llm-security-commons/spec/conformance-corpus.md

# Conformance corpus

**Status: normative.** This document defines how the files under [`conformance/`](../conformance/)
are to be read. Where it disagrees with any informative document in `docs/`, this wins.

RFC 2119 language is used deliberately: MUST, MUST NOT, SHOULD, MAY.

## 1. What a case is

A case is a directory under `conformance/` holding exactly two files:

```
conformance/<case-id>/input.txt        the exact bytes to scan
conformance/<case-id>/expected.json    the findings a conforming runtime produces
```

A runtime claiming conformance MUST run every case. It MUST NOT skip a case because its
engine rejects the pattern behind it — a silently skipped case is an invisible false
negative, which is the failure mode this corpus exists to catch. A case that cannot be run
MUST be reported as an error, not as a pass.

### 1.1 Declared tables and `not-applicable`

The runtimes that share this core do not implement the same set of data files, and some
never will: a table can be meaningful in an output gate and meaningless in the surface next
to it. §1 as stated would make every such case a permanent failure, which reports an
architectural difference as a defect and tells a reader nothing.

A runtime claiming conformance therefore MUST declare **the set of commons data files it
implements**, and MUST publish that set alongside its conformance result. A case whose
`scope` (§4) names a data file outside the declared set MUST be reported as
**`not-applicable`** — a third verdict beside pass and fail, and a different thing from the
error of §1. §1's error means *this runtime tried and could not*; `not-applicable` means
*this question was never addressed to this runtime*.

A `not-applicable` case MUST still be enumerated in the result. It MUST NOT be counted as a
pass, and MUST NOT be silently dropped from the denominator: `76/83 passed` and
`76 passed, 7 not-applicable` describe different runtimes, and only the second one can be
checked.

Two constraints keep the verdict from becoming an exit:

- A runtime MUST NOT withdraw a table from its declared set in order to convert failing
  cases into `not-applicable` ones. The declaration describes what the runtime implements,
  not what it would prefer to be asked. Narrowing it is a visible change to a published
  claim, and it MUST be reported as such rather than made quietly between runs.
- `not-applicable` attaches to a **table**, never to a case. A runtime that declares a table
  MUST run every case scoped to it, including the ones it fails. Per-case opt-out is exactly
  the silent skip §1 forbids.

**What the verdict does not say.** `not-applicable` records that a runtime does not implement
a named commons table. It is not a statement that the runtime is blind to the phenomenon
behind it — a runtime may well detect the same construct through some other mechanism that
this corpus does not constrain, and reading the verdict as a coverage gap would assert
something nobody measured. See §8.

## 2. `input.txt` is bytes, not text

`input.txt` holds the input **verbatim**, UTF-8 encoded. A runtime MUST read it as bytes
and MUST NOT strip, trim, normalise or re-encode anything before scanning.

There is **no trailing newline**. A trailing newline would be part of the input, and no
case wants one. Two of the current cases carry characters that are invisible on screen — a
zero-width space and a Cyrillic homoglyph — so an editor that "cleans up" a fixture can
change what it tests without changing how it looks. For that reason every `expected.json`
records the input's byte length and SHA-256, and a runtime SHOULD verify both before
scanning. A digest mismatch means the fixture has been altered; the result of scanning it
means nothing.

## 3. `expected.json`

```json
{
  "case_id": "hybrid-xss__script-tag",
  "input": { "file": "input.txt", "bytes": 24, "sha256": "…" },
  "scope": ["lexicon/injection-lexicon.json"],
  "match": "exact-within-scope",
  "findings": [{ "pattern_id": "hybrid-xss:script-tag" }],
  "observed_out_of_scope": { "llm_ingestion_guard": ["active:raw-html"] }
}
```

| Field | Normative? | Meaning |
| --- | --- | --- |
| `$comment` | no | Provenance prose. Carries no contract. |
| `case_id` | yes | Equals the directory name. |
| `input` | yes | Integrity of the input file. See §2. |
| `scope` | yes | Which commons data files this case constrains. See §4. |
| `match` | yes | How `findings` is to be compared. See §4. |
| `findings` | yes | The expected findings, named by commons `pattern_id`. See §3.1. |
| `observed_out_of_scope` | **no — informative** | What a named runtime was measured emitting outside `scope`. Evidence, never expectation. See §5. |

