WinterGram/submodules/InstantPageUI/Sources/InstantPageRenderer.swift

import Foundation
import UIKit
import AsyncDisplayKit
import Display
import CheckNode
import SwiftSignalKit
import TelegramCore
import TelegramPresentationData
import TelegramUIPreferences
import AccountContext
import GalleryUI
import ComponentFlow
import TextFormat
import EmojiTextAttachmentView
import AnimationCache
import MultiAnimationRenderer
import InvisibleInkDustNode
import ShimmeringMask

// MARK: - Stable item identity (for view reuse on re-layouts)

/// Stable identity for an `InstantPageV2LaidOutItem` across `update()` calls. The renderer
/// uses this to harvest existing item views and reuse them when the new layout still has
/// an item with the same id — preventing the media wrappers from torching their fetch
/// signals + image content on every chat-bubble re-apply.
///
/// Media items use their `media.index` (already unique within a page and used as the
/// gallery registry key). Details items use their `details.index`. Other items have no
/// intrinsic identity, so the renderer assigns them a `(case-tag, positional-index-in-items)`
/// pair.
public enum InstantPageV2StableItemId: Hashable {
    case media(Int)                          // media.index (4 media cases share this namespace)
    case details(Int)                        // details.index
    case thinking(Int)                       // thinking-block sequence index (own namespace)
    case positional(InstantPageV2ItemKind, Int)  // (caseTag, items-array position)
}

public enum InstantPageV2ItemKind: Hashable {
    case text, codeBlock, divider, listMarker, blockQuoteBar, shape, mediaPlaceholder, table, anchor, formula, slideshow
}

// MARK: - Render context

/// Bundle of render-time dependencies required to display real media inside an InstantPage V2
/// view. Tied to an `InstantPageV2View` for the view's lifetime — if any field would change
/// (typically because the bubble was recycled with a different webpage), the caller must
/// rebuild the V2View with a fresh render context.
///
/// `renderContext == nil` is permitted: the V2View falls back to grey-placeholder rendering
/// for the four media kinds (image/video/map/coverImage). This keeps the existing zero-arg
/// `InstantPageV2View()` constructor usable.
public final class InstantPageV2RenderContext {
    public let context: AccountContext
    public private(set) var webpage: TelegramMediaWebpage
    public let sourceLocation: InstantPageSourceLocation
    public let imageReference: (TelegramMediaImage) -> ImageMediaReference
    public let fileReference: (TelegramMediaFile) -> FileMediaReference
    public let present: (ViewController, Any?) -> Void
    public let push: (ViewController) -> Void
    public let openUrl: (InstantPageUrlItem) -> Void
    public let baseNavigationController: () -> NavigationController?
    /// A reference to the message hosting this page, when rendered inside a chat bubble. Used to
    /// key audio playback per message (`.richMessage(message.id)`) AND to fetch audio files via a
    /// message reference (so a stale file reference can revalidate); `nil` in the send preview,
    /// which falls back to the webpage-keyed playlist id + webpage file reference.
    public let message: MessageReference?

    public init(
        context: AccountContext,
        webpage: TelegramMediaWebpage,
        sourceLocation: InstantPageSourceLocation,
        imageReference: @escaping (TelegramMediaImage) -> ImageMediaReference,
        fileReference: @escaping (TelegramMediaFile) -> FileMediaReference,
        present: @escaping (ViewController, Any?) -> Void,
        push: @escaping (ViewController) -> Void,
        openUrl: @escaping (InstantPageUrlItem) -> Void,
        baseNavigationController: @escaping () -> NavigationController?,
        message: MessageReference?
    ) {
        self.context = context
        self.webpage = webpage
        self.sourceLocation = sourceLocation
        self.imageReference = imageReference
        self.fileReference = fileReference
        self.present = present
        self.push = push
        self.openUrl = openUrl
        self.baseNavigationController = baseNavigationController
        self.message = message
    }

    /// Update the content-bearing fields for a later chunk of the SAME message. Enables the
    /// streaming bubble to reuse one V2View across `stableVersion` bumps instead of rebuilding.
    /// Only `webpage` changes across chunks; the `imageReference`/`fileReference` closures keep
    /// their construction-time `MessageReference` snapshot, which is acceptable because the message
    /// id is stable across chunks (media resolves by id) and streamed AI content carries no media.
    public func updateContent(webpage: TelegramMediaWebpage) {
        self.webpage = webpage
    }
}

// MARK: - Inline image view data

private struct InlineImageKey: Hashable {
    let fileId: Int64
    let occurrenceIndex: Int
}

/// Per-inline-image state owned by `InstantPageV2View`.
/// `textView` is a weak reference back to the parent so `updateImageReveal` can
/// look up the current per-text-view character count.
private final class InstantPageInlineImageData {
    let view: InstantPageV2InlineImageView
    weak var textView: InstantPageV2TextView?
    var charIndexInItem: Int = 0
    var revealed: Bool = false

    init(view: InstantPageV2InlineImageView) {
        self.view = view
    }
}

// MARK: - Emoji layer data

private final class InstantPageEmojiLayerData {
    let itemLayer: InlineStickerItemLayer
    weak var textView: InstantPageV2TextView?
    var charIndexInItem: Int = 0
    var revealed: Bool = false

    init(itemLayer: InlineStickerItemLayer) {
        self.itemLayer = itemLayer
    }
}

// MARK: - Public renderer

public final class InstantPageV2View: UIView {
    public private(set) var currentLayout: InstantPageV2Layout?
    public private(set) var currentTheme: InstantPageTheme?

    /// Invoked when a details title is tapped. Bubble routes to its expand-state mutation + requestUpdate.
    public var detailsTapped: ((_ index: Int) -> Void)?

    var itemViews: [InstantPageItemView] = []
    private var itemViewStableIds: [InstantPageV2StableItemId] = []

    public let renderContext: InstantPageV2RenderContext?

    private var inlineStickerItemLayers: [InlineStickerItemLayer.Key: InstantPageEmojiLayerData] = [:]
    private var inlineImageViews: [InlineImageKey: InstantPageInlineImageData] = [:]
    private var emojiEnableLooping: Bool = true

    /// Scroll-visibility rect in this view's coordinate space; gates emoji animation looping.
    /// `nil` means "not visible" → emoji don't animate. The root rect is set by the bubble and
    /// propagated down the nested tree (details/table) by `propagateVisibilityRect`.
    public var visibilityRect: CGRect? {
        didSet {
            if oldValue != self.visibilityRect {
                self.updateEmojiVisibility()
            }
        }
    }
    public private(set) var displayContentsUnderSpoilers: Bool = false

    // Weak references to every media wrapper in the tree, keyed by `InstantPageMedia.index`.
    // Used by `transitionArgsFor` and `applyHiddenMedia` so the gallery transition + hidden-source
    // state can find a wrapper without walking the view hierarchy. Nested V2Views (details body,
    // table cells) forward their registrations to the root via `rootMediaRegistryHost`.
    var mediaRegistry: [Int: Weak<UIView>] = [:]

    // Pointer to the root V2View's registry host. The root sets this to `self`; nested views
    // inherit it via `propagateRegistryHost(to:)` in `update(layout:theme:animation:)`.
    weak var rootMediaRegistryHost: InstantPageV2View?

    var effectiveRegistryHost: InstantPageV2View {
        return self.rootMediaRegistryHost ?? self
    }

    /// Walks the `rootMediaRegistryHost` chain transitively until it finds a self-referencing
    /// host (the true root). Necessary because nested details blocks can leave an inner body's
    /// `rootMediaRegistryHost` pointing at an intermediate body rather than the outer root —
    /// `propagateRegistryHost(to:)` only walks one hop, so the chain must be followed at lookup.
    var trueRegistryRoot: InstantPageV2View {
        var host: InstantPageV2View = self
        while let next = host.rootMediaRegistryHost, next !== host {
            host = next
        }
        return host
    }

    public init(renderContext: InstantPageV2RenderContext?) {
        self.renderContext = renderContext
        super.init(frame: .zero)
        self.backgroundColor = .clear
        self.isOpaque = false
        self.rootMediaRegistryHost = self
    }

    public convenience init() {
        self.init(renderContext: nil)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    /// Rebuilds the child view hierarchy from `layout`. The caller is responsible for
    /// sizing `self.frame` to `layout.contentSize`; this method does not touch its own frame.
    ///
    /// Reuse pass: existing item views are harvested into a `[stableId: view]` map keyed
    /// off `itemViewStableIds`. For each new item we look up its stable id; on a hit (and
    /// matching concrete view class) the existing view is reused via its typed
    /// `update(item:theme:[renderContext:])`, on a miss we fall back to `makeItemView`. Un-reused
    /// views are removed from the superview at the end. This preserves the four media wrappers
    /// (and any nested V2Views inside details/table) across chat-bubble re-applies, which would
    /// otherwise torch in-flight image fetches on every list update.
    public func update(
        layout: InstantPageV2Layout,
        theme: InstantPageTheme,
        animation: ListViewItemUpdateAnimation
    ) {
        // Build map of existing views by stable id.
        var oldViewsById: [InstantPageV2StableItemId: InstantPageItemView] = [:]
        for (oldIndex, oldId) in self.itemViewStableIds.enumerated() {
            oldViewsById[oldId] = self.itemViews[oldIndex]
        }

        var newItemViews: [InstantPageItemView] = []
        var newStableIds: [InstantPageV2StableItemId] = []
        var reusedIds: Set<InstantPageV2StableItemId> = []

