#!/usr/bin/env python3
"""ksim - Kubernetes certification exam simulator (CKA / CKAD / CKS tracks).
Hands-on tasks graded per-check, each on its own cluster that you reach with `ssh <host>` from a
remote desktop in the browser - the way the real exams run - with an exam clock, attempt history,
a weak-spot log, drills, and a study path through each curriculum."""
import concurrent.futures
import http.server
import importlib
import json
import os
import random
import re
import shutil
import signal
import subprocess
import sys
import textwrap
import threading
import time
import urllib.parse
from collections.abc import Callable
from datetime import datetime
from typing import Any

VERSION = "2026.10.12.1"
ROOT = os.path.dirname(os.path.abspath(__file__))
sys.path.insert(0, ROOT)
from sim import desktop, envs  # noqa: E402

# ------------------------------------------------------------ track ----
ARGV = sys.argv[1:]
TRACKS = ["cka", "ckad", "cks"]
TRACK_ID = ""
TRACK = {}
QUESTIONS = []
DOMAINS = {}
QUOTA = {}
QUOTA_HARD = {}
QBYID = {}
SETS = {}
POOL = []
EXAM_SECONDS = 0
PASS_PCT = 0
STATE_FILE = ""
HISTORY_FILE = ""
WEAK_FILE = ""
STUDY_FILE = ""   # tasks solved in study mode (the objective checklist reads it; history never does)
OBJECTIVES = []   # the track's curriculum, objective by objective (<track>/curriculum.py), if it has one
STUDY_ORDER = []  # domains in the order the path walks them, when that differs from the curriculum's own
K8S = ""          # Kubernetes minor the track's real exam runs, e.g. "v1.35": picks the exam host image
PENDING = {}      # tasks of the bank that are held back, id -> why (PENDING in <track>/questions.py)


def load_track(track_id):
    """Bind every track-dependent global. Called at startup and when the UI switches track."""
    try:
        mod = importlib.import_module(f"{track_id}.questions")
    except ModuleNotFoundError as e:
        if e.name not in (track_id, f"{track_id}.questions"):
            raise
        sys.exit(f"unknown track '{track_id}' (no {track_id}/questions.py)")
    importlib.reload(mod)
    track = mod.TRACK
    pending = dict(getattr(mod, "PENDING", {}))
    workers = dict(getattr(mod, "WORKERS", {}))
    try:   # scripted solutions, for ./ksim audit (<track>/solve.py)
        solve = dict(importlib.reload(importlib.import_module(f"{track_id}.solve")).SOLVE)
    except ModuleNotFoundError as e:
        if e.name != f"{track_id}.solve":
            raise
        solve = {}
    if not envs.vm_ready(track["k8s"]):
        for q in mod.QUESTIONS:
            if q.get("backend") == "vm":
                pending.setdefault(q["id"], f"needs the VM exam host - build it with: ./ksim build {track_id} --vm")
    questions = [q for q in mod.QUESTIONS if q["id"] not in pending]
    try:
        cur = importlib.import_module(f"{track_id}.curriculum")
        cur = importlib.reload(cur)
        objectives = [dict(o, tasks=[i for i in o["tasks"] if i not in pending]) for o in cur.OBJECTIVES]
        study_order = list(getattr(cur, "STUDY_ORDER", []))
    except ModuleNotFoundError as e:
        if e.name != f"{track_id}.curriculum":
            raise
        objectives, study_order = [], []  # no objective map for this track: study/drill by domain only
    for q in questions:
        q["weight"] = sum(c["pts"] for c in q["checks"])
        q.setdefault("difficulty", "normal")
        q.setdefault("set", None)
        if q["id"] in workers:
            q["workers"] = workers[q["id"]]
        if q["id"] in solve:
            q["solve"] = solve[q["id"]]
        # Every task has a cluster to itself, so nothing it breaks can reach another task: the flags
        # that kept such tasks apart on a shared cluster ("breaks", "solo", "disruptive") are void.
        for k in ("breaks", "solo", "disruptive"):
            q.pop(k, None)
    g = globals()
    g.update(
        TRACK_ID=track_id, TRACK=track, QUESTIONS=questions, DOMAINS=track["domains"],
        QUOTA=track.get("quota", {}), QUOTA_HARD=track.get("quota_hard", track.get("quota", {})),
        QBYID={q["id"]: q for q in questions},
        SETS=track.get("sets", {}),
        POOL=[q for q in questions if not q.get("set")],
        EXAM_SECONDS=track["minutes"] * 60, PASS_PCT=track["pass_pct"],
        STATE_FILE=os.path.join(ROOT, ".state", f"state-{track_id}.json"),
        HISTORY_FILE=os.path.join(ROOT, f"history-{track_id}.jsonl"),
        WEAK_FILE=os.path.join(ROOT, f"weak-spots-{track_id}.md"),
        STUDY_FILE=os.path.join(ROOT, f"study-{track_id}.json"), OBJECTIVES=objectives, STUDY_ORDER=study_order,
        K8S=track["k8s"], PENDING=pending,
    )


def set_questions(name):
    return [q for q in QUESTIONS if q.get("set") == name]


STATE_DIR = os.path.join(ROOT, ".state")
# How {WS} reads in a task and its solution: the directory of the task's files on its own host.
# Graders see the same directory on this machine as $WS (it is mounted into the host).
WS_DISPLAY = envs.COURSE
DRILL_SECONDS_PER_TASK = 6 * 60
DRILL_SECONDS_PER_TASK_HARD = 5 * 60
DRILL_SIZE = 5
# Clusters provisioned (and tasks graded) at the same time: one per four cores, at most 8.
PARALLEL = max(1, int(os.environ.get("KSIM_PARALLEL") or max(2, min(8, (os.cpu_count() or 8) // 4))))

# ---------------------------------------------- a task's own cluster ----
_WORKER_REF = re.compile(r"(?:\$\{?|\{(?:SHELL_)?)W([123])\b")

def node_image():
    """The exam host image of the current track: its Kubernetes minor, in the track's own flavour if it has one."""
    return envs.node_image(K8S, TRACK.get("image"))


def is_vm(q):
    """The task's host is a virtual machine ("backend": "vm") - for what a container host cannot do."""
    return q.get("backend") == "vm"


def make_host(q):
    """Create the host of a task: a kind cluster of containers, or a VM. Raises envs.EnvError."""
    if is_vm(q):
        return envs.create_vm(host_of(q), K8S)
    return envs.create(host_of(q), node_image(), workers_of(q))


def workers_of(q):
    """Worker nodes in a task's cluster. A task says so with "workers" (or its track's WORKERS
    map); otherwise one that names a worker anywhere gets the three the bank was written against,
    and every other task the track's default. A VM host is a single node."""
    if is_vm(q):
        return 0
    if "workers" in q:
        return int(q["workers"])
    if "_workers" not in q:
        text = " ".join([str(q.get("task", "")), str(q.get("setup", "")), str(q.get("solution", ""))]
                        + [str(c["script"]) for c in q["checks"]])
        q["_workers"] = 3 if _WORKER_REF.search(text) else int(TRACK.get("workers", 0))
    return q["_workers"]

def host_of(q):
    """The host a task is solved on - `ssh cka0037` - which is also the name of its cluster."""
    return envs.host_of(TRACK_ID, q["id"])

def nodes_of(q):
    return envs.node_names(host_of(q), workers_of(q))

def shell_hint(q, key):
    """How a task tells you to reach a node: its host is the control plane; workers are a hop from it."""
    return f"ssh {host_of(q)}" if key == "CP" else f"ssh {nodes_of(q)[key]}"

PRELUDE = r"""
set -uo pipefail
: "${KUBECONFIG:?}"; K=kubectl               # KUBECONFIG is this task's own cluster - never your kubectl context
WS="$WORKSPACE"                            # the task's /opt/course, as a directory on this machine
PRIV="${WS%/*}/private"; mkdir -p "$PRIV"  # beside it and not mounted into the host: what a setup records for its checks
# j [kubectl get args...] '{jsonpath}'  -> prints the jsonpath result ("" on error)
j() { local n=$#; local path="${!n}"; $K get "${@:1:n-1}" -o "jsonpath=$path" 2>/dev/null; }
eq() { [ "$1" = "$2" ]; }
CP="${KSIM_CP:?}"; W1="${KSIM_W1:-}"; W2="${KSIM_W2:-}"; W3="${KSIM_W3:-}"   # the nodes of this task's cluster
# nx NODE 'command' -> run a shell command as root on a node (stdin is forwarded). The node of a VM
# host is a container that only runs QEMU: there the command goes on into the machine over ssh.
nx() {
  local n="$1"; shift
  [ -n "$n" ] || { echo "nx: this task's cluster has no such node (set \"workers\" on the task)" >&2; return 1; }
  if [ -n "${KSIM_VM:-}" ]; then command "${KSIM_RUNTIME:-podman}" exec -i "$n" ssh vm "$*"
  else command "${KSIM_RUNTIME:-podman}" exec -i "$n" sh -c "$*"; fi
}
# podman ARGS -> root's podman on the task's host: the store `sudo podman` (and the host's podman
# and docker aliases) builds into. A path under $WS becomes the host's own path for it.
podman() {
  local a q=""
  for a in "$@"; do a=${a//"$WS"//opt/course}; q+=" $(printf '%q' "$a")"; done
  command "${KSIM_RUNTIME:-podman}" exec -i "$CP" bash -c "podman$q"
}
# ensure_etcd_tools -> etcdctl and etcdutl on the control-plane node, as on the real exam. The exam
# host image carries them, at the version of the cluster's etcd (images/node/Containerfile).
ensure_etcd_tools() {
  nx "$CP" 'command -v etcdctl >/dev/null 2>&1 && command -v etcdutl >/dev/null 2>&1' </dev/null
}
# ensure_gateway_crds -> the Gateway API CRDs (standard channel), which kind does not ship.
ensure_gateway_crds() {
  $K get crd gateways.gateway.networking.k8s.io >/dev/null 2>&1 && return 0
  curl -sfL --max-time 60 https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.1/standard-install.yaml \
    | $K apply -f - >/dev/null 2>&1 \
    && $K wait --for=condition=Established --timeout=60s crd/gatewayclasses.gateway.networking.k8s.io \
         crd/gateways.gateway.networking.k8s.io crd/httproutes.gateway.networking.k8s.io >/dev/null 2>&1
}
# ensure_metrics_server -> a working metrics API for `kubectl top`. kind ships none, and kind's
# kubelet serving certs have no IP SANs, so it only becomes Ready with --kubelet-insecure-tls.
# Pinned: v0.9.x supports Kubernetes 1.34+, so it serves the v1.35 and v1.37 hosts alike.
METRICS_SERVER_URL=https://github.com/kubernetes-sigs/metrics-server/releases/download/v0.9.0/components.yaml
ensure_metrics_server() {
  if ! $K -n kube-system get deploy metrics-server >/dev/null 2>&1; then
    curl -sfL --max-time 60 "$METRICS_SERVER_URL" | $K apply -f - >/dev/null 2>&1 || return 1
  fi
  if ! $K -n kube-system get deploy metrics-server -o jsonpath='{.spec.template.spec.containers[0].args}' | grep -q kubelet-insecure-tls; then
    $K -n kube-system patch deploy metrics-server --type=json \
      -p '[{"op":"add","path":"/spec/template/spec/containers/0/args/-","value":"--kubelet-insecure-tls"}]' >/dev/null 2>&1
  fi
  $K -n kube-system rollout status deploy metrics-server --timeout=150s >/dev/null 2>&1
}
"""

def _pick_track_arg(argv):
    t = os.environ.get("KSIM_TRACK", "cka")
    if "--track" in argv:
        i = argv.index("--track"); t = argv[i + 1]; del argv[i:i + 2]
    return t


load_track(_pick_track_arg(ARGV))

TTY = sys.stdout.isatty()
def c(code, s): return f"\033[{code}m{s}\033[0m" if TTY else s
def green(s): return c("32", s)
def red(s): return c("31", s)
def yellow(s): return c("33", s)
def bold(s): return c("1", s)
def dim(s): return c("2", s)
class Die(SystemExit):
    """SystemExit that carries its message, so the web UI can show why a start was refused."""

def die(msg, code=1):
    print(red(msg))
    e = Die(code); e.msg = msg
    raise e

# ------------------------------------------------------------- state ----
def load_state() -> dict[str, Any] | None:
    if not os.path.exists(STATE_FILE):
        return None
    with open(STATE_FILE) as f:
        return json.load(f)

def save_state(st: dict[str, Any]) -> None:
    os.makedirs(STATE_DIR, exist_ok=True)
    with open(STATE_FILE, "w") as f:
        json.dump(st, f, indent=2)

def paused_total(st: dict[str, Any] | None) -> float:
    """Seconds spent paused so far, including the current pause if any."""
    if not st:
        return 0.0
    t = float(st.get("paused_total", 0))
    if st.get("paused_at"):
        t += time.time() - float(st["paused_at"])
    return t

def untimed(st: dict[str, Any] | None) -> bool:
    return bool(st and st.get("untimed"))

def remaining(st: dict[str, Any] | None) -> float:
    if not st:
        return 0.0
    if untimed(st):
        return float("inf")
    return float(st.get("started_at", 0)) + float(st.get("duration", EXAM_SECONDS)) + paused_total(st) - time.time()

def set_paused(st: dict[str, Any], on: bool) -> None:
    if on and not st.get("paused_at"):
        st["paused_at"] = time.time()
    elif not on and st.get("paused_at"):
        st["paused_total"] = float(st.get("paused_total", 0)) + (time.time() - float(st["paused_at"])); st["paused_at"] = None
    save_state(st)

def fmt(secs: float | int) -> str:
    secs_int = max(0, int(secs))
    return f"{secs_int // 3600:02d}:{(secs_int % 3600) // 60:02d}:{secs_int % 60:02d}"

def require_started() -> dict[str, Any]:
    st = load_state()
    if not st:
        die("No session in progress. Run:  ./ksim start   (or ./ksim drill weak)")
    assert st is not None
    return st