A finding carries a `pattern_id` and nothing else. Severity, OWASP anchor and human label
are properties of the pattern, published once in [`lexicon/injection-lexicon.json`](../lexicon/injection-lexicon.json)
and looked up there by that id. They MUST NOT be restated in a fixture: a value written in
two places is a value that will eventually disagree with itself.

### 3.1 `pattern_id` is not the finding `id`

The field is called `pattern_id` and not `id` because this repository already publishes a
different `id`, and confusing the two produces a runtime that fails every case for a reason
unrelated to detection.

| | Identifies | Stable? |
| --- | --- | --- |
| `pattern_id` — here; `families[].patterns[].id` in the lexicon | the **detection rule** | Yes. A stable cross-runtime contract, ratified by both seeding runtimes. |
| `id` — in [`schema/finding.schema.json`](../schema/finding.schema.json) | one **emitted finding** in one run | No. `DS-<scanner>-<counter>`, from a process-global counter: not stable across runs, not unique across processes. The schema says so itself. |

A runtime therefore MUST NOT compare a serialized finding's `id` to a fixture's
`pattern_id`. They answer different questions.

**Getting from a runtime's own label to a `pattern_id`.** Nothing requires a runtime to name
its patterns the way this repository does, and the two seeding runtimes do not: the same rule
is `override: ignore previous instructions` in one and `override:ignore-previous` in the
other. The mapping is published, per pattern, in the lexicon's `aliases` object:

```json
{
  "id": "override:ignore-previous",
  "aliases": {
    "llm_security": "override: ignore previous instructions",
    "llm_ingestion_guard": "override:ignore-previous"
  }
}
```

(The lexicon's own field is spelled `id`, because that name is ratified and renaming it
would break both consumers. `pattern_id` here refers to exactly that value.)

A runtime SHOULD carry that id directly on its own pattern table, which makes the
comparison a lookup rather than a translation. A runtime that instead maps through `aliases`
MUST register its own alias there — a runtime absent from that object has no published way to
be compared, and a mapping maintained privately in a consumer is the drift this repository
exists to prevent.

Fixture files carry **no individual `version` field**, which is the one place this
repository's "every JSON file has a top-level `version`" convention does not apply. The
corpus is versioned as a whole in [`conformance/manifest.json`](../conformance/manifest.json).
The exception is deliberate and stated here rather than left to be discovered.

## 4. `exact-within-scope`

This is the only `match` value defined in this version, and it means:

> Restricted to findings whose id belongs to a data file named in `scope`, the runtime's
> finding set MUST equal `findings` exactly. Findings outside that scope MUST be ignored
> by the comparison — neither required nor forbidden.

So a runtime MUST NOT raise a lexicon finding this case does not list, and MUST raise every
one it does. Whether the same runtime also flags the input as active content, as a carrier,
or as anything else is **not** this case's business.

**"Belongs to" means published in that file, never "shares its prefix."** A runtime MUST
decide membership by looking the id up in the scoped data file, and MUST NOT infer it from
the id's leading segment. The two are not the same set, and the difference is not
hypothetical: one seeding runtime emits `active:oversize-input`, a self-safety flag about its
own scan cap, which carries the `active:` prefix but is no construct in
[`signatures/active-content.json`](../signatures/active-content.json) and is therefore out of
scope for a case scoped there. A prefix-matching implementation would pull it into the
comparison and fail a case over a finding the corpus makes no claim about.

The scoping is what makes the exactness safe. The two seeding runtimes do not implement the
same set of tables — one has no active-content table at all — so a whole-report comparison
would fail for reasons that have nothing to do with the pattern under test. Scoping the
comparison to one published table asks a question about that table alone.