        // Two independent position counters so thinking-block churn never renumbers content
        // blocks' stable ids (requirement: adding/removing a thinking block must not affect other
        // blocks). Content items are numbered ignoring thinking items; thinking items get their
        // own .thinking(index) namespace.
        var contentPosition = 0
        var thinkingPosition = 0
        for item in layout.items {
            let id: InstantPageV2StableItemId
            if case .thinking = item {
                id = InstantPageV2View.stableId(for: item, atPosition: thinkingPosition)
                thinkingPosition += 1
            } else {
                id = InstantPageV2View.stableId(for: item, atPosition: contentPosition)
                contentPosition += 1
            }

            if let existing = oldViewsById[id], let reusedView = self.reuse(existingView: existing, for: item, theme: theme, animation: animation) {
                let newFrame = InstantPageV2View.actualFrame(forItem: item)   // parent positions child
                if animation.isAnimated && reusedView.frame != newFrame {
                    // A collapsing details view keeps its body alive; remove it once this
                    // frame-shrink (the clip that hides it) finishes — see finalizePendingCollapse().
                    let detailsView = reusedView as? InstantPageV2DetailsView
                    animation.animator.updateFrame(layer: reusedView.layer, frame: newFrame, completion: { [weak detailsView] _ in
                        detailsView?.finalizePendingCollapse()
                    })
                } else {
                    reusedView.frame = newFrame
                    (reusedView as? InstantPageV2DetailsView)?.finalizePendingCollapse()
                }
                newItemViews.append(reusedView)
                newStableIds.append(id)
                reusedIds.insert(id)
                // Already in subviews from the previous update; just keep it.
            } else {
                guard let newView = self.makeItemView(for: item, theme: theme) else { continue }
                newItemViews.append(newView)
                newStableIds.append(id)
                self.addSubview(newView)
                self.propagateRegistryHost(to: newView)
            }
        }

        // Remove views that weren't reused.
        for (id, view) in oldViewsById where !reusedIds.contains(id) {
            view.removeFromSuperview()
        }

        // Z-order: bring the reused views to the front in declaration order so the
        // sublayer/subview stack matches `layout.items` order.
        for view in newItemViews {
            self.bringSubviewToFront(view)
        }

        self.itemViews = newItemViews
        self.itemViewStableIds = newStableIds
        self.currentLayout = layout
        self.currentTheme = theme
        self.updateInlineImages()
        self.updateInlineEmoji()
        let enableSpoilerAnimations = self.renderContext.map { $0.context.sharedContext.energyUsageSettings.fullTranslucency } ?? true
        for view in self.itemViews {
            if let textView = view as? InstantPageV2TextView {
                // Both fresh (makeItemView) and reused text views now build their dust through the
                // single init→update→updateSpoiler path, so we only push the external animation
                // setting here; its didSet rebuilds the dust if the value actually changed.
                textView.enableSpoilerAnimations = enableSpoilerAnimations
            }
        }
        // Force the current reveal state (true OR false) onto every text view every layout, so a
        // positionally-reused text view cannot retain a stale reveal flag from prior content.
        self.setDisplayContentsUnderSpoilers(self.displayContentsUnderSpoilers, atLocation: nil, animated: false)
    }

    func updateInlineEmoji() {
        guard let rc = self.renderContext else { return }
        let context = rc.context
        let cache = context.animationCache
        let renderer = context.animationRenderer
        self.emojiEnableLooping = context.sharedContext.energyUsageSettings.loopEmoji

        var nextIndexById: [Int64: Int] = [:]
        var validIds: [InlineStickerItemLayer.Key] = []

        for view in self.itemViews {
            // Top-level `.text` items host their emoji directly. The thinking block hosts emoji on
            // its shimmer-wrapped inner text view, which the page never sees as a top-level item —
            // so without this it is skipped and the emoji never get layers (invisible). Nested V2
            // sub-layouts (details bodies, table cells) instead run their own updateInlineEmoji.
            let textView: InstantPageV2TextView
            if let topLevelTextView = view as? InstantPageV2TextView {
                textView = topLevelTextView
            } else if let thinkingView = view as? InstantPageV2ThinkingView {
                textView = thinkingView.textView
            } else {
                continue
            }
            let textItem = textView.item.textItem
            let boundsWidth = textItem.frame.size.width
            for line in textItem.lines {
                if line.emojiItems.isEmpty { continue }
                let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
                for emojiItem in line.emojiItems {
                    let index = nextIndexById[emojiItem.emoji.fileId] ?? 0
                    nextIndexById[emojiItem.emoji.fileId] = index + 1
                    let id = InlineStickerItemLayer.Key(id: emojiItem.emoji.fileId, index: index)
                    validIds.append(id)

                    let itemSize = emojiItem.frame.width
                    let localX = lineFrame.minX + (emojiItem.frame.minX - line.frame.minX)
                    let itemFrame = CGRect(
                        x: localX + v2TextViewClippingInset,
                        y: emojiItem.frame.minY + v2TextViewClippingInset,
                        width: itemSize,
                        height: itemSize
                    )

                    var textColor: UIColor?
                    if emojiItem.range.location < textItem.attributedString.length {
                        textColor = textItem.attributedString.attribute(.foregroundColor, at: emojiItem.range.location, effectiveRange: nil) as? UIColor
                    }

                    let data: InstantPageEmojiLayerData
                    if let existing = self.inlineStickerItemLayers[id] {
                        data = existing
                        if data.itemLayer.superlayer !== textView.emojiContainerView.layer {
                            textView.emojiContainerView.layer.addSublayer(data.itemLayer)
                        }
                    } else {
                        let pointSize = floor(itemSize * 1.3)
                        let layer = InlineStickerItemLayer(
                            context: context,
                            userLocation: .other,
                            attemptSynchronousLoad: false,
                            emoji: emojiItem.emoji,
                            file: emojiItem.emoji.file,
                            cache: cache,
                            renderer: renderer,
                            placeholderColor: UIColor(white: 0.5, alpha: 0.3),
                            pointSize: CGSize(width: pointSize, height: pointSize),
                            dynamicColor: textColor
                        )
                        layer.opacity = 0.0
                        data = InstantPageEmojiLayerData(itemLayer: layer)
                        self.inlineStickerItemLayers[id] = data
                        textView.emojiContainerView.layer.addSublayer(layer)
                    }

                    data.itemLayer.dynamicColor = textColor
                    data.itemLayer.frame = itemFrame
                    data.textView = textView
                    data.charIndexInItem = emojiItem.range.location
                }
            }
        }

        var removeKeys: [InlineStickerItemLayer.Key] = []
        for (key, data) in self.inlineStickerItemLayers where !validIds.contains(key) {
            removeKeys.append(key)
            data.itemLayer.removeFromSuperlayer()
        }
        for key in removeKeys {
            self.inlineStickerItemLayers.removeValue(forKey: key)
        }

        self.updateEmojiReveal(animated: false)
    }

    func updateInlineImages() {
        guard let renderContext = self.renderContext,
              let layout = self.currentLayout,
              let theme = self.currentTheme
        else { return }
        let context = renderContext.context

        var nextIndexById: [Int64: Int] = [:]
        var validKeys: Set<InlineImageKey> = []

        for view in self.itemViews {
            // Same nesting as updateInlineEmoji: top-level `.text` items host their inline images
            // directly; the thinking block hosts them on its shimmer-wrapped inner text view, which
            // the page never sees as a top-level item. Nested V2 sub-layouts run their own pass.
            let textView: InstantPageV2TextView
            if let topLevelTextView = view as? InstantPageV2TextView {
                textView = topLevelTextView
            } else if let thinkingView = view as? InstantPageV2ThinkingView {
                textView = thinkingView.textView
            } else {
                continue
            }
            let textItem = textView.item.textItem
            let boundsWidth = textItem.frame.size.width
            for line in textItem.lines {
                if line.imageItems.isEmpty { continue }
                let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
                for imageItem in line.imageItems {
                    let index = nextIndexById[imageItem.id.id] ?? 0
                    nextIndexById[imageItem.id.id] = index + 1
                    let key = InlineImageKey(fileId: imageItem.id.id, occurrenceIndex: index)
                    guard let media = layout.media[imageItem.id] else { continue }
                    validKeys.insert(key)

                    let localX = lineFrame.minX + (imageItem.frame.minX - line.frame.minX)
                    let itemFrame = CGRect(
                        x: localX + v2TextViewClippingInset,
                        y: imageItem.frame.minY + v2TextViewClippingInset,
                        width: imageItem.frame.width,
                        height: imageItem.frame.height
                    )

                    let data: InstantPageInlineImageData
                    if let existing = self.inlineImageViews[key] {
                        data = existing
                        if data.view.superview !== textView.imageContainerView {
                            textView.imageContainerView.addSubview(data.view)
                        }
                    } else {
                        let newView = InstantPageV2InlineImageView(
                            media: media,
                            webpage: layout.webpage,
                            frame: itemFrame,
                            context: context,
                            userLocation: .other,
                            theme: theme
                        )
                        // Image starts hidden; updateImageReveal pops it in when the streaming
                        // cursor crosses its char-index. For non-streaming pages (no
                        // `TypingDraftMessageAttribute`), `revealed = true` (via the fallback in
                        // updateImageReveal) sets alpha = 1 unconditionally on the next call.
                        newView.alpha = 0.0
                        data = InstantPageInlineImageData(view: newView)
                        self.inlineImageViews[key] = data
                        textView.imageContainerView.addSubview(newView)
                    }

                    data.view.frame = itemFrame
                    data.textView = textView
                    data.charIndexInItem = imageItem.range.location
                }
            }
        }

        var removeKeys: [InlineImageKey] = []
        for (key, data) in self.inlineImageViews where !validKeys.contains(key) {
            removeKeys.append(key)
            data.view.removeFromSuperview()
        }
        for key in removeKeys {
            self.inlineImageViews.removeValue(forKey: key)
        }

        self.updateImageReveal(animated: false)
    }

    func updateEmojiReveal(animated: Bool) {
        for (_, data) in self.inlineStickerItemLayers {
            let revealed: Bool
            if let textView = data.textView, let count = textView.currentRevealCharacterCount {
                revealed = data.charIndexInItem < count
            } else {
                revealed = true
            }
            if data.revealed == revealed {
                continue
            }
            data.revealed = revealed
            if revealed {
                if animated {
                    data.itemLayer.opacity = 1.0
                    let opacityAnim = CABasicAnimation(keyPath: "opacity")
                    opacityAnim.fromValue = 0.0
                    opacityAnim.toValue = 1.0
                    opacityAnim.duration = 0.2
                    data.itemLayer.add(opacityAnim, forKey: "emojiRevealOpacity")
                    let scaleAnim = CABasicAnimation(keyPath: "transform.scale")
                    scaleAnim.fromValue = 0.1
                    scaleAnim.toValue = 1.0
                    scaleAnim.duration = 0.2
                    scaleAnim.timingFunction = CAMediaTimingFunction(name: .easeOut)
                    data.itemLayer.add(scaleAnim, forKey: "emojiRevealScale")
                } else {
                    data.itemLayer.opacity = 1.0
                }
            } else {
                data.itemLayer.opacity = 0.0
            }
        }
        self.updateEmojiVisibility()
    }

    func updateImageReveal(animated: Bool) {
        for (_, data) in self.inlineImageViews {
            let revealed: Bool
            if let textView = data.textView, let count = textView.currentRevealCharacterCount {
                revealed = data.charIndexInItem < count
            } else {
                revealed = true
            }
            if data.revealed == revealed {
                continue
            }
            data.revealed = revealed
            if revealed {
                if animated {
                    data.view.layer.opacity = 1.0
                    let opacityAnim = CABasicAnimation(keyPath: "opacity")
                    opacityAnim.fromValue = 0.0
                    opacityAnim.toValue = 1.0
                    opacityAnim.duration = 0.2
                    data.view.layer.add(opacityAnim, forKey: "inlineImageRevealOpacity")
                    let scaleAnim = CABasicAnimation(keyPath: "transform.scale")
                    scaleAnim.fromValue = 0.1
                    scaleAnim.toValue = 1.0
                    scaleAnim.duration = 0.2
                    scaleAnim.timingFunction = CAMediaTimingFunction(name: .easeOut)
                    data.view.layer.add(scaleAnim, forKey: "inlineImageRevealScale")
                } else {
                    data.view.layer.opacity = 1.0
                }
            } else {
                data.view.layer.opacity = 0.0
            }
        }
    }

    func updateEmojiVisibility() {
        for (_, data) in self.inlineStickerItemLayers {
            let onScreen: Bool
            if let visibilityRect = self.visibilityRect, let textView = data.textView {
                let rectInSelf = textView.convert(data.itemLayer.frame, to: self)
                onScreen = rectInSelf.intersects(visibilityRect)
            } else {
                // No visibility rect == not tracked / off-screen → don't animate. The root view's
                // rect is propagated down the nested tree (details bodies, table cells/title) by
                // `propagateVisibilityRect`, so a nil here genuinely means "not visible".
                onScreen = false
            }
            data.itemLayer.isVisibleForAnimations = self.emojiEnableLooping && data.revealed && onScreen
        }
        self.propagateVisibilityRect()
    }

    // Pushes this view's `visibilityRect` down into every nested V2 view (details body, table
    // title + cells), converted into each child's coordinate space. Each child's `visibilityRect`
    // didSet re-runs `updateEmojiVisibility`, which propagates one level further — so a single
    // root assignment fans out across the whole tree.
    private func propagateVisibilityRect() {
        for view in self.itemViews {
            for nested in InstantPageV2View.nestedV2Views(of: view) {
                let childRect = self.visibilityRect.map { self.convert($0, to: nested) }
                if nested.visibilityRect != childRect {
                    nested.visibilityRect = childRect
                }
            }
        }
    }

    /// Reveals (or re-hides) every spoiler in this view and nested details/table V2 views.
    /// `location` (this view's coords) drives the dust explosion origin for whichever text view
    /// contains it; the rest just toggle. Single-flag behavior mirrors ChatMessageTextBubbleContentNode.
    public func setDisplayContentsUnderSpoilers(_ value: Bool, atLocation location: CGPoint?, animated: Bool) {
        self.displayContentsUnderSpoilers = value
        for view in self.itemViews {
            if let textView = view as? InstantPageV2TextView {
                let childLocation = location.map { self.convert($0, to: textView) }
                textView.setDisplayContentsUnderSpoilers(value, atLocation: childLocation, animated: animated)
            }
            for nested in InstantPageV2View.nestedV2Views(of: view) {
                let childLocation = location.map { self.convert($0, to: nested) }
                nested.setDisplayContentsUnderSpoilers(value, atLocation: childLocation, animated: animated)
            }
        }
    }

    private static func nestedV2Views(of view: InstantPageItemView) -> [InstantPageV2View] {
        if let detailsView = view as? InstantPageV2DetailsView {
            return detailsView.bodyView.map { [$0] } ?? []
        } else if let tableView = view as? InstantPageV2TableView {
            var result: [InstantPageV2View] = []
            if let titleSubView = tableView.titleSubView {
                result.append(titleSubView)
            }
            result.append(contentsOf: tableView.cellSubViews)
            return result
        }
        return []
    }

    /// Returns the input view typed-updated against `item`, or `nil` if the existing view's
    /// concrete class doesn't match the item's case (e.g. a `text` slot has been replaced by
    /// a `divider` in the new layout). Caller falls back to `makeItemView`.
    private func reuse(existingView: InstantPageItemView, for item: InstantPageV2LaidOutItem, theme: InstantPageTheme, animation: ListViewItemUpdateAnimation) -> InstantPageItemView? {
        switch item {
        case let .text(text):
            guard let v = existingView as? InstantPageV2TextView else { return nil }
            v.update(item: text, theme: theme)
            return v
        case let .codeBlock(block):
            guard let v = existingView as? InstantPageV2CodeBlockView else { return nil }
            v.update(item: block, theme: theme)
            return v
        case let .divider(divider):
            guard let v = existingView as? InstantPageV2DividerView else { return nil }
            v.update(item: divider, theme: theme)
            return v
        case let .listMarker(marker):
            guard let v = existingView as? InstantPageV2ListMarkerView else { return nil }
            v.update(item: marker, theme: theme)
            return v
        case let .blockQuoteBar(bar):
            guard let v = existingView as? InstantPageV2BlockQuoteBarView else { return nil }
            v.update(item: bar, theme: theme)
            return v
        case let .shape(shape):
            guard let v = existingView as? InstantPageV2ShapeView else { return nil }
            v.update(item: shape, theme: theme)
            return v
        case let .mediaPlaceholder(media):
            guard let v = existingView as? InstantPageV2MediaPlaceholderView else { return nil }
            v.update(item: media, theme: theme)
            return v
        case let .details(details):
            guard let v = existingView as? InstantPageV2DetailsView else { return nil }
            v.update(item: details, theme: theme, renderContext: self.renderContext, animation: animation)
            return v
        case let .table(table):
            guard let v = existingView as? InstantPageV2TableView else { return nil }
            v.update(item: table, theme: theme)
            return v
        case let .anchor(anchor):
            guard let v = existingView as? InstantPageV2AnchorView else { return nil }
            v.update(item: anchor, theme: theme)
            return v
        case let .formula(formula):
            guard let v = existingView as? InstantPageV2FormulaView else { return nil }
            v.update(item: formula, theme: theme)
            return v
        case let .mediaImage(media):
            guard let v = existingView as? InstantPageV2MediaImageView, let rc = self.renderContext else { return nil }
            v.update(item: media, theme: theme, renderContext: rc)
            return v
        case let .mediaVideo(media):
            guard let v = existingView as? InstantPageV2MediaVideoView, let rc = self.renderContext else { return nil }
            v.update(item: media, theme: theme, renderContext: rc)
            return v
        case let .mediaMap(media):
            guard let v = existingView as? InstantPageV2MediaMapView, let rc = self.renderContext else { return nil }
            v.update(item: media, theme: theme, renderContext: rc)
            return v
        case let .mediaCoverImage(media):
            guard let v = existingView as? InstantPageV2MediaCoverImageView, let rc = self.renderContext else { return nil }
            v.update(item: media, theme: theme, renderContext: rc)
            return v
        case let .mediaAudio(media):
            guard let v = existingView as? InstantPageV2MediaAudioView, let rc = self.renderContext else { return nil }
            v.update(item: media, theme: theme, renderContext: rc)
            return v
        case let .thinking(thinking):
            guard let v = existingView as? InstantPageV2ThinkingView else { return nil }
            v.update(item: thinking, theme: theme)
            return v
        case let .slideshow(slideshow):
            guard let v = existingView as? InstantPageV2SlideshowView, let rc = self.renderContext else { return nil }
            v.update(item: slideshow, theme: theme, renderContext: rc)
            return v
        }
    }

    static func stableId(for item: InstantPageV2LaidOutItem, atPosition position: Int) -> InstantPageV2StableItemId {
        switch item {
        case let .mediaImage(m):       return .media(m.media.index)
        case let .mediaVideo(m):       return .media(m.media.index)
        case let .mediaMap(m):         return .media(m.media.index)
        case let .mediaCoverImage(m):  return .media(m.media.index)
        case let .mediaAudio(m):       return .media(m.media.index)
        case let .details(d):          return .details(d.index)
        case .text:                    return .positional(.text, position)
        case .codeBlock:               return .positional(.codeBlock, position)
        case .divider:                 return .positional(.divider, position)
        case .listMarker:              return .positional(.listMarker, position)
        case .blockQuoteBar:           return .positional(.blockQuoteBar, position)
        case .shape:                   return .positional(.shape, position)
        case .mediaPlaceholder:        return .positional(.mediaPlaceholder, position)
        case .table:                   return .positional(.table, position)
        case .anchor:                  return .positional(.anchor, position)
        case .formula:                 return .positional(.formula, position)
        case .thinking:                return .thinking(position)
        case .slideshow:               return .positional(.slideshow, position)
        }
    }

    private func propagateRegistryHost(to view: InstantPageItemView) {
        let host = self.effectiveRegistryHost
        if let details = view as? InstantPageV2DetailsView {
            details.forEachSubLayoutView { sub in
                sub.rootMediaRegistryHost = host
            }
        }
        if let table = view as? InstantPageV2TableView {
            table.forEachSubLayoutView { sub in
                sub.rootMediaRegistryHost = host
            }
        }
    }

    /// Looks up the wrapper view registered under `media.index` and returns gallery transition
    /// arguments backed by its wrapped `InstantPageImageNode`. Returns `nil` if the wrapper is
    /// not currently registered (e.g. the media is inside a collapsed details block).
    func transitionArgsFor(_ media: InstantPageMedia, addToTransitionSurface: @escaping (UIView) -> Void) -> GalleryTransitionArguments? {
        guard let wrapperBox = self.trueRegistryRoot.mediaRegistry[media.index], let wrapper = wrapperBox.value else {
            return nil
        }
        guard let itemView = wrapper as? InstantPageItemView else { return nil }
        guard let transitionNode = itemView.instantPageTransitionNode(for: media) else { return nil }
        return GalleryTransitionArguments(transitionNode: transitionNode, addToTransitionSurface: addToTransitionSurface)
    }

    /// Forwards a hidden-media tick from the gallery's `hiddenMedia` signal to every registered
    /// wrapper, calling `updateHiddenMedia(media:)` on each wrapped image node.
    func applyHiddenMedia(_ hidden: InstantPageMedia?) {
        for (_, weakBox) in self.trueRegistryRoot.mediaRegistry {
            guard let wrapper = weakBox.value else { continue }
            (wrapper as? InstantPageItemView)?.instantPageUpdateHiddenMedia(hidden)
        }
    }

    private func makeItemView(for item: InstantPageV2LaidOutItem, theme: InstantPageTheme) -> InstantPageItemView? {
        switch item {
        case let .text(text):
            return InstantPageV2TextView(item: text, theme: theme)
        case let .divider(divider):
            return InstantPageV2DividerView(item: divider, theme: theme)
        case let .anchor(anchor):
            return InstantPageV2AnchorView(item: anchor, theme: theme)
        case let .listMarker(marker):
            return InstantPageV2ListMarkerView(item: marker, theme: theme)
        case let .codeBlock(block):
            return InstantPageV2CodeBlockView(item: block, theme: theme)
        case let .blockQuoteBar(bar):
            return InstantPageV2BlockQuoteBarView(item: bar, theme: theme)
        case let .shape(shape):
            return InstantPageV2ShapeView(item: shape, theme: theme)
        case let .mediaPlaceholder(media):
            return InstantPageV2MediaPlaceholderView(item: media, theme: theme)
        case let .details(details):
            let view = InstantPageV2DetailsView(item: details, theme: theme, renderContext: self.renderContext)
            view.onTitleTapped = { [weak self] index in
                self?.detailsTapped?(index)
            }
            return view
        case let .table(table):
            return InstantPageV2TableView(item: table, theme: theme, renderContext: self.renderContext)
        case let .mediaImage(media):
            if let renderContext = self.renderContext {
                return InstantPageV2MediaImageView(item: media, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: placeholderFallback(for: media), theme: theme)
            }
        case let .mediaVideo(media):
            if let renderContext = self.renderContext {
                return InstantPageV2MediaVideoView(item: media, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: placeholderFallback(for: media), theme: theme)
            }
        case let .mediaMap(media):
            if let renderContext = self.renderContext {
                return InstantPageV2MediaMapView(item: media, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: placeholderFallback(for: media), theme: theme)
            }
        case let .mediaCoverImage(media):
            if let renderContext = self.renderContext {
                return InstantPageV2MediaCoverImageView(item: media, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: placeholderFallback(for: media), theme: theme)
            }
        case let .mediaAudio(media):
            if let renderContext = self.renderContext {
                return InstantPageV2MediaAudioView(item: media, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: InstantPageV2MediaPlaceholderItem(frame: media.frame, kind: .audio, cornerRadius: 0.0), theme: theme)
            }
        case let .formula(formula):
            return InstantPageV2FormulaView(item: formula, theme: theme)
        case let .thinking(thinking):
            return InstantPageV2ThinkingView(item: thinking, theme: theme)
        case let .slideshow(slideshow):
            if let renderContext = self.renderContext {
                return InstantPageV2SlideshowView(item: slideshow, renderContext: renderContext, theme: theme)
            } else {
                return InstantPageV2MediaPlaceholderView(item: InstantPageV2MediaPlaceholderItem(frame: slideshow.frame, kind: .slideshow, cornerRadius: 0.0), theme: theme)
            }
        }
    }

    /// Returns the frame the parent should assign to the view for `item`.
    ///
    /// For most item types this is `item.frame`. `InstantPageV2TextView` widens its backing store
    /// by `v2TextViewClippingInset` on every side to accommodate glyph overhang and underline
    /// rendering past the text's logical `maxY` — the same inset its `init` applies when
    /// constructing the view. The reuse path must apply the same expansion so that re-layout
    /// (theme change, bubble resize, etc.) does not clip italic glyphs or underlines.
    ///
    /// Keep this helper aligned with each view class's init-time frame computation.
    private static func actualFrame(forItem item: InstantPageV2LaidOutItem) -> CGRect {
        switch item {
        case let .text(textItem):
            return textItem.frame.insetBy(dx: -v2TextViewClippingInset, dy: -v2TextViewClippingInset)
        default:
            return item.frame
        }
    }
}

// MARK: - Placeholder fallbacks for the four typed media items
//
// Used by `makeItemView` when `renderContext == nil` (the zero-arg V2View constructor):
// we still need to emit a sized grey rectangle for image/video/map/coverImage so the
// surrounding layout doesn't collapse. Each helper synthesizes a placeholder item with
// the same frame + cornerRadius as the typed item, picking the kind that matches the
// closest existing placeholder visual.

private func placeholderFallback(for item: InstantPageV2MediaImageItem) -> InstantPageV2MediaPlaceholderItem {
    return InstantPageV2MediaPlaceholderItem(frame: item.frame, kind: .image, cornerRadius: item.cornerRadius)
}

private func placeholderFallback(for item: InstantPageV2MediaVideoItem) -> InstantPageV2MediaPlaceholderItem {
    return InstantPageV2MediaPlaceholderItem(frame: item.frame, kind: .video, cornerRadius: item.cornerRadius)
}

private func placeholderFallback(for item: InstantPageV2MediaMapItem) -> InstantPageV2MediaPlaceholderItem {
    return InstantPageV2MediaPlaceholderItem(frame: item.frame, kind: .map, cornerRadius: item.cornerRadius)
}

private func placeholderFallback(for item: InstantPageV2MediaCoverImageItem) -> InstantPageV2MediaPlaceholderItem {
    return InstantPageV2MediaPlaceholderItem(frame: item.frame, kind: .webEmbed, cornerRadius: item.cornerRadius)
}

// MARK: - Item view protocol

protocol InstantPageItemView: UIView {
    /// Frame in the parent V2 view's coordinate space (== `item.frame`).
    var itemFrame: CGRect { get }
    /// Recursion hook for nested layouts (details body, table cells, table title).
    var subLayoutView: InstantPageV2View? { get }
    /// Gallery open: the transition source for `media` if this view (or a descendant) shows it.
    /// Default nil (non-media views). Media views forward to their wrapped `InstantPageImageNode`;
    /// the slideshow forwards to its matching page.
    func instantPageTransitionNode(for media: InstantPageMedia) -> (ASDisplayNode, CGRect, () -> (UIView?, UIView?))?
    /// Gallery hidden-media tick: hide/show the source for `media`. Default no-op.
    func instantPageUpdateHiddenMedia(_ media: InstantPageMedia?)
}

extension InstantPageItemView {
    var subLayoutView: InstantPageV2View? { return nil }
    func instantPageTransitionNode(for media: InstantPageMedia) -> (ASDisplayNode, CGRect, () -> (UIView?, UIView?))? { return nil }
    func instantPageUpdateHiddenMedia(_ media: InstantPageMedia?) { }
}

// MARK: - Text view (port of V1 InstantPageTextItem.drawInTile)

/// Per-side padding applied to `InstantPageV2TextView`'s backing store, beyond the
/// item's typographic frame. Marker rounded rects extend ±2pt past their run, italic
/// or accented glyphs can overhang past the line's advance width, and the last line's
/// underline sits 2pt below `lineFrame.maxY`. The view grows by this amount on each
/// side and the draw context translates by the same amount so visual position is
/// unchanged.
private let v2TextViewClippingInset: CGFloat = 4.0

final class InstantPageV2TextView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2TextItem
    var itemFrame: CGRect { return self.item.frame }

    private let renderContainer: UIView
    private let renderView: TextRenderView
    /// Sibling of `renderContainer`, holds inline `InstantPageV2InlineImageView`s
    /// owned by the parent `InstantPageV2View`. Sits BELOW `emojiContainerView`
    /// (so a colocated emoji renders above an image) and ABOVE `renderContainer`
    /// (so the reveal mask wipes text without clipping images).
    let imageContainerView: UIView = UIView()
    let emojiContainerView: UIView = UIView()
    let spoilerContainerView: UIView = UIView()
    private var dustNode: InvisibleInkDustNode?
    private var displayContentsUnderSpoilers: Bool = false
    var enableSpoilerAnimations: Bool = true {
        didSet {
            if oldValue != self.enableSpoilerAnimations, let dustNode = self.dustNode {
                self.dustNode = nil
                dustNode.view.removeFromSuperview()
                self.updateSpoiler(animated: false)
            }
        }
    }