_TRACK_K8S: dict[str, str] = {}
def track_k8s():
    """Each track's Kubernetes minor, for the lobby's track picker (looked up once per process)."""
    if not _TRACK_K8S:
        for t in TRACKS:
            try:
                _TRACK_K8S[t] = importlib.import_module(f"{t}.questions").TRACK.get("k8s", "?")
            except Exception:  # noqa: BLE001 - a bank mid-edit must not take the other tracks' UI down
                _TRACK_K8S[t] = "?"
    return _TRACK_K8S

def session_questions(st: dict[str, Any] | None) -> list[dict[str, Any]]:
    if not st:
        return list(QUESTIONS)
    ids = st.get("ids") or [q["id"] for q in QUESTIONS]
    # Preserve the session's own order. Filtering QUESTIONS (which is sorted by id) threw it away,
    # so compose_exam's rng.shuffle never reached the candidate and every exam arrived grouped by
    # domain and difficulty - base tasks first, then hard, then the sim sets. Real exams are not
    # ordered by difficulty, and practising triage on a sorted list teaches the wrong instinct.
    by_id = {q["id"]: q for q in QUESTIONS}
    return [by_id[i] for i in ids if i in by_id]

def q_by_id(n: int) -> dict[str, Any]:
    for q in QUESTIONS:
        if q["id"] == n:
            return q
    # ids run 1..N without gaps today, but print the real ranges rather than "1-<count>" so a
    # future gap can never make this message name ids that do not exist.
    ids = sorted(q["id"] for q in QUESTIONS)
    ranges, start, prev = [], ids[0], ids[0]
    for i in ids[1:] + [None]:
        if i != prev + 1:
            ranges.append(str(start) if start == prev else f"{start}-{prev}")
            start = i
        prev = i
    die(f"No question {n}. Valid: {', '.join(ranges)}")
    return {}

_USE_CONTEXT = re.compile(r"^.*config use-context %\{ctx\}.*\n?", re.M)

def render(text, params, q=None):
    """Substitute %{param} and {WS}, and for a task its own nodes: {CP}, {W1}.. and {SHELL_CP}.."""
    t = text.replace("{WS}", WS_DISPLAY)
    for k, v in (params or {}).items():
        t = t.replace("%{" + k + "}", str(v))
    if q is not None:
        for k, v in nodes_of(q).items():
            t = t.replace("{SHELL_" + k + "}", shell_hint(q, k)).replace("{" + k + "}", v)
    return t

def prose(text, params, q):
    """Task or solution text as the candidate reads it. Tasks written for the pre-2025 exams open
    by switching kubectl context; here every task has a host of its own instead, so that line goes."""
    return render(_USE_CONTEXT.sub("", text), params, q).strip()

def session_params(st, q):
    """Params drawn for this session; outside a session, a fixed sample so text still reads naturally."""
    p = (st or {}).get("params", {}).get(str(q["id"]))
    return p if p is not None else make_params(q, random.Random(q["id"]))

def task_text(q, params=None):
    return prose(q["task"], params if params is not None else session_params(load_state(), q), q)

def solution_text(q, params=None):
    return prose(str(q.get("solution", "")), params if params is not None else session_params(load_state(), q), q)

def make_params(q, rng):
    fn = q.get("params")
    return fn(rng) if fn else {}

# -------------------------------------------------------------- shell ----
def run(q, script, timeout=180, params=None):
    """Run a setup or check script of task q against q's own cluster."""
    host = host_of(q)
    env = dict(os.environ, KUBECONFIG=envs.kubeconfig(host), WORKSPACE=envs.course_dir(host), KSIM_ROOT=ROOT,
               KSIM_HOST=host, KSIM_RUNTIME=envs.RUNTIME, KSIM_VM="1" if is_vm(q) else "",
               **{f"KSIM_{k}": v for k, v in nodes_of(q).items()})
    p = subprocess.run(["bash", "-c", PRELUDE + render(script, params, q)], env=env, capture_output=True, text=True,
                       timeout=timeout, stdin=subprocess.DEVNULL)
    return p.returncode, (p.stdout + p.stderr).strip()

# `podman exec` as the candidate, with the environment an ssh login has: a kind node's container
# environment points KUBECONFIG at admin.conf, which only root can read and sshd never passes on.
AS_CANDIDATE = ["-u", "candidate", "-w", "/home/candidate", "-e", "KUBECONFIG=/home/candidate/.kube/config"]

def solve_on_host(q, params, timeout=600):
    """Run a task's scripted solution the way a candidate would type it: as `candidate`, in an
    interactive shell on the task's host, so the host's aliases and profile apply."""
    into = ["ssh", "candidate@vm", "bash -i"] if is_vm(q) else ["bash", "-i"]
    try:
        p = subprocess.run([envs.RUNTIME, "exec", "-i", *([] if is_vm(q) else AS_CANDIDATE), nodes_of(q)["CP"], *into],
                           input=render(q["solve"], params, q), capture_output=True, text=True, timeout=timeout)
    except subprocess.TimeoutExpired:
        return 1, f"solution script timed out after {timeout}s"
    return p.returncode, p.stdout[-400:]

def k8s_version():
    """The Kubernetes release the track's exam hosts run, e.g. v1.35.8 (from the pinned node image)."""
    m = re.search(r":(v[\d.]+)", envs.BASE_IMAGES.get(K8S, ""))
    return m.group(1) if m else K8S

def hosts_down(st):
    """Hosts of a session that are not running - after a reboot, say - so grading them would
    record zeros for work that was never looked at."""
    return [h for h in (envs.host_of(TRACK_ID, i) for i in (st or {}).get("ids", [])) if not envs.running(h)]

def down_message(down):
    return (f"{len(down)} of this session's hosts are not running ({', '.join(down[:6])}{'...' if len(down) > 6 else ''}), "
            "so their checks would all fail and be recorded.\n"
            "  Start them again:  ./ksim hosts start     or discard the session:  ./ksim abort --yes")

def grade_one(q, params=None):
    """Run every check independently. Returns a result dict with partial credit."""
    if params is None:
        params = session_params(load_state(), q)
    checks = []
    for ch in q["checks"]:
        try:
            rc, out = run(q, ch["script"], timeout=240, params=params)
        except subprocess.TimeoutExpired:
            rc, out = 1, "timed out"
        checks.append({"name": render(ch["name"], params, q), "pts": ch["pts"], "pass": rc == 0, "out": out[-400:]})
    earned = sum(ch["pts"] for ch in checks if ch["pass"])
    return {"pass": earned == q["weight"], "earned": earned, "total": q["weight"],
            "checks": checks, "at": time.time(), "difficulty": q["difficulty"]}

def result_detail(r):
    return "\n".join(("  ✓ " if ch["pass"] else "  ✗ ") + ch["name"] + f" ({ch['pts']} pt)" for ch in r["checks"])

def score(st, results=None):
    results = results if results is not None else st["results"]
    qs = session_questions(st)
    total = sum(q["weight"] for q in qs)
    earned = sum(results.get(str(q["id"]), {}).get("earned", 0) for q in qs)
    return earned, total, (round(100 * earned / total, 1) if total else 0)

# ----------------------------------------------------------- history ----
def load_history(include_synthetic=False):
    """Attempts from history-<track>.jsonl. Entries marked "synthetic" (a scripted verification
    run, not a person sitting the tasks) stay in the file for the record but are left out of every
    statistic, weak list and "latest exam" unless explicitly asked for."""
    if not os.path.exists(HISTORY_FILE):
        return []
    with open(HISTORY_FILE) as f:
        entries = [json.loads(l) for l in f if l.strip()]
    return entries if include_synthetic else [e for e in entries if not e.get("synthetic")]

def record_attempt(st):
    earned, total, pct = score(st)
    entry = {"at": datetime.now().isoformat(timespec="minutes"), "mode": st.get("mode", "exam"), "hard": st.get("hard", False),
             "k8s": st.get("k8s"),  # server version it ran on; older entries predate per-track clusters
             "ids": [q["id"] for q in session_questions(st)], "score_pct": pct, "earned": earned, "total": total,
             "time_used": int(st["ended_at"] - st["started_at"] - paused_total(st)),
             "results": {k: {"pass": v["pass"], "earned": v["earned"], "total": v["total"],
                             "failed": [ch["name"] for ch in v["checks"] if not ch["pass"]]}
                         for k, v in st["results"].items()}}
    with open(HISTORY_FILE, "a") as f:
        f.write(json.dumps(entry) + "\n")
    write_weak_spots()
    return entry

class AggEntry:
    def __init__(self) -> None:
        self.attempts: int = 0
        self.fails: int = 0
        self.last: Any = None
        self.last_fail_at: str = ""
        self.failed: list[str] = []
        self.last_earned: str = ""
        self.streak: int = 0          # consecutive full passes at the end of the history

    def __getitem__(self, item: str) -> Any:
        return getattr(self, item)

    def __setitem__(self, item: str, value: Any) -> None:
        setattr(self, item, value)

    def to_dict(self) -> dict[str, Any]:
        return {
            "attempts": self.attempts,
            "fails": self.fails,
            "last": self.last,
            "last_fail_at": self.last_fail_at,
            "failed": self.failed,
            "last_earned": self.last_earned,
            "streak": self.streak,
        }


def stats() -> dict[int, AggEntry]:
    agg: dict[int, AggEntry] = {int(q["id"]): AggEntry() for q in QUESTIONS}
    for e in load_history():
        for k, r in e.get("results", {}).items():
            a = agg.get(int(k))
            if a is None:
                continue
            a.attempts += 1
            a.last = r.get("pass")
            a.last_earned = f"{r.get('earned', 0)}/{r.get('total', 0)}"
            a.streak = a.streak + 1 if r.get("pass") else 0
            if not r.get("pass"):
                a.fails += 1
                a.last_fail_at = str(e.get("at", ""))
                a.failed = list(r.get("failed", []))
    return agg

def last_seen():
    """question id -> index of the most recent session it appeared in (higher = more recent)."""
    seen = {}
    for i, e in enumerate(load_history()):
        for k in e["results"]:
            seen[int(k)] = i
    return seen

def drilled_domains():
    out = {d: 0 for d in DOMAINS}
    for e in load_history():
        if e["mode"] != "drill":
            continue
        for k in e["results"]:
            q = QBYID.get(int(k))
            if q:
                out[q["domain"]] += 1
    return out

def breaks_of(q):
    """A task's "breaks" as a set. It is a string or a list: Q61 damages the scheduler AND the
    controller-manager, and declaring only one let it share a session with Q38."""
    b = q.get("breaks")
    return set() if not b else ({b} if isinstance(b, str) else set(b))

def no_conflicts(cands, n, taken=()):
    """Take up to n tasks, never two that break the same thing (or clash with tasks already taken).
    A "solo" task (Q45's etcd restore rolls the WHOLE cluster back to its snapshot, wiping every
    other task's seed and answers) is only ever taken on its own."""
    used = set().union(*(breaks_of(q) for q in taken)) if taken else set()
    out = []
    for q in cands:
        if q.get("solo") and (taken or out):
            continue
        if any(x.get("solo") for x in list(taken) + out):
            break
        b = breaks_of(q)
        if b & used:
            continue
        out.append(q)
        used |= b
        if len(out) == n:
            break
    return out

def split_solo(qs):
    """Pull solo tasks out of a multi-task selection; they have to be drilled alone."""
    if len(qs) <= 1:
        return list(qs), []
    return [q for q in qs if not q.get("solo")], [q for q in qs if q.get("solo")]

def pick(domain, n, hard, rng, exclude=(), taken=(), unseen_only=False):
    """n tasks from a domain: unseen first, then least recently seen; hard sessions prefer hard tasks."""
    seen = last_seen()

    def build(allow_hard):
        pool = [q for q in POOL if q["domain"] == domain and q["id"] not in exclude and not q.get("solo")
                and (allow_hard or q["difficulty"] == "normal") and not (unseen_only and q["id"] in seen)]
        rng.shuffle(pool)
        pool.sort(key=lambda q: (0 if (hard and q["difficulty"] == "hard") else 1, seen.get(q["id"], -1)))
        return pool

    got = no_conflicts(build(hard), n, taken)
    if len(got) < n and not hard:
        # A domain whose only tasks are "hard" contributes NOTHING to a normal session and drops
        # out of the blueprint entirely - CKS SUPPLY and RUNTIME (20% each) were both unreachable
        # via ./ksim start. Better to hand over a hard task than to silently skip the domain.
        got = no_conflicts(build(True), n, taken)
    return got

def compose_exam(hard, rng):
    quota = QUOTA_HARD if hard else QUOTA
    # Scarcest domain first. Two tasks that "breaks" the same thing can't share a session, so a
    # one-task domain loses every such tie to a bigger domain that claimed the shared slot earlier
    # and then contributes nothing: CKS RUNTIME (only Q9, apiserver-flag) was never drawn in ANY
    # mode because SETUP was iterated first and took that slot with Q2.
    order = sorted(quota, key=lambda d: len([q for q in POOL if q["domain"] == d]))
    qs, short = [], {}
    for d in order:
        got = pick(d, quota[d], hard, rng, taken=qs)
        if len(got) < quota[d]:
            short[d] = (len(got), quota[d])
        qs += got
    if short:
        # Never truncate in silence - a short session still gets scored out of its own total, so
        # the missing domains look like they were simply not on the blueprint.
        print(yellow("  warning: bank too small to fill the blueprint - "
                     + ", ".join(f"{d} {g}/{w}" for d, (g, w) in short.items())))
    rng.shuffle(qs)
    return qs

def campaign_batch(hard, rng):
    """'drill all': DRILL_SIZE tasks you have never attempted, round-robin across domains,
    hard tasks included when --hard. When everything has been seen once, falls back to weak tasks."""
    seen = last_seen()
    pool = [q for q in POOL if q["id"] not in seen and not q.get("solo") and (hard or q["difficulty"] == "normal")]
    if not pool:
        return None, []
    qs, domains = [], list(DOMAINS)
    rng.shuffle(pool)
    pool.sort(key=lambda q: 0 if (hard and q["difficulty"] == "hard") else 1)
    while len(qs) < DRILL_SIZE and pool:
        progressed = False
        for d in domains:
            cand = [q for q in pool if q["domain"] == d and q not in qs]
            got = no_conflicts(cand, 1, qs)
            if got:
                qs += got; progressed = True
                if len(qs) == DRILL_SIZE:
                    break
        if not progressed:
            break
    total = len([q for q in POOL if hard or q["difficulty"] == "normal"])
    return f"{total - len(pool)}/{total} attempted", qs

def solution_allowed(st: dict[str, Any] | None, qid: int | str) -> bool:
    """Study: always. Drill: once the task has been graded. Exam: only after submit."""
    if not st or st.get("ended_at") or untimed(st):
        return True
    return bool(st.get("mode") == "drill" and str(qid) in st.get("results", {}))

def cmd_solution(args):
    if not args:
        die("usage: ./ksim solution N   (drills: after grading the task; exams: after submit; --force to peek anyway)")
    force = "--force" in args; args = [a for a in args if a != "--force"]
    q = q_by_id(int(args[0])); st = load_state()
    if not solution_allowed(st, int(q["id"])) and not force:
        die("Not yet: in a drill, grade the task first (./ksim grade N); in an exam, submit first. --force overrides.")
    print(bold(f"Solution - Q{q['id']} {q['title']}")); print("-" * 64)
    print(solution_text(q, session_params(st, q))); print("-" * 64)
    print(dim(f"One correct way, not the only one. $do = --dry-run=client -o yaml, k = kubectl. Run it on the task's host: ssh {host_of(q)}"))

def cmd_progress(args):
    seen = last_seen(); agg = stats()
    print(bold(f"{'Domain':<8}{'attempted':>11}{'passed':>9}   {'hard attempted':>15}{'hard passed':>13}"))
    for d in DOMAINS:
        dq = [q for q in QUESTIONS if q["domain"] == d]
        n = [q for q in dq if q["difficulty"] == "normal"]; h = [q for q in dq if q["difficulty"] == "hard"]
        att = lambda L: sum(1 for q in L if q["id"] in seen); ok = lambda L: sum(1 for q in L if agg.get(int(q["id"])) and agg[int(q["id"])].last is True)
        print(f"{d:<8}{att(n):>6}/{len(n):<4}{ok(n):>6}/{len(n):<4}   {att(h):>9}/{len(h):<4}{ok(h):>8}/{len(h):<4}")
    left = [q["id"] for q in QUESTIONS if q["id"] not in seen]
    print(dim(f"\n{len(QUESTIONS) - len(left)}/{len(QUESTIONS)} tasks attempted at least once." + (f"  Never seen: Q{', Q'.join(map(str, left))}" if left and len(left) <= 25 else "")))
    print(dim("passed = latest attempt was a full pass.  ./ksim drill all [--hard] works through what's left."))

