feat(tracing): collect skill usage events (#6727)

* 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>

* fix(tests): scope the trace-listener handlers, assert the forwarded event

CrewAIEventsBus is a singleton, so constructing one in the fixture still
registered against the process-wide bus. _register_action_event_handlers
attached every action handler with no cleanup, leaving them live after the
patch ended -- firing against a listener built with __new__, which has no
batch_manager, in whatever test ran next. scoped_handlers clears them.

Also assert the event object itself is forwarded, not just its type: the
collector serializes the event, so dropping or replacing it would lose every
attribution field while still passing a type-only check.

Both raised in review on #6727.

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

* test: assert the forwarded skill event by identity

Comparing field values would still pass if a handler forwarded a
reconstructed copy rather than the event itself. Bind the event and assert
`forwarded is event`.

Raised in review on #6727.

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

---------

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 +1,102 @@
+"""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 crewai_event_bus
+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 the bus, with event handling captured.
+
+    ``scoped_handlers`` is required, not tidiness: ``CrewAIEventsBus`` is a
+    singleton, so registering on a locally constructed one still mutates the
+    process-wide bus. Without the scope these handlers outlive the test and
+    fire against a listener built with ``__new__`` -- no ``batch_manager`` --
+    in whatever runs next.
+    """
+    listener = TraceCollectionListener.__new__(TraceCollectionListener)
+
+    with (
+        crewai_event_bus.scoped_handlers(),
+        patch.object(TraceCollectionListener, "_handle_action_event") as handled,
+    ):
+        listener._register_action_event_handlers(crewai_event_bus)
+        yield crewai_event_bus, handled
+
+
+def _event_types(handled) -> list[str]:
+    return [call.args[0] for call in handled.call_args_list]
+
+
+def _events_of_type(handled, event_type: str) -> list:
+    """The event objects forwarded for one collected type."""
+    return [call.args[2] for call in handled.call_args_list if call.args[0] == event_type]
+
+
+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_the_event_itself_is_forwarded_intact(self, registered_listener):
+        """The type alone is not enough -- the collector serializes the event,
+        so dropping or replacing it would lose every attribution field.
+
+        Asserted by identity: comparing field values would still pass if a
+        handler forwarded a reconstructed copy.
+        """
+        bus, handled = registered_listener
+        event = SkillUsedEvent(
+            skill_name="pdf-processing",
+            skill_path=Path("/skills/pdf-processing"),
+        )
+
+        bus.emit(None, event)
+        bus.flush()
+
+        [forwarded] = _events_of_type(handled, "skill_used")
+        assert forwarded is event
+
+    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)