v0.3.0 made the untrusted upload path unusable: measured on both doors, an
ordinary remote image fail_secure'd and an ordinary link/autolink/refdef
quarantined, so only documents without external references persisted.
Two independent defects compounded; neither fix works alone:
1. `markdown-image: HIGH` fired on any external image. The exfil primitive is a
URL that moves bytes outward, not an image. `is_ordinary_url` now grades on
shape - http(s)/protocol-relative, no query, no userinfo, no percent-escape,
no opaque host label or path segment -> LOW; anything data-carrying keeps the
carrier's severity. raw-html and data: URIs stay HIGH unconditionally.
Opacity reuses entropy's primitives; floors calibrated against real doc URLs
(worst legit token H=4.08, exfil segments 4.36-4.54) and frozen in
calibration.
2. The quarantine_default floor fired on ANY finding, a premise that broke when
every ordinary link became a finding. It now fires at MEDIUM+ - a no-op for
every detector that shipped before 0.3.0 (no LOW/INFO exists), which is what
makes this a patch rather than a minor.
The corpus blind spot that let this pass 522 green tests is closed: the FP
corpus carries realistic markdown and is asserted on the OUTPUT gate under
PRESET_USER_UPLOAD, with a counter-corpus of exfil-shaped URLs that must still
block. Beaconing and short opaque segments are conceded in LIMITATIONS and
asserted by the coverage matrix rather than papered over.
No new public API; no new preset (0.4.0 work); allow_reserved default unchanged.
Answers the gap that the README said what it does NOT stop (a long limitations
section) but never plainly listed what it DOES. Add a 'What it protects against'
section high up: attack classes grouped by OWASP anchor (LLM01 injection + 83
lexicon classes + carriers, LLM02 egress, LLM05 EchoLeak, LLM06 agency, LLM10
fail-secure, OKF T1-T6, container front-end), each driven by a live coverage-matrix
payload. Move the full honest-limitations list to docs/LIMITATIONS.md; README keeps
a high-impact summary + link. Net: protection and limits read in balance, 261 -> 216
lines. Coverage 126/126 and 522 tests unchanged; every class listed is real.
