/**
 * The life-threatening-alert gate, the selection rule, and the banner copy.
 *
 * Zero I/O by design (CLAUDE.md design pattern 6): this module decides whether
 * a NOAA alert is life-threatening and renders the fixed banner, and something
 * else does the fetching. `src/handlers/criticalAlertBanner.ts` is that
 * something else — the one place that touches a service — so the failure
 * posture exists once rather than in each of the three render sites.
 *
 * **Every interpolated field is upstream free text and is treated as data.**
 * The banner carries an imperative line addressed to the reading model, so an
 * upstream that could break out of its own clause and continue the sentence
 * would be a prompt-injection surface — trusted publisher or not. Hence
 * `sanitizeField` below, and hence the rule that no upstream *prose* field
 * (`headline`, `description`, `instruction`) is read here at all. That rule has
 * no acceptable exception.
 *
 * The gate constants live in `src/config/displayThresholds.ts` so calibration
 * against the live national feed is a config change, not a code change.
 */
/**
 * The subset of NOAA `AlertProperties` this module reads.
 *
 * Every field is optional even though `src/types/noaa.ts:238-247` declares them
 * required: that interface describes the documented shape, and a third-party
 * response may omit any field at runtime. CLAUDE.md's "every field of a
 * third-party response optional" rule is the reason. A missing field must never
 * throw and must never fire the gate.
 */
export interface CriticalAlertCandidate {
    event?: string;
    severity?: string;
    urgency?: string;
    certainty?: string;
    response?: string;
    senderName?: string;
    expires?: string;
}
/**
 * Is this alert life-threatening enough to interrupt a weather question?
 *
 * ```
 * critical  ⟺  (severity ∈ severities && urgency ∈ urgencies && certainty ∈ certainties)
 *           ||  response ∈ responses
 * ```
 *
 * The starting rule is deliberately tight: `Extreme` severity catches Tornado,
 * Tsunami, Extreme Wind and Hurricane warnings while excluding Severe
 * Thunderstorm Warning (`Severe`), which is far too common to justify an
 * interrupt. The `response` leg stands alone because an official instruction to
 * evacuate is life-threatening whatever severity was attached to it.
 *
 * The three-axis leg is an **and**, so a single missing axis cannot fire it;
 * an all-undefined candidate is not critical.
 */
export declare function isCriticalAlert(a: CriticalAlertCandidate): boolean;
/**
 * The first critical alert in the list's given order, or `undefined`.
 *
 * **First, not most severe, and the order is the caller's.** NOAA's
 * `/alerts/active?point=` returns newest-first, which is the order a reader
 * would expect the banner to follow, so re-sorting here would only invent a
 * second opinion about precedence that nothing else in the codebase holds.
 *
 * **No array cap.** G8 says a bounded array that trims must never be used for
 * an exclusion decision without disclosing the trim — and there is nothing
 * honest to disclose in a positive-assertion-only element, so the right answer
 * is not to cap at all. If a future change adds one, G8 binds and the cap has
 * to be surfaced.
 */
export declare function selectCriticalAlert(list: CriticalAlertCandidate[]): CriticalAlertCandidate | undefined;
/**
 * The banner, or `''` when there is nothing to warn about.
 *
 * Every byte of this block is server-authored except four interpolated fields —
 * `event`, `senderName`, the formatted `expires`, and `response` — each of
 * which is sanitized or validated above. Absence of the banner claims nothing:
 * it is a positive assertion only, which is what makes the silent-omit failure
 * posture in `src/handlers/criticalAlertBanner.ts` safe (D1).
 *
 * @param a The alert to warn about, or `undefined` for "nothing to say"
 * @param totalActive How many alerts are active at the point, for the closing line
 * @param timezone IANA zone the expiry is rendered in; UTC when omitted
 */
export declare function formatCriticalAlertBanner(a: CriticalAlertCandidate | undefined, totalActive: number, timezone?: string): string;
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