    // Reveal mask state — populated in Task 5.
    private var maxCharacterDrawCount: Int?
    private var previousMaxCharacterDrawCount: Int = 0
    private var revealMaskLayer: SimpleLayer?
    private var revealLineMaskLayers: [SimpleLayer] = []
    private var animatingSnippetLayers: [SnippetLayer] = []

    init(item: InstantPageV2TextItem, theme: InstantPageTheme) {
        self.item = item
        self.renderContainer = UIView()
        self.renderView = TextRenderView(item: item)
        super.init(frame: item.frame.insetBy(dx: -v2TextViewClippingInset, dy: -v2TextViewClippingInset))
        // Structural wiring only (one-time); all frames/content live in update(item:theme:).
        self.backgroundColor = .clear
        self.isOpaque = false
        self.renderContainer.backgroundColor = .clear
        self.renderContainer.isOpaque = false
        self.addSubview(self.renderContainer)
        self.renderContainer.addSubview(self.renderView)
        self.imageContainerView.isUserInteractionEnabled = false
        self.addSubview(self.imageContainerView)
        self.emojiContainerView.isUserInteractionEnabled = false
        self.addSubview(self.emojiContainerView)
        self.spoilerContainerView.isUserInteractionEnabled = false
        self.addSubview(self.spoilerContainerView)
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func update(item: InstantPageV2TextItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
        // Lay every container out from the item's own (clipping-inset-expanded) frame rather than
        // self.bounds, so the single path is correct regardless of when the parent assigns our
        // frame — and so a reused text view that changed size (e.g. AI streaming) re-frames its
        // renderContainer/renderView too, which the old update path skipped.
        let containerBounds = CGRect(origin: .zero, size: item.frame.insetBy(dx: -v2TextViewClippingInset, dy: -v2TextViewClippingInset).size)
        self.renderContainer.frame = containerBounds
        self.renderView.frame = containerBounds
        self.renderView.item = item
        self.renderView.setNeedsDisplay()
        self.imageContainerView.frame = containerBounds
        self.emojiContainerView.frame = containerBounds
        self.spoilerContainerView.frame = containerBounds
        self.renderView.displayContentsUnderSpoilers = self.displayContentsUnderSpoilers
        self.updateSpoiler(animated: false)
    }

    private func spoilerRectsInContainer() -> [CGRect] {
        let textItem = self.item.textItem
        let boundsWidth = textItem.frame.size.width
        var rects: [CGRect] = []
        for line in textItem.lines {
            if line.spoilerItems.isEmpty { continue }
            let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
            for spoiler in line.spoilerItems {
                let localX = lineFrame.minX + (spoiler.frame.minX - line.frame.minX)
                rects.append(CGRect(x: localX + v2TextViewClippingInset, y: spoiler.frame.minY + v2TextViewClippingInset, width: spoiler.frame.width, height: spoiler.frame.height))
            }
        }
        return rects
    }

    func updateSpoiler(animated: Bool) {
        let rects = self.spoilerRectsInContainer()
        if rects.isEmpty || self.displayContentsUnderSpoilers {
            if let dustNode = self.dustNode {
                self.dustNode = nil
                dustNode.view.removeFromSuperview()
            }
            return
        }

        let dustNode: InvisibleInkDustNode
        if let current = self.dustNode {
            dustNode = current
        } else {
            dustNode = InvisibleInkDustNode(textNode: nil, enableAnimations: self.enableSpoilerAnimations)
            self.dustNode = dustNode
            self.spoilerContainerView.addSubview(dustNode.view)
        }

        var color: UIColor = UIColor(white: 0.0, alpha: 1.0)
        let textItem = self.item.textItem
        if let firstRange = textItem.lines.first(where: { !$0.spoilerItems.isEmpty })?.spoilerItems.first?.range, firstRange.location < textItem.attributedString.length {
            if let fg = textItem.attributedString.attribute(.foregroundColor, at: firstRange.location, effectiveRange: nil) as? UIColor {
                color = fg
            }
        }

        dustNode.view.frame = self.spoilerContainerView.bounds
        dustNode.update(size: self.spoilerContainerView.bounds.size, color: color, textColor: color, rects: rects, wordRects: rects)
    }

    func setDisplayContentsUnderSpoilers(_ value: Bool, atLocation location: CGPoint?, animated: Bool) {
        if self.displayContentsUnderSpoilers == value {
            return
        }
        self.displayContentsUnderSpoilers = value
        self.renderView.displayContentsUnderSpoilers = value
        self.renderView.setNeedsDisplay()
        if value {
            if let dustNode = self.dustNode {
                if let location, animated {
                    dustNode.revealAtLocation(self.convert(location, to: self.spoilerContainerView))
                } else {
                    dustNode.update(revealed: true, animated: animated)
                }
            }
        } else {
            self.updateSpoiler(animated: animated)
        }
    }

    func updateRevealCharacterCount(value: Int?, animated: Bool) {
        if self.maxCharacterDrawCount == value {
            return
        }
        self.maxCharacterDrawCount = value
        self.updateRevealMask(animateNewSegments: animated)
    }

    var currentRevealCharacterCount: Int? {
        return self.maxCharacterDrawCount
    }

    private struct RevealLineInfo {
        let lineFrame: CGRect
        let lineHeight: CGFloat
        let revealedWidth: CGFloat
        let isFull: Bool
        let isRTL: Bool
    }

    private func computeRevealedLines(characterLimit: Int) -> [RevealLineInfo] {
        var result: [RevealLineInfo] = []
        var remainingCharacters = characterLimit

        let textItem = self.item.textItem
        let boundsWidth = textItem.frame.size.width

        for line in textItem.lines {
            let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
            // Translate from textItem-local to renderView-local coords (renderView's draw(_) translates by the inset).
            let renderLocalLineFrame = lineFrame.offsetBy(dx: v2TextViewClippingInset, dy: v2TextViewClippingInset)
            let lineHeight = lineFrame.size.height

            guard let characterRects = line.characterRects else {
                let revealedWidth: CGFloat = remainingCharacters > 0 ? renderLocalLineFrame.width : 0.0
                result.append(RevealLineInfo(lineFrame: renderLocalLineFrame, lineHeight: lineHeight, revealedWidth: revealedWidth, isFull: remainingCharacters > 0, isRTL: line.isRTL))
                if remainingCharacters > 0 {
                    remainingCharacters -= line.range.length
                }
                continue
            }

            if remainingCharacters <= 0 {
                result.append(RevealLineInfo(lineFrame: renderLocalLineFrame, lineHeight: lineHeight, revealedWidth: 0.0, isFull: false, isRTL: line.isRTL))
                continue
            }

            let revealCount = min(characterRects.count, remainingCharacters)
            var revealedWidth: CGFloat = 0.0
            if line.isRTL {
                var minX: CGFloat = .greatestFiniteMagnitude
                for j in 0 ..< revealCount {
                    let rect = characterRects[j]
                    if !rect.isEmpty {
                        minX = min(minX, rect.minX)
                    }
                }
                if minX != .greatestFiniteMagnitude {
                    revealedWidth = ceil(renderLocalLineFrame.width - minX)
                }
            } else {
                for j in 0 ..< revealCount {
                    let rect = characterRects[j]
                    if !rect.isEmpty {
                        revealedWidth = max(revealedWidth, rect.maxX)
                    }
                }
                revealedWidth = ceil(revealedWidth)
            }

            remainingCharacters -= characterRects.count
            let isFull = remainingCharacters >= 0

            result.append(RevealLineInfo(lineFrame: renderLocalLineFrame, lineHeight: lineHeight, revealedWidth: revealedWidth, isFull: isFull, isRTL: line.isRTL))
        }

        return result
    }

    private func updateRevealMask(animateNewSegments: Bool) {
        let textItem = self.item.textItem
        let lines = textItem.lines
        let boundsWidth = textItem.frame.size.width
        let layerSize = self.renderContainer.bounds.size

        let effectiveCharacterDrawCount: Int
        if let maxCharacterDrawCount = self.maxCharacterDrawCount {
            effectiveCharacterDrawCount = maxCharacterDrawCount
        } else {
            if self.previousMaxCharacterDrawCount > 0 || !self.animatingSnippetLayers.isEmpty {
                var totalCharCount = 0
                for line in lines {
                    if let characterRects = line.characterRects {
                        totalCharCount += characterRects.count
                    } else {
                        totalCharCount += line.range.length
                    }
                }
                effectiveCharacterDrawCount = totalCharCount
            } else {
                if let _ = self.revealMaskLayer {
                    self.renderContainer.layer.mask = nil
                    self.revealMaskLayer = nil
                    self.revealLineMaskLayers.removeAll()
                }
                self.previousMaxCharacterDrawCount = 0
                return
            }
        }

        let revealMaskLayer: SimpleLayer
        if let existing = self.revealMaskLayer {
            revealMaskLayer = existing
        } else {
            revealMaskLayer = SimpleLayer()
            revealMaskLayer.backgroundColor = UIColor.clear.cgColor
            self.revealMaskLayer = revealMaskLayer
            self.renderContainer.layer.mask = revealMaskLayer
        }
        revealMaskLayer.frame = CGRect(origin: .zero, size: layerSize)

        let currentLineInfos = self.computeRevealedLines(characterLimit: effectiveCharacterDrawCount)

