동반 소스, 그리고 패널의 관문들

    private func contextReply(requestID: String?) async -> PippaPanelReply {
        let stamp = sourceStamp
        guard let (tab, page) = readablePage(), let context = await page.readContext(),
              stamp == sourceStamp, context.url == stamp.url else {
            return .noContext(reason: unreadableReason(), requestID: requestID)
        }
        var payload = identified(WebPagePayload(tab: tab.id, context: context, at: now()), tab: tab)
        var companions: [WebPagePayload] = []
        for source in selectedRelatedTabs {
            guard stamp == sourceStamp, let sourcePage = source.page,
                  let read = await sourcePage.readContext(), stamp == sourceStamp,
                  read.url == source.status.url else {
                return .noContext(reason: "A selected source changed or could not be read. Refresh or deselect it.", requestID: requestID)
            }
            companions.append(identified(WebPagePayload(tab: source.id, context: read, at: now()), tab: source))
        }
        guard stamp == sourceStamp else { return .noContext(reason: "The selected sources changed.", requestID: requestID) }
        payload.related_sources = companions
        return .context(payload, requestID: requestID)
    }

/// The gates on a message from the panel's page, as a plain value so each one
/// has its own test: the panel's own web view, its main frame, the panel's
/// origin both for the frame that spoke and for where the web view is now,
/// and a cap on what the host will read.
struct PanelMessageGate: Equatable {
    static let maximumBytes = 256 * 1024

    var isSameWebView: Bool
    var isMainFrame: Bool
    var frameOrigin: PageOrigin?
    var webViewOrigin: PageOrigin?
    var byteCount: Int

    func admits(for panelOrigin: PageOrigin) -> Bool {
        isSameWebView && isMainFrame && frameOrigin == panelOrigin && webViewOrigin == panelOrigin
            && byteCount <= Self.maximumBytes
    }
}

    /// Pippa's own page, in the panel's main frame, hears Dad without a
    /// prompt: it is her voice. Anything else in the panel is refused.
    func webView(
        _ webView: WKWebView, decideMediaCapturePermissionsFor origin: WKSecurityOrigin,
        initiatedBy frame: WKFrameInfo, type: WKMediaCaptureType
    ) async -> WKPermissionDecision {
        Self.captureDecision(asking: Self.origin(of: origin), isMainFrame: frame.isMainFrame, panelOrigin: self.origin)
    }

    static func captureDecision(asking: PageOrigin, isMainFrame: Bool, panelOrigin: PageOrigin) -> WKPermissionDecision {
        isMainFrame && asking == panelOrigin ? .grant : .deny
    }