

src/activity_core/context_resolvers/event_payload.py

@@ -0,0 +1,51 @@
+"""Event payload context adapter.
+
+Registered as source type ``event-payload``. It exposes the triggering
+EventEnvelope attributes to event-triggered ActivityDefinitions without
+requiring an external context service call.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from activity_core.context_resolvers.base import CONTEXT_RESOLVER_REGISTRY, ContextResolver
+
+
+class EventPayloadContextResolver(ContextResolver):
+    """Resolve context from the triggering event envelope attributes."""
+
+    def resolve(self, query: str, event: Any, params: dict[str, Any]) -> Any:
+        attributes = _event_attributes(event)
+        if query in {"", "attributes"}:
+            return attributes
+        if query.startswith("attributes."):
+            return _resolve_path(attributes, query.removeprefix("attributes."))
+        return _resolve_path(attributes, query)
+
+
+def _event_attributes(event: Any) -> dict[str, Any]:
+    if not isinstance(event, dict):
+        raise RuntimeError("event-payload source requires an event envelope")
+    attributes = event.get("attributes")
+    if not isinstance(attributes, dict):
+        raise RuntimeError("event-payload source requires envelope attributes")
+    return attributes
+
+
+def _resolve_path(root: dict[str, Any], path: str) -> Any:
+    if not path:
+        return root
+    current: Any = root
+    for part in path.split("."):
+        if not part:
+            return {}
+        if not isinstance(current, dict):
+            return {}
+        current = current.get(part)
+        if current is None:
+            return {}
+    return current
+
+
+CONTEXT_RESOLVER_REGISTRY["event-payload"] = EventPayloadContextResolver