feat(backend): offline-capable signed licensing; fix expiry grace; state in data dir (KI-006)

- services/license.py: verifies the cloud's Ed25519-signed license token
  (public key built in) and decides purely: valid → licensed until expiry,
  then a 5-day grace, then blocked - never mid-service (deferred while a
  workday is open, applied at close). Works offline for as long as the
  license lasts: the "unlicensed after 72h without heartbeat" rule is gone.
- Tamper resistance: an edited token fails the signature ("unverified");
  a clock earlier than the latest provable time (token issued_at, newest
  order in the DB, stored high-water mark; 1 day tolerance) → "clock".
- apply_license() re-evaluates from the stored token at startup, after
  every heartbeat attempt and when a workday closes. Cloud lock/unlock from
  the token keeps the workday-deferred behaviour. Transition: a cloud
  without tokens is trusted 72h per successful heartbeat.
- FIX: the promised 5-day grace after expiry never happened - the cloud's
  licensed=false was applied immediately (402 on everything).
- FIX: license_state.json lived inside the container and was lost on every
  re-creation; it now lives in the data volume (old path read once).
- /api/system/status: offline_days, license_verified, license_problem,
  grace_over; lock_reason "clock"/"unverified"; grace days from the license
  module (rounded up).

Tests: 18 unit checks (signature, tamper, other site/key, 364 days
offline, grace ±workday, inactive, clock rollback, transition) + 17 E2E
checks with a real cloud + site process (400 days offline, tampered file →
402, clock behind newest order, expiry deferred until workday close,
renewal, remote lock/unlock).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

local_backend/routers/business_day.py

@@ -168,8 +168,10 @@ def close_business_day(
     if license_state.get("lock_pending"):
         license_state["lock_pending"] = False
         license_state["locked"] = True
-        from services.cloud_sync import _persist_state
-        _persist_state()
+    # Re-evaluate the license now that no workday is open (an expiry whose grace
+    # ended mid-service takes effect here) — also persists the state
+    from services.cloud_sync import apply_license
+    apply_license()
 
     return day
 

local_backend/routers/system.py

@@ -60,9 +60,23 @@ def identity(db: Session = Depends(get_db)):
     }
 
 
+def _lock_reason() -> str | None:
+    """Why the site is (or will be) blocked, for the manager's banner:
+    "admin" (locked/lock pending) · "clock" (system clock set back) ·
+    "unverified" (no genuine license yet) · "expired" (expiry grace over /
+    site deactivated) · None."""
+    if license_state.get("locked") or license_state.get("lock_pending"):
+        return "admin"
+    problem = license_state.get("license_problem")
+    if problem in ("clock", "unverified"):
+        return problem
+    if problem in ("expired", "inactive") or not license_state.get("licensed", True):
+        return "expired"
+    return None
+
+
 @router.get("/status")
 def system_status(db: Session = Depends(get_db), user: User = Depends(get_current_user)):
-    from datetime import datetime, timezone
     printers = db.query(Printer).filter(Printer.is_active == True).all()
     printer_statuses = []
     for p in printers:
@@ -78,26 +92,10 @@ def system_status(db: Session = Depends(get_db), user: User = Depends(get_curren
     days_until_expiry = license_state.get("days_until_expiry")
     grace_expires_at = license_state.get("grace_expires_at")
 
-    # Determine lock_reason for the frontend banner logic
-    # "admin"   — locked by sysadmin (immediately or deferred)
-    # "expired" — license grace period over, site is blocked
-    # None      — all good
-    lock_reason = None
-    if locked or lock_pending:
-        lock_reason = "admin"
-    elif not licensed:
-        lock_reason = "expired"
+    lock_reason = _lock_reason()
 