def is_weak(q, a):
    """Weak = failed on the latest attempt, or failed at least twice and not yet passed twice in a
    row since - a flaky task has to prove itself - or never attempted (outside the fixed sets).
    The old rule ("failed twice, ever") kept a task weak forever: 13 of 29 listed were passing."""
    if a.attempts == 0:
        return not q.get("set")
    return a.last is False or (a.fails >= 2 and a.streak < 2)

def weak_ids(agg=None):
    agg = agg or stats()
    return [q["id"] for q in QUESTIONS if is_weak(q, agg[q["id"]])]

def weak_lines(a):
    """What to show under a weak task: the failing checks if it failed last time, otherwise how
    close it is to dropping off the list - not the ✗ list of some older, since-fixed attempt."""
    if a.last is False:
        return [f"✗ {n}" for n in (a.failed or [])]
    return [f"passed last time ({a.last_earned}) - one more clean pass takes it off this list"]

def exam_domain_scores(e):
    """domain -> (earned, total) over the tasks that were actually IN that attempt. Summing the
    weight of every task in the bank instead made a 100% run read "ARCH 38/266"."""
    out = {}
    for k, r in e.get("results", {}).items():
        q = QBYID.get(int(k))
        if q:
            de, dt = out.get(q["domain"], (0, 0))
            out[q["domain"]] = (de + r.get("earned", 0), dt + r.get("total", 0))
    return out

def write_weak_spots():
    agg = stats(); hist = load_history()
    L = [f"# {TRACK_ID.upper()} weak spots", "", f"_Generated by exam from {len(hist)} attempt(s); regenerated on every `end`._", ""]
    exams = [e for e in hist if e["mode"] == "exam"]
    if exams:
        e = exams[-1]; ds = exam_domain_scores(e)
        L += [f"## Domain scores (latest full exam, {e['at']}, {e['score_pct']}%)", ""]
        for d, name in DOMAINS.items():
            if d in ds:
                L.append(f"- **{d}** {ds[d][0]}/{ds[d][1]} — {name}")
        L.append("")
    L += ["## Drill next  (`./ksim drill weak`)", ""]
    weak = [q for q in QUESTIONS if q["id"] in weak_ids(agg) and agg[q["id"]]["attempts"] > 0]
    if not weak:
        L.append("Nothing failing right now.")
    for q in weak:
        a = agg[q["id"]]
        L.append(f"### Q{q['id']:02d} · {q['domain']} · {q['title']}  ({a['fails']}/{a['attempts']} failed, last {a['last_earned']} pts, last failed {a['last_fail_at']})")
        L += [f"- {n}" for n in weak_lines(a)]
        L.append("")
    L += ["## Attempt matrix", "", "| Q | Domain | Title | " + " | ".join(f"{e['mode'][0].upper()}{i + 1}" for i, e in enumerate(hist)) + " |",
          "|---|---|---|" + "---|" * len(hist)]
    for q in QUESTIONS:
        cells = []
        for e in hist:
            r = e["results"].get(str(q["id"]))
            cells.append("·" if r is None else ("✓" if r["pass"] else f"{r['earned']}/{r['total']}"))
        L.append(f"| {q['id']} | {q['domain']} | {q['title']} | " + " | ".join(cells) + " |")
    L += ["", "_E = full exam, D = drill, · = not in that session, n/m = partial credit._", ""]
    with open(WEAK_FILE, "w") as f:
        f.write("\n".join(L))

# --------------------------------------------------------- curriculum ----
# A track may ship tracks/<id>/curriculum.py: the exam's objectives in order, each with study
# notes and the tasks that practise it. It turns the bank into a path - study an objective with
# the solutions open, then prove it against the clock - and `./ksim objectives` shows where you are.
def find_objective(arg):
    """An objective by id (3.2) or key (probes, or any unambiguous start of it); None if none fits."""
    a = str(arg).lower()
    for o in OBJECTIVES:
        if a in (o["id"], o["key"]):
            return o
    hits = [o for o in OBJECTIVES if len(a) >= 3 and o["key"].startswith(a)]
    return hits[0] if len(hits) == 1 else None

def objective_tasks(o, with_sets=False):
    """An objective's tasks in its own order. Tasks of the fixed simulator sets stay out unless
    asked for: meeting them one objective at a time would spoil the mock they are kept for."""
    return [QBYID[i] for i in o["tasks"] if i in QBYID and (with_sets or not QBYID[i].get("set"))]

def objectives_of(qid):
    return [o for o in OBJECTIVES if qid in o["tasks"]]

def objective_domains():
    """Domain codes in the order the curriculum lists them (TRACK["domains"] may order them otherwise)."""
    return list(dict.fromkeys(o["domain"] for o in OBJECTIVES))

def load_focus():
    """Domains you put at the front of the path with ./ksim focus, in that order."""
    return load_progress()["focus"]

def path_domains():
    """Domain codes in the order the path walks them: your focus first (./ksim focus - the domains
    a real exam report or a mock said are weakest), then the track's STUDY_ORDER (CKA leaves
    Troubleshooting for last - it builds on all the rest), then the curriculum's own order."""
    return list(dict.fromkeys([*load_focus(), *(d for d in STUDY_ORDER if d in DOMAINS), *objective_domains()]))

def path_objectives():
    """Objectives in the order the path walks them: by path_domains(), curriculum order within a domain."""
    order = path_domains()
    return sorted(OBJECTIVES, key=lambda o: order.index(o["domain"]))   # stable sort

def objective_session(o, how, with_sets=False, n=None):
    """The tasks of one sitting on an objective: what is still open first ("study": never solved;
    "drill": not yet passed against the clock), at most n, never two that break the same thing.
    A big objective therefore takes several sittings, each on new ground."""
    agg, studied = stats(), load_study()
    closed = ((lambda q: task_solved(q["id"], agg, studied)) if how == "study"
              else (lambda q: task_state(q["id"], agg, studied) == "passed"))
    qs = objective_tasks(o, with_sets)
    todo = [q for q in qs if not closed(q)] or qs     # nothing open: go over all of it again
    return no_conflicts(todo, n or DRILL_SIZE), len(todo)

def load_progress():
    """study-<track>.json, next to the history so it survives ./teardown.sh as the history does:
      tasks       task id -> its latest result in a study session ("passed" sticks once earned)
      objectives  objective id -> when it was first studied and first completed
      focus       domains the path walks first, in that order (./ksim focus)
    Study results are kept apart from the history on purpose: a pass with the solution open is
    practice, not proof, so it never reaches the statistics, the weak list or the exam gate."""
    try:
        with open(STUDY_FILE) as f:
            d = json.load(f)
    except (OSError, ValueError):
        d = {}
    return {"tasks": {int(k): v for k, v in d.get("tasks", {}).items()}, "objectives": dict(d.get("objectives", {})),
            "focus": [x for x in d.get("focus", []) if x in DOMAINS]}

def save_progress(prog):
    with open(STUDY_FILE, "w") as f:
        json.dump({"tasks": {str(k): prog["tasks"][k] for k in sorted(prog["tasks"])},
                   "objectives": {k: prog["objectives"][k] for k in sorted(prog["objectives"])},
                   **({"focus": prog["focus"]} if prog.get("focus") else {})}, f, indent=1)
        f.write("\n")

def load_study():
    return load_progress()["tasks"]

def record_study(st, ids=None):
    """Note what a study session graded (all of it, or just `ids`)."""
    if not untimed(st):
        return
    prog = load_progress(); log = prog["tasks"]
    for k, r in st.get("results", {}).items():
        if ids is not None and int(k) not in ids:
            continue
        log[int(k)] = {"at": datetime.now().isoformat(timespec="minutes"), "pass": r["pass"], "earned": r["earned"],
                       "total": r["total"], "passed": bool(r["pass"] or log.get(int(k), {}).get("passed"))}
    save_progress(prog)

def task_state(qid, agg, studied):
    """passed = the latest attempt against the clock was a full pass; failed = it was not;
    studied = solved in study mode but never attempted against the clock; new = neither."""
    a = agg.get(int(qid))
    if a is not None and a.attempts:
        return "passed" if a.last else "failed"
    return "studied" if studied.get(int(qid), {}).get("passed") else "new"

def task_solved(qid, agg, studied):
    """Solved at least once, with the solution open or against the clock."""
    a = agg.get(int(qid))
    return bool(studied.get(int(qid), {}).get("passed") or (a is not None and a.attempts > a.fails))

MARKS = {"passed": ("✓", green), "studied": ("~", yellow), "failed": ("✗", red), "new": ("·", dim), "started": ("-", yellow)}

def mark(state):
    ch, col = MARKS[state]
    return col(ch)

def objective_state(o, agg, studied):
    """The two stages every objective goes through, and where it is:
      studied  every pool task solved at least once (study mode counts)
      done     every pool task passed against the clock on its latest attempt - exam conditions
    before that: started (something attempted) or new."""
    qs = objective_tasks(o)
    states = [task_state(q["id"], agg, studied) for q in qs]
    if qs and all(x == "passed" for x in states):
        return "done"
    if qs and all(task_solved(q["id"], agg, studied) for q in qs):
        return "studied"
    return "started" if any(x != "new" for x in states) else "new"

OBJECTIVE_MARK = {"done": "passed", "studied": "studied", "started": "started", "new": "new"}

def next_objective(agg=None, studied=None):
    """(objective, how) for the first objective in curriculum order that is not done: "study" it
    until every task has been solved once, then "drill" it against the clock. (None, None) when
    every objective is done."""
    agg = stats() if agg is None else agg
    studied = load_study() if studied is None else studied
    for o in path_objectives():
        state = objective_state(o, agg, studied)
        if state != "done":
            return o, ("drill" if state == "studied" else "study")
    return None, None

def mock_scores():
    """Scores of the full mocks and of each fixed simulator set, from the history."""
    full, fixed = [], {k: [] for k in SETS}
    members = {k: {q["id"] for q in set_questions(k)} for k in SETS}
    for e in load_history():
        if e["mode"] != "exam":
            continue
        hit = next((k for k in SETS if set(e["ids"]) == members[k]), None)
        (fixed[hit] if hit else full).append(e["score_pct"])
    return full, fixed

def next_step(agg=None, studied=None):
    """The next move on the path to the exam, as {kind, cmd, why[, objective | set]}:
    study an objective -> drill it against the clock -> ... every objective -> a full mock ->
    the fixed simulator sets. Each stage is closer to the real exam than the one before."""
    agg = stats() if agg is None else agg
    studied = load_study() if studied is None else studied
    o, how = next_objective(agg, studied)
    if o and how == "study":
        return {"kind": "study", "objective": o, "cmd": f"./ksim study {o['id']}",
                "why": f"{o['id']} {o['text']} - notes, then its tasks with no clock and the solutions open"}
    if o:
        return {"kind": "drill", "objective": o, "cmd": f"./ksim drill {o['id']}",
                "why": f"{o['id']} {o['text']} - studied; now the same tasks against the clock, no solution until graded"}
    full, fixed = mock_scores()
    if not any(x >= PASS_PCT for x in full):
        return {"kind": "mock", "cmd": "./ksim start",
                "why": f"every objective is done - a full mock: {sum(QUOTA.values())} tasks, {TRACK['minutes']} minutes, no feedback until you submit"}
    for k in SETS:
        if not any(x >= PASS_PCT for x in fixed[k]):
            return {"kind": "sim", "set": k, "cmd": f"./ksim sim {k}",
                    "why": f"{SETS[k]}: {len(set_questions(k))} fixed tasks, {TRACK['minutes']} minutes, exam rules"}
    return {"kind": "done", "cmd": "./ksim start --hard",
            "why": f"every objective done and every mock passed at {PASS_PCT}% or better - keep sharp with a fresh mock"}

def update_milestones():
    """Stamp each objective the first time it is studied and the first time it is done, and
    return what was newly reached as [(objective, "studied" | "done")]. Called whenever results
    are recorded, so the checklist keeps the date you got there."""
    if not OBJECTIVES:
        return []
    prog = load_progress(); agg = stats(); new = []
    now = datetime.now().isoformat(timespec="minutes")
    for o in OBJECTIVES:
        state = objective_state(o, agg, prog["tasks"])
        seen = prog["objectives"].setdefault(o["id"], {})
        for level in ("studied", "done"):
            if state in (level, "done") and level not in seen:
                seen[level] = now
                new.append((o, level))
        if not seen:
            del prog["objectives"][o["id"]]
    if new:
        save_progress(prog)
    # reaching "done" in one go also stamps "studied"; only the higher one is news
    return [(o, lv) for o, lv in new if not (lv == "studied" and (o, "done") in new)]

