# evals/public_demo — Lane Contract

**ADR:** ADR-0099
**Invariants:**
- ``public_showcase_pure_composition``
- ``public_showcase_all_claims_supported``
- ``public_showcase_json_byte_equality``

## Purpose

Prove that ADR-0099's `core demo showcase` is a single 30-second
artifact composing four invariants (determinism, honest unknown,
reviewed learning, multi-hop with trace) **without introducing any
new mechanism**. Every claim it makes is backed by an existing,
shipped, separately-tested adapter.

## Cases

- ``determinism_run_to_run_byte_equality`` — two consecutive
  showcase runs produce byte-identical JSON (after stripping
  ``total_runtime_ms``). SHA-256 pinned.
- ``all_claims_supported`` — single run reports
  ``all_claims_supported=True`` and every scene reports
  ``all_claims_supported=True``.
- ``runtime_under_budget`` — total runtime ≤ 30 seconds on the
  reference dev hardware.
- ``pure_composition_no_new_mechanism`` — grep gate over
  ``core/demos/showcase.py``'s import graph refuses any symbol whose
  module path is not within the existing shipped packages
  (``core/``, ``chat/``, ``generate/``, ``language_packs/``,
  ``teaching/``, ``evals/`` for adapter-lane bridges).

## Determinism

Two showcase runs produce identical JSON bytes when
``total_runtime_ms`` is excluded (timing is the one legitimate piece
of non-determinism — every other field is pinned by the showcase
contract and the underlying adapter byte-equality from ADR-0098).

## Exit code

Non-zero on any case whose actual outcome diverges from the case spec.

## Known Environment Caveat

**`runtime_under_budget` is environment-sensitive.**

The pinned artifact (`results/v1_dev.json`) records all 4 cases
passing, including `runtime_under_budget` (`divergence: null`).
However, live CI runs on slower or shared hardware have reproducibly
exceeded the 30s wall-clock budget (observed: 47–48s) during PRs
#684, #685, #686, and #687 gate runs.

This is a timing flake, not a content regression:

- All content lanes match their pinned SHAs in every observed run.
- `determinism_run_to_run_byte_equality`, `all_claims_supported`,
  and `pure_composition_no_new_mechanism` pass unconditionally.
- The lane was deliberately **not re-pinned** on slower-hardware runs
  per standing guidance — the pinned artifact reflects a passing run
  on reference dev hardware.

**Implication for evaluators:** if reproducing this lane in a
constrained or shared environment, a `runtime_under_budget` failure
is an infrastructure signal, not a correctness failure. All
behavioral and compositional invariants remain intact.