Through version 0.1.1 this paragraph ended "…asks a question both can answer", which held
only while every case was scoped to the one table both runtimes implement. It stopped being
true the moment a case was scoped to `signatures/active-content.json`, which only one of them
has. Scope narrows *what* is compared; it does not guarantee that every runtime is a valid
addressee of the comparison. That second question is answered by the declared table set in
§1.1, and a case scoped outside a runtime's declared set is `not-applicable` there rather
than failed.

The exactness is what makes the corpus worth running. A corpus that only checks that the
expected finding is *present* is passed by a runtime that flags everything.

A future case MAY declare a different `scope` or a different `match`. A runtime MUST reject
a `match` value it does not implement rather than degrade to a weaker comparison.

## 5. `observed_out_of_scope` is evidence, not expectation

This block records what a **named** runtime, at a **named** commit, was measured emitting
outside the case's scope. It exists so that a reader can see what was left out of the
contract instead of having to trust that nothing was.

A runtime MUST NOT be failed for disagreeing with it, and MUST NOT be required to reproduce
it.

**Absence of a runtime's key means unmeasured, not measured-empty.** The current corpus
carries no `llm_security` key anywhere, because that runtime was measured through its
injection-scanner entry point, which cannot emit an out-of-scope finding by construction.
Reading that absence as "this runtime emits nothing else" would be a claim nobody made.

## 6. Case ids

```
case_id  = pattern_id with ":" replaced by "__"
pattern_id = case_id with "__" replaced by ":"
```

`:` is not a legal filename character on Windows, and fork-and-own is a supported use of
this repository, so the id space cannot reach the filesystem unchanged. `__` does not occur
anywhere in the ratified id space, so the transform is one-to-one — verified collision-free
across all cases rather than assumed.

The transform carries a consequence that is easy to miss: **a case id is derived from a
pattern id alone, so the corpus holds at most one case per `pattern_id` in single-finding
scopes.** There is nowhere in the name to put a second one. That is a real constraint, not a
formality — a source runtime's own test matrix may well drive two payloads at the same
pattern, as one of the seeding runtimes does for `active:markdown-image`. When it does, the
two payloads MUST be compared *within the case's scope* before a second case is minted: if
their in-scope finding sets are equal, the second case cannot fail in any way the first does
not, and its distinguishing signal lies outside the scope where this corpus makes no claim.
Such a payload MUST NOT be given a discriminated case id; the derivation rule is the
contract, and a suffix would break the reverse transform. It SHOULD instead be recorded as
a named omission in `conformance/manifest.json`, so the drop is visible rather than
inferred from a count.

**A case id is a stable identifier. Changing one is a BREAKING change** and requires a major
bump of the corpus version, exactly like changing a pattern id. Consumers name cases in
their own test suites; a renamed case is a silently disappeared test.

## 7. When a runtime and a fixture disagree

The fixture is ground truth. A runtime that disagrees is wrong — **unless the fixture itself
is proven wrong**, in which case the fixture changes in its own commit, with the reason
written down, and the corpus version is bumped.

This ordering is the whole point of the repository. Two implementations that return
different verdicts on the same input are not holding different opinions; one of them has a
bug.

## 8. What conformance does and does not prove

Passing this corpus proves that a runtime agrees with the other runtimes that pass it, on
these inputs. It does not prove the fixtures are right. A wrong `expected.json` makes every
passing runtime wrong in the same way, which is a real failure mode and not a rhetorical
one — it is why each case records how it was produced.

Nor is the corpus a coverage claim. It covers the pattern tables named in
`conformance/manifest.json` under `scope_covered`, and the tables under `scope_planned` are
named there precisely so that their absence is visible rather than inferred.

And a result is only readable next to the declared table set of §1.1. A pass count on its
own does not say which questions were asked: a runtime that implements one table and one
that implements four can print the same number. The declared set is what turns the number
back into a claim — which is also why a `not-applicable` verdict proves nothing in either
direction about the runtime's actual detection. It says the corpus did not ask.