feat(tracing): collect skill usage events

PR #6652 added SkillUsedEvent but deliberately shipped no listener wiring,
so the event reached no collector. The trace listener subscribed to the five
setup events -- discovery, load, activation, failure -- and none of them can
answer the question skills observability is for: activation is idempotent and
fires once at setup, so an agent using a skill across twenty turns produces
exactly one event.

SkillUsedEvent is the only runtime signal and the only one that re-fires per
execution. Subscribing to it lets a trace attribute skill usage to an agent
and a task.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/crewai/src/crewai/events/listeners/tracing/trace_listener.py

@@ -119,6 +119,7 @@ from crewai.events.types.skill_events import (
     SkillDiscoveryStartedEvent,
     SkillLoadFailedEvent,
     SkillLoadedEvent,
+    SkillUsedEvent,
 )
 from crewai.events.types.system_events import SignalEvent, on_signal
 from crewai.events.types.task_events import (
@@ -609,6 +610,13 @@ class TraceCollectionListener(BaseEventListener):
         def on_skill_load_failed(source: Any, event: SkillLoadFailedEvent) -> None:
             self._handle_action_event("skill_load_failed", source, event)
 
+        @event_bus.on(SkillUsedEvent)
+        def on_skill_used(source: Any, event: SkillUsedEvent) -> None:
+            # The other five describe setup; this is the only one that says a
+            # skill was actually used, and the only one that re-fires per
+            # execution. Without it a trace cannot attribute usage to a task.
+            self._handle_action_event("skill_used", source, event)
+
     def _register_a2a_event_handlers(self, event_bus: CrewAIEventsBus) -> None:
         """Register handlers for A2A (Agent-to-Agent) events."""
 

lib/crewai/tests/tracing/test_skill_used_tracing.py

@@ -0,0 +1,69 @@
+"""Skill usage must reach the trace collector.
+
+The five setup events (discovery, load, activation, failure) describe how an
+agent was configured and fire once. ``SkillUsedEvent`` is the only runtime
+signal -- it re-fires on every execution -- so without it a trace cannot say
+which skills an agent actually used, on which task, or how often.
+"""
+
+from pathlib import Path
+from unittest.mock import patch
+
+from crewai.events.event_bus import CrewAIEventsBus
+from crewai.events.listeners.tracing.trace_listener import TraceCollectionListener
+from crewai.events.types.skill_events import (
+    SkillActivatedEvent,
+    SkillUsedEvent,
+)
+import pytest
+
+
+@pytest.fixture
+def registered_listener():
+    """A listener wired to an isolated bus, with event handling captured."""
+    bus = CrewAIEventsBus()
+    listener = TraceCollectionListener.__new__(TraceCollectionListener)
+
+    with patch.object(TraceCollectionListener, "_handle_action_event") as handled:
+        listener._register_action_event_handlers(bus)
+        yield bus, handled
+
+
+def _event_types(handled) -> list[str]:
+    return [call.args[0] for call in handled.call_args_list]
+
+
+class TestSkillUsedIsCollected:
+    def test_skill_used_reaches_the_collector(self, registered_listener):
+        bus, handled = registered_listener
+
+        bus.emit(
+            None,
+            SkillUsedEvent(
+                skill_name="pdf-processing",
+                skill_path=Path("/skills/pdf-processing"),
+            ),
+        )
+        bus.flush()
+
+        assert "skill_used" in _event_types(handled), (
+            "SkillUsedEvent was emitted but the trace listener ignored it"
+        )
+
+    def test_every_use_is_collected(self, registered_listener):
+        """Activation is idempotent; usage is not. One event per use."""
+        bus, handled = registered_listener
+
+        for _ in range(3):
+            bus.emit(None, SkillUsedEvent(skill_name="pdf-processing"))
+        bus.flush()
+
+        assert _event_types(handled).count("skill_used") == 3
+
+    def test_setup_events_are_still_collected(self, registered_listener):
+        bus, handled = registered_listener
+
+        bus.emit(None, SkillActivatedEvent(skill_name="pdf-processing"))
+        bus.flush()
+
+        assert "skill_activated" in _event_types(handled)