        // Snippet spawn pass — animate newly-revealed characters.
        if self.previousMaxCharacterDrawCount < effectiveCharacterDrawCount,
           let contents = self.renderView.layer.contents,
           animateNewSegments {
            let containerOrigin = self.renderContainer.frame.origin
            var previousRemaining = self.previousMaxCharacterDrawCount
            var currentRemaining = effectiveCharacterDrawCount
            var globalCharIndex = 0

            for i in 0 ..< lines.count {
                let line = lines[i]
                let lineInfo = currentLineInfos[i]
                guard let characterRects = line.characterRects else { continue }

                let lineCharCount = characterRects.count
                let prevCount = min(max(0, previousRemaining), lineCharCount)
                let curCount = min(max(0, currentRemaining), lineCharCount)

                previousRemaining -= lineCharCount
                currentRemaining -= lineCharCount

                if curCount <= prevCount {
                    globalCharIndex += lineCharCount
                    continue
                }

                for j in prevCount ..< curCount {
                    let charRect = characterRects[j]
                    if charRect.isEmpty { continue }

                    let snippetRect = CGRect(
                        x: lineInfo.lineFrame.minX + charRect.origin.x,
                        y: lineInfo.lineFrame.minY,
                        width: charRect.width,
                        height: lineInfo.lineHeight
                    )

                    if snippetRect.width < 0.5 { continue }

                    let contentsRect = CGRect(
                        x: snippetRect.minX / layerSize.width,
                        y: snippetRect.minY / layerSize.height,
                        width: snippetRect.width / layerSize.width,
                        height: snippetRect.height / layerSize.height
                    )

                    let snippetLayer = SnippetLayer(characterIndex: globalCharIndex + j)
                    snippetLayer.contents = contents
                    snippetLayer.contentsRect = contentsRect
                    snippetLayer.contentsScale = self.renderView.layer.contentsScale
                    snippetLayer.contentsGravity = self.renderView.layer.contentsGravity
                    snippetLayer.frame = snippetRect.offsetBy(dx: containerOrigin.x, dy: containerOrigin.y)

                    self.layer.addSublayer(snippetLayer)
                    self.animatingSnippetLayers.append(snippetLayer)

                    ComponentTransition(animation: .curve(duration: 0.22, curve: .easeInOut)).animateBlur(layer: snippetLayer, fromRadius: 2.0, toRadius: 0.0)
                    snippetLayer.animateAlpha(from: 0.0, to: 1.0, duration: 0.2)
                    snippetLayer.animatePosition(from: CGPoint(x: 0.0, y: 6.0), to: .zero, duration: 0.2, additive: true)
                    snippetLayer.animateScale(from: 0.5, to: 1.0, duration: 0.2, completion: { [weak self, weak snippetLayer] _ in
                        guard let self, let snippetLayer else { return }
                        snippetLayer.removeFromSuperlayer()
                        self.animatingSnippetLayers.removeAll(where: { $0 === snippetLayer })
                        self.updateRevealMask(animateNewSegments: false)
                    })
                }
                globalCharIndex += lineCharCount
            }
        }

        // Mask rebuild — when snippets are in flight, clamp to the lowest animating one
        // (so the mask never exposes a char a snippet is still flying for). With no animations
        // in flight, snap directly to the current target — `previousMaxCharacterDrawCount`
        // would lag by one call (it's updated at the end of this function) and is 0 on a fresh
        // view, which would hide every char until the next tick.
        let maskCharacterLimit: Int
        if let lowestAnimating = self.animatingSnippetLayers.min(by: { $0.characterIndex < $1.characterIndex })?.characterIndex {
            maskCharacterLimit = lowestAnimating
        } else {
            maskCharacterLimit = effectiveCharacterDrawCount
        }
        // Build mask rects from each revealed glyph's ink bbox, unioned per line.
        // Per-character rects are stored in line-local CT coords (y positive-up,
        // baseline-relative; rect.minY is negative for descenders); convert to
        // renderContainer-local UIKit coords as:
        //   x = renderLocalLineFrame.minX + rect.minX
        //   y = renderLocalLineFrame.minY + lineAscent - rect.maxY
        // where `lineAscent = lineFrame.size.height` (top of line frame → baseline).
        //
        // Per-glyph rect captures descenders, italic overhang, accents exactly. Per
        // line we accumulate the union of revealed glyphs into one mask rect (one
        // CALayer sublayer per line), and consecutive fully-revealed lines collapse
        // further into a single rect — so a fully-revealed prefix is always one
        // sublayer regardless of line count.
        //
        // Lines without per-character data (computeRevealCharacterRects == false on
        // a non-streaming layout) fall back to a line-spanning rect, treated as a
        // full line for merging.
        var maskRects: [CGRect] = []
        var pendingFullPrefix: CGRect? = nil
        var remainingChars = maskCharacterLimit

        for line in lines {
            if remainingChars <= 0 {
                break
            }

            let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
            let renderLocalLineFrame = lineFrame.offsetBy(dx: v2TextViewClippingInset, dy: v2TextViewClippingInset)
            let lineAscent = lineFrame.size.height

            let lineUnion: CGRect?
            let isFullLine: Bool
            if let characterRects = line.characterRects {
                let revealCount = min(characterRects.count, remainingChars)
                isFullLine = revealCount >= characterRects.count
                var union: CGRect? = nil
                for j in 0 ..< revealCount {
                    let rect = characterRects[j]
                    if rect.isEmpty {
                        continue
                    }
                    let glyphRect = CGRect(
                        x: renderLocalLineFrame.minX + rect.minX,
                        y: renderLocalLineFrame.minY + lineAscent - rect.maxY,
                        width: rect.width,
                        height: rect.height
                    )
                    union = union?.union(glyphRect) ?? glyphRect
                }
                lineUnion = union
                remainingChars -= characterRects.count
            } else {
                // No per-character data — expose the whole line.
                lineUnion = line.range.length > 0 ? renderLocalLineFrame : nil
                isFullLine = remainingChars >= line.range.length
                remainingChars -= line.range.length
            }

            guard let lineUnion else {
                continue
            }

            if isFullLine {
                pendingFullPrefix = pendingFullPrefix?.union(lineUnion) ?? lineUnion
            } else {
                if let pending = pendingFullPrefix {
                    maskRects.append(pending)
                    pendingFullPrefix = nil
                }
                maskRects.append(lineUnion)
            }
        }
        if let pending = pendingFullPrefix {
            maskRects.append(pending)
        }

        while self.revealLineMaskLayers.count < maskRects.count {
            let childLayer = SimpleLayer()
            childLayer.backgroundColor = UIColor.white.cgColor
            revealMaskLayer.addSublayer(childLayer)
            self.revealLineMaskLayers.append(childLayer)
        }
        while self.revealLineMaskLayers.count > maskRects.count {
            let removed = self.revealLineMaskLayers.removeLast()
            removed.removeFromSuperlayer()
        }
        for i in 0 ..< maskRects.count {
            self.revealLineMaskLayers[i].frame = maskRects[i]
        }

        self.previousMaxCharacterDrawCount = effectiveCharacterDrawCount

        if self.maxCharacterDrawCount == nil && self.animatingSnippetLayers.isEmpty {
            self.renderContainer.layer.mask = nil
            self.revealMaskLayer = nil
            self.revealLineMaskLayers.removeAll()
        }
    }
}

private final class TextRenderView: UIView {
    var item: InstantPageV2TextItem
    var displayContentsUnderSpoilers: Bool = false

    init(item: InstantPageV2TextItem) {
        self.item = item
        super.init(frame: .zero)
        self.backgroundColor = .clear
        self.isOpaque = false
        self.contentMode = .redraw
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else { return }

        context.saveGState()
        context.textMatrix = CGAffineTransform(scaleX: 1.0, y: -1.0)
        context.translateBy(x: v2TextViewClippingInset, y: v2TextViewClippingInset)

        if !self.displayContentsUnderSpoilers {
            let textItemForClip = self.item.textItem
            let clipBoundsWidth = textItemForClip.frame.size.width
            var spoilerRects: [CGRect] = []
            for line in textItemForClip.lines {
                if line.spoilerItems.isEmpty { continue }
                let lineFrame = v2FrameForLine(line, boundingWidth: clipBoundsWidth, alignment: textItemForClip.alignment)
                for spoiler in line.spoilerItems {
                    spoilerRects.append(spoiler.frame.offsetBy(dx: lineFrame.minX - line.frame.minX, dy: 0.0))
                }
            }
            if !spoilerRects.isEmpty {
                // Even-odd subtracts each spoiler rect from the full-bounds rect. Spoiler rects never
                // overlap (same-line ranges are horizontally monotonic; cross-line rects differ in y),
                // so no hole is accidentally re-included by an odd crossing count.
                let path = CGMutablePath()
                path.addRect(CGRect(origin: .zero, size: textItemForClip.frame.size).insetBy(dx: -v2TextViewClippingInset, dy: -v2TextViewClippingInset))
                for rect in spoilerRects {
                    path.addRect(rect)
                }
                context.addPath(path)
                context.clip(using: .evenOdd)
            }
        }

        let textItem = self.item.textItem
        let boundsWidth = textItem.frame.size.width
        let intersectRect = rect.offsetBy(dx: -v2TextViewClippingInset, dy: -v2TextViewClippingInset)

        for line in textItem.lines {
            let lineFrame = v2FrameForLine(line, boundingWidth: boundsWidth, alignment: textItem.alignment)
            if !intersectRect.intersects(lineFrame) {
                continue
            }

            let lineOrigin = lineFrame.origin
            context.textPosition = CGPoint(x: lineOrigin.x, y: lineOrigin.y + lineFrame.size.height)

            if !line.markedItems.isEmpty {
                context.saveGState()
                for item in line.markedItems {
                    let itemFrame = item.frame.offsetBy(dx: lineFrame.minX, dy: 0.0)
                    context.setFillColor(item.color.cgColor)

                    let height = floor(item.frame.size.height * 2.2)
                    let markRect = CGRect(x: itemFrame.minX - 2.0, y: floor(itemFrame.minY + (itemFrame.height - height) / 2.0), width: itemFrame.width + 4.0, height: height)
                    let path = UIBezierPath(roundedRect: markRect, cornerRadius: 3.0)
                    context.addPath(path.cgPath)
                    context.fillPath()
                }
                context.restoreGState()
            }

            if textItem.opaqueBackground {
                context.setBlendMode(.normal)
            }

