Name card folders by GPU UUID, record serial in serial.txt

Folder identity switches from the physical serial (which neither
nvflash nor nvidia-smi exposes on the 170HX) to the auto-read GPU
UUID from nvidia-smi. The physical serial probe result (or N/A) is
saved to <folder>/serial.txt and report.json. No manual serial
prompt anymore; --serial only overrides the recorded serial.
Unidentified runs fall back to unidentified/<bdf>/. AGENTS.md
invariant and README updated to match.

cxlib.py

@@ -14,6 +14,7 @@ from pathlib import Path
 SCRIPT_DIR = Path(__file__).resolve().parent
 HARNESS_DIR = SCRIPT_DIR / "harness"
 CARDS_DIR = SCRIPT_DIR / "cards"
+UNIDENTIFIED_DIR = SCRIPT_DIR / "unidentified"
 
 REPOS = {
     "170th-Street": "https://github.com/amoghmunikote/170th-Street.git",
@@ -633,12 +634,7 @@ def get_serial(nf, args):
         warn("nvflash present but exposes no serial/UUID for this card")
     else:
         warn("nvflash unavailable - cannot auto-read serial")
-    serial = ""
-    while not serial:
-        serial = ask("Enter serial number from the card label (folder name)")
-        if not serial:
-            warn("serial is required for the folder name")
-    return serial, "manual-label"
+    return "N/A", "unavailable"
 
 
 def save_bios(nf, out_path, args):
@@ -692,6 +688,20 @@ def nvidia_smi_info():
     return {"available": True, "gpus": rows}
 
 
+def get_gpu_uuid():
+    """First GPU UUID from nvidia-smi (e.g. GPU-xxxx...), or None."""
+    if not which("nvidia-smi"):
+        return None
+    q = run(["nvidia-smi", "--query-gpu=uuid", "--format=csv,noheader"], timeout=30)
+    if q["rc"] != 0:
+        return None
+    for line in q["out"].splitlines():
+        line = line.strip()
+        if line.startswith("GPU-"):
+            return line
+    return None
+
+
 def run_verify_unlocker():
     if not VERIFY_SH.exists():
         return {"ran": False, "note": "harness/cmpunlocker not cloned"}