def milestone_lines(new):
    out = []
    for o, level in new:
        n = len(objective_tasks(o))
        if level == "done":
            out.append(f"✓ Objective {o['id']} {o['key']} complete - {n}/{n} tasks passed against the clock.")
        else:
            out.append(f"~ Objective {o['id']} {o['key']} studied - every task solved once. Prove it against the clock: ./ksim drill {o['id']}")
    return out

def curriculum_gaps():
    """What would make the path lie: a task no objective lists, a listed id that does not exist,
    an objective too thin to study."""
    listed = {i for o in OBJECTIVES for i in o["tasks"]}
    out = []
    orphans = [q["id"] for q in QUESTIONS if q["id"] not in listed]
    if orphans:
        out.append(f"not listed under any objective: Q{', Q'.join(map(str, orphans))}")
    ghosts = sorted(listed - set(QBYID))
    if ghosts:
        out.append(f"listed but not in the bank: Q{', Q'.join(map(str, ghosts))}")
    thin = [o["id"] for o in OBJECTIVES if len(objective_tasks(o)) < 2]
    if thin:
        out.append(f"fewer than two pool tasks: {', '.join(thin)}")
    wrong = [f"{o['id']} ({o['domain']})" for o in OBJECTIVES if o["domain"] not in DOMAINS]
    if wrong:
        out.append(f"unknown domain: {', '.join(wrong)}")
    return out

def require_objectives():
    if not OBJECTIVES:
        die(f"Track '{TRACK_ID}' has no objective map (tracks/{TRACK_ID}/curriculum.py).\n"
            f"  Study it by domain instead:  ./ksim study {next(iter(DOMAINS))}")

def cmd_objectives(args):
    """The curriculum as a checklist: every objective, its tasks, and how far you are."""
    require_objectives()
    agg, studied = stats(), load_study()
    cols = shutil.get_terminal_size((120, 24)).columns
    sets = len(QUESTIONS) - len(POOL)
    print(bold(f"{TRACK['name']} - study path") + dim(f"   {len(OBJECTIVES)} objectives · {len(POOL)} tasks"
                                                       + (f" · {sets} more in the fixed sets [in brackets]" if sets else "")))
    print(dim("tasks: ✓ passed against the clock  ~ solved in study mode  ✗ failed last time  · not yet"
              "      objectives: ✓ complete  ~ studied  - started"))
    def cell(q):
        return f"{MARKS[task_state(q['id'], agg, studied)][0]}{q['id']}", f"{mark(task_state(q['id'], agg, studied))}{q['id']}"
    rows = []
    for o in OBJECTIVES:
        pool = [cell(q) for q in objective_tasks(o)]
        fixed = [cell(q) for q in objective_tasks(o, True) if q.get("set")]
        plain = " ".join(c[0] for c in pool) + (" [" + " ".join(c[0] for c in fixed) + "]" if fixed else "")
        shown = " ".join(c[1] for c in pool) + (dim(" [") + " ".join(c[1] for c in fixed) + dim("]") if fixed else "")
        rows.append((o, plain, shown))
    tw = max(28, min(max(len(o["text"]) for o in OBJECTIVES), cols - 26 - max(len(r[1]) for r in rows)))
    focus = load_focus()
    for d in objective_domains():
        print(bold(f"\n{DOMAINS[d]}") + (yellow(f"   focus {focus.index(d) + 1}") if d in focus else ""))
        for o, plain, shown in rows:
            if o["domain"] != d:
                continue
            state = objective_state(o, agg, studied)
            text = o["text"] if len(o["text"]) <= tw else o["text"][:tw - 1] + "…"
            print(f" {mark(OBJECTIVE_MARK[state])} {o['id']:<4}{o['key']:<16}{text:<{tw}}  {shown}")
    print_path(agg, studied)
    for g in curriculum_gaps():
        print(yellow(f"curriculum.py: {g}"))

def print_path(agg=None, studied=None):
    """The ladder from first reading to exam conditions, how far up you are, and the next rung."""
    agg = stats() if agg is None else agg
    studied = load_study() if studied is None else studied
    states = [objective_state(o, agg, studied) for o in OBJECTIVES]
    n, done = len(OBJECTIVES), states.count("done")
    full, fixed = mock_scores()
    step = next_step(agg, studied)
    def best(scores):
        if not scores:
            return dim("not sat yet")
        b = max(scores)
        return (green if b >= PASS_PCT else red)(f"best {b}%") + dim(f" of {len(scores)}, pass mark {PASS_PCT}%")
    rows = [("study", "Study", "each objective's tasks, notes and solutions open", f"{done + states.count('studied')}/{n} objectives"),
            ("drill", "Clock", "the same tasks as a timed drill, graded per check", f"{done}/{n} objectives")]
    rows.append(("mock", "Mock exam", f"{sum(QUOTA.values())} random tasks, {TRACK['minutes']} min, no feedback until submit", best(full)))
    rows += [("sim", f"Set {k.upper()}", f"{len(set_questions(k))} fixed tasks, {TRACK['minutes']} min, exam rules", best(fixed[k])) for k in SETS]
    print(bold("\nPath to the exam"))
    for i, (kind, name, what, where) in enumerate(rows, 1):
        here = step["kind"] == kind and (kind != "sim" or name == f"Set {step['set'].upper()}")
        print(f" {green('→') if here else ' '} {i}  {name:<11}{dim(f'{what:<54}')}{where}")
    focus = load_focus()
    if focus:
        print(dim(f"\nFocus: {', '.join(focus)} first, then the rest of the curriculum   (./ksim focus shows it, ./ksim focus clear undoes it)"))
    print(bold(f"\nNext:  {step['cmd']}") + dim("   (or just ./ksim next)"))
    print(dim(f"       {step['why']}"))
    if step.get("objective"):
        print(dim(f"       ./ksim notes {step['objective']['id']}   what to know, the fastest commands, the traps, the docs to open"))

def cmd_next(args):
    """Start whatever is next on the path: study an objective, drill it, a mock, a simulator set."""
    require_objectives()
    step = next_step()
    print(bold(f"Next on the path:  {step['cmd']}") + dim(f"\n  {step['why']}"))
    if step["kind"] == "study":
        cmd_study([step["objective"]["id"]] + args)
    elif step["kind"] == "drill":
        cmd_drill([step["objective"]["id"]] + args)
    elif step["kind"] == "sim":
        cmd_sim([step["set"]] + args)
    else:
        cmd_start((["--hard"] if step["kind"] == "done" else []) + args)

def cmd_focus(args):
    """Put domains at the front of the path - the ones an exam report or a mock said are weakest:
    ./ksim focus DEPLOY NET ENV, ./ksim focus clear, ./ksim focus (show). Nothing else changes: a
    mock still samples every domain, and any objective can still be studied at any time."""
    prog = load_progress(); before = list(prog["focus"])
    if args:
        if args[0].lower() in ("clear", "none", "off"):
            prog["focus"] = []
        else:
            want = list(dict.fromkeys(a.upper() for a in args))
            bad = [a for a in want if a not in DOMAINS]
            if bad:
                die(f"'{bad[0]}' is not a domain of the {TRACK_ID.upper()} track. Domains:\n  "
                    + "\n  ".join(f"{d:<8}{name}" for d, name in DOMAINS.items()) + "\n  ./ksim focus clear   back to the usual order")
            prog["focus"] = want
        if prog["focus"] != before:
            save_progress(prog)
    focus = prog["focus"]
    if not focus:
        print("No focus set - the path follows " + ("the track's study order." if STUDY_ORDER else "the curriculum's order.")
              + dim(f"\n  ./ksim focus {' '.join(list(DOMAINS)[:2])}   puts those domains first"))
        return
    agg, studied = stats(), prog["tasks"]
    print(bold("Focus") + dim("   these domains come first on the path, in this order"))
    for i, d in enumerate(focus, 1):
        objs = [o for o in OBJECTIVES if o["domain"] == d]
        states = [objective_state(o, agg, studied) for o in objs]
        pool = [q for q in POOL if q["domain"] == d]
        solved = sum(1 for q in pool if task_solved(q["id"], agg, studied))
        passed = sum(1 for q in pool if task_state(q["id"], agg, studied) == "passed")
        where = (f"objectives {states.count('done') + states.count('studied')}/{len(objs)} studied, {states.count('done')}/{len(objs)} on the clock · "
                 if objs else "")
        print(f" {i}  {DOMAINS[d]:<58}" + dim(f"{where}tasks {solved}/{len(pool)} solved, {passed}/{len(pool)} passed on the clock"))
    if OBJECTIVES:
        step = next_step(agg, studied)
        print(bold(f"\nNext:  {step['cmd']}") + dim("   (or just ./ksim next)") + dim(f"\n       {step['why']}"))
    else:
        print(dim("\n./ksim drill and ./ksim study with no argument pick these first among the domains you have drilled least."))

def paint_code(text):
    """`code` in a note: highlighted on a terminal, left as written (it is Markdown) in a pipe."""
    return re.sub(r"`([^`]+)`", lambda m: bold(m.group(1)), text) if TTY else text

def print_notes(o, agg=None, studied=None):
    agg = stats() if agg is None else agg
    studied = load_study() if studied is None else studied
    w = min(shutil.get_terminal_size((100, 24)).columns, 104)
    def bullets(items):
        for it in items:
            print(paint_code("\n".join(textwrap.wrap(it, w, initial_indent="  - ", subsequent_indent="    "))))
    print(bold(f"{o['id']} {o['key']}") + dim(f"  ·  {DOMAINS[o['domain']]}"))
    print(bold(o["text"])); print("-" * 64)
    print(bold("Know")); bullets(o["know"])
    print(bold("\nFast")); print("\n".join("  " + line for line in o["fast"].strip("\n").splitlines()))
    print(bold("\nTraps")); bullets(o["traps"])
    print(bold("\nDocs") + dim("  (pages you may open during the exam)"))
    for u in o["docs"]:
        print("  " + u)
    print(bold("\nTasks"))
    for q in objective_tasks(o, True):
        print(f"  {mark(task_state(q['id'], agg, studied))} Q{q['id']:<3} {q['title']}" + (dim(f"   [{SETS.get(q['set'], q['set'])}]") if q.get("set") else ""))
    print("-" * 64)

def notes_markdown(objs):
    """The same notes as a Markdown document (./ksim notes all --md > CKAD_STUDY_GUIDE.md)."""
    L = [f"# {TRACK_ID.upper()} study guide", "",
         f"The {len(OBJECTIVES)} objectives of the {TRACK['name']} curriculum, in its own words and order: what to know, "
         "the fastest commands, the traps, the documentation pages the exam lets you open, and the tasks in this "
         "simulator that practise each one.", "",
         f"_Generated by `./ksim --track {TRACK_ID} notes all --md` from `tracks/{TRACK_ID}/curriculum.py` - edit that file, not this one._", "",
         "```", f"./ksim objectives        # the path and your progress", "./ksim study 3.2         # one objective: these notes, then its tasks, no clock, solutions open",
         "./ksim drill 3.2         # the same tasks against the clock", "```", ""]
    for d in objective_domains():
        mine = [o for o in objs if o["domain"] == d]
        if not mine:
            continue
        L += [f"## {DOMAINS[d]}", ""]
        for o in mine:
            L += [f"### {o['id']} {o['text']}", "", f"`./ksim study {o['id']}` (or `{o['key']}`)", "", "**Know**", ""]
            L += [f"- {x}" for x in o["know"]]
            L += ["", "**Fast**", "", "```", o["fast"].strip("\n"), "```", "", "**Traps**", ""]
            L += [f"- {x}" for x in o["traps"]]
            L += ["", "**Docs**", ""] + [f"- <{u}>" for u in o["docs"]]
            L += ["", "**Tasks**", ""]
            L += [f"- Q{q['id']} {q['title']}" + (f" _({SETS.get(q['set'], q['set'])})_" if q.get("set") else "") for q in objective_tasks(o, True)]
            L.append("")
    return "\n".join(L)

def cmd_notes(args):
    """Study notes for an objective, a domain or the whole curriculum."""
    require_objectives()
    rest = [a for a in args if not a.startswith("--")]
    if not rest:
        st = load_state()
        o = find_objective(st.get("objective")) if st and not st.get("ended_at") and st.get("objective") else None
        objs = [o or next_objective()[0] or OBJECTIVES[0]]
    elif rest[0] == "all":
        objs = list(OBJECTIVES)
    elif rest[0].upper() in DOMAINS:
        objs = [o for o in OBJECTIVES if o["domain"] == rest[0].upper()]
    else:
        objs = [find_objective(a) for a in rest]
        if None in objs:
            die(f"'{rest[objs.index(None)]}' is not an objective. Ids and keys:\n  "
                + "\n  ".join(f"{o['id']:<5}{o['key']:<16}{o['text']}" for o in OBJECTIVES))
    if "--md" in args:
        print(notes_markdown(objs)); return
    agg, studied = stats(), load_study()
    for i, o in enumerate(objs):
        if i:
            print()
        print_notes(o, agg, studied)
    if len(objs) == 1:
        print(dim(f"./ksim study {objs[0]['id']}   its tasks, no clock, solutions open        ./ksim drill {objs[0]['id']}   against the clock"))

