Verification and development

This guide describes the verification harness and its evidence. The intended public semantics are specified separately in the technical contract.

Setup and checks

Use Gleam 1.18.1 or later and Node 24 (enforced by npm scripts; other Node majors are unverified). Dependencies are pinned in the project manifests and resolved lockfiles. Run npm ci and gleam deps download on first setup, then npm test for the available tests. After dependencies are fetched, tests must run offline.

Run npm run verify for the complete Node verification run. It checks formatting, runs Gleam and Node tests, enforces generated coverage thresholds, and writes reports/evidence.json with source hashes, dependency versions, logs, conformance selection and per-row evidence. After fetching dependencies, this command runs offline. npm run check:release accepts only a successful report whose source fingerprint and logs are unchanged. These checks provide test evidence, not a mathematical proof.

The harness currently retains a known Ajv 8.20.0 discrepancy for a declared __proto__ property in a closed record. Its characterization test passing means the discrepancy remains visible, not that Ajv agrees in this case. Pinned Hyperjump 1.18.0 checks every generated definition/input pair, as well as the dedicated verification/supplementary-oracle.test.mjs fixtures. A split is classified only when renaming the declared hostile key restores Ajv agreement; unexplained splits fail verification. The generated report counts classified splits. This explicitly documented exception does not change schemas, decoder behavior or Ajv options. See verification/known-oracle-discrepancies.json.

Verification coverage

Verification covers generated inputs, mutations, runtime behavior, typed outputs, compile-negative cases, independent validators, selected official JSON Schema cases. The generated suite includes 10,000 seeded pairs, all 345 generic parent/child combinations and fourteen depth-50 chains. Thirty-one compiled JavaScript library mutations must fail behavioral assertions. They cover numeric constraints, recursion, tuples, key constraints, membership, conditionals and exclusion. The suite also runs foundation, typed-value and hardening checks. Twenty forbidden Gleam programs must fail compilation after a positive baseline.

The official suite is pinned to commit 7de0e6a06031ede80028583dd45d0cd41105ae5b. All 46 core files are retained with hashes and licence. verification/official/selection.json identifies 27 selected groups and 357 exclusions with reasons. No unsupported schema is strengthened to make it fit our constructors. Optional suite collections and full-dialect conformance are not claimed. Safe-integer limits and Unicode string lengths have dedicated checks.

See PRESERVATION.md for constructor reasoning and generated notes for failure retention, shrinking, and implementation findings. reports/evidence.json is the current verification result; it is generated locally and excluded from source control. Browser checks cover Chrome 155, Firefox 157 and Safari 27; see Browser compatibility. Other browsers and native runtimes outside the tested matrix remain unverified.

Output and evidence details

dictionary(child) decodes to a Gleam List(#(String, a)) (key/value pairs), not a JavaScript object. The test adapter explicitly maps that list to an object.

Generated checks compare decoded output with an independent recipe interpreter, including optional presence, defaults, nullable values, union selection and maps. Coverage records visits and outcomes by definition-node path, and requires both acceptance and rejection for every constructor at nested positions. This is a bounded corpus, not exhaustive path coverage for every generated definition.

Reports identify the tested source snapshot by file hashes and record dependency versions and logs. A report becomes stale when that source changes. Preservation arguments require separate review; automated tests do not prove them.

Native Erlang verification

With Erlang/OTP 29, make and a C compiler installed, run npm run verify:erlang-primitives. The command runs seventeen groups covering the actual native library, numeric and scalar admission checks, immutable recursion, process transfer and exit, native regex behavior and operational failures. Historical prototypes and regex counterexamples remain as regression evidence. The production fixtures use the vendored regex helper, not a JavaScript adapter.

The typed generated gate runs 886 definitions and 17,788 cases through both compiled targets. Ajv and Hyperjump check emitted schemas; an independent recipe interpreter checks 6,459 accepted outputs. Full diagnostic structures are compared across targets. The deployment gate removes source checkouts and tests an exported Gleam shipment with an explicitly installed helper. See Native Erlang setup for installation.

All 109 selected official schema cases also run through both typed targets, with the original validity expectations unchanged and both original and emitted schemas checked by Ajv and Hyperjump. The 357 unsupported groups remain excluded.

Current native evidence covers macOS arm64/OTP 29 and Ubuntu 24.04 x86_64 with OTP 28.5.0.7 and 29.1.1, using Gleam 1.18.1 and the Node 24.10.0/Unicode 16 reference. It does not establish other platforms or OTP releases, every deployment tool or exhaustive ECMAScript conformance. The source retains detailed investigation and measurement reports in docs/erlang-portability.md, docs/native-oracle-evidence.md and docs/regex-workload-measurements.md.

Archive checks

Run npm run prepare:release to regenerate both target gates, documentation and an exported Hex archive, then inspect the archive and run fresh consumers on both targets. It writes reports/release-preparation.json, including archive hashes and support boundaries. The packaged README must match the source, and all configured HexDocs pages and their local links must be present. It does not tag, push or publish. The separate npm run check:release remains a JavaScript evidence check; it is not a whole Erlang release qualification.

The Linux CI workflow in .github/workflows/native-qualification.yml runs the same checks on Ubuntu 24.04 with OTP 28 and 29.