-    # Grace days remaining (only meaningful while in expiry grace period)
-    grace_days_remaining = None
-    if grace_expires_at:
-        try:
-            grace_dt = datetime.fromisoformat(grace_expires_at)
-            if grace_dt.tzinfo is None:
-                grace_dt = grace_dt.replace(tzinfo=timezone.utc)
-            grace_days_remaining = max(0, (grace_dt - datetime.now(timezone.utc)).days)
-        except ValueError:
-            pass
+    # Computed by services/license.py (only set during the expiry grace period)
+    grace_days_remaining = license_state.get("grace_days_remaining")
 
     return {
         "uptime_seconds": int(time.time() - _start_time),
@@ -113,6 +111,12 @@ def system_status(db: Session = Depends(get_db), user: User = Depends(get_curren
         "grace_days_remaining": grace_days_remaining,
         "sync_failed": license_state.get("sync_failed", False),
         "last_sync": license_state.get("last_sync"),
+        # Offline licensing (KI-006): days without cloud contact; the signed license
+        # keeps the site running until expiry regardless
+        "offline_days": license_state.get("offline_days"),
+        "license_verified": license_state.get("license_verified", False),
+        "license_problem": license_state.get("license_problem"),
+        "grace_over": license_state.get("grace_over", False),
         "waiter_domain": license_state.get("waiter_domain"),
         "site_id": settings.SITE_ID or None,
         "lan_ip": lan.get("effective"),
@@ -155,11 +159,7 @@ async def sync_license_now(user: User = Depends(require_manager)):
         "licensed": license_state.get("licensed", True),
         "locked": license_state.get("locked", False),
         "lock_pending": license_state.get("lock_pending", False),
-        "lock_reason": (
-            "admin" if (license_state.get("locked") or license_state.get("lock_pending"))
-            else "expired" if not license_state.get("licensed", True)
-            else None
-        ),
+        "lock_reason": _lock_reason(),
         "expires_at": license_state.get("expires_at"),
         "days_until_expiry": license_state.get("days_until_expiry"),
         "sync_failed": license_state.get("sync_failed", False),

local_backend/services/cloud_sync.py

@@ -1,28 +1,28 @@
 """
 Periodic cloud check-in. Runs every 5 minutes as an asyncio background task.
-Grace period: 72 hours (3 days) before marking unlicensed on connectivity failure.
 
-Lock behaviour:
-  - cloud sets locked=true  → set lock_pending=true in state
-  - lock_pending is enforced at workday-close time (see business_day router)
-  - while a workday is open, the site keeps running; lock applies once it closes
+Licensing (KI-006, see services/license.py): the cloud is needed to RENEW a
+license, not to RUN one. Each heartbeat returns a signed license token; the
+site stores it and enforces it offline — until expiry (+5 days grace), however
+long it has no internet. apply_license() re-evaluates the stored token without
+network: at startup, after every heartbeat attempt and when a workday closes.
 
-License expiry behaviour:
-  - 5 days before expiry   → warning only (days_until_expiry in state)
-  - on expiry              → 5-day grace period begins (grace_expires_at in state)
-  - after grace + no open workday → licensed=False enforced by business_day router
+Lock behaviour (unchanged):
+  - cloud sets locked=true  → lock_pending while a workday is open, locked once it closes
+  - expiry past grace / site deactivated → likewise never mid-service
 """
 import asyncio
 import json
 import logging
 import os
-from datetime import datetime, timedelta, timezone
+from datetime import datetime, timezone
 from pathlib import Path
 
 import httpx
 
 from config import settings
 from middleware.license_check import license_state
+from services.license import evaluate, parse_dt, verify_token
 
 ORDER_POLL_INTERVAL = settings.CONNECT_SYNC_INTERVAL_SECONDS
 
@@ -30,20 +30,30 @@ logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger(__name__)
 
 SYNC_INTERVAL_SECONDS = 5 * 60          # 5 minutes
-GRACE_HOURS = 72                         # 3 days offline grace
-EXPIRY_GRACE_DAYS = 5                    # days after expiry before blocking
-EXPIRY_WARNING_DAYS = 5                  # days before expiry to show warning
-STATE_FILE = Path(__file__).parent.parent / "license_state.json"
+
+
+def _data_dir() -> Path:
+    """Directory of the SQLite database — the persistent data volume in Docker."""
+    from services.tls_identity import tls_dir
+    return tls_dir().parent
+
+
+# In the data volume: it must survive container re-creation (image updates,
+# compose changes), or an offline site would lose its license. Earlier versions
+# kept it inside the container at local_backend/license_state.json.
+STATE_FILE = _data_dir() / "license_state.json"
+LEGACY_STATE_FILE = Path(__file__).parent.parent / "license_state.json"
 
 
 def _load_persisted_state():
-    if STATE_FILE.exists():
-        try:
-            data = json.loads(STATE_FILE.read_text())
-            license_state.update(data)
-            logger.info("Loaded persisted license state: %s", data)
-        except Exception as e:
-            logger.warning("Could not load license state file: %s", e)
+    for path in (STATE_FILE, LEGACY_STATE_FILE):
+        if path.exists():
+            try:
+                license_state.update(json.loads(path.read_text()))
+                logger.info("Loaded persisted license state from %s", path)
+                return
+            except Exception as e:
+                logger.warning("Could not load license state file %s: %s", path, e)
 
 
 def _persist_state():
@@ -53,29 +63,54 @@ def _persist_state():
         logger.warning("Could not persist license state: %s", e)
 
 
-def _compute_expiry_fields(expires_at_str: str | None) -> dict:
-    """Return days_until_expiry and grace_expires_at derived from expires_at."""
-    if not expires_at_str:
-        return {"days_until_expiry": None, "grace_expires_at": None}
+def _latest_activity(db) -> datetime | None:
+    """Newest order timestamp in the database — the clock can't be set before it."""
+    from sqlalchemy import func
+    from models.order import Order, OrderItem
+    stamps = [db.query(func.max(Order.opened_at)).scalar(), db.query(func.max(OrderItem.added_at)).scalar()]
+    stamps = [parse_dt(x) for x in stamps if x]
+    return max(stamps, default=None)
 
+
+def apply_license(now: datetime | None = None) -> None:
+    """Re-evaluate the license from the stored signed token (no network)."""
+    if not settings.SITE_ID:
+        return  # dev / unregistered install: licensing off, as before
+    from database import SessionLocal
+    from models.business_day import BusinessDay
+
+    now = now or datetime.now(timezone.utc)
+    payload = verify_token(license_state.get("license_token"), settings.SITE_ID)
+    db = SessionLocal()
     try:
-        expires_at = datetime.fromisoformat(expires_at_str)
-        if expires_at.tzinfo is None:
-            expires_at = expires_at.replace(tzinfo=timezone.utc)
-    except ValueError:
-        return {"days_until_expiry": None, "grace_expires_at": None}
+        workday_open = db.query(BusinessDay).filter(BusinessDay.status == "open").first() is not None
+        latest_activity = _latest_activity(db)
+    finally:
+        db.close()
 
-    now = datetime.now(timezone.utc)
-    days_until = (expires_at - now).days  # negative once expired
+    floors = [parse_dt(license_state.get("time_high_water")), latest_activity,
+              parse_dt(payload["issued_at"]) if payload else None]
+    floor = max((f for f in floors if f), default=None)
+    result = evaluate(payload, now, floor, workday_open, parse_dt(license_state.get("legacy_ok_at")))
+    if result["license_problem"] != "clock":
+        license_state["time_high_water"] = max(floor or now, now).isoformat()
 
-    grace_expires_at = None
-    if days_until < 0:
-        grace_expires_at = (expires_at + timedelta(days=EXPIRY_GRACE_DAYS)).isoformat()
+    if payload:  # lock requested by the cloud — deferred while a workday is open
+        if payload.get("locked"):
+            if workday_open and not license_state.get("locked"):
+                license_state["lock_pending"] = True
+            else:
+                license_state["lock_pending"] = False
+                license_state["locked"] = True
+        else:
+            license_state["lock_pending"] = False
+            license_state["locked"] = False
 
-    return {
-        "days_until_expiry": days_until,
-        "grace_expires_at": grace_expires_at,
-    }
+    last_sync = parse_dt(license_state.get("last_sync"))
+    license_state.update({**result, "offline_days": (now - last_sync).days if last_sync else None})
+    _persist_state()
+    if result["license_problem"]:
+        logger.warning("License problem: %s (licensed=%s)", result["license_problem"], result["licensed"])
 
 
 def _get_local_ip() -> str | None:
@@ -112,69 +147,39 @@ async def _sync_once():
             resp.raise_for_status()
             data = resp.json()
 