            let glyphRuns = CTLineGetGlyphRuns(line.line) as NSArray
            if glyphRuns.count != 0 {
                for run in glyphRuns {
                    let run = run as! CTRun
                    let glyphCount = CTRunGetGlyphCount(run)
                    CTRunDraw(run, context, CFRangeMake(0, glyphCount))
                }
            }

            if textItem.opaqueBackground {
                context.setBlendMode(.copy)
            }

            if !line.strikethroughItems.isEmpty {
                for item in line.strikethroughItems {
                    let itemFrame = item.frame.offsetBy(dx: lineFrame.minX, dy: 0.0)
                    context.fill(CGRect(x: itemFrame.minX, y: itemFrame.minY + floor((itemFrame.size.height / 2.0) + 1.0), width: itemFrame.size.width, height: 1.0))
                }
            }

            if !line.underlineItems.isEmpty {
                for item in line.underlineItems {
                    var color: UIColor? = item.color
                    if color == nil {
                        textItem.attributedString.enumerateAttributes(in: item.range, options: []) { attributes, _, _ in
                            if let foreground = attributes[NSAttributedString.Key.foregroundColor] as? UIColor {
                                color = foreground
                            }
                        }
                    }
                    if let color {
                        context.setFillColor(color.cgColor)
                    }
                    let itemFrame = item.frame.offsetBy(dx: lineFrame.minX, dy: 0.0)
                    context.fill(CGRect(x: itemFrame.minX, y: itemFrame.minY + itemFrame.size.height + 2.0, width: itemFrame.size.width, height: 1.0))
                }
            }
        }

        context.restoreGState()
    }
}

/// Private snippet layer for the streaming reveal pop-in animation.
/// Each instance represents one character cropped from the renderView's backing texture,
/// animating in (blur + alpha + position + scale) before the mask absorbs its rect.
private final class SnippetLayer: SimpleLayer {
    let characterIndex: Int

    init(characterIndex: Int) {
        self.characterIndex = characterIndex
        super.init()
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override init(layer: Any) {
        if let other = layer as? SnippetLayer {
            self.characterIndex = other.characterIndex
        } else {
            self.characterIndex = 0
        }
        super.init(layer: layer)
    }
}

// MARK: - Divider view

final class InstantPageV2DividerView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2DividerItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2DividerItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2DividerItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
        self.backgroundColor = item.color
    }
}

// MARK: - Anchor view (zero-height; nothing to render)

final class InstantPageV2AnchorView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2AnchorItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2AnchorItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.isHidden = true   // structural: zero-height, never renders
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2AnchorItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
    }
}

// MARK: - List marker view

final class InstantPageV2ListMarkerView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2ListMarkerItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2ListMarkerItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.backgroundColor = .clear   // structural
        self.isOpaque = false           // structural
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2ListMarkerItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
        self.rebuildContents()
    }

    private func rebuildContents() {
        for subview in Array(self.subviews) {
            subview.removeFromSuperview()
        }
        if let sublayers = self.layer.sublayers {
            for sublayer in Array(sublayers) {
                sublayer.removeFromSuperlayer()
            }
        }

        let item = self.item
        switch item.kind {
        case .bullet:
            let radius: CGFloat = min(item.frame.width, item.frame.height) / 2.0
            let dot = CALayer()
            dot.backgroundColor = item.color.cgColor
            dot.frame = CGRect(
                x: (item.frame.width - radius * 2.0) / 2.0,
                y: (item.frame.height - radius * 2.0) / 2.0,
                width: radius * 2.0,
                height: radius * 2.0
            )
            dot.cornerRadius = radius
            self.layer.addSublayer(dot)
        case let .number(text):
            let label = UILabel()
            label.text = text
            label.textColor = item.color
            label.font = UIFont.systemFont(ofSize: 17.0)
            label.textAlignment = .right
            label.frame = CGRect(origin: .zero, size: item.frame.size)
            self.addSubview(label)
        case let .checklist(checked, colors):
            let checkNodeTheme = CheckNodeTheme(
                backgroundColor: colors.background,
                strokeColor: colors.stroke,
                borderColor: colors.border,
                overlayBorder: false,
                hasInset: false,
                hasShadow: false
            )
            let checkNode = CheckNode(theme: checkNodeTheme, content: .check(isRectangle: true))
            checkNode.displaysAsynchronously = false
            checkNode.isUserInteractionEnabled = false
            checkNode.frame = CGRect(origin: .zero, size: item.frame.size)
            checkNode.setSelected(checked, animated: false)
            self.addSubview(checkNode.view)
        }
    }
}

// MARK: - Quote bar view

final class InstantPageV2BlockQuoteBarView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2BarItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2BarItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2BarItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
        self.backgroundColor = item.color
        self.layer.cornerRadius = item.cornerRadius
    }
}

// MARK: - Shape view (for pullQuote line ornaments)

final class InstantPageV2ShapeView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2ShapeItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2ShapeItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2ShapeItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item
        self.applyKind()
    }

    private func applyKind() {
        switch self.item.kind {
        case let .roundedRect(cornerRadius):
            self.backgroundColor = self.item.color
            self.layer.cornerRadius = cornerRadius
        case .line(_):
            self.backgroundColor = self.item.color
            self.layer.cornerRadius = 0.0
        }
    }
}

// MARK: - Media placeholder view (V0: gray rectangle)

final class InstantPageV2MediaPlaceholderView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2MediaPlaceholderItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2MediaPlaceholderItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2MediaPlaceholderItem, theme: InstantPageTheme) {
        self.item = item
        self.backgroundColor = theme.imageTintColor?.withAlphaComponent(0.2) ?? UIColor(white: 0.85, alpha: 1.0)
        self.layer.cornerRadius = item.cornerRadius
        self.clipsToBounds = item.cornerRadius > 0.0
    }
}

// MARK: - Details view

final class InstantPageV2DetailsView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2DetailsItem
    var itemFrame: CGRect { return self.item.frame }

    let titleTextView: InstantPageV2TextView
    private let chevronView: UIImageView
    private let separator: UIView
    var bodyView: InstantPageV2View?
    private let titleHitView: UIView

    // The expanded chevron is the collapsed one rotated 180° (down → up).
    private static let expandedChevronTransform = CATransform3DMakeRotation(CGFloat.pi, 0.0, 0.0, 1.0)
    // On an animated collapse the body is kept until the toggle animation finishes (so the
    // shrinking clip can hide it), then removed in finalizePendingCollapse() — which the parent
    // (InstantPageV2View.update) calls from the completion of the frame-shrink (clip) animation.
    private var bodyPendingRemoval = false

    var onTitleTapped: ((Int) -> Void)?

    var subLayoutView: InstantPageV2View? { return self.bodyView }

    func forEachSubLayoutView(_ body: (InstantPageV2View) -> Void) {
        if let bodyView = self.bodyView { body(bodyView) }
    }

    init(item: InstantPageV2DetailsItem, theme: InstantPageTheme, renderContext: InstantPageV2RenderContext?) {
        self.item = item

        let titleV2Item = InstantPageV2TextItem(
            frame: item.titleTextItem.frame,
            textItem: item.titleTextItem
        )
        self.titleTextView = InstantPageV2TextView(item: titleV2Item, theme: theme)
        self.titleTextView.isUserInteractionEnabled = false

        self.chevronView = UIImageView()
        self.chevronView.image = UIImage(bundleImageName: "Item List/ExpandingItemVerticalRegularArrow")?.withRenderingMode(.alwaysTemplate)
        self.chevronView.contentMode = .scaleAspectFit
        // Decorative: let taps fall through to titleHitView (which carries the toggle gesture).
        self.chevronView.isUserInteractionEnabled = false

        self.separator = UIView()
        self.separator.isUserInteractionEnabled = false

        self.titleHitView = UIView()
        self.titleHitView.backgroundColor = .clear

        super.init(frame: item.frame)
        self.backgroundColor = .clear   // structural
        self.clipsToBounds = true       // structural — the parent's frame-height animation clips the body

        self.addSubview(self.titleTextView)
        self.addSubview(self.chevronView)
        self.addSubview(self.separator)

        let tap = UITapGestureRecognizer(target: self, action: #selector(self.titleTapped))
        self.insertSubview(self.titleHitView, at: 0)
        self.titleHitView.addGestureRecognizer(tap)

        // All content (title, chevron tint/position, separator, titleHit frame, body) flows through
        // update — its expanded branch lazily creates the body, so init no longer builds it itself.
        self.update(item: item, theme: theme, renderContext: renderContext, animation: .None)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    @objc private func titleTapped() {
        self.onTitleTapped?(self.item.index)
    }

    func update(item: InstantPageV2DetailsItem, theme: InstantPageTheme, renderContext: InstantPageV2RenderContext?, animation: ListViewItemUpdateAnimation) {
        self.item = item

        let titleV2Item = InstantPageV2TextItem(
            frame: item.titleTextItem.frame,
            textItem: item.titleTextItem
        )
        self.titleTextView.update(item: titleV2Item, theme: theme)

        self.chevronView.tintColor = theme.secondaryControlColor
        let chevronSize = CGSize(width: 18.0, height: 18.0)
        self.chevronView.bounds = CGRect(origin: .zero, size: chevronSize)
        self.chevronView.center = CGPoint(
            x: item.sideInset + chevronSize.width / 2.0,
            y: item.titleFrame.midY + 1.0
        )

        self.titleHitView.frame = item.titleFrame

        // Body lifecycle. The reveal/hide of the body is produced by the parent animating this
        // view's own frame height (clipsToBounds = true), not by the body itself — see
        // InstantPageV2View.update. The body's internal layout is forwarded `animation` so a
        // *nested* details block inside the body can also animate its own toggle.
        let blockHeight: CGFloat
        if item.isExpanded {
            if let innerLayout = item.innerLayout {
                let body: InstantPageV2View
                if let existingBody = self.bodyView {
                    // Reuse: covers expanded→expanded content updates and a re-expand that
                    // interrupts a still-pending collapse removal.
                    body = existingBody
                    self.bodyPendingRemoval = false
                } else {
                    body = InstantPageV2View(renderContext: renderContext)
                    self.addSubview(body)
                    self.bodyView = body
                }
                body.update(layout: innerLayout, theme: theme, animation: animation)
                body.frame = CGRect(
                    origin: CGPoint(x: 0.0, y: item.titleFrame.maxY),
                    size: innerLayout.contentSize
                )
                blockHeight = body.frame.maxY
            } else {
                blockHeight = item.titleFrame.maxY
            }
        } else {
            if let existingBody = self.bodyView {
                if animation.isAnimated {
                    // Keep the body visible while the parent's frame-shrink clips it away;
                    // it is removed in finalizePendingCollapse() (called from that clip animation's
                    // completion in InstantPageV2View.update).
                    self.bodyPendingRemoval = true
                } else {
                    existingBody.removeFromSuperview()
                    self.bodyView = nil
                }
            }
            blockHeight = item.titleFrame.maxY
        }
        
        self.separator.backgroundColor = item.separatorColor
        animation.animator.updateFrame(layer: self.separator.layer, frame: CGRect(
            x: 8.0,
            y: blockHeight - UIScreenPixel,
            width: item.frame.width - 8.0 * 2.0,
            height: UIScreenPixel
        ), completion: nil)

