feat(prepare-win): pre-snapshot idle CPU/RAM check (abort if busy)

After the final reboot and just before the graceful shutdown for the
snapshot, sample the guest's idle CPU and used-RAM percentages (CIM
Win32_PerfFormattedData — locale-independent — averaged over ~5s after a
settle delay). If either exceeds its threshold, abort prepare without
taking the snapshot, so a busy/leaky template isn't frozen into every clone.

New options: --max-idle-cpu (10%), --max-idle-ram (50%), --idle-settle
(30s), --skip-idle-check.

src/ci_orchestrator/commands/template.py

@@ -360,6 +360,56 @@ def _wait_winrm(transport: WinRmTransport, timeout: int) -> None:
     raise click.ClickException(f"WinRM not ready within {timeout}s.")
 
 
+def _check_guest_idle(
+    transport: WinRmTransport, *, max_cpu: float, max_ram: float, settle_s: int
+) -> None:
+    """Sample guest CPU/RAM after a settle period; abort if above thresholds.
+
+    Run just before the snapshot so a busy/leaky template (e.g. a service stuck
+    spinning after the toolchain install) is caught instead of being frozen into
+    every build clone. CPU via Win32_PerfFormattedData (0-100, locale-independent);
+    RAM as used-physical percent.
+    """
+    click.echo(
+        f"[prepare-win] Idle check (settle {settle_s}s; thresholds "
+        f"CPU<={max_cpu}% RAM<={max_ram}%) ..."
+    )
+    ps = (
+        f"Start-Sleep -Seconds {settle_s}\n"
+        "$s = 0..4 | ForEach-Object { (Get-CimInstance "
+        "Win32_PerfFormattedData_PerfOS_Processor -Filter \"Name='_Total'\")"
+        ".PercentProcessorTime; Start-Sleep -Milliseconds 1000 }\n"
+        "$cpu = [math]::Round((($s | Measure-Object -Average).Average), 1)\n"
+        "$os = Get-CimInstance Win32_OperatingSystem\n"
+        "$ram = [math]::Round((1 - ($os.FreePhysicalMemory / "
+        "$os.TotalVisibleMemorySize)) * 100, 1)\n"
+        "[pscustomobject]@{cpu=$cpu; ram=$ram} | ConvertTo-Json -Compress\n"
+    )
+    res = transport.run(ps, check=False)
+    lines = [ln for ln in res.stdout.splitlines() if ln.strip()]
+    try:
+        data = json.loads(lines[-1])
+        cpu = float(data["cpu"])
+        ram = float(data["ram"])
+    except (json.JSONDecodeError, KeyError, ValueError, IndexError) as exc:
+        raise click.ClickException(
+            f"Idle check: could not parse guest metrics.\n{res.stdout}\n{res.stderr}"
+        ) from exc
+    click.echo(f"[prepare-win]   idle CPU {cpu}%  RAM {ram}%")
+    problems: list[str] = []
+    if cpu > max_cpu:
+        problems.append(f"CPU {cpu}% > {max_cpu}%")
+    if ram > max_ram:
+        problems.append(f"RAM {ram}% > {max_ram}%")
+    if problems:
+        raise click.ClickException(
+            "Guest not idle before snapshot: "
+            + "; ".join(problems)
+            + ". Aborting — snapshot NOT taken; investigate the template."
+        )
+    click.echo("[prepare-win]   idle OK.")
+
+
 def _run_with_heartbeat(
     transport: WinRmTransport,
     script: str,
@@ -442,6 +492,14 @@ def _run_with_heartbeat(
 @click.option("--gui/--nogui", "gui", default=False, show_default=True,
               help="Start the VM with the Workstation window (--gui, needs an X display) "
                    "or headless (--nogui, the default).")
+@click.option("--max-idle-cpu", default=10.0, show_default=True,
+              help="Abort before snapshot if idle CPU exceeds this percent.")
+@click.option("--max-idle-ram", default=50.0, show_default=True,
+              help="Abort before snapshot if used RAM exceeds this percent.")
+@click.option("--idle-settle", default=30, show_default=True,
+              help="Seconds to let the guest settle before sampling idle CPU/RAM.")
+@click.option("--skip-idle-check", is_flag=True, default=False,
+              help="Skip the pre-snapshot idle CPU/RAM check.")
 def template_prepare_win(
     vmx: str,
     guest_ip: str,
@@ -460,6 +518,10 @@ def template_prepare_win(
     credential_target: str,
     recreate_snapshot: bool,
     gui: bool,
+    max_idle_cpu: float,
+    max_idle_ram: float,
+    idle_settle: int,
+    skip_idle_check: bool,
 ) -> None:
     """Provision a Windows template VM via pypsrp (Linux-host compatible).
 
@@ -742,6 +804,15 @@ Register-ScheduledTask -TaskName 'CI-StaticIp' `
             "}\n"
         )
 
+        # Pre-snapshot idle check — abort (no snapshot) if the template is busy.
+        if not skip_idle_check:
+            _check_guest_idle(
+                transport,
+                max_cpu=max_idle_cpu,
+                max_ram=max_idle_ram,
+                settle_s=idle_settle,
+            )
+
         # Graceful shutdown
         click.echo("[prepare-win] Sending graceful shutdown ...")
         with contextlib.suppress(TransportError):