Let a worker say what machine it is

A worker reported its labels and nothing about the machine behind them, so the
engine could route a node to a GPU box but not tell whether that box had a GPU
free. Inventory — cores, GPUs, memory — now arrives with the hello frame, and
the run frame carries back what the engine allocated for that call.

Which is protocol 2 on both ends. GPUs are never probed: asking a vendor tool
would make the one dependency two, so a GPU is what the batch job says it was
given or what --gpus says. A worker that reports nothing still attaches and is
scheduled by its label alone.

Two things a job scheduler needs: --max-idle stops a worker started for one job
rather than letting it hold its allocation to the walltime, and a refusal is now
fatal instead of a reconnect loop that reads as a hang in a job's log.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A6HeySA27EkGANZN95QySW

backend/fluksio/api/routes/workers.py

@@ -21,7 +21,12 @@ from pydantic import BaseModel, Field
 
 from fluksio.api.deps import get_current_active_superuser, get_current_user
 from fluksio.core import security
-from fluksio.flow.remote import PROTOCOL, RemoteWorker, RemoteWorkerHub
+from fluksio.flow.remote import (
+    PROTOCOL,
+    RemoteWorker,
+    RemoteWorkerHub,
+    WorkerInventory,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -40,6 +45,9 @@ class WorkerInfo(BaseModel):
     last_seen: float = 0.0
     python: str = ""
     venv_digest: str = ""
+    cpus: int = 1
+    gpus: int = 0
+    ram_mb: int | None = None
 
 
 class TokenRequest(BaseModel):
@@ -74,6 +82,9 @@ def read_workers(request: Request) -> Any:
             last_seen=worker.last_seen,
             python=str(worker.info.get("python") or ""),
             venv_digest=str(worker.info.get("venv_digest") or ""),
+            cpus=worker.inventory.cpus,
+            gpus=worker.inventory.gpus,
+            ram_mb=worker.inventory.ram_mb,
         )
         for worker in _hub(request.app).workers()
     ]
@@ -163,6 +174,7 @@ async def attach(websocket: WebSocket, token: str = "") -> None:
             "python": hello.get("python"),
             "venv_digest": hello.get("venv_digest"),
         },
+        inventory=WorkerInventory.from_hello(hello.get("inventory")),
     )
     hub.attach(worker)
     await websocket.send_json({"op": "welcome", "protocol": PROTOCOL, "name": name})