# ------------------------------------------------------------ session ----
def preflight(qs):
    """Everything a session needs before any cluster is made: the tools, the images, the memory."""
    for tool, why in (("podman", "runs the exam hosts and the desktop"), ("kind", "builds each task's cluster"),
                      ("kubectl", "seeds and grades the tasks"), ("ssh-keygen", "makes the key the desktop logs in with")):
        if not shutil.which(tool):
            die(f"'{tool}' is not installed - it {why}.")
    missing = [i for i in (node_image(), envs.DESKTOP_IMAGE) if not envs.image_exists(i)]
    if missing:
        die(f"Not built yet: {', '.join(missing)}\n  Build the exam host and desktop images (once, a few minutes):  ./ksim build")
    if any(is_vm(q) for q in qs) and not (envs.vm_ready(K8S) and envs.image_exists(envs.VM_IMAGE)):
        die(f"Not built yet: the VM exam host, which {sum(is_vm(q) for q in qs)} of these tasks need.\n"
            f"  Build it (once, about ten minutes):  ./ksim build {TRACK_ID} --vm")
    need, have = sum(envs.memory_mb(workers_of(q), is_vm(q)) for q in qs), envs.available_mb()
    nodes = sum(1 + workers_of(q) for q in qs)
    print(dim(f"  track: {TRACK_ID}  Kubernetes {k8s_version()}  {len(qs)} task(s) = {len(qs)} cluster(s), {nodes} node(s), about {need / 1024:.1f} GB"))
    if have is not None and need > have - 1536 and not os.environ.get("KSIM_FORCE"):
        die(f"These {len(qs)} clusters need about {need / 1024:.1f} GB and {have / 1024:.1f} GB is available.\n"
            "  Free some memory, pick fewer tasks, or set KSIM_FORCE=1 to try anyway.")
    for tool, why in (("helm", "seeding the Helm tasks"), ("openssl", "seeding the certificate tasks"), ("curl", "seeding tasks that fetch manifests")):
        if not shutil.which(str(tool)):
            print(yellow(f"  warning: '{tool}' not found on this machine - needed for {why}"))

def _log_msg(*args: Any, **kwargs: Any) -> None:
    print(*args, **kwargs)


def provision(q, params, log: Callable[..., Any] = _log_msg):
    """One task, start to finish: its cluster, its scenario, and the hand-over to `candidate`.
    Returns None, or what went wrong."""
    host, tag = host_of(q), f"Q{q['id']:02d} {q['title']}"
    try:
        make_host(q)
    except envs.EnvError as e:
        log(f"  ! {host}  {tag}\n{dim(str(e)[-500:])}")
        return f"{host}: no cluster"
    try:
        rc, out = run(q, q["setup"], params=params, timeout=300)
    except subprocess.TimeoutExpired:
        rc, out = 1, "setup timed out after 300s"
    # a task that says "the current namespace" (ctx_ns) starts with its kubeconfig pointing there
    envs.hand_over(host, (params or {}).get("ns") if q.get("ctx_ns") else None)
    log(f"  {'✓' if rc == 0 else '!'} {host}  {tag}" + ("" if rc == 0 else f"\n{dim(out[-300:])}"))
    return None if rc == 0 else f"{host}: setup failed"

def seed(qs, log: Callable[..., Any] = _log_msg, params_by_id=None):
    """Provision and seed every task of a session, PARALLEL clusters at a time. Tasks cannot
    disturb each other any more, so there is no order to respect."""
    params_by_id = params_by_id or {}
    with concurrent.futures.ThreadPoolExecutor(max_workers=PARALLEL) as pool:
        problems = [p for p in pool.map(lambda q: provision(q, params_by_id.get(str(q["id"])), log), qs) if p]
    return problems

def audits_running():
    """PIDs of `./ksim audit` runs in progress. An audit and a session share the host names, and
    starting a session deletes every host there is - so a session waits for an audit to finish."""
    pids = []
    for name in os.listdir(STATE_DIR) if os.path.isdir(STATE_DIR) else []:
        m = re.match(r"audit-(\d+)\.lock$", name)
        if not m:
            continue
        if os.path.isdir(f"/proc/{m.group(1)}") and int(m.group(1)) != os.getpid():
            pids.append(int(m.group(1)))
        elif int(m.group(1)) != os.getpid():
            os.remove(os.path.join(STATE_DIR, name))   # left by an audit that was killed
    return pids

def clear_hosts(keep=()):
    """Delete the exam hosts left by earlier sessions (they stay up after a session for review)."""
    old = [h for h in envs.existing() if h not in keep]
    with concurrent.futures.ThreadPoolExecutor(max_workers=PARALLEL) as pool:
        list(pool.map(envs.destroy, old))
    return old

def open_sessions_elsewhere():
    """Tracks other than this one with a session that has not ended. One session at a time: they
    share the desktop, and a new session clears the hosts of the last one."""
    out = []
    for t in TRACKS:
        if t == TRACK_ID:
            continue
        try:
            with open(os.path.join(STATE_DIR, f"state-{t}.json")) as f:
                if not json.load(f).get("ended_at"):
                    out.append(t)
        except (OSError, ValueError):
            pass
    return out

def begin_session(qs, mode, duration, force, log: Callable[..., Any] = _log_msg, hard=False, untimed_session=False, other_ok=None,
                  objective=None):
    st = load_state()
    if st and not st.get("ended_at") and not force:
        die("A session is already in progress. './ksim end' it first, or add --force.")
    others = open_sessions_elsewhere()
    if others:
        t = others[0]
        die(f"A {t.upper()} session is still open, and its hosts would be deleted by this one.\n"
            f"  Finish it first:  ./ksim --track {t} end   (or  ./ksim --track {t} abort --yes  to discard it)"
            + ("" if other_ok is None else "  - in the browser: switch to it in the lobby and submit."))
    if not qs:
        die(f"Track '{TRACK_ID}' has no questions yet.")
    running = audits_running()
    if running:
        die(f"A bank audit is running (./ksim audit, pid {running[0]}). Starting a session deletes every host, the audit's included.\n"
            "  Let it finish, or stop it, then start the session.")
    preflight(qs)
    update_milestones()   # stamp what the history already proves, so this session only announces its own
    rng = random.Random()
    params_by_id = {str(q["id"]): make_params(q, rng) for q in qs}
    hosts = [host_of(q) for q in qs]
    if not envs.ensure_registry():
        log(yellow("  warning: the image cache (ksim-registry) is not running - hosts pull straight from Docker Hub, which allows 100 pulls an hour"))
    old = clear_hosts()
    if old:
        log(dim(f"  removed {len(old)} host(s) of the previous session"))
    # a fresh desktop for every session, as on the day: no shell history, no open tabs
    desktop.up(fresh=True)
    desktop.configure(TRACK_ID, hosts, open_web=bool(os.environ.get("KSIM_OPEN_WEB")))
    log(bold(f"Preparing {len(qs)} exam host(s){' [HARD]' if hard else ''} - one cluster per task, {PARALLEL} at a time..."))
    problems = seed(qs, log, params_by_id)
    if any("no cluster" in p for p in problems):
        clear_hosts()
        die("Could not create every host (see above), so the session was not started.\n"
            "  Usual causes: not enough memory, or podman's limits - try fewer tasks or KSIM_PARALLEL=3.")
    st = {"mode": mode, "track": TRACK_ID, "hard": hard, "untimed": untimed_session, "ids": [q["id"] for q in qs],
          "params": params_by_id, "duration": duration, "started_at": time.time(), "ended_at": None,
          "k8s": k8s_version(), "results": {}, "flags": [], "notes": "",
          "objective": objective}   # the curriculum objective a study/drill session was started for, if any
    save_state(st)
    log("")
    log(bold("=" * 64))
    kind = "STUDY" if untimed_session else ("EXAM" if mode == "exam" else "DRILL")
    log(bold(f"  {TRACK_ID.upper()} {kind}{' · HARD' if hard else ''} - {'no clock, solutions open' if untimed_session else 'clock started'}"))
    log(f"  Hosts   : {hosts[0]}" + (f" .. {len(hosts)} in all" if len(hosts) > 1 else "")
        + f"  (Kubernetes {st['k8s']}, as the real {TRACK_ID.upper()} runs {K8S})")
    if not untimed_session:
        log(f"  Ends    : {datetime.fromtimestamp(st['started_at'] + duration).strftime('%H:%M:%S')}  ({duration // 60} min)")
    log(f"  Tasks   : {', '.join('Q%02d' % q['id'] for q in qs) if mode == 'drill' else len(qs)}"
        + ("" if untimed_session else f"   Pass mark: {PASS_PCT}%"))
    if problems:
        log(yellow(f"  Seeding had problems on: {', '.join(problems)}  -  ./ksim reset N  rebuilds one task's host"))
    log(bold("=" * 64))
    log("  ./ksim web         the exam in the browser: task pane, remote desktop, clock\n"
        + ("  ./ksim list / show N / grade N / solution N / end   terminal workflow\n" if untimed_session else
           "  ./ksim list / show N / grade N / timer / end   terminal workflow\n")
        + f"  Every task names its host:  ssh {hosts[0]}  from the desktop's terminal, then  sudo -i  when you need root.\n"
        + f"  Files a task asks for go under {WS_DISPLAY}/ on its host.")
    return st

def finish_session(st, log: Callable[..., Any] = _log_msg):
    qs = session_questions(st)
    over = remaining(st) <= 0
    set_paused(st, False)
    log(bold(f"Submitting - grading {len(qs)} task(s)..."))
    # tasks are graded side by side: each one's checks only ever touch its own cluster
    with concurrent.futures.ThreadPoolExecutor(max_workers=PARALLEL) as pool:
        graded = list(pool.map(lambda q: grade_one(q, session_params(st, q)), qs))
    for q, r in zip(qs, graded):
        st["results"][str(q["id"])] = r
        tag = green("PASS") if r["pass"] else (yellow(f"{r['earned']}/{r['total']}") if r["earned"] else red("FAIL"))
        log(f"Q{q['id']:02d} {tag}  {q['title']}" + ("" if r["pass"] else f"\n{dim(result_detail(r))}"))
    st["ended_at"] = time.time()
    st["over_time"] = over
    save_state(st)
    entry = None
    if untimed(st):
        record_study(st)
    else:
        entry = record_attempt(st)
    # objectives this session got over a line: shown by ./ksim end and by the results page
    st["milestones"] = st.get("milestones", []) + milestone_lines(update_milestones())
    save_state(st)
    return entry

# ----------------------------------------------------------- commands ----
def cmd_start(args):
    hard = "--hard" in args; force = "--force" in args
    undrilled = [d for d, n in drilled_domains().items() if n == 0]
    if undrilled and not force:
        die("Drill every domain at least once before a full exam (that is the point of the drills).\n"
            f"  Not yet drilled: {', '.join(undrilled)}\n  Run:  ./ksim drill      (picks the next domain)\n"
            "  or:   ./ksim start --force   to skip the gate.")
    begin_session(compose_exam(hard, random.Random()), "exam", EXAM_SECONDS, force, hard=hard)

def next_drill(hard, rng):
    """No-arg drill: the least-drilled domain, DRILL_SIZE tasks, least-recently-seen first."""
    cov = drilled_domains()
    order = list(dict.fromkeys([*load_focus(), *DOMAINS]))   # equally drilled: your focus first
    domain = min(DOMAINS, key=lambda d: (cov[d], order.index(d)))
    return domain, pick(domain, DRILL_SIZE, hard, rng)

def cmd_drill(args):
    force = "--force" in args; hard = "--hard" in args
    args = [a for a in args if a not in ("--force", "--hard")]
    minutes = None
    if "--time" in args:
        i = args.index("--time"); minutes = int(args[i + 1]); del args[i:i + 2]
    per_task = DRILL_SECONDS_PER_TASK_HARD if hard else DRILL_SECONDS_PER_TASK
    if not args:
        domain, qs = next_drill(hard, random.Random())
        cov = drilled_domains()
        print(bold(f"Drill: {DOMAINS[domain]}") + dim(f"  ({sum(1 for v in cov.values() if v)}/{len(DOMAINS)} domains drilled so far)"))
        begin_session(qs, "drill", (minutes * 60) if minutes else per_task * len(qs), force, hard=hard)
        return
    if args[0] == "all":
        label, qs = campaign_batch(hard, random.Random())
        if not qs:
            print(bold("Every task in the bank has been attempted." ) + " Switching to weak tasks.")
            qs, _ = split_solo([q for q in QUESTIONS if q["id"] in weak_ids()])
            qs = no_conflicts(qs, DRILL_SIZE)
            if not qs:
                die("Nothing weak either - you have passed everything on its latest attempt. Time for ./ksim start --hard.")
        else:
            print(bold(f"Campaign: {label}") + dim(f"  this batch: Q{', Q'.join(str(q['id']) for q in qs)}"))
        begin_session(qs, "drill", (minutes * 60) if minutes else per_task * len(qs), force, hard=hard)
        return
    objective = None
    if args[0] == "weak":
        ids = weak_ids()
        if not ids:
            die("Nothing marked weak - finish a session with './ksim end' first, or name tasks: ./ksim drill 2 17")
    else:
        ids = []
        for a in args:
            if a.lower().replace("set", "") in SETS and a.lower().startswith("set"):
                ids += [q["id"] for q in set_questions(a.lower().replace("set", ""))]
            elif a.upper() in DOMAINS:
                ids += [q["id"] for q in QUESTIONS if q["domain"] == a.upper()]
            elif a.isdigit():
                ids.append(q_by_id(int(a))["id"])
            elif find_objective(a):
                sitting, open_n = objective_session(find_objective(a), "drill")
                ids += [q["id"] for q in sitting]
                objective = objective or find_objective(a)["id"]
                if open_n > len(sitting):
                    print(dim(f"  {find_objective(a)['id']}: {len(sitting)} of its {open_n} open tasks in this sitting - run it again for the rest."))
            else:
                die(f"'{a}' is not a task id, a domain ({', '.join(DOMAINS)}), a set "
                    f"({', '.join('set' + k for k in SETS) or 'none'})"
                    + (" or an objective (./ksim objectives)." if OBJECTIVES else "."))
    ids = sorted(set(ids))
    qs, solo = split_solo([q for q in QUESTIONS if q["id"] in ids])
    if solo:
        print(yellow(f"Dropped Q{', Q'.join(str(q['id']) for q in solo)}: restoring it rolls the whole cluster back and would "
                     f"wipe the other tasks. Drill it on its own: ./ksim drill {solo[0]['id']}"))
    kept = no_conflicts(qs, len(qs))
    if len(kept) < len(qs):
        dropped = [q["id"] for q in qs if q not in kept]
        print(yellow(f"Dropped Q{', Q'.join(map(str, dropped))}: they break the same thing as another task in this set. Drill them separately."))
    # Shuffle AFTER resolving conflicts, so which task gets dropped stays deterministic while the
    # order you meet them in does not. A drill listed by id walks you from easy to hard in
    # lockstep, which is the one ordering the real exam will never give you.
    random.Random().shuffle(kept)
    begin_session(kept, "drill", (minutes * 60) if minutes else per_task * len(kept), force, hard=hard,
                  objective=objective if len(args) == 1 else None)

