Merge pull request 'Security: request-size caps, concurrency limits, model-pull allowlist' (#3) from Athena/NexusOS:harden/3-resource-limits into main

interface/web/src/Chatbot.jsx

@@ -18,6 +18,7 @@ export function Chatbot({ conversationId, setConversationId, onConversationChang
   const [images, setImages] = useState([]); // {name, b64} for vision models
   const [activeTool, setActiveTool] = useState(null); // playbook tool currently running
   const [pendingApproval, setPendingApproval] = useState(null); // [{name, arguments}] awaiting yes/no
+  const [approvalToken, setApprovalToken] = useState(null); // single-use token authorizing /chat/approve
   const [editingIdx, setEditingIdx] = useState(null); // user message being edited
   const [editText, setEditText] = useState("");
   const [listening, setListening] = useState(false); // mic dictation active
@@ -286,7 +287,11 @@ export function Chatbot({ conversationId, setConversationId, onConversationChang
               continue;
             }
             if (pendingEventType === "tool_request") {
-              try { setPendingApproval(JSON.parse(payload)); } catch { /* ignore */ }
+              try {
+                const parsed = JSON.parse(payload);
+                setPendingApproval(parsed.actions || []);
+                setApprovalToken(parsed.token || null);
+              } catch { /* ignore */ }
               pendingEventType = null;
               continue;
             }
@@ -401,13 +406,15 @@ export function Chatbot({ conversationId, setConversationId, onConversationChang
   // Approve or deny the pending action tool(s); the open chat stream resumes.
   const resolveApproval = async (approve) => {
     const req = pendingApproval || [];
+    const token = approvalToken;
     setPendingApproval(null);
+    setApprovalToken(null);
     const decisions = {};
     req.forEach(a => { decisions[a.name] = approve; });
     try {
       await fetch(`${API_BASE}/chat/approve`, {
         method: "POST", headers: { "Content-Type": "application/json" },
-        body: JSON.stringify({ conversation_id: conversationId, decisions }),
+        body: JSON.stringify({ conversation_id: conversationId, token, decisions }),
       });
     } catch { /* ignore */ }
   };

management/ncp.py

@@ -112,6 +112,12 @@ class Service:
         return self._argv() if callable(self._argv) else self._argv
 
 
+# Bind loopback by default: the backend/memory REST APIs are unauthenticated, so
+# binding 0.0.0.0 handed the full admin+data plane to any host on the LAN. Set
+# NEXUS_BIND_HOST=0.0.0.0 to opt into LAN exposure once real auth is in place.
+BIND_HOST = os.environ.get("NEXUS_BIND_HOST", "127.0.0.1")
+
+
 def _uvicorn(app: str, port: int):
     # No --reload. It is a dev-loop flag: uvicorn's reloader runs a supervisor
     # that spawns the real server as a CHILD, so every service became two
@@ -120,7 +126,7 @@ def _uvicorn(app: str, port: int):
     # terminals for what should have been a silent start. launch_nexus.sh still
     # passes --reload for the Linux dev loop, where a visible console is the
     # point; this launcher is the one users run.
-    return [str(PYTHON), "-m", "uvicorn", app, "--host", "0.0.0.0",
+    return [str(PYTHON), "-m", "uvicorn", app, "--host", BIND_HOST,
             "--port", str(port)]
 
 

synapse/chat.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import asyncio
 import json as _json
 import logging
+import secrets
 import threading
 from typing import AsyncGenerator, Dict, List, Optional, Any
 
@@ -171,12 +172,20 @@ async def _run_tool_loop(manager, messages, model, tool_schemas, temperature, nu
         action_calls = [c for c in calls if _tools.is_action(c.get("function", {}).get("name", ""))]
         if policy == "ask" and action_calls:
             event = asyncio.Event()
-            pending_approvals[conversation_id] = {"event": event, "decisions": {}}
-            yield "__approve__" + _json.dumps([
-                {"name": c.get("function", {}).get("name", ""),
-                 "arguments": c.get("function", {}).get("arguments")}
-                for c in action_calls
-            ])
+            # Single-use capability token, delivered only to the client that owns
+            # this stream. /chat/approve requires it, so knowing the (guessable,
+            # enumerable) conversation_id is no longer enough to approve someone
+            # else's pending action.
+            token = secrets.token_urlsafe(32)
+            pending_approvals[conversation_id] = {"event": event, "decisions": {}, "token": token}
+            yield "__approve__" + _json.dumps({
+                "token": token,
+                "actions": [
+                    {"name": c.get("function", {}).get("name", ""),
+                     "arguments": c.get("function", {}).get("arguments")}
+                    for c in action_calls
+                ],
+            })
             try:
                 await asyncio.wait_for(event.wait(), timeout=_APPROVAL_TIMEOUT)
                 decisions = pending_approvals[conversation_id]["decisions"]

