llm-security/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.

## 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.

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 both can answer.

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.

**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.