core/agent: enrich ErrorEvent and CancelledEvent metadata

Add retryable/source on errors and optional reason on cancel; show them
in the CLI renderer.

src/plyngent/agent/events.py

@@ -30,10 +30,12 @@ class MaxRoundsEvent(Struct, tag_field="type", tag="max_rounds"):
 
 class ErrorEvent(Struct, tag_field="type", tag="error"):
     message: str
+    retryable: bool = True
+    source: str = ""
 
 
 class CancelledEvent(Struct, tag_field="type", tag="cancelled"):
-    pass
+    reason: str = ""
 
 
 type AgentEvent = (

src/plyngent/cli/display.py

@@ -52,8 +52,16 @@ async def render_events(events: AsyncIterator[AgentEvent]) -> None:  # noqa: C90
             one_line = preview.replace("\n", " ")
             click.secho(f"[tool ok] {one_line}", fg="magenta")
         elif isinstance(event, ErrorEvent):
-            click.secho(f"\n[error] {event.message}", fg="bright_red")
+            suffix = ""
+            if event.source:
+                suffix += f" source={event.source}"
+            if not event.retryable:
+                suffix += " (fatal)"
+            click.secho(f"\n[error]{suffix} {event.message}", fg="bright_red")
         elif isinstance(event, CancelledEvent):
+            if event.reason:
+                click.secho(f"\n[cancelled] {event.reason}", fg="yellow")
+            else:
                 click.secho("\n[cancelled]", fg="yellow")
         elif isinstance(event, MaxRoundsEvent):
             if event.continued: