Address PR review feedback:
- detection_pattern(()) with an empty tag set compiled to an overly-broad regex
(the empty alternation matches any [start ...]/[end ...] run), which would turn
the forgery scanner into a false-positive generator. Reject an empty or
all-empty tag set up front. Not reachable from the sole caller today, but it is
a public, security-relevant helper.
- Clarify build_operator_instruction_declaration's docstring: the trusted region
is delimited by both the start and end markers (each carrying the nonce), not
just the opening marker.
Swap the trust-fence marker shape from <tag_nonce>...</tag_nonce> to
[start tag_nonce]...[end tag_nonce] for both the operator fold (system-reminder)
and the output-guard judge (tool_output). Angle-bracket markup pushed some local
models out of distribution and toward emitting their own turn-structure tokens:
chat templates built around rigid <...>-style structural tokens derail once a
few folded reminders accumulate. The start/end keywords carry no slash (no </ or
[/ closing-tag shape) and read as ordinary text.
Single-source the shape in fence.py (_OPEN_KW/_CLOSE_KW + detection_pattern) so
wrap, neutralize, the forgery/leak detector, and both trust declarations track
one definition. The nonce still rides both boundaries (unforgeable close); the
leak-vs-forgery split and the forge-in / break-out defang are preserved. The
fold is wire-only, so there is no migration; the legacy persisted-envelope
readers keep the old shape.
Add regression tests pinning each trust declaration to fence.wrap's emission so
a future keyword change fails loudly instead of silently desyncing the anchors.
Phase-1 review follow-ups:
- neutralize() now tolerates whitespace between '<' and the slash ('< /tag',
'< /tag'), matching output_guard's detection regex so a marker can no longer
be detected-but-not-defanged (a leaked-nonce break-out gap).
- Add direct tests for the sec-1 forge-in defence: _neutralize_host defangs a
forged <system-reminder_{nonce}> in both string- and list-content untrusted
hosts before the real fence is appended, and the host is defanged exactly once
so consecutive folds don't corrupt the first appended fence.
Both the operator fold and the output-guard judge wrap spans in nonce-delimited
fences, but the two had drifted: the operator path minted a 32-bit nonce reused
per session with no body escaping, while the judge used a 64-bit per-call nonce
plus closing-tag escaping. Extract the shared mechanism (mint/neutralise/wrap)
into turnstone/core/fence.py and put both callers on it so they cannot diverge
again.
- Operator fold (sec-1): 64-bit nonce; fence.wrap neutralises the operator
body's close marker, and _fold_system_turns neutralises the untrusted host
turn's <system-reminder> markers once before the first fold, so a leaked or
guessed per-session nonce still cannot forge a trusted block. Per-session +
cached declaration kept (the declaration pins the exact value, so per-turn
rotation would bust the prompt cache). Marker is now <system-reminder_{nonce}>.
- Judge: refactored onto fence (behaviour-preserving; still per-call).
- Forgery detection: output_guard scans tool output for trust-fence markers —
an exact session-nonce match is HIGH (operator_marker_leak: the token has
leaked and is being replayed), any other marker LOW (operator_marker_forgery).
Removes mint_envelope_nonce / wrap_system_context (folded into fence.wrap).
Patrick Buckley