-        licensed = data.get("licensed", True)
-        cloud_locked = data.get("locked", False)
-        expires_at = data.get("expires_at")
-        expiry_fields = _compute_expiry_fields(expires_at)
-
-        # If cloud says locked, check whether a workday is currently open.
-        # No open workday → lock immediately.
-        # Open workday → defer to workday close (business_day router enforces it).
-        if cloud_locked:
-            from database import SessionLocal
-            from models.business_day import BusinessDay
-            db = SessionLocal()
-            try:
-                open_day = db.query(BusinessDay).filter(BusinessDay.status == "open").first()
-            finally:
-                db.close()
-
-            if open_day:
-                if not license_state.get("lock_pending"):
-                    license_state["lock_pending"] = True
-                    logger.info("Cloud requested lock — workday open, deferring to workday close")
+        token = data.get("license_token")
+        if token:
+            if verify_token(token, settings.SITE_ID):
+                license_state["license_token"] = token
+            else:
+                logger.error("Cloud sent a license token that does not verify - keeping the previous one")
+        else:
+            # Cloud without license signing (transition): trust this answer for 72h,
+            # keep the old immediate lock handling
+            if data.get("licensed", True):
+                license_state["legacy_ok_at"] = datetime.now(timezone.utc).isoformat()
+            license_state["expires_at"] = data.get("expires_at")
+            if data.get("locked"):
+                license_state["lock_pending"] = True
             else:
                 license_state["lock_pending"] = False
-                license_state["locked"] = True
-                logger.info("Cloud requested lock — no open workday, locking immediately")
-
-        # If cloud lifts the lock, clear pending too
-        if not cloud_locked:
-            license_state["lock_pending"] = False
-            license_state["locked"] = False
+                license_state["locked"] = False
 
         license_state.update({
-            "licensed": licensed,
-            "expires_at": expires_at,
             "latest_version": data.get("latest_version"),
             "waiter_domain": data.get("waiter_domain"),
             "site_numeric_id": data.get("site_numeric_id"),
             "last_sync": datetime.now(timezone.utc).isoformat(),
             "sync_failed": False,
-            **expiry_fields,
         })
-        _persist_state()
-        logger.info("Cloud sync OK: licensed=%s locked=%s expires_at=%s", licensed, cloud_locked, expires_at)
+        logger.info("Cloud sync OK (signed license: %s)", bool(token))
 
     except Exception as e:
         logger.warning("Cloud sync failed: %s", e)
         license_state["sync_failed"] = True
 
-        last_sync_str = license_state.get("last_sync")
-        if last_sync_str:
-            try:
-                last_sync = datetime.fromisoformat(last_sync_str)
-                grace_expires = last_sync + timedelta(hours=GRACE_HOURS)
-                if datetime.now(timezone.utc) > grace_expires:
-                    logger.error("72-hour offline grace period expired — marking unlicensed")
-                    license_state["licensed"] = False
-            except ValueError:
-                pass
-
-        # Recompute expiry fields from cached expires_at even when offline
-        expiry_fields = _compute_expiry_fields(license_state.get("expires_at"))
-        license_state.update(expiry_fields)
-
+    # Online or not: the stored signed license decides (no more 72h offline rule)
+    apply_license()
 
 IMAGE_DIR = Path("/app/data/product_images")
 
@@ -397,6 +402,7 @@ async def _pull_pending_orders():
 
 async def _sync_loop():
     _load_persisted_state()
+    apply_license()  # decide from the stored license before the first network attempt
     while True:
         await _sync_once()
         await asyncio.sleep(SYNC_INTERVAL_SECONDS)

