/**
 * Max attachments rendered from one envelope — a room peer's plaintext body
 * is untrusted input; without a cap a hostile message claiming hundreds of
 * attachment entries would force MessageList to render that many bubbles
 * (each triggering an authenticated fetchAttachmentBlob call) per message.
 * Exported so tests can assert against it without hardcoding the number.
 */
export declare const MAX_ATTACHMENTS = 10;
export interface EnvelopeAttachment {
    id: string;
    mime: string;
    filename: string;
    sizeBytes: number;
    width?: number;
    height?: number;
    durationMs?: number;
    /** Downsampled waveform peaks (float[0,1], length ≤ MAX_VOICE_PEAKS).
     *  Additive-optional like durationMs: no envelope version bump, decoder
     *  tolerates absence (flat fallback waveform), sanitizePeaks clamps on
     *  decode — a room peer's plaintext body is untrusted input. */
    peaks?: number[];
}
export interface AttachmentEnvelope {
    body: string;
    attachments: EnvelopeAttachment[];
}
/** Encode a caption + attachment list as the UTF-8 `sealed` bytes for client.send(). */
export declare function encodeAttachmentEnvelope(body: string, attachments: readonly EnvelopeAttachment[]): ArrayBuffer;
/**
 * Decode a plaintext message body as an attachment envelope.
 * Returns null when the string is not a well-formed envelope of OUR shape —
 * callers must fall back to treating the original string as the plain body.
 * This is the read-side inverse of encodeAttachmentEnvelope(), applied to
 * every room member's message stream (not just the sender's own optimistic UI).
 */
export declare function decodeAttachmentEnvelope(plaintext: string): AttachmentEnvelope | null;
/**
 * Build the GET /api/sdk/attachments/{id} download URL (server: JWT-authenticated —
 * callers must fetch with an Authorization header, not assign this directly to
 * `<img src>`; see MessageListClient.fetchAttachmentBlob).
 */
export declare function attachmentUrl(baseUrl: string, attachmentId: string): string;
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