Add _EventSubscription handle class returned from subscribe(), enabling
callers to dispose their subscription via handle.dispose(). Add explicit
unsubscribe(handler) method to the EventBus protocol, ReactiveEventBus,
and LoggingEventBus implementations. Both return True when handler was
found/removed, False otherwise. Update test suite with Behave scenarios,
Robot Framework integration tests, and helper functions.

@@ -121,0 +122,4 @@
+  # ReactiveEventBus unsubscribe (handle-based)
+  # ---------------------------------------------------------------------------
+
+  Scenario: ReactiveEventBus unsubscribes a handler via dispose

@@ -197,0 +217,4 @@
+@when('I call unsubscribe on a handler that was never subscribed TO "{et}"')
+def step_unsubscribe_unknown_handler(ctx: Context, et: str) -> None:
+    """Call unsubscribe with a brand-new lambda (never subscribed)."""
+    result = ctx.bus.unsubscribe(lambda e: None)  # type: ignore[arg-type]

@@ -204,2 +237,3 @@
     "plan_lifecycle_emits_event": plan_lifecycle_emits_event,
-    "container_event_bus_singleton": container_event_bus_singleton,
+    "reactive_unsubscribe": reactive_unsubscribe,
+    "logging_unsubscribe": logging_unsubscribe,

@@ -108,0 +118,4 @@
+        handle = _EventSubscription()
+        handle._handler = handler  # dispose uses this to find the dispatch entry
+        handle._parent_bus = self  # dispose navigates to bus internals
+        handle._subscription_handles = (self._subscription_handles,)

@@ -0,0 +19,4 @@
+if TYPE_CHECKING:
+    from typing import Protocol
+else:
+    Protocol = object  # type: ignore[misc, assignment]