local_backend/services/license.py

@@ -0,0 +1,106 @@
+"""
+Offline-capable licensing (KI-006).
+
+The cloud is needed to RENEW a license, not to RUN one. Every heartbeat
+brings a license token signed by the cloud (Ed25519). The site stores it and
+enforces it by itself, so a venue that paid for a year keeps working for that
+year even if it never goes online again. The old rule ("unlicensed after 72h
+without a heartbeat") is gone.
+
+Tamper resistance:
+  - Editing the stored token breaks the signature → treated as no license.
+  - Turning the clock back: "now" may not be earlier than the latest time this
+    system has provably seen — the token's signed cloud time, the newest order
+    in the database, and a stored high-water mark (1 day tolerance).
+  Limits (documented): someone with root on the server could still patch the
+  code itself, and a remote lock only reaches a site when it next goes online.
+
+Rules (evaluate()):
+  valid token, clock OK:
+    active and not expired                    → licensed
+    expired: 5-day grace                      → licensed, warnings in the manager
+    grace over / site deactivated             → unlicensed, but never mid-service:
+                                                deferred while a workday is open
+  no valid token:
+    old cloud without tokens, heartbeat said licensed < 72h ago → licensed (transition)
+    otherwise                                 → unlicensed ("unverified")
+  Locks from the cloud (token.locked) keep the existing workday-deferred behaviour.
+"""
+import base64
+import json
+import math
+from datetime import datetime, timedelta, timezone
+
+from cryptography.exceptions import InvalidSignature
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
+
+# Matches LICENSE_SIGNING_KEY in the cloud's .env (generated 2026-09-28).
+# Built into the code on purpose: a key taken from configuration could simply
+# be replaced together with a self-made token.
+LICENSE_PUBLIC_KEY = "2oeFHV6hgAlJsx/ZBvG6fqmWYn5tjSW5hURrrPhLoOw="
+
+EXPIRY_GRACE = timedelta(days=5)
+CLOCK_TOLERANCE = timedelta(days=1)
+LEGACY_UNSIGNED_OK = timedelta(hours=72)   # only while the cloud sends no tokens
+
+
+def _b64url_decode(s: str) -> bytes:
+    return base64.urlsafe_b64decode(s + "=" * (-len(s) % 4))
+
+
+def parse_dt(value) -> datetime | None:
+    if not value:
+        return None
+    try:
+        dt = datetime.fromisoformat(value) if isinstance(value, str) else value
+    except ValueError:
+        return None
+    return dt if dt.tzinfo else dt.replace(tzinfo=timezone.utc)
+
+
+def verify_token(token: str | None, site_id: str, public_key_b64: str = LICENSE_PUBLIC_KEY) -> dict | None:
+    """Payload of a genuine token for this site, else None."""
+    if not token or "." not in token:
+        return None
+    body, _, sig = token.partition(".")
+    try:
+        Ed25519PublicKey.from_public_bytes(base64.b64decode(public_key_b64)).verify(_b64url_decode(sig), body.encode())
+        payload = json.loads(_b64url_decode(body))
+    except (InvalidSignature, ValueError, TypeError):
+        return None
+    if payload.get("v") != 1 or payload.get("site_id") != site_id:
+        return None
+    if not parse_dt(payload.get("expires_at")) or not parse_dt(payload.get("issued_at")):
+        return None
+    return payload
+
+
+def evaluate(payload: dict | None, now: datetime, floor: datetime | None, workday_open: bool,
+             legacy_ok_at: datetime | None = None) -> dict:
+    """Pure license decision. `floor` = latest time this system has provably seen."""
+    base = {"license_verified": payload is not None, "license_problem": None, "grace_over": False,
+            "days_until_expiry": None, "grace_expires_at": None, "grace_days_remaining": None}
+
+    if payload is None:
+        legacy = legacy_ok_at is not None and now - legacy_ok_at <= LEGACY_UNSIGNED_OK
+        return {**base, "licensed": legacy, "license_problem": None if legacy else "unverified"}
+
+    if floor is not None and now < floor - CLOCK_TOLERANCE:
+        return {**base, "licensed": False, "license_problem": "clock"}
+
+    expires = parse_dt(payload["expires_at"])
+    grace_end = expires + EXPIRY_GRACE
+    days_until = (expires - now).days                       # negative once expired
+    grace_over = now > grace_end
+    fields = {
+        **base,
+        "expires_at": expires.isoformat(),
+        "days_until_expiry": days_until,
+        "grace_expires_at": grace_end.isoformat() if days_until < 0 else None,
+        # Rounded up: 2 days 23 hours left reads as "3 days", as people count it
+        "grace_days_remaining": math.ceil((grace_end - now) / timedelta(days=1)) if days_until < 0 and not grace_over else None,
+        "grace_over": grace_over,
+    }
+    problem = "inactive" if not payload.get("active", True) else "expired" if grace_over else None
+    # Never cut a restaurant off mid-service: an open workday finishes first
+    return {**fields, "licensed": problem is None or workday_open, "license_problem": problem}