def cmd_study(args):
    """No clock, solutions unlocked from the start, nothing written to history."""
    hard = "--hard" in args; force = "--force" in args; with_sets = "--all" in args
    rest = [a for a in args if not a.startswith("--")]
    n = DRILL_SIZE
    if "--count" in args:
        n = int(args[args.index("--count") + 1]); rest = [a for a in rest if a != str(n)]
    rng = random.Random()
    obj = None
    if rest and rest[0].upper() in DOMAINS:
        domain = rest[0].upper()
        qs = pick(domain, n, hard, rng)
        print(bold(f"Study: {DOMAINS[domain]}"))
    elif rest and rest[0] == "weak":
        qs = no_conflicts(split_solo([q for q in QUESTIONS if q["id"] in weak_ids()])[0], n)
        print(bold("Study: tasks you have been failing"))
    elif OBJECTIVES and (not rest or rest[0] == "next" or find_objective(rest[0])):
        # one objective of the curriculum: the one named, else the next one on the path
        if rest and rest[0] != "next":
            obj = find_objective(rest[0])
        else:
            agg, studied = stats(), load_study()
            obj = next((o for o in path_objectives() if objective_state(o, agg, studied) in ("new", "started")), None)
            if obj is None:
                die("Every objective has been studied - name one to revisit (./ksim objectives lists them),\n"
                    f"  or carry on up the path:  {next_step(agg, studied)['cmd']}   (./ksim next)")
        qs, open_n = objective_session(obj, "study", with_sets, n if "--count" in args else None)
        print(bold(f"Study: {obj['id']} {obj['text']}") + dim(f"   {DOMAINS[obj['domain']]}"))
        if open_n > len(qs):
            print(dim(f"  {len(qs)} of its {open_n} open tasks in this sitting - run the same command again for the rest."))
    elif rest:
        qs = no_conflicts(split_solo([q_by_id(int(a)) if a.isdigit() else die(
            f"'{a}' is not a task id, a domain ({', '.join(DOMAINS)}), 'weak'"
            + (" or an objective (./ksim objectives)." if OBJECTIVES else ".")) for a in rest])[0], len(rest))
        print(bold("Study: " + ", ".join(f"Q{q['id']}" for q in qs)))
    else:
        domain, qs = next_drill(hard, rng)
        print(bold(f"Study: {DOMAINS[domain]}"))
    begin_session(qs, "drill", EXAM_SECONDS, force, hard=hard, untimed_session=True, objective=obj and obj["id"])
    if obj:
        print(); print_notes(obj)
        print(dim("  ./ksim show N   read a task      ./ksim grade N   check it      ./ksim solution N   reference answer\n"
                  "  ./ksim notes    these notes again      ./ksim end   finish (./ksim objectives then shows what you solved)"))

def cmd_sim(args):
    """A fixed simulator set, full exam rules and clock."""
    force = "--force" in args
    names = [a.lower() for a in args if not a.startswith("--")]
    if not names or names[0] not in SETS:
        die(f"usage: ./ksim sim {'|'.join(SETS) or '<set>'} [--force]\n  "
            + "\n  ".join(f"{k}: {v} ({len(set_questions(k))} tasks)" for k, v in SETS.items()))
    name = names[0]
    qs = set_questions(name)
    print(bold(f"{SETS[name]} - {len(qs)} tasks, {TRACK['minutes']} minutes, exam rules (no feedback until you submit)"))
    begin_session(qs, "exam", EXAM_SECONDS, force, hard=True)

def cmd_list(args):
    st = load_state()
    results = st["results"] if st and "results" in st else {}
    qs = session_questions(st) if st and not st.get("ended_at") else list(QUESTIONS)
    agg = stats()
    print(bold(f"{'#':>3}  {'Domain':<8}{'Pts':>4}  {'Now':<8} {'History':<9} Title"))
    for q in qs:
        r = results.get(str(q["id"]))
        now = "-" if r is None else (green("PASS") if r.get("pass") else yellow(f"{r.get('earned')}/{r.get('total')}"))
        a = agg.get(int(q["id"])) or AggEntry()
        hist = "" if a.attempts == 0 else f"{a.attempts - a.fails}/{a.attempts}"
        if a.attempts and a.last is False:
            hist = red(hist + " ✗")
        print(f"{q['id']:>3}  {q['domain']:<8}{q['weight']:>4}  {now:<17} {hist:<18} {q['title']}{'  [hard]' if q['difficulty'] == 'hard' else ''}")
    print(dim("\nHistory = full passes/attempts across sessions, ✗ = failed most recently."))
    if st and not st.get("ended_at"):
        print(status_line(st))

def cmd_show(args):
    if not args:
        die("usage: ./ksim show N")
    q = q_by_id(int(args[0]))
    st0 = load_state()
    sq = session_questions(st0) if st0 and not st0.get("ended_at") else []
    pos = f"{sq.index(q) + 1} of {len(sq)}  |  " if q in sq else ""
    print(bold(f"{pos}Q{q['id']}  |  {DOMAINS[q['domain']]}  |  {q['weight']} pts{'  |  HARD' if q['difficulty'] == 'hard' else ''}"))
    print(bold(q["title"])); print(f"Solve this question on:  ssh {host_of(q)}"); print("-" * 64); print(task_text(q)); print("-" * 64)
    st = load_state()
    if st and not st.get("ended_at"):
        print(status_line(st))

def cmd_grade(args):
    st = require_started()
    force = "--force" in args; args = [a for a in args if a != "--force"]
    if not args:
        die("usage: ./ksim grade N | all")
    # The web UI already refused this; the CLI handed out per-check feedback mid-exam, which a sim
    # meant to rehearse the real thing (no feedback until you submit) must not do by default.
    if st.get("mode") == "exam" and not st.get("ended_at") and not force:
        die("No feedback during an exam - the real one gives none. Submit with ./ksim end (--force to peek anyway).")
    ids = [q["id"] for q in session_questions(st)] if args[0] == "all" else [int(a) for a in args]
    for n in ids:
        q = q_by_id(n); r = grade_one(q)
        st["results"][str(n)] = r
        tag = green("PASS") if r.get("pass") else yellow(f"{r.get('earned')}/{r.get('total')}")
        print(f"Q{n:02d} {tag}  {q['title']}"); print(dim(result_detail(r)))
    save_state(st)
    record_study(st, set(ids))
    if untimed(st):
        reached = milestone_lines(update_milestones())
        if reached:   # kept with the session, so ./ksim end and the results page show them again
            st["milestones"] = st.get("milestones", []) + reached; save_state(st)
        for line in reached:
            print(green(line))
    if args[0] == "all":
        print_score(st)

def print_score(st):
    qs = session_questions(st)
    earned, total, pct = score(st)
    print(); print(bold("Per-domain:"))
    for d, name in DOMAINS.items():
        dq = [q for q in qs if q["domain"] == d]
        if not dq:
            continue
        dt = sum(q["weight"] for q in dq); de = sum(st["results"].get(str(q["id"]), {}).get("earned", 0) for q in dq)
        n = int(20 * de / dt)
        print(f"  {d:<7} {'█' * n}{'░' * (20 - n)} {de:>3}/{dt:<3} {dim(name)}")
    verdict = green("PASS") if pct >= PASS_PCT else red("FAIL")
    print(f"\n{bold('Score:')} {earned}/{total} = {pct}%  ->  {verdict} (pass mark {PASS_PCT}%)")

def status_line(st):
    if untimed(st):
        return green("study mode - no clock") + dim(f"  [{len(session_questions(st))} tasks, kept out of the history]")
    r = remaining(st)
    if st.get("paused_at"):
        return yellow(f"⏸  PAUSED - {fmt(r)} remaining") + dim("  ./ksim resume")
    if r <= 0:
        return red("⏰ TIME IS UP - run ./ksim end")
    col = green if r > 30 * 60 else (yellow if r > 10 * 60 else red)
    return col(f"⏱  {fmt(r)} remaining") + dim(f"  [{st.get('mode', 'exam')}]")

def cmd_status(args):
    st = require_started()
    if st.get("ended_at"):
        print("Session ended."); print_score(st); return
    print(status_line(st))
    print(dim(f"{sum(1 for v in st['results'].values() if v['pass'])} passed / {len(st['results'])} graded / {len(session_questions(st))} in session"))

def cmd_timer(args):
    st = require_started()
    if st.get("ended_at"):
        die("Session already ended.")
    if untimed(st):
        die("This is a study session - there is no clock.")
    try:
        while True:
            st = load_state(); r = remaining(st)
            if st.get("paused_at"):
                sys.stdout.write("\r" + yellow(bold(f"⏸  {fmt(r)} PAUSED   ")) + dim("   ./ksim resume        ")); sys.stdout.flush(); time.sleep(1); continue
            if r <= 0:
                print("\r" + red(bold("⏰  00:00:00  TIME IS UP - run ./ksim end       "))); break
            col = green if r > 30 * 60 else (yellow if r > 10 * 60 else red)
            sys.stdout.write("\r" + col(bold(f"⏱  {fmt(r)} remaining")) + dim("   (Ctrl-C to hide)")); sys.stdout.flush()
            if int(r) in (30 * 60, 15 * 60, 5 * 60) and TTY:
                sys.stdout.write("\a")
            time.sleep(1)
    except KeyboardInterrupt:
        print()

def cmd_pause(args):
    st = require_started()
    if st.get("ended_at"):
        die("Session already ended.")
    set_paused(st, True); print(status_line(st))

def cmd_resume(args):
    st = require_started()
    set_paused(st, False); print(status_line(st))

def cmd_end(args):
    st = require_started()
    if st.get("ended_at"):
        die("Session already ended and recorded.")
    down = hosts_down(st)
    if down:
        die(down_message(down))
    if remaining(st) <= 0:
        print(yellow("Note: time expired before submission."))
    entry = finish_session(st)
    print_score(st)
    def path_note():
        if not OBJECTIVES:
            return
        print()
        for line in st.get("milestones", []):
            print(green(line))
        step = next_step()
        print(bold(f"Next on the path:  {step['cmd']}") + dim(f"   {step['why']}"))
    if entry is None:
        print(dim("Study session - not added to history or weak-spots.")); path_note(); return
    print(dim(f"Time used: {fmt(st['ended_at'] - st['started_at'] - paused_total(st))}" + ("  (over time)" if st.get("over_time") else "")))
    failed = sorted(int(k) for k, v in entry["results"].items() if not v["pass"])
    print(dim(f"Attempt #{len(load_history())} logged to {os.path.basename(HISTORY_FILE)}; {os.path.basename(WEAK_FILE)} updated."))
    if failed:
        print(bold("\nTo drill what you missed:  ./ksim drill weak") + dim(f"   (Q{', Q'.join(map(str, failed))})"))
    path_note()

def cmd_abort(args):
    """End a session without grading it, and delete its hosts."""
    st = load_state()
    if not st or st.get("ended_at"):
        die("No session in progress.")
    assert st is not None
    if "--yes" not in args:
        die(f"This discards the {st.get('mode', 'exam')} in progress without grading or recording it.\n"
            "  Confirm:  ./ksim abort --yes        (to grade and keep it instead: ./ksim end)")
    st["ended_at"] = time.time(); st["aborted"] = True
    save_state(st)
    gone = clear_hosts()
    print(yellow("Session discarded. Nothing was graded or written to history."))
    print(dim(f"  Its {len(gone)} host(s) are deleted."))

def cmd_weak(args):
    agg = stats(); hist = load_history()
    if not hist:
        die("No history yet - finish a session with './ksim end'.")
    ids = [i for i in weak_ids(agg) if agg[i]["attempts"] > 0]
    print(bold(f"Weak spots after {len(hist)} attempt(s):"))
    if not ids:
        print(green("  none - everything attempted has passed on its latest try"))
    for i in ids:
        q = q_by_id(i); a = agg[i]
        print(f"\n{red('Q%02d' % i)} {q['domain']:<7} {q['title']}  " + dim(f"{a['fails']}/{a['attempts']} failed, last {a['last_earned']} pts, last failed {a['last_fail_at']}"))
        for n in weak_lines(a):
            print(dim("    " + n))
    never = [q["id"] for q in QUESTIONS if agg[q["id"]]["attempts"] == 0]
    if never:
        print(dim(f"\nNever attempted: Q{', Q'.join(map(str, never))}"))
    print(dim(f"\nFull log: {WEAK_FILE}     Drill them: ./ksim drill weak"))

def cmd_history(args):
    hist = load_history(include_synthetic=True)
    if not hist:
        die("No history yet.")
    print(bold(f"{'#':>3}  {'when':<17}{'mode':<7}{'score':>7}  {'time':<9} tasks"))
    for i, e in enumerate(hist, 1):
        col = green if e["score_pct"] >= PASS_PCT else red
        tasks = f"all {len(QUESTIONS)}" if len(e["ids"]) == len(QUESTIONS) else "Q" + ",".join(map(str, e["ids"]))
        tag = dim("  [scripted verification - not counted]") if e.get("synthetic") else ""
        print(f"{i:>3}  {e['at']:<17}{(e['mode'] + ('*' if e.get('hard') else '')):<7}{col('%5.1f%%' % e['score_pct']):>16}  {fmt(e['time_used']):<9} {tasks}{tag}")
    exams = [e for e in hist if e["mode"] == "exam" and not e.get("synthetic")]
    print(dim("* = hard"))
    if len(exams) >= 2:
        print(bold("\nDomain trend (full exams, % of that exam's points in the domain):"))
        for d in DOMAINS:
            cells = []
            for e in exams:
                de, dt = exam_domain_scores(e).get(d, (0, 0))
                cells.append(f"{round(100 * de / dt):>3}%" if dt else "   -")
            print(f"  {d:<7} " + " → ".join(cells))

def cmd_reset(args):
    """Throw a task's cluster away and build it again, scenario included."""
    if not args:
        die("usage: ./ksim reset N   (rebuild one task's host from scratch: new cluster, scenario seeded again)")
    st = require_started(); q = q_by_id(int(args[0]))
    print(dim(f"  rebuilding {host_of(q)} - about a minute..."))
    problem = provision(q, session_params(st, q))
    print(("rebuilt " if not problem else "problem rebuilding ") + f"Q{q['id']:02d}: {q['title']}")

