Keep the engine's own history, and a screen that reads it

A second bus subscriber folds executions, errors, timings and queue lag
into per-minute rollups, keeps failures with their traceback and an audit
trail of who published what, and records one row per cascade — manual runs
and previews included, under an id of their own that writes no idempotency
markers. Read back through /observability/*, which always answers 200 so a
degraded engine still renders its own health screen.

Also fixes two things found on the way: node-health alerts read `status`
where the engine publishes `health`, so a device dropping never alerted
anyone, and the Redis queue reported `parked: 0` whatever was held.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017MeiWk3Yq12n2pTvnQWYvt

backend/app/mcp/server.py

@@ -265,3 +265,45 @@ async def apply_modules(requirements: str) -> Any:
     manifest that does not resolve changes nothing.
     """
     return await _call("POST", "/modules/apply", json={"requirements": requirements})
+
+
+# -----------------------------------------------------------------------------
+# Observability
+# -----------------------------------------------------------------------------
+
+
+@mcp.tool()
+async def get_health() -> Any:
+    """How the engine is doing: flows, nodes, queue, loop lag and recent failures."""
+    return await _call("GET", "/observability/summary")
+
+
+@mcp.tool()
+async def get_metrics(
+    flow: str | None = None, node: str | None = None, hours: int = 24
+) -> Any:
+    """Executions, errors and timings per minute over the last few hours."""
+    params: dict[str, Any] = {"hours": hours}
+    if flow:
+        params["flow"] = flow
+    if node:
+        params["node"] = node
+    return await _call("GET", "/observability/timeseries", params=params)
+
+
+@mcp.tool()
+async def list_failures(flow: str | None = None, limit: int = 50) -> Any:
+    """Recent failures with their tracebacks, newest first."""
+    params: dict[str, Any] = {"kind": "failure", "limit": limit}
+    if flow:
+        params["flow"] = flow
+    return await _call("GET", "/observability/events", params=params)
+
+
+@mcp.tool()
+async def list_runs(flow: str | None = None, limit: int = 50) -> Any:
+    """Recent cascades: what triggered them, how long they took, how they ended."""
+    params: dict[str, Any] = {"limit": limit}
+    if flow:
+        params["flow"] = flow
+    return await _call("GET", "/observability/runs", params=params)