jev-assert

Turns a natural-language, user-observable UI expectation into an executed semantic verdict. It reads a page's captured text state, asks TypeSafe's Jev model one narrow judgment, and emits a verify-behavior receipt the rest of this repo already consumes. It never drives a browser, never applies a fix, and never writes code — it is a read-only verification primitive, the semantic sibling of verify-behavior.

This SKILL.md is a thin index. Detailed rules live in rules/*.md and load on demand.

What it returns

The terminal deliverable is one receipt line, byte-compatible with the canonical vocabulary in verification-receipt.md:

[receipt] tier: 3 | tool: jev | target: <page/spec>
[receipt] question: Does the page state show that <expectation>?
[receipt] jev: noul=0.94
[receipt] verdict: confirms

The five verdicts and when each is emitted are owned by rules/receipt-mapping.md. null (ran, no support) and unobtainable (could not run) are distinct and never collapsed — the same rule verification-receipt.md enforces.

Why Jev, and why text-only

Jev is a TypeSafe System One model: it takes structured natural-language state and returns a typed answer with a probability (Noul / Choice / Score), not generated prose. That is exactly the shape a test assertion needs — a decision code can gate on, with calibrated confidence. Jev evaluates text, not images, so the browser side must feed it an accessibility snapshot or page text; a screenshot is never a valid input. See rules/state-extraction.md.

Workflow

Run these three steps in order; each has a gate.

Invocation contract

Callers supply two things — the page text state and the expectation — and receive one receipt.

• <expectation> — a user-observable outcome in plain language, phrased as something a person looking at the screen could confirm. Provenance (Step 0) rejects an expectation that merely restates the captured text (assertion-by-construction).
• --state-file <path> — a file holding the captured text state. When omitted, the caller passes the state inline (the spec runners do this).
• --threshold-high N / --threshold-low N — override the default decision bands (see rules/receipt-mapping.md); both are calibration knobs, not magic numbers.

The concrete call path is the committed, zero-dependency script — it builds the Noul question, POSTs it, and maps the probability to a verdict per receipt-mapping.md:

node ${CLAUDE_SKILL_DIR}/scripts/jev-call.mjs \
  --expectation "the user sees an order-confirmation number" \
  --state-file <captured-state.txt> --target <page-or-spec-id>

State also reads from stdin when --state-file is omitted (the runners pipe captured page text in). The script follows the TypeSafe HTTP API contract documented by the official typesafe@typesafe-ai skill — install that skill for the API guidance, prompting patterns, and SDK; this skill owns only the semantic contract (question template, thresholds, receipt mapping) and does not fork the wire format. The API is keyed by the TYPESAFE_API_KEY environment variable. When TYPESAFE_API_KEY is unset or the API is unreachable, the check could not run — the script emits unobtainable, never a confirms / contradicts guess. Run node ${CLAUDE_SKILL_DIR}/scripts/jev-call.mjs --self-test to verify the mapping offline.

Consumer: the semantic THEN assertion

The primary consumer is the shared UI spec grammar (spec-run-contract.md). A spec author writes a semantic assertion with the semantic: prefix, mirroring the existing network: form:

- WHEN {role: "button", name: "Place order"} is clicked
  THEN semantic: the user sees an order-confirmation number

Both runners (aw-tester and aw-tester-chrome) capture the page text state, call this skill, and fold its receipt into the spec verdict: confirms → the assertion passes; contradicts / null → it fails; ambiguous / unobtainable → the spec is inconclusive, never a silent pass. ui-verify reuses that grammar verbatim, so a semantic THEN flows through to PR/preview verification with no extra wiring.

Core Principles

1. A receipt, not a score. This skill emits a verify-behavior verdict and the raw Jev probability; it never invents its own grading number — confidence(code) owns any score.
2. User-observable outcomes only. An expectation the agent could confirm by re-reading the state text it was handed is assertion-by-construction and is refused, mirroring observe-run's assertion-provenance rule.
3. Text in, typed out. Jev never sees a screenshot; the input is always captured accessibility/page text.
4. Fail honest, not confident. No key, no state, or an unreachable API is unobtainable — a verdict about the tooling, never a guessed pass or fail.
5. Driver-agnostic. The same call works over Playwright or claude-in-chrome state; there is one implementation, not one per driver.

Evaluation

• Golden set separates user-observable-outcome expectations (accept) from by-construction / DOM-restatement expectations (reject), balanced and resistant to a single-keyword shortcut — see evals/evals.json.
• evals/triggers.jsonl covers should-trigger and adjacent near-miss queries.
• The repo eval obligation is met: the receipt-token set is a mechanical contract guarded in scripts/eval/l1.mjs; the accept/reject provenance decision is an enumerable judgment guarded by a golden set.

Anti-patterns

• Feeding Jev a screenshot or an image path — it is text-only.
• Phrasing the expectation as "the page contains the string I just read".
• Treating unobtainable as a failure, or null as a pass.
• Duplicating the TypeSafe API guidance instead of installing typesafe@typesafe-ai — jev-call.mjs follows its documented contract, it does not replace the guidance.
• Emitting a bespoke verdict word outside the five canonical receipt tokens.

Definition of Done

• Every planned file written and within its line cap.
• name / description validate; node ${CLAUDE_SKILL_DIR}/scripts/validate-skill.mjs (run from create-skill) reports PASS.
• The receipt tokens match verification-receipt.md exactly.
• The semantic: assertion form is wired into spec-run-contract.md, specs.md.template, and both runners.
• Inventory rows added to CLAUDE.md and README.md.