Backend: real alert test results, state cleanup on delete/rename, node trigger errors, queue and collector fixes

`AlertManager.send` swallowed every delivery failure, so the alerts screen's
Test button answered 200 whatever happened — the one thing it exists for. It
takes `raise_on_error` now, which only the test route passes; the per-channel
loop keeps the swallow, because one dead channel must not stop the others
hearing about the same fault. A refused delivery answers 502 with whatever the
sender said.

Renaming a flow left its values under the old name for good: the delete path
already swept them, the rename path never did. It calls the same `forget_flow`,
which covers the messages and the `__ts__`/`__version__`/`__history__`
bookkeeping keyed by message name. Cleanup, not migration — they repopulate
under the new name on the next run.

Triggering a node by hand ran `Node.__call__` with nothing catching it, so a
node that raised produced a 500 and a stack trace in the server log, and
nothing at all on the canvas. `Pipeline.publish_error` is the reporting half of
`_execute_node` lifted out; both paths go through it, so a manual failure now
reads the same on the canvas and in the metrics as a queued one. The route
answers 400 with the node's error.

`MemoryWorkQueue.stats()` counts claimed-but-unacknowledged work rather than
reporting zero, so the health tile means something without Redis. The metrics
collector's held tracebacks are capped at `DETAIL_CAP` and swept on the same
`RUN_STALE_S` cutoff the open runs use, instead of one untruncated traceback
per node kept for the life of the process — a traceback still survives the
flush between the log and the failure it belongs to.

`GET /observability/events` takes `since`/`until`, the window `/runs` already
took, so a failures list can cover the span the charts beside it are drawn from.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XC2jX6Hdj7pxGGKzBTrbqB

backend/app/api/routes/alerts.py

@@ -74,12 +74,18 @@ async def test_channel(channel_name: str, controller: FlowControllerDep) -> Any:
     if channel is None:
         raise HTTPException(status_code=404, detail=f"No channel '{channel_name}'")
 
-    await controller.alerts.send(
-        channel,
-        Alert(
-            title="Fluksio test alert",
-            body="If you are reading this, the channel works.",
-            severity="warning",
-        ),
-    )
+    try:
+        await controller.alerts.send(
+            channel,
+            Alert(
+                title="Fluksio test alert",
+                body="If you are reading this, the channel works.",
+                severity="warning",
+            ),
+            raise_on_error=True,
+        )
+    except Exception as exc:
+        # Whatever the sender said, verbatim: it is the only clue the operator
+        # has about why the channel does not work.
+        raise HTTPException(status_code=502, detail=str(exc) or type(exc).__name__)
     return Message(message=f"Sent a test alert through '{channel_name}'")

backend/app/api/routes/flows.py

@@ -432,6 +432,10 @@ async def rename_flow(
     except FlowExists as exc:
         raise HTTPException(status_code=409, detail=str(exc))
 
+    # The old name is nobody's namespace now; its values would sit there under a
+    # flow that no longer exists. They repopulate under the new name on the next
+    # run, so this is cleanup rather than a migration.
+    await run_in_threadpool(controller.forget_flow, name)
     await controller.reload()
     return _detail(controller, renamed)
 
@@ -633,13 +637,17 @@ async def trigger_node(
     """Feed values into a single node."""
     _require_enabled(controller, name)
     try:
-        await run_in_threadpool(
+        error = await run_in_threadpool(
             controller.trigger_node, f"{name}.{node_id}", body.values
         )
     except KeyError:
         raise HTTPException(
             status_code=404, detail=f"No node named '{node_id}' in flow '{name}'"
         )
+    if error:
+        # The canvas already has the failure from the bus; the person who
+        # clicked gets to read it too, instead of a stack trace in the log.
+        raise HTTPException(status_code=400, detail=error)
     return _flow_state(controller, name)
 
 

backend/app/api/routes/observability.py

@@ -306,9 +306,15 @@ def read_events(
     session: SessionDep,
     kind: Literal["failure", "audit"] = "failure",
     flow: str | None = None,
+    since: datetime | None = None,
+    until: datetime | None = None,
     limit: int = 100,
 ) -> Any:
-    """What went wrong, or who changed what. Newest first."""
+    """What went wrong, or who changed what. Newest first.
+
+    ``since`` is inclusive and ``until`` exclusive, the same window ``/runs``
+    takes, so a list can cover the span the charts beside it are drawn from.
+    """
     statement = select(EngineEvent).order_by(col(EngineEvent.ts).desc())
     if kind == "audit":
         statement = statement.where(col(EngineEvent.type) == "audit")
@@ -316,6 +322,10 @@ def read_events(
         statement = statement.where(col(EngineEvent.type) != "audit")
     if flow:
         statement = statement.where(col(EngineEvent.flow) == flow)
+    if since:
+        statement = statement.where(col(EngineEvent.ts) >= _aware(since))
+    if until:
+        statement = statement.where(col(EngineEvent.ts) < _aware(until))
     return list(session.exec(statement.limit(min(limit, 500))))