/**
 * Wire-format constants for records on `session.out` / `session.in`.
 *
 * Three kinds of records can appear on a Session stream:
 *
 * 1. **Data records** — JSON body shaped as `{data: <UIMessageChunk>, id:
 *    <partId>}`, no special headers. The substance of the conversation.
 *
 * 2. **Trigger control records** — empty body, `headers` carry `[
 *    ["trigger-control", <subtype>], ...]` plus any subtype-specific sibling
 *    headers (e.g. `public-access-token` on `turn-complete`). Routed to a
 *    consumer's `onControl` callback; never surfaced as data chunks.
 *
 * 3. **S2 command records** — opaque body, `headers` first entry has an
 *    empty name (only valid for S2-interpreted directives like `trim` and
 *    `fence`). Filtered out at the SSE parser; consumers never see them.
 *
 * See `docs/ai-chat/client-protocol.mdx#records-on-session-out` for the
 * customer-facing contract.
 */
/** Header name carrying the Trigger control subtype on control records. */
export declare const TRIGGER_CONTROL_HEADER: "trigger-control";
/** Header name carrying the refreshed `publicAccessToken` on `turn-complete`. */
export declare const PUBLIC_ACCESS_TOKEN_HEADER: "public-access-token";
/** Header name carrying the agent's last S2 event id on a handover bridge. */
export declare const SESSION_STATE_LAST_EVENT_ID_HEADER: "last-event-id";
/**
 * Header on `turn-complete` records carrying the highest `session.in`
 * seq_num the agent committed to processing during this turn. Read on
 * the next worker boot to seed `.in`'s resume cursor — anything past
 * this seq is new and gets delivered; anything at-or-before was already
 * processed and is skipped. Decimal-string form of the seq_num.
 *
 * Omitted when no `.in` records have been consumed yet (first turn of a
 * fresh chat triggered via the wire payload).
 */
export declare const SESSION_IN_EVENT_ID_HEADER: "session-in-event-id";
/**
 * Sibling of {@link SESSION_IN_EVENT_ID_HEADER}: the highest `.in` sequence this
 * run had actually consumed at the turn boundary, unclamped.
 *
 * The resume cursor is held back behind records still waiting to be handled, so
 * resuming from it necessarily re-delivers records that WERE handled. A message
 * re-delivered that way is the point. A control record re-delivered that way is
 * a bug: it applies a second time to whatever turn is live on the new run. On
 * boot this bound tells the run which control records it has already seen.
 */
export declare const SESSION_IN_CONSUMED_ID_HEADER: "session-in-consumed-id";
/**
 * Header marking a session as closed. Carried by the `session-closed` control
 * record, and also stamped on a `turn-complete` record when the close was
 * decided before that turn ended — readers terminate their stream on
 * turn-complete, so that is the last moment a live client can be told.
 */
export declare const SESSION_CLOSED_HEADER: "session-closed";
/**
 * Header on `session-closed` records carrying the reason the session was
 * closed, as supplied to `chat.close({ reason })` / `sessions.close()`.
 * Omitted when no reason was given.
 */
export declare const SESSION_CLOSED_REASON_HEADER: "session-closed-reason";
export declare const TRIGGER_CONTROL_SUBTYPE: {
    readonly TURN_COMPLETE: "turn-complete";
    readonly UPGRADE_REQUIRED: "upgrade-required";
    readonly SESSION_CLOSED: "session-closed";
    readonly PENDING_VERSION: "pending-version";
};
export type TriggerControlSubtype = (typeof TRIGGER_CONTROL_SUBTYPE)[keyof typeof TRIGGER_CONTROL_SUBTYPE];
/** Read a single header value by name. Returns the first match. */
export declare function headerValue(headers: ReadonlyArray<readonly [string, string]> | undefined, name: string): string | undefined;
/**
 * Return the Trigger control subtype carried by a record's headers, if any.
 * Returns `undefined` for data records and S2 command records.
 */
export declare function controlSubtype(headers: ReadonlyArray<readonly [string, string]> | undefined): string | undefined;
/**
 * Is this record an S2 command record? Detected via the empty-name first
 * header, which S2 permits only for command records (trim/fence).
 */
export declare function isS2CommandRecord(headers: ReadonlyArray<readonly [string, string]> | undefined): boolean;
/** Event payload delivered to a Session-stream `onControl` callback. */
export type ControlEvent = {
    /** Subtype value from the `trigger-control` header (e.g. `turn-complete`). */
    subtype: string;
    /** All headers on the underlying record. Read additional metadata here. */
    headers: ReadonlyArray<readonly [string, string]>;
    /** S2 sequence number of the control record. */
    seqNum: number;
    /** S2 arrival timestamp of the control record (ms since epoch). */
    timestamp: number;
};