Structural hardening per user request, following the 3rd round of the
same bypass class on PR #5313's reasoning_efforts feature:
Round 1: plain-ordering regression (provider-config short-circuit ran
before the nested-route deny).
Round 2: a provider-qualified hint (@custom:<slug>:vertex/gemini-...)
left a slug fragment that the deny's prefix-match missed.
Both were legitimate, narrowly-targeted fixes, but the pattern —
_nested_route_reasoning_denied() requiring the model string to START
WITH the route prefix — meant every future wrapper/nesting scheme
would need the strip logic to be updated in lockstep, and a missed
case fails OPEN (reasoning re-enabled on a route that must never show
it), which is the wrong failure mode for a security-adjacent guard.
This commit removes that class of bug instead of patching its latest
instance: _nested_route_reasoning_denied() now searches for the
vertex/gemini- or gemini_cli/gemini- pattern ANYWHERE in the string at
a non-alphanumeric boundary, rather than requiring it at position 0.
Correctness no longer depends on _strip_provider_hint_for_reasoning()
having stripped exactly the right prefix first — any number of opaque
wrapper layers (@provider:, a named custom-provider slug, or any
nesting scheme not yet invented) can precede the route and the deny
still fires.
Verified: all historical bypass strings (round 1 and round 2, plus a
hypothetical deeper double-wrapped case) now correctly deny; embedded
substrings that must NOT match (e.g. 'notvertex/gemini-x') correctly
don't, thanks to the boundary lookbehind.
Added test_nested_route_deny_is_boundary_based_not_prefix_based
locking in the structural invariant directly, independent of any
particular wrapper scheme.
Verification:
./scripts/test.sh tests/test_reasoning_effort_model_capabilities.py tests/test_custom_provider_bare_model_reasoning.py
# 54 passed in 1.31s
Full suite: 11257 passed, 64 pre-existing failures (identical file/test
set as the prior commit's baseline — network/credential/profile-isolation/fd-leak
tests, unrelated to reasoning_efforts).
Charles Inglis
f9de93f42e