# --------------------------------------------------------------- web ----
class Api(http.server.BaseHTTPRequestHandler):
    """Serves web/index.html plus a small JSON API. State lives in the same files the CLI uses."""
    lock = threading.Lock()
    log_lines = []
    seeding = False
    seed_error = None
    desktop_ok = False
    desktop_error = None

    def log_message(self, format: str, *args: Any) -> None:  # quiet
        pass

    def _json(self, obj, code=200):
        body = json.dumps(obj).encode()
        self.send_response(code); self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body))); self.end_headers(); self.wfile.write(body)

    def _read_json(self):
        n = int(self.headers.get("Content-Length") or 0)
        return json.loads(self.rfile.read(n) or b"{}")

    def do_GET(self):
        p = urllib.parse.urlparse(self.path)
        if p.path in ("/", "/index.html"):
            with open(os.path.join(ROOT, "web", "index.html"), "rb") as f:
                body = f.read()
            self.send_response(200); self.send_header("Content-Type", "text/html; charset=utf-8")
            self.send_header("Content-Length", str(len(body))); self.end_headers(); self.wfile.write(body); return
        if p.path == "/api/session":
            with Api.lock:
                return self._json(self.session_payload())
        if p.path == "/api/history":
            return self._json({"history": load_history(), "weak": weak_ids(), "stats": {str(k): v.to_dict() for k, v in stats().items()}})
        self._json({"error": "not found"}, 404)

    def do_POST(self):
        p = urllib.parse.urlparse(self.path); body = self._read_json()
        with Api.lock:
            st = load_state()
            if p.path == "/api/track":
                t = body.get("track")
                if t not in TRACKS:
                    return self._json({"error": f"unknown track {t}"}, 400)
                if Api.seeding:
                    return self._json({"error": "a session is being seeded"}, 409)
                load_track(t)
                Api.log_lines = []
                return self._json(self.session_payload())
            if p.path == "/api/clip":   # a value clicked in a task lands on the desktop's clipboard
                desktop.clip(str(body.get("text", ""))[:20000])
                return self._json({"ok": True})
            if p.path == "/api/start":
                if Api.seeding:
                    return self._json({"error": "already seeding"}, 409)
                mode = body.get("mode", "exam"); hard = bool(body.get("hard")); rng = random.Random()
                Api.log_lines = []; Api.seed_error = None; Api.seeding = True
                ansi = __import__("re").compile(r"\x1b\[[0-9;]*m")
                ulog = lambda line: Api.log_lines.append(ansi.sub("", line))
                def work():
                    try:
                        if body.get("sim") in SETS:
                            begin_session(set_questions(body["sim"]), "exam", EXAM_SECONDS, True, log=ulog, hard=True, other_ok=False)
                        elif mode == "exam":
                            begin_session(compose_exam(hard, rng), "exam", EXAM_SECONDS, True, log=ulog, hard=hard, other_ok=False)
                        else:
                            objective = find_objective(body["objective"]) if body.get("objective") else None
                            if objective:
                                qs, _ = objective_session(objective, "study" if body.get("study") else "drill", bool(body.get("all")))
                            elif body.get("domain") in DOMAINS:
                                qs = pick(body["domain"], DRILL_SIZE, hard, rng)
                            elif body.get("campaign"):
                                _, qs = campaign_batch(hard, rng)
                                if not qs:
                                    qs = no_conflicts(split_solo([q for q in QUESTIONS if q["id"] in weak_ids()])[0], DRILL_SIZE)
                            elif body.get("next"):
                                _, qs = next_drill(hard, rng)
                            else:
                                ids = body.get("ids") or weak_ids()
                                qs = no_conflicts(split_solo([q for q in QUESTIONS if q["id"] in ids])[0], len(ids))
                            per = DRILL_SECONDS_PER_TASK_HARD if hard else DRILL_SECONDS_PER_TASK
                            begin_session(qs, "drill", per * len(qs), True, log=ulog, hard=hard,
                                          untimed_session=bool(body.get("study")), other_ok=False,
                                          objective=objective and objective["id"])
                    except SystemExit as e:
                        Api.seed_error = (getattr(e, "msg", None) or "\n".join(l for l in Api.log_lines if l.strip())
                                          or "start failed - see the terminal running ./ksim web")
                    except Exception as e:  # noqa: BLE001
                        Api.seed_error = f"{type(e).__name__}: {e}"
                    finally:
                        Api.seeding = False
                threading.Thread(target=work, daemon=True).start()
                return self._json({"seeding": True})
            if not st:
                return self._json({"error": "no session"}, 400)
            if p.path == "/api/flag":
                qid = int(body["id"]); flags = set(st.get("flags", []))
                flags.symmetric_difference_update({qid}); st["flags"] = sorted(flags); save_state(st)
            elif p.path == "/api/pause":
                set_paused(st, bool(body.get("paused", True)))
            elif p.path == "/api/notes":
                st["notes"] = body.get("notes", ""); save_state(st)
            elif p.path == "/api/grade":
                if st.get("mode") != "drill" and not st.get("ended_at"):
                    return self._json({"error": "No feedback during an exam. Submit to see results."}, 403)
                q = q_by_id(int(body["id"]))
                if "results" not in st or not isinstance(st["results"], dict):
                    st["results"] = {}
                st["results"][str(q["id"])] = grade_one(q, session_params(st, q)); save_state(st)
                record_study(st, {q["id"]})
                if untimed(st):
                    st["milestones"] = st.get("milestones", []) + milestone_lines(update_milestones()); save_state(st)
            elif p.path == "/api/end":
                if not st.get("ended_at"):
                    down = hosts_down(st)  # grading hosts that are not running would record zeros
                    if down:
                        return self._json({"error": down_message(down)}, 503)
                    finish_session(st, log=lambda *_: None)
            elif p.path == "/api/reset":
                q = q_by_id(int(body["id"])); provision(q, session_params(st, q), log=lambda *_: None)
            else:
                return self._json({"error": "not found"}, 404)
            return self._json(self.session_payload())

    def session_payload(self) -> dict[str, Any]:
        st = load_state()
        qs = session_questions(st) if st else QUESTIONS
        payload: dict[str, Any] = {
            "track": TRACK, "track_id": TRACK_ID, "workspace": WS_DISPLAY, "version": VERSION,
            "desktop": desktop.url() if Api.desktop_ok else None, "desktop_error": Api.desktop_error, "setup_log": Api.log_lines,
            "questions": [{"id": q["id"], "domain": q["domain"], "title": q["title"], "weight": q["weight"], "difficulty": q["difficulty"],
                           "host": host_of(q), "nodes": 1 + workers_of(q),
                           "task": task_text(q, session_params(st, q)), "checks": [{"name": c["name"], "pts": c["pts"]} for c in q["checks"]],
                           "solution": solution_text(q, session_params(st, q)) if solution_allowed(st, int(q["id"])) else None,
                           # which objective a task belongs to is a hint, so it follows the solution's rule
                           "objectives": [o["id"] for o in objectives_of(q["id"])] if solution_allowed(st, int(q["id"])) else []}
                          for q in qs],
            "bank": [{"id": q["id"], "domain": q["domain"], "title": q["title"], "difficulty": q["difficulty"]} for q in QUESTIONS],
            "tracks": TRACKS, "track_k8s": track_k8s(),
            "k8s": k8s_version(), "pending": len(PENDING), "drilled": drilled_domains(), "sets": {k: {"name": v, "count": len(set_questions(k))} for k, v in SETS.items()},
            "seen": sorted(last_seen()),
            "seeding": Api.seeding, "seed_error": Api.seed_error,
            "session": None,
        }
        payload.update(self.path_payload())
        if st:
            earned, total, pct = score(st)
            payload["session"] = {"mode": st.get("mode"), "hard": st.get("hard", False), "started_at": st["started_at"], "duration": st.get("duration", EXAM_SECONDS),
                                  "ends_at": st["started_at"] + st.get("duration", EXAM_SECONDS), "ended_at": st.get("ended_at"),
                                  "over_time": st.get("over_time", False), "flags": st.get("flags", []),
                                  "paused": bool(st.get("paused_at")), "paused_total": paused_total(st),
                                  "untimed": untimed(st), "notes": st.get("notes", ""),
                                  "objective": st.get("objective"), "milestones": st.get("milestones", []),
                                  "results": st["results"], "score": {"earned": earned, "total": total, "pct": pct, "pass_pct": PASS_PCT},
                                  "domains": self.domain_scores(st), "server_time": time.time()}
        return payload

    def path_payload(self) -> dict[str, Any]:
        """The curriculum as the UI shows it: every objective with its notes, tasks and state, how
        many are studied and done, and the next step on the path. Empty for a track without one."""
        if not OBJECTIVES:
            return {"objectives": [], "focus": [], "path": None}
        agg, studied = stats(), load_study()
        objs = [{"id": o["id"], "key": o["key"], "domain": o["domain"], "text": o["text"], "state": objective_state(o, agg, studied),
                 "know": o["know"], "fast": o["fast"].strip("\n"), "traps": o["traps"], "docs": o["docs"],
                 "tasks": [{"id": q["id"], "title": q["title"], "set": q.get("set"), "state": task_state(q["id"], agg, studied)}
                           for q in objective_tasks(o, True)]} for o in OBJECTIVES]
        step = next_step(agg, studied); full, fixed = mock_scores()
        states = [o["state"] for o in objs]
        return {"objectives": objs, "focus": load_focus(),
                "path": {"total": len(objs), "done": states.count("done"), "studied": states.count("done") + states.count("studied"),
                         "mock_best": max(full) if full else None, "set_best": {k: (max(v) if v else None) for k, v in fixed.items()},
                         "next": {"kind": step["kind"], "cmd": step["cmd"], "why": step["why"], "set": step.get("set"),
                                  "objective": step["objective"]["id"] if step.get("objective") else None}}}

    def domain_scores(self, st: dict[str, Any]) -> dict[str, Any]:
        qs = session_questions(st); out = {}
        st_results: dict[str, Any] = st.get("results", {})
        for d in DOMAINS:
            dq = [q for q in qs if q["domain"] == d]
            if dq:
                out[d] = {"earned": sum(st_results.get(str(q["id"]), {}).get("earned", 0) for q in dq),
                          "total": sum(q["weight"] for q in dq)}
        return out

def ensure_desktop():
    """The desktop, running and pointed at the open session if there is one. A running desktop is
    kept, so restarting the UI in the middle of a session does not cost you your terminals."""
    was_running = desktop.running()
    desktop.up()
    st = load_state()
    if not was_running and st and not st.get("ended_at"):
        desktop.configure(TRACK_ID, [envs.host_of(TRACK_ID, i) for i in st.get("ids", [])],
                          open_web=bool(os.environ.get("KSIM_OPEN_WEB")))

def cmd_web(args):
    port = 8080
    if "--port" in args:
        port = int(args[args.index("--port") + 1])
    if "--desktop-port" in args:
        desktop.PORT = int(args[args.index("--desktop-port") + 1])
    import socket
    def port_free(pt):
        with socket.socket() as sk:
            sk.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            try:
                sk.bind(("127.0.0.1", pt)); return True
            except OSError:
                return False
    if not port_free(port):
        die(f"Port {port} is already in use - probably another './ksim web' still running.\n"
            f"  Find it:  ss -ltnp | grep :{port}      or start on another port:  ./ksim web --port {port + 10}")
    try:
        ensure_desktop()
        Api.desktop_ok = True
        print(dim(f"  desktop: {desktop.NAME} on 127.0.0.1:{desktop.PORT} (XFCE over noVNC, loopback only)"))
    except envs.EnvError as e:
        Api.desktop_error = str(e)
        print(yellow(f"  no desktop: {e}"))
    http.server.ThreadingHTTPServer.allow_reuse_address = True
    srv = http.server.ThreadingHTTPServer(("127.0.0.1", port), Api)  # type: ignore[arg-type]
    print(bold(f"\n  {TRACK_ID.upper()} exam UI:  http://127.0.0.1:{port}   (ksim {VERSION})\n")
          + dim("  Ctrl-C stops the UI - not the exam clock, the desktop or the hosts (./ksim down removes those)."))
    def stop(*_):
        srv.shutdown()
    signal.signal(signal.SIGINT, lambda *_: threading.Thread(target=stop).start())
    signal.signal(signal.SIGTERM, lambda *_: threading.Thread(target=stop).start())
    srv.serve_forever()

def cmd_version(args):
    print(f"ksim {VERSION}  track={TRACK_ID}  k8s={k8s_version()}  bank={len(QUESTIONS)} tasks"
          + (f" (+{len(PENDING)} held back)" if PENDING else "") + f"  python={sys.version.split()[0]}")

def cmd_build(args):
    """Build the exam host image of a track's Kubernetes minor, and the desktop image."""
    names = [a for a in args if not a.startswith("--")] or [TRACK_ID]
    tracks = TRACKS if "all" in names else names
    for t in tracks:
        if t not in TRACKS:
            die(f"usage: ./ksim build [{'|'.join(TRACKS)}|all] [--vm]   (default: the current track, {TRACK_ID})")
    minors, variants = [], []
    for t in tracks:
        load_track(t)
        if K8S not in minors:
            minors.append(K8S)
        if TRACK.get("image") and (K8S, TRACK["image"]) not in variants:
            variants.append((K8S, TRACK["image"]))
    print(bold(f"Building images for {', '.join(t.upper() for t in tracks)} - the first build downloads a few hundred MB..."))
    try:
        for k8s in minors:
            envs.build_node_image(k8s)       # unchanged layers come from the build cache
        for k8s, variant in variants:        # a track's own flavour, on top of the common image
            envs.build_variant_image(k8s, variant)
        envs.build_desktop_image()
        if "--vm" in args:                   # the VM exam host, for tasks that need a kernel of their own
            for k8s in minors:
                envs.build_vm_image(k8s)
    except envs.EnvError as e:
        die(str(e))
    print(green("Done.") + dim("   ./ksim web   opens the exam UI"))

def cmd_hosts(args):
    """The hosts of the session, or - `hosts start` - bring stopped ones back after a reboot."""
    st = load_state()
    ids = (st or {}).get("ids", [])
    if args and args[0] == "start":
        for i in ids:
            h = envs.host_of(TRACK_ID, i)
            if not envs.running(h):
                print(f"  starting {h}" if envs.start(h) else red(f"  {h} no longer exists - ./ksim reset {i} rebuilds it"))
        try:
            ensure_desktop()
        except envs.EnvError as e:
            print(yellow(f"  no desktop: {e}"))
        print(dim("  Give the API servers half a minute before grading."))
        return
    alive = set(envs.existing())
    if not ids:
        print("No session." + (f"  Hosts still up: {', '.join(sorted(alive))}  (./ksim down removes them)" if alive else ""))
        return
    print(bold(f"{'task':<6}{'host':<11}{'nodes':<7}{'state':<10}title"))
    for i in ids:
        q = QBYID.get(i)
        if not q:
            continue
        h = host_of(q)
        state = green("up") if envs.running(h) else (yellow("stopped") if h in alive else red("gone"))
        print(f"Q{i:<5}{h:<11}{1 + workers_of(q):<7}{state:<19}{q['title']}")
    print(dim(f"\ndesktop: {'up' if desktop.running() else 'not running'}     ./ksim ssh N   a shell on a task's host from this terminal"))

def cmd_ssh(args):
    """A shell on a task's host from your own terminal - the desktop's `ssh <host>` without the desktop."""
    if not args:
        die("usage: ./ksim ssh N")
    q = q_by_id(int(args[0])); node = nodes_of(q)["CP"]
    if not envs.running(host_of(q)):
        die(f"{host_of(q)} is not running - it exists only while a session with Q{q['id']} is open (./ksim hosts).")
    if is_vm(q):
        os.execvp(envs.RUNTIME, [envs.RUNTIME, "exec", "-it", node, "ssh", "-t", "candidate@vm"])
    os.execvp(envs.RUNTIME, [envs.RUNTIME, "exec", "-it", *AS_CANDIDATE, node, "bash", "-l"])

