feat: a GPU agent on the CPU shows as degraded, in the System view and on its own page (4410)

torch and onnxruntime both fall back to the CPU without raising, so the agent
that ran CPU-bound for weeks after a driver update leased and checked in like
a healthy one.

- The agent sends its startup accel report on every lease and heartbeat.
- The server keeps a bounded copy on the roster row. A running agent with a
  runtime off the GPU becomes `degraded`, with a sentence naming the runtime
  and the reason.
- The top nav shows it amber.
- The agent page carries a banner, and its pill reads "CPU only".

Also: the bandwidth field gets the page's − / + stepper, and both number
fields drop the browser's spin arrows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

backend/app/api/gpu.py

@@ -245,6 +245,29 @@ async def errors_recover(image_id: int):
 
 # --- Agent (bearer token): lease / submit / heartbeat / fail ------------
 
+
+def _accel_detail(body: dict) -> dict:
+    """The agent's own report of which runtime got the GPU, kept on its roster
+    row so the System view can call a CPU-bound agent degraded (#4410).
+
+    Only a dict of {runtime: {device, error?}} is kept, and each value is
+    reduced to those two short strings: this is written on every lease, by a
+    client the server does not control. An agent that sends nothing (an
+    older build) simply has no `accel`, which reads as not-yet-reported.
+    """
+    raw = body.get("accel")
+    if not isinstance(raw, dict):
+        return {}
+    accel = {}
+    for name, entry in list(raw.items())[:4]:
+        if not isinstance(entry, dict):
+            continue
+        clean = {"device": str(entry.get("device") or "")[:16]}
+        if entry.get("error"):
+            clean["error"] = str(entry["error"])[:200]
+        accel[str(name)[:16]] = clean
+    return {"accel": accel} if accel else {}
+
 @gpu_bp.route("/jobs/lease", methods=["POST"])
 async def lease():
     body = await request.get_json(silent=True) or {}
@@ -267,7 +290,10 @@ async def lease():
             key=f"agent:{agent_id}",
             kind="agent",
             display_name="GPU agent" if agent_id == "agent" else f"GPU agent ({agent_id})",
-            details={"agent_id": agent_id, "last_call": "lease", "leased": len(jobs)},
+            details={
+                "agent_id": agent_id, "last_call": "lease", "leased": len(jobs),
+                **_accel_detail(body),
+            },
         )
         ml = await MLSettings.load(session)
         # image rows for url/mime in one shot
@@ -347,7 +373,10 @@ async def heartbeat():
             key=f"agent:{agent_id}",
             kind="agent",
             display_name="GPU agent" if agent_id == "agent" else f"GPU agent ({agent_id})",
-            details={"agent_id": agent_id, "last_call": "heartbeat", "extended": n},
+            details={
+                "agent_id": agent_id, "last_call": "heartbeat", "extended": n,
+                **_accel_detail(body),
+            },
         )
         await session.commit()
     return jsonify({"extended": n})