render_preview validates markup and hands it to the browser, which renders it
in an opaque-origin sandboxed iframe. Nothing executes server-side. That model
fits HTML/SVG/JSX and cannot fit C, Rust or Erlang, which need a real
toolchain - so those get a second tool instead of a widened first one.
The split is the feature: the model picks a track by picking a tool, rather
than picking a `lang` value from an enum where half the entries run
server-side and half do not.
synapse/code_run.py compiles and runs one file in a throwaway directory and
returns a ```nexus-run fence carrying the source and its captured output
together, so a model cannot paste output without the code that produced it.
Backticks in the source are re-encoded as ` - still valid JSON, and it
cannot close the fence early.
It is not a sandbox, and the module docstring says so up front. What it gives
is containment by layers: consent (an action tool, gated by
action_tool_policy, per-call Approve/Deny on "ask"), static screening, a
scrubbed environment in a temp dir, wall-clock and POSIX rlimits, and a
network namespace on Linux where unprivileged userns are available. Screening
is a tripwire against a model reaching for `requests` out of habit, not a
boundary against an adversary; layers 1 and 3-5 are the load-bearing ones.
Backend RUN_LANGS and frontend run-langs.js are separate registries because
the two sides need different things - one executes, one labels - and neither
should depend on the other at runtime. tests/test_tools.py asserts the key
sets and the fence tag stay equal, so drift fails the gate instead of
rendering a run result under the wrong language.
tests/snippet_probes/ is a data catalog rather than inlined cases, so adding a
language is a data change and the meta-tests can assert every RUN_LANGS key
has both a smoke probe and a screening probe. Probes skip cleanly on hosts
without the toolchain.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Two tool/agent-layer hardening changes:
* fetch_url now resolves the target host and refuses to connect if any
resolved address is loopback, private (RFC1918/ULA), link-local (incl. the
169.254.169.254 cloud-metadata endpoint), multicast, reserved, or
unspecified. IPv4-mapped IPv6 is unwrapped first, and the guard re-runs on
every redirect hop so a public URL cannot 302 its way to an internal target.
* /chat/approve now requires a single-use token minted when the stream pauses
for approval and delivered only in that stream's tool_request event, compared
in constant time. Previously the pending approval was keyed solely on a
client-supplied conversation_id, so anyone who could enumerate a
conversation_id could approve another client's pending action.
The frontend threads the token from the tool_request event into the approve
call.
Co-authored-by: Cursor <cursoragent@cursor.com>
3-way action_tool_policy (off/ask/allow). In "ask", the chat stream stays
open and the tool loop awaits approval: emits event:tool_request, the UI
shows Approve/Deny, POST /chat/approve resumes the same stream. Declined
actions return a denied result; a timeout denies.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
AthenaandCursor
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