TARGET_PER_DOMAIN = (17, 20)   # pool tasks a domain should have, so every concept in it gets practised

def cmd_coverage(args):
    """Tasks per domain and per objective against the target - what the bank still needs."""
    lo, hi = TARGET_PER_DOMAIN
    print(bold(f"{TRACK['name']} - bank coverage") + dim(f"   target: {lo}-{hi} pool tasks per domain (fixed simulator sets are counted apart)"))
    print(bold(f"\n{'domain':<9}{'pool':>5}{'in sets':>9}{'to write':>10}   name"))
    need = 0
    for d, name in DOMAINS.items():
        dq = [q for q in QUESTIONS if q["domain"] == d]; pool = [q for q in dq if not q.get("set")]
        gap = max(0, lo - len(pool)); need += gap
        col = green if not gap else (yellow if gap <= 5 else red)
        print(f"{d:<9}{len(pool):>5}{len(dq) - len(pool):>9}{col((('+' + str(gap)) if gap else 'ok').rjust(10))}   {name}")
    print(dim(f"\n{len(POOL)} pool tasks, {len(QUESTIONS) - len(POOL)} in fixed sets" + (f", {len(PENDING)} held back" if PENDING else "")
              + f".  {need} more pool tasks reach {lo} in every domain."))
    if OBJECTIVES:
        print(bold(f"\n{'obj':<6}{'domain':<8}{'pool':>5}{'sets':>6}   objective"))
        for o in OBJECTIVES:
            ts = [QBYID[i] for i in o["tasks"] if i in QBYID]; pool = [q for q in ts if not q.get("set")]
            col = red if len(pool) < 2 else (yellow if len(pool) < 4 else (lambda x: x))
            print(col(f"{o['id']:<6}{o['domain']:<8}{len(pool):>5}{len(ts) - len(pool):>6}   {o['text']}"))
        print(dim("  a task may sit under several objectives, so these do not add up to the domain totals"))
    else:
        print(yellow(f"\nNo {TRACK_ID}/curriculum.py yet: no objectives, study notes or study path for this track."))
    for i, why in PENDING.items():
        print(dim(f"  held back: Q{i} - {why}"))

def cmd_audit(args):
    """Bank audit: build each task's host, seed it, grade it untouched, then - for a task with a
    scripted solution in <track>/solve.py - solve it on the host and grade it again. A clean seed
    and no full marks untouched is the least a task must manage; only the script proves it can be
    solved as written."""
    for t in TRACKS:
        try:
            with open(os.path.join(STATE_DIR, f"state-{t}.json")) as f:
                if not json.load(f).get("ended_at"):
                    die(f"A {t.upper()} session is open and the audit rebuilds hosts under the same names. End it first.")
        except (OSError, ValueError):
            pass
    settle = 0   # seconds between seeding and the untouched grade: a stopped kubelet takes ~40 s to show as NotReady
    if "--settle" in args:
        i = args.index("--settle"); settle = int(args[i + 1]); args = args[:i] + args[i + 2:]
    names = [a for a in args if not a.startswith("--")]
    if not names or names == ["all"]:
        qs = list(QUESTIONS)
    else:
        qs = [q for q in QUESTIONS if str(q["id"]) in names or q["domain"] in [n.upper() for n in names]]
    if not qs:
        die(f"usage: ./ksim audit [all|DOMAIN..|N..] [--settle SECONDS] [--keep]   (domains: {', '.join(DOMAINS)})")
    preflight(qs[:PARALLEL])
    envs.ensure_registry()
    lock = os.path.join(STATE_DIR, f"audit-{os.getpid()}.lock")   # keeps sessions from starting meanwhile
    os.makedirs(STATE_DIR, exist_ok=True)
    open(lock, "w").close()
    import atexit
    atexit.register(lambda: os.path.exists(lock) and os.remove(lock))
    print(bold(f"Bank audit of {len(qs)} {TRACK_ID.upper()} task(s), {PARALLEL} at a time - each gets its own cluster, is seeded, graded untouched and removed."))
    def one(q):
        params = make_params(q, random.Random(q["id"])); host = host_of(q); t0 = time.time()
        res = {"id": q["id"], "domain": q["domain"], "title": q["title"], "host": host, "workers": workers_of(q), "total": q["weight"]}
        try:
            make_host(q)
        except envs.EnvError as e:
            res.update(verdict="no cluster", detail=str(e)[-400:], secs=int(time.time() - t0))
            return res
        try:
            rc, out = run(q, q["setup"], params=params, timeout=300)
        except subprocess.TimeoutExpired:
            rc, out = 1, "setup timed out after 300s"
        envs.hand_over(host, params.get("ns") if q.get("ctx_ns") else None)
        res["seed_secs"] = int(time.time() - t0)
        time.sleep(settle)
        r = grade_one(q, params)
        res.update(earned=r["earned"], passing=[c["name"] for c in r["checks"] if c["pass"]])
        if rc != 0:
            res.update(verdict="seed failed", detail=out[-400:])
        elif r["earned"] == r["total"]:
            res.update(verdict="full marks unsolved")
        elif q.get("solve"):
            _, sout = solve_on_host(q, params)
            r2 = grade_one(q, params)
            # What a script created may still be starting. A candidate watches it come up before
            # moving on, so the task counts as solved if it reaches full marks within 90 s.
            waited = 0
            while not r2["pass"] and waited < 90:
                time.sleep(15); waited += 15
                r2 = grade_one(q, params)
            res.update(solved=r2["earned"], verdict="ok" if r2["pass"] else "solve failed")
            if not r2["pass"]:
                res["detail"] = "; ".join(f"✗ {c['name']}" for c in r2["checks"] if not c["pass"])[-400:]
        else:
            res.update(verdict="ok", setup_note=out[-200:] if out else "")
        if "--keep" not in args:
            envs.destroy(host)
        res["secs"] = int(time.time() - t0)
        return res
    results = []
    with concurrent.futures.ThreadPoolExecutor(max_workers=PARALLEL) as pool:
        for fut in concurrent.futures.as_completed([pool.submit(one, q) for q in qs]):   # as they finish
            res = fut.result()
            results.append(res)
            col = green if res["verdict"] == "ok" else red
            free = f"  {res['earned']}/{res['total']} pts for nothing" if res.get("earned") else ""
            proven = dim("  solved by script") if res["verdict"] == "ok" and "solved" in res else ""
            print(f"  {col(res['verdict']):<28} Q{res['id']:<4}{res['domain']:<8}{res['secs']:>4}s  {res['title']}{yellow(free) if free else ''}{proven}", flush=True)
            if res.get("detail"):
                print(dim("      " + res["detail"].replace("\n", "\n      ")), flush=True)
    results.sort(key=lambda r: r["id"])
    out_dir = os.path.join(STATE_DIR, "audit"); os.makedirs(out_dir, exist_ok=True)
    path = os.path.join(out_dir, f"audit-{TRACK_ID}.json")
    now = datetime.now().isoformat(timespec="minutes")
    for r in results:
        r["at"] = now
    try:   # the report holds the latest result of every task ever audited, not only this run's
        with open(path) as f:
            merged = {r["id"]: r for r in json.load(f)["results"]}
    except (OSError, ValueError, KeyError):
        merged = {}
    merged.update({r["id"]: r for r in results})
    with open(path, "w") as f:
        json.dump({"k8s": k8s_version(), "results": [merged[i] for i in sorted(merged)]}, f, indent=1)
    bad = [r for r in results if r["verdict"] != "ok"]
    proven = sum(1 for r in results if r["verdict"] == "ok" and "solved" in r)
    print(bold(f"\n{len(results) - len(bad)}/{len(results)} seed cleanly and give no full marks untouched; {proven} of them also solved by their script.") + (red(f"  {len(bad)} need work: Q" + ", Q".join(str(r['id']) for r in bad)) if bad else ""))
    print(dim(f"  report: {os.path.relpath(path, ROOT)}"))

def cmd_down(args):
    """Delete every exam host and the desktop. History, study progress and images are kept."""
    for t in TRACKS:
        try:
            with open(os.path.join(STATE_DIR, f"state-{t}.json")) as f:
                if not json.load(f).get("ended_at") and "--yes" not in args:
                    die(f"A {t.upper()} session is still open; its hosts hold your work.\n"
                        f"  Submit it (./ksim --track {t} end), or confirm:  ./ksim down --yes")
        except (OSError, ValueError):
            pass
    gone = clear_hosts()
    desktop.down()
    envs.stop_registry()
    print(f"Removed {len(gone)} host(s) and the desktop." + dim("  History, images and the image cache's contents are kept."))

def cmd_help(args):
    print(__doc__ + f"\nversion {VERSION}")
    objective_help = "" if not OBJECTIVES else (
        f"  objectives               the curriculum as a path to the exam: {len(OBJECTIVES)} objectives, their tasks, your progress\n"
        "  next                     start the next step on that path (study an objective, then drill it, then the mocks)\n"
        "  focus [DOMAIN..|clear]   walk these domains first on the path - the ones an exam report said are weakest\n"
        "  notes [OBJ|DOMAIN|all]   what to know, fastest commands, traps and docs for an objective (3.2 or probes)\n"
        "  study [OBJ|next]         an objective's notes and tasks; with no argument, the next one on the path\n"
        "                           (--all adds its Simulator Set tasks);  drill OBJ = the same tasks against the clock\n")
    print(f"""usage: ./ksim [--track cka|ckad|cks] <command>        (current track: {TRACK_ID}, {len(QUESTIONS)} tasks)
       Every task runs on its own cluster at the exam's Kubernetes version ({TRACK_ID}: {k8s_version()}),
       reached with `ssh <host>` from the remote desktop.

  build [TRACK|all]        build the exam host and desktop images (once per Kubernetes minor)
  build cks --vm           also build the VM exam host that the Falco and AppArmor tasks need (about ten minutes)
  web [--port 8080]        the exam in the browser: task pane, remote desktop, clock, submit
  study [DOMAIN|weak|N..]  no clock, solutions unlocked, kept out of the history  (--count N, default {DRILL_SIZE})
{objective_help}  drill                    next domain you have drilled least: {DRILL_SIZE} tasks, 6 min each  (--hard: 5 min, hard tasks)
  drill all [--hard]       campaign: {DRILL_SIZE} never-attempted tasks per session until the bank is done, then weak ones
  drill weak|N..|DOMAIN..  chosen tasks  (--time MIN, --force, --hard)
  progress                 attempted/passed per domain, normal and hard
  solution N               reference solution (drills: after grading N; exams: after submit)
  sim {'|'.join(SETS) or '<set>'}{' ' * max(1, 20 - len('|'.join(SETS)))}fixed simulator set, exam rules, {TRACK['minutes']} min
  start [--hard]           full exam: {sum(QUOTA.values()) or '?'} tasks sampled by domain ({sum(QUOTA_HARD.values()) or '?'} in hard mode), {TRACK['minutes']} min.
                           Requires every domain drilled once first (--force skips). Hard mode adds traps,
                           exact-output tasks, compound failures and collateral checks.
  list                     tasks in this session, with current + historical results
  show N                   display task N and the host it is solved on
  grade N|all              grade one task (or all) per check - drills only (--force to peek in an exam)
  status / timer           time remaining (timer = live countdown)
  pause / resume           stop the clock (not recorded anywhere - but the real exam has no pause)
  end                      submit: grade per check, score, log attempt, update weak-spots
  weak                     what you keep getting wrong, with the failing checks
  history                  every attempt, scores, and per-domain trend
  reset N                  rebuild the host of task N from scratch (new cluster, scenario seeded again)
  hosts [start]            the session's hosts and their state; `start` brings them back after a reboot
  ssh N                    a shell on the host of task N from this terminal
  down                     delete every host and the desktop (history and images are kept)
  coverage                 tasks per domain and objective against the 17-20 per domain target
  audit [all|DOMAIN|N..]   bank check: build each task's host, seed it, grade it untouched, solve it with its
                           script if it has one (<track>/solve.py), remove it   (--settle SECONDS, --keep)
""")

COMMANDS = {"start": cmd_start, "drill": cmd_drill, "list": cmd_list, "show": cmd_show, "grade": cmd_grade,
            "status": cmd_status, "timer": cmd_timer, "pause": cmd_pause, "resume": cmd_resume, "end": cmd_end, "weak": cmd_weak, "history": cmd_history,
            "reset": cmd_reset, "web": cmd_web, "abort": cmd_abort, "progress": cmd_progress, "solution": cmd_solution, "sim": cmd_sim, "study": cmd_study, "version": cmd_version, "help": cmd_help,
            "build": cmd_build, "hosts": cmd_hosts, "ssh": cmd_ssh, "down": cmd_down, "audit": cmd_audit, "coverage": cmd_coverage,
            "objectives": cmd_objectives, "curriculum": cmd_objectives, "notes": cmd_notes, "next": cmd_next, "focus": cmd_focus}

if __name__ == "__main__":
    cmd = ARGV[0] if ARGV else "help"
    COMMANDS.get(cmd, cmd_help)(ARGV[1:])