synapse/main.py

@@ -2,7 +2,9 @@
 from __future__ import annotations
 
 import asyncio as _asyncio
+import contextlib as _contextlib
 import json as _json
+import secrets as _secrets
 import uuid as _uuid
 from collections import Counter as _Counter
 from typing import Any, AsyncGenerator, Dict, List, Optional, Tuple
@@ -12,11 +14,16 @@ import httpx
 import os as _os
 import platform as _platform
 from pathlib import Path
-from fastapi import FastAPI, HTTPException, Body
+from fastapi import FastAPI, HTTPException, Body, Request
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import StreamingResponse, FileResponse
+from starlette.middleware.trustedhost import TrustedHostMiddleware
+from fastapi.responses import StreamingResponse, FileResponse, JSONResponse
 
-from .nexus_config import settings, VERSION, DEFAULT_CHAT_MODEL
+from .nexus_config import (
+    settings, VERSION, DEFAULT_CHAT_MODEL, ALLOWED_HOSTS, ALLOWED_ORIGINS,
+    MAX_REQUEST_BYTES, MAX_UPLOAD_BYTES, MAX_PDF_PAGES,
+    MAX_CONCURRENT_CHATS, MAX_CONCURRENT_UPLOADS, model_pull_allowed,
+)
 from .chat import generate_chat_response, stream_chat_response, _synapse_trace
 from . import chat as _chat
 from .ollama_manager import initialize_ollama, initialize_ollama_async, get_ollama_manager
@@ -179,18 +186,82 @@ app = FastAPI(title="Synapse Backend", version=VERSION)
 # Alias for startup scripts
 sio_app = app
 
-# --- CORS ---
-# allow_credentials=True is incompatible with allow_origins=["*"] — browsers
-# reject such responses. Since this is a local-only service with no cookies/auth,
-# wildcard origins without credentials is correct.
+# --- Local-access guard ---
+# These APIs are unauthenticated and meant for this machine only. Two layers:
+#   1. TrustedHostMiddleware rejects a foreign Host header, which is what defeats
+#      DNS-rebinding — the browser treats a rebound attacker domain as
+#      same-origin, so CORS alone can't stop it.
+#   2. CORS is scoped to known local origins (not "*"), so a malicious page can't
+#      read responses cross-origin from the victim's browser.
+# NEXUS_ALLOWED_HOSTS=* / a custom NEXUS_ALLOWED_ORIGINS opts into LAN exposure,
+# and should only be used once real authentication is in front of these apps.
+if "*" not in ALLOWED_HOSTS:
+    app.add_middleware(TrustedHostMiddleware, allowed_hosts=ALLOWED_HOSTS)
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["*"],
+    allow_origins=ALLOWED_ORIGINS,
     allow_credentials=False,
     allow_methods=["*"],
     allow_headers=["*"],
 )
 
+
+# --- Request-size cap ---
+# Reject oversized bodies before they are buffered/decoded (a base64 upload or a
+# giant chat payload could otherwise exhaust memory). Header-based: covers the
+# realistic clients (browsers/httpx always send Content-Length for JSON). A
+# chunked request with no length still reaches the handler, where the upload path
+# enforces its own decoded-byte cap as a backstop.
+@app.middleware("http")
+async def _limit_request_body(request: Request, call_next):
+    cl = request.headers.get("content-length")
+    if cl:
+        try:
+            if int(cl) > MAX_REQUEST_BYTES:
+                return JSONResponse(
+                    status_code=413,
+                    content={"detail": f"request body too large (max {MAX_REQUEST_BYTES} bytes)"},
+                )
+        except ValueError:
+            pass
+    return await call_next(request)
+
+
+class _InFlightLimiter:
+    """Bounds concurrent in-flight ops for one expensive entry point so a single
+    caller can't fan out unlimited inference/embedding work. The server runs on
+    one asyncio loop, so a plain counter is safe — there's no await between the
+    check and the increment. Over the limit -> HTTP 429."""
+
+    def __init__(self, limit: int, label: str):
+        self._limit = max(1, int(limit))
+        self._label = label
+        self._n = 0
+
+    def acquire(self) -> None:
+        if self._n >= self._limit:
+            raise HTTPException(
+                status_code=429,
+                detail=f"{self._label} is busy ({self._limit} concurrent max) — retry shortly",
+            )
+        self._n += 1
+
+    def release(self) -> None:
+        if self._n > 0:
+            self._n -= 1
+
+    @_contextlib.contextmanager
+    def slot(self):
+        self.acquire()
+        try:
+            yield
+        finally:
+            self.release()
+
+
+_CHAT_INFLIGHT = _InFlightLimiter(MAX_CONCURRENT_CHATS, "chat")
+_UPLOAD_INFLIGHT = _InFlightLimiter(MAX_CONCURRENT_UPLOADS, "document ingest")
+
 # --- GLOBALS ---
 playbooks = PlaybookManager()
 ollama = None
@@ -236,6 +307,11 @@ async def root():
 # -------------------------
 @app.post("/chat/stream")
 async def chat_stream_endpoint(payload: Dict[str, Any]):
+    # Bound concurrent chats so a flood can't fan out unlimited model inference.
+    # Acquired here (covers the pre-stream RAG/embedding work too) and released
+    # when the SSE stream finishes — see the guarded wrapper below.
+    _CHAT_INFLIGHT.acquire()
+    _chat_slot_held = True
     try:
         message = payload.get("message", "")
         app_settings = store.get_settings()
@@ -489,23 +565,48 @@ async def chat_stream_endpoint(payload: Dict[str, Any]):
                 except Exception as e:
                     _synapse_trace(f"\n⚠ memory extraction call failed: {e}\n")
 
-        return StreamingResponse(event_stream(), media_type="text/event-stream")
+        # Hold the concurrency slot for the stream's lifetime, then release it
+        # exactly once when the generator is exhausted or closed (client
+        # disconnect). Ownership passes to the wrapper, so the endpoint's own
+        # finally must not also release.
+        _inner = event_stream()
+
+        async def _guarded_stream() -> AsyncGenerator[str, None]:
+            try:
+                async for _chunk in _inner:
+                    yield _chunk
+            finally:
+                _CHAT_INFLIGHT.release()
+
+        _chat_slot_held = False
+        return StreamingResponse(_guarded_stream(), media_type="text/event-stream")
 
     except HTTPException:
         raise
     except Exception as e:
         raise HTTPException(status_code=500, detail=str(e))
+    finally:
+        if _chat_slot_held:
+            _CHAT_INFLIGHT.release()
 
 
 @app.post("/chat/approve")
 async def chat_approve(payload: Dict[str, Any] = Body(...)):
     """Resolve a pending per-call tool approval. `decisions` maps tool name ->
-    bool; the awaiting chat stream resumes and runs the approved actions."""
+    bool; the awaiting chat stream resumes and runs the approved actions.
+
+    The `token` (issued in the stream's tool_request event) is required: without
+    it, anyone who can guess/enumerate a conversation_id could approve another
+    client's pending action. Compared in constant time."""
     conversation_id = payload.get("conversation_id") or ""
+    token = payload.get("token") or ""
     decisions = payload.get("decisions") or {}
     waiter = _chat.pending_approvals.get(conversation_id)
     if not waiter:
         raise HTTPException(status_code=404, detail="no pending approval for this conversation")
+    expected = waiter.get("token") or ""
+    if not token or not _secrets.compare_digest(str(token), str(expected)):
+        raise HTTPException(status_code=403, detail="invalid or missing approval token")
     waiter["decisions"] = {k: bool(v) for k, v in decisions.items()}
     waiter["event"].set()
     return {"status": "resumed"}
@@ -667,6 +768,11 @@ async def pull_model(payload: Dict[str, Any] = Body(...)):
     name = payload.get("name", "").strip()
     if not name:
         raise HTTPException(status_code=400, detail="Missing model name")
+    if not model_pull_allowed(name):
+        raise HTTPException(
+            status_code=403,
+            detail=f"model '{name}' is not in NEXUS_MODEL_ALLOWLIST",
+        )
 
     async def _stream():
         try:
@@ -1103,7 +1209,13 @@ def _extract_text(filename: str, data: bytes) -> str:
     if name.endswith(".pdf"):
         from pypdf import PdfReader
         reader = PdfReader(io.BytesIO(data))
-        return "\n\n".join((page.extract_text() or "") for page in reader.pages)
+        pages = reader.pages
+        if len(pages) > MAX_PDF_PAGES:
+            raise HTTPException(
+                status_code=413,
+                detail=f"PDF has {len(pages)} pages (max {MAX_PDF_PAGES})",
+            )
+        return "\n\n".join((page.extract_text() or "") for page in pages)
     if name.endswith(".docx"):
         import docx
         doc = docx.Document(io.BytesIO(data))
@@ -1125,14 +1237,26 @@ async def upload_document(payload: Dict[str, Any] = Body(...)):
         raw = base64.b64decode(b64)
     except Exception:
         raise HTTPException(status_code=400, detail="data must be base64")
-    try:
-        text = _extract_text(filename, raw).strip()
-    except Exception as e:
-        raise HTTPException(status_code=400, detail=f"could not read {filename}: {e}")
-    if not text:
-        raise HTTPException(status_code=400, detail="no extractable text in file")
-    title = _os.path.splitext(_os.path.basename(filename))[0] or filename
-    return await store.add_document(title, text, get_ollama_manager().embed, _active_project())
+    # Decoded-byte backstop: the body-size middleware caps the encoded payload,
+    # but base64 inflates ~33% and a chunked request has no Content-Length, so
+    # enforce the real decoded ceiling here too.
+    if len(raw) > MAX_UPLOAD_BYTES:
+        raise HTTPException(
+            status_code=413,
+            detail=f"file too large: {len(raw)} bytes (max {MAX_UPLOAD_BYTES})",
+        )
+    # Bound concurrent ingests: extract + chunk + embed is CPU/model-heavy.
+    with _UPLOAD_INFLIGHT.slot():
+        try:
+            text = _extract_text(filename, raw).strip()
+        except HTTPException:
+            raise
+        except Exception as e:
+            raise HTTPException(status_code=400, detail=f"could not read {filename}: {e}")
+        if not text:
+            raise HTTPException(status_code=400, detail="no extractable text in file")
+        title = _os.path.splitext(_os.path.basename(filename))[0] or filename
+        return await store.add_document(title, text, get_ollama_manager().embed, _active_project())
 
 
 @app.get("/documents/{doc_id}")

synapse/memory/service.py

@@ -19,17 +19,24 @@ from typing import Any, Dict, List, Optional
 
 from fastapi import FastAPI, HTTPException, Body
 from fastapi.middleware.cors import CORSMiddleware
+from starlette.middleware.trustedhost import TrustedHostMiddleware
 from pydantic import BaseModel
 
 from .store import store, MemoryItem
 from .extractor import extract_memory
 from ..ollama_manager import get_ollama_manager
+from ..nexus_config import ALLOWED_HOSTS, ALLOWED_ORIGINS
 
 app = FastAPI(title="Nexus Memory Service", version="1.0")
 
+# Same unauthenticated-local-only posture as the main backend: reject foreign
+# Host headers (anti DNS-rebind) and scope CORS to known local origins rather
+# than "*". See nexus_config.ALLOWED_HOSTS / ALLOWED_ORIGINS for env overrides.
+if "*" not in ALLOWED_HOSTS:
+    app.add_middleware(TrustedHostMiddleware, allowed_hosts=ALLOWED_HOSTS)
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["*"],
+    allow_origins=ALLOWED_ORIGINS,
     allow_credentials=False,
     allow_methods=["*"],
     allow_headers=["*"],

synapse/nexus_config.py

@@ -143,6 +143,65 @@ class Settings:
             "ollama_timeout": self.ollama_timeout,
         }
 