        // Chevron rotation. The body teardown on collapse is NOT tied to this completion — see
        // finalizePendingCollapse(), which the parent calls from the frame-shrink (clip) animation.
        let targetTransform = item.isExpanded ? InstantPageV2DetailsView.expandedChevronTransform : CATransform3DIdentity
        animation.animator.updateTransform(layer: self.chevronView.layer, transform: targetTransform, completion: nil)
    }

    /// Removes the body kept alive across an animated collapse. The parent (InstantPageV2View.update)
    /// calls this from the completion of the frame-shrink animation that clips the body away, so the
    /// body is torn down exactly when it finishes being hidden. The guard makes a re-expand that
    /// interrupts the collapse safe — the re-expand clears `bodyPendingRemoval` first.
    func finalizePendingCollapse() {
        if !self.item.isExpanded, self.bodyPendingRemoval {
            self.bodyView?.removeFromSuperview()
            self.bodyView = nil
            self.bodyPendingRemoval = false
        }
    }
}

// MARK: - Code block view

final class InstantPageV2CodeBlockView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2CodeBlockItem
    var itemFrame: CGRect { return self.item.frame }

    private let backgroundLayer: CALayer
    let textView: InstantPageV2TextView

    init(item: InstantPageV2CodeBlockItem, theme: InstantPageTheme) {
        self.item = item

        self.backgroundLayer = CALayer()

        // item.textItem.frame is already in code-block content-area coords (x=17, y=backgroundInset).
        let innerV2TextItem = InstantPageV2TextItem(
            frame: item.textItem.frame,
            textItem: item.textItem
        )
        self.textView = InstantPageV2TextView(item: innerV2TextItem, theme: theme)

        super.init(frame: item.frame)
        self.backgroundColor = .clear                 // structural
        self.layer.addSublayer(self.backgroundLayer)  // structural
        self.addSubview(self.textView)                // structural
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2CodeBlockItem, theme: InstantPageTheme) {
        self.item = item
        self.backgroundLayer.backgroundColor = item.backgroundColor.cgColor
        self.backgroundLayer.cornerRadius = item.cornerRadius
        self.backgroundLayer.frame = CGRect(origin: .zero, size: item.frame.size)

        let innerV2TextItem = InstantPageV2TextItem(
            frame: item.textItem.frame,
            textItem: item.textItem
        )
        self.textView.update(item: innerV2TextItem, theme: theme)
    }
}

// MARK: - Thinking view (dimmed shimmering reasoning block)

/// A top-level thinking block: dimmed text drawn fully, masked by a continuously-running
/// `ShimmeringMaskView`. Reveal is whole-block alpha (driven from the cost map), NOT char-by-char,
/// and the block contributes zero reveal cost. Structure mirrors `InstantPageV2CodeBlockView`
/// (container hosting an inner `InstantPageV2TextView`).
final class InstantPageV2ThinkingView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2ThinkingItem
    var itemFrame: CGRect { return self.item.frame }

    private let shimmerView: ShimmeringMaskView
    let textView: InstantPageV2TextView   // exposed so the parent V2 view can host its inline emoji

    init(item: InstantPageV2ThinkingItem, theme: InstantPageTheme) {
        self.item = item
        self.shimmerView = ShimmeringMaskView(peakAlpha: 0.3, duration: 1.0)
        let innerV2TextItem = InstantPageV2TextItem(frame: item.textItem.frame, textItem: item.textItem)
        self.textView = InstantPageV2TextView(item: innerV2TextItem, theme: theme)

        super.init(frame: item.frame)
        self.backgroundColor = .clear                              // structural
        self.addSubview(self.shimmerView)                          // structural
        self.shimmerView.contentView.addSubview(self.textView)     // structural
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    /// Parent positions self at the item frame (the bare line box). The shimmer and its gradient
    /// mask are sized to the text view's clipping-inset-EXPANDED frame and shifted to
    /// `(-inset, -inset)`, so the mask doesn't crop the glyph overhang the inset reserves (tall
    /// ascenders, descenders, the last line's underline) — the symptom of sizing the mask to the
    /// bare line box. The inner text view fills the shimmer; its `+inset` render translate lands the
    /// glyphs back at self's origin, so the text position is unchanged. Mirrors how a `.text` view's
    /// frame is inset-expanded (`actualFrame` / `InstantPageV2TextView.init`).
    private func layoutContents() {
        let inset = v2TextViewClippingInset
        let expandedSize = CGSize(width: self.item.frame.size.width + inset * 2.0,
                                  height: self.item.frame.size.height + inset * 2.0)
        self.shimmerView.frame = CGRect(x: -inset, y: -inset, width: expandedSize.width, height: expandedSize.height)
        self.textView.frame = CGRect(origin: .zero, size: expandedSize)
        self.shimmerView.update(
            size: expandedSize,
            containerWidth: expandedSize.width,
            offsetX: 0.0,
            gradientWidth: 200.0,
            transition: .immediate
        )
    }

    func update(item: InstantPageV2ThinkingItem, theme: InstantPageTheme) {
        self.item = item
        let innerV2TextItem = InstantPageV2TextItem(frame: item.textItem.frame, textItem: item.textItem)
        self.textView.update(item: innerV2TextItem, theme: theme)
        self.layoutContents()
    }
}

// MARK: - Table view

/// The set of grid corners a cell occupies, so a filled corner cell's stripe can be rounded to
/// follow the table's rounded outer border. `cellFrame` is table-grid-local (pre-`gridOffsetY`).
private func tableStripeCornerMask(cellFrame: CGRect, gridWidth: CGFloat, gridHeight: CGFloat, effectiveBorderWidth: CGFloat) -> CACornerMask {
    let edge = effectiveBorderWidth / 2.0 + 0.5
    let firstCol = cellFrame.minX <= edge
    let firstRow = cellFrame.minY <= edge
    let lastCol = cellFrame.maxX >= gridWidth - edge
    let lastRow = cellFrame.maxY >= gridHeight - edge
    var mask: CACornerMask = []
    if firstRow && firstCol { mask.insert(.layerMinXMinYCorner) }
    if firstRow && lastCol { mask.insert(.layerMaxXMinYCorner) }
    if lastRow && firstCol { mask.insert(.layerMinXMaxYCorner) }
    if lastRow && lastCol { mask.insert(.layerMaxXMaxYCorner) }
    return mask
}

final class InstantPageV2TableView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2TableItem
    var itemFrame: CGRect { return self.item.frame }

    private let scrollView: UIScrollView
    let contentView: UIView
    var titleSubView: InstantPageV2View?
    var cellSubViews: [InstantPageV2View] = []
    private var stripeLayers: [CALayer] = []
    private var lineLayers: [CALayer] = []

    var subLayoutView: InstantPageV2View? { return nil }

    func forEachSubLayoutView(_ body: (InstantPageV2View) -> Void) {
        if let titleView = self.titleSubView { body(titleView) }
        for cellView in self.cellSubViews { body(cellView) }
    }

    init(item: InstantPageV2TableItem, theme: InstantPageTheme, renderContext: InstantPageV2RenderContext?) {
        self.item = item
        self.scrollView = UIScrollView()
        self.contentView = UIView()
        super.init(frame: item.frame)
        self.backgroundColor = .clear

        // Structural, one-time scroll-view configuration. Frames / contentSize / indicator
        // visibility all depend on the item and are (re)applied by update(item:theme:).
        // Scrollable tables clip to the full width with no inset on the clip; the inset lives inside
        // the scroll content width as a margin on BOTH sides (`contentInset * 2.0`, mirroring V1's
        // `InstantPageScrollableNode`), so a scrolled-to-the-end table keeps a symmetric trailing
        // inset instead of jamming its right border flush against the screen edge.
        self.scrollView.clipsToBounds = true
        self.scrollView.alwaysBounceHorizontal = false
        self.scrollView.alwaysBounceVertical = false
        self.scrollView.showsVerticalScrollIndicator = false
        self.scrollView.disablesInteractiveTransitionGestureRecognizer = true
        self.addSubview(self.scrollView)
        self.scrollView.addSubview(self.contentView)

        // Build the (content-less) child structure sized to the construction-time item; update fills
        // every frame / colour / sub-layout below. Insertion order matches the original interleaved
        // build so the layer/subview z-order is unchanged (stripes at the bottom, then the title and
        // cell sub-views, then the inner grid lines). Cell-count changes on later reuse are not
        // reconciled here (pre-existing limitation) — update's index-guarded loops refresh in place.
        if item.titleSