feat: web push notifications (VAPID)

- push_utils.py: subscription storage + send helper (auto-prunes 410 endpoints)
- routers/push.py: GET /api/push/vapid-key (public), POST/DELETE /api/push/subscribe
- sw.js: push event listener shows notification; notificationclick focuses/opens tab
- app.js: subscribe/unsubscribe flow + "Enable notifications" toggle in settings dropdown
- tools/notify.py: web_push orchestrator tool (user-level, no admin required)
- VAPID keys in .env; pywebpush added to requirements.txt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/push_utils.py

@@ -0,0 +1,115 @@
+"""
+Web Push (VAPID) helpers.
+
+Subscriptions are stored per-user at:
+  home/{user}/push_subscriptions.json  →  list of {endpoint, keys:{p256dh, auth}}
+
+send_push(username, title, body, url) iterates all stored subscriptions for that
+user and fires a push. Stale endpoints (410 Gone) are pruned automatically.
+"""
+import asyncio
+import base64
+import json
+import logging
+from pathlib import Path
+
+from config import settings
+
+logger = logging.getLogger(__name__)
+
+
+def _subs_path(username: str) -> Path:
+    return settings.home_root() / username / "push_subscriptions.json"
+
+
+def load_subscriptions(username: str) -> list[dict]:
+    path = _subs_path(username)
+    if not path.exists():
+        return []
+    try:
+        return json.loads(path.read_text())
+    except Exception:
+        return []
+
+
+def _save_subscriptions(username: str, subs: list[dict]) -> None:
+    path = _subs_path(username)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(subs, indent=2))
+
+
+def add_subscription(username: str, sub: dict) -> None:
+    """Upsert a subscription by endpoint URL."""
+    subs = load_subscriptions(username)
+    endpoint = sub.get("endpoint", "")
+    subs = [s for s in subs if s.get("endpoint") != endpoint]
+    subs.append(sub)
+    _save_subscriptions(username, subs)
+
+
+def remove_subscription(username: str, endpoint: str) -> bool:
+    subs = load_subscriptions(username)
+    new_subs = [s for s in subs if s.get("endpoint") != endpoint]
+    if len(new_subs) == len(subs):
+        return False
+    _save_subscriptions(username, new_subs)
+    return True
+
+
+def _get_private_key_pem() -> str:
+    """Decode the base64-encoded PEM private key from settings."""
+    raw = settings.vapid_private_key_b64.strip()
+    if not raw:
+        raise RuntimeError("VAPID_PRIVATE_KEY_B64 is not set in .env")
+    return base64.b64decode(raw).decode()
+
+
+def _send_one(sub: dict, payload: dict) -> bool:
+    """Send a push to a single subscription. Returns False if the endpoint is stale (410)."""
+    from pywebpush import webpush, WebPushException
+
+    try:
+        webpush(
+            subscription_info=sub,
+            data=json.dumps(payload),
+            vapid_private_key=_get_private_key_pem(),
+            vapid_claims={"sub": settings.vapid_contact},
+        )
+        return True
+    except WebPushException as e:
+        if e.response is not None and e.response.status_code == 410:
+            logger.info("push endpoint gone (410), pruning: %s", sub.get("endpoint", "")[:60])
+            return False
+        logger.warning("push failed: %s", e)
+        return True  # keep the sub; might be transient
+
+
+async def send_push(username: str, title: str, body: str, url: str = "") -> dict:
+    """
+    Send a push notification to all subscriptions for username.
+    Returns {"sent": n, "pruned": m}.
+    """
+    if not settings.vapid_public_key or not settings.vapid_private_key_b64:
+        return {"error": "VAPID keys not configured"}
+
+    subs = load_subscriptions(username)
+    if not subs:
+        return {"error": f"No push subscriptions for {username}"}
+
+    payload = {"title": title, "body": body, "url": url}
+    keep = []
+    sent = 0
+    pruned = 0
+
+    for sub in subs:
+        alive = await asyncio.to_thread(_send_one, sub, payload)
+        if alive:
+            keep.append(sub)
+            sent += 1
+        else:
+            pruned += 1
+
+    if pruned:
+        _save_subscriptions(username, keep)
+
+    return {"sent": sent, "pruned": pruned}