+# --- local-access allowlists (shared by the backend + memory FastAPI apps) ---
+# The REST APIs are unauthenticated, so they are meant to be reached only from
+# this machine. Two independent browser-side defenses depend on these lists:
+#   * ALLOWED_ORIGINS drives CORS — blocks a malicious page from *reading*
+#     responses cross-origin (was previously "*", which let any site read them).
+#   * ALLOWED_HOSTS drives TrustedHostMiddleware — rejects a foreign Host header,
+#     which is what stops DNS-rebinding (same-origin from the browser's view, so
+#     CORS can't help there).
+# Both accept a comma-separated env override for the intentional-LAN case, to be
+# paired with real auth. NEXUS_ALLOWED_HOSTS=* disables the Host check.
+def _csv_env(name: str, default: list) -> list:
+    raw = os.getenv(name, "").strip()
+    return [p.strip() for p in raw.split(",") if p.strip()] if raw else list(default)
+
+_LOCAL_HOSTS = ["localhost", "127.0.0.1", "[::1]", "::1", "testserver"]
+_LOCAL_ORIGINS = [
+    f"http://{h}:{p}"
+    for h in ("localhost", "127.0.0.1")
+    for p in (8000, 8001, 5173)
+]
+ALLOWED_HOSTS = _csv_env("NEXUS_ALLOWED_HOSTS", _LOCAL_HOSTS)
+ALLOWED_ORIGINS = _csv_env("NEXUS_ALLOWED_ORIGINS", _LOCAL_ORIGINS)
+
+
+# --- resource limits (DoS guardrails for the unauthenticated local APIs) ---
+# Even local-only, an unbounded base64 upload or a flood of concurrent inference
+# requests can exhaust RAM/CPU. These are generous defaults for single-user use,
+# all env-overridable.
+def _int_env(name: str, default: int) -> int:
+    try:
+        return int((os.getenv(name) or "").strip() or default)
+    except ValueError:
+        return default
+
+MAX_REQUEST_BYTES = _int_env("NEXUS_MAX_REQUEST_MB", 32) * 1024 * 1024
+MAX_UPLOAD_BYTES = _int_env("NEXUS_MAX_UPLOAD_MB", 20) * 1024 * 1024
+MAX_PDF_PAGES = _int_env("NEXUS_MAX_PDF_PAGES", 500)
+MAX_CONCURRENT_CHATS = _int_env("NEXUS_MAX_CONCURRENT_CHATS", 4)
+MAX_CONCURRENT_UPLOADS = _int_env("NEXUS_MAX_CONCURRENT_UPLOADS", 2)
+
+# Opt-in allowlist for /models/pull. Empty (default) = unrestricted, preserving
+# current behaviour. Set NEXUS_MODEL_ALLOWLIST=mistral,llama3 to bound which
+# models can be downloaded; a bare repo name (before the ':tag') matches all of
+# its tags, so "mistral" permits "mistral:latest", "mistral:7b", etc.
+MODEL_ALLOWLIST = _csv_env("NEXUS_MODEL_ALLOWLIST", [])
+
+
+def model_pull_allowed(name: str) -> bool:
+    """True if `name` may be pulled: always when no allowlist is configured,
+    otherwise when the full name or its repo part (before the first ':') is
+    listed. Case-insensitive."""
+    if not MODEL_ALLOWLIST:
+        return True
+    n = (name or "").strip().lower()
+    if not n:
+        return False
+    allow = {a.lower() for a in MODEL_ALLOWLIST}
+    return n in allow or n.split(":", 1)[0] in allow
+
 # exported instance
 settings = Settings()
 
@@ -152,7 +211,11 @@ __all__ = ["Settings", "settings", "path", "VERSION",
            "PROJECT_ROOT", "DATA_DIR", "MODELS_DIR", "RUNTIME_DIR",
            "MEMORY_DIR", "LOGS_DIR", "PLAYBOOK_DIR", "UPLOADS_DIR",
            "EXPORTS_DIR", "MEMORY_DB",
-           "BACKEND_LOG", "OLLAMA_LOG", "CHAT_LOG"]
+           "BACKEND_LOG", "OLLAMA_LOG", "CHAT_LOG",
+           "ALLOWED_HOSTS", "ALLOWED_ORIGINS",
+           "MAX_REQUEST_BYTES", "MAX_UPLOAD_BYTES", "MAX_PDF_PAGES",
+           "MAX_CONCURRENT_CHATS", "MAX_CONCURRENT_UPLOADS",
+           "MODEL_ALLOWLIST", "model_pull_allowed"]
            
 # --- quick runtime sanity check when run directly (no side effects on import) ---
 if __name__ == "__main__":

synapse/tools.py

@@ -60,20 +60,83 @@ async def _web_search(query: str = "", **_) -> str:
     return res or "(no results)"
 
 
+_FETCH_MAX_REDIRECTS = 5
+
+
+def _ip_is_blocked(ip: str) -> bool:
+    """True if an address is one an outbound fetch has no business reaching:
+    loopback, RFC1918/ULA private, link-local (incl. 169.254.169.254 cloud
+    metadata), multicast, reserved, or unspecified. IPv4-mapped IPv6 is unwrapped
+    first so ::ffff:127.0.0.1 can't sneak a loopback past the check."""
+    import ipaddress
+    try:
+        addr = ipaddress.ip_address(ip.split("%")[0])  # drop any IPv6 zone id
+    except ValueError:
+        return True  # unparseable -> refuse rather than guess
+    mapped = getattr(addr, "ipv4_mapped", None)
+    if mapped is not None:
+        addr = mapped
+    return (
+        addr.is_loopback or addr.is_private or addr.is_link_local
+        or addr.is_multicast or addr.is_reserved or addr.is_unspecified
+    )
+
+
+def _ssrf_guard(host: str) -> str | None:
+    """Resolve a hostname and return an error string if ANY of its A/AAAA
+    records is a blocked address, else None. Checking every answer stops a name
+    from smuggling one private record alongside a public one.
+
+    ponytail: this validates then httpx re-resolves on connect, so a sub-second
+    DNS-rebind could still slip a private address through the TOCTOU gap. That's
+    an advanced attack against a playbook-gated, single-user tool; pin the
+    connection to the resolved IP if this ever faces untrusted callers."""
+    import socket
+    if not host:
+        return "missing host"
+    try:
+        infos = socket.getaddrinfo(host, None)
+    except socket.gaierror as e:
+        return f"cannot resolve host: {e}"
+    ips = {info[4][0] for info in infos}
+    if not ips:
+        return "host did not resolve"
+    blocked = [ip for ip in ips if _ip_is_blocked(ip)]
+    if blocked:
+        return f"refusing to fetch a private/loopback/link-local address ({', '.join(sorted(blocked))})"
+    return None
+
+
 async def _fetch_url(url: str = "", **_) -> str:
     import re
     import httpx
+    from urllib.parse import urlparse, urljoin
     url = (url or "").strip()
     if not url.startswith(("http://", "https://")):
         return json.dumps({"error": "url must start with http:// or https://"})
-    # ponytail: no SSRF allow/deny-list — local single-user assistant, and the
-    # tool only runs when a playbook explicitly grants fetch_url. Add host
-    # filtering if this ever serves multiple/untrusted users.
+    # SSRF guard: validate the host of the initial URL AND every redirect hop
+    # against the private/loopback/link-local block-list before connecting, so a
+    # granted fetch_url can't be steered at 127.0.0.1:11434, cloud metadata, or
+    # LAN hosts — and a public URL can't 302 its way there either.
     try:
-        async with httpx.AsyncClient(timeout=15.0, follow_redirects=True) as c:
-            r = await c.get(url, headers={"User-Agent": "NexusOS/1.0"})
-            r.raise_for_status()
-            html = r.text
+        async with httpx.AsyncClient(timeout=15.0, follow_redirects=False) as c:
+            for _ in range(_FETCH_MAX_REDIRECTS + 1):
+                parsed = urlparse(url)
+                if parsed.scheme not in ("http", "https"):
+                    return json.dumps({"error": "only http(s) URLs are allowed"})
+                err = _ssrf_guard(parsed.hostname or "")
+                if err:
+                    return json.dumps({"error": f"blocked: {err}"})
+                r = await c.get(url, headers={"User-Agent": "NexusOS/1.0"})
+                location = r.headers.get("location")
+                if r.is_redirect and location:
+                    url = urljoin(url, location)
+                    continue
+                r.raise_for_status()
+                html = r.text
+                break
+            else:
+                return json.dumps({"error": "too many redirects"})
     except Exception as e:
         return json.dumps({"error": f"fetch failed: {e}"})
     text = re.sub(r"(?is)<(script|style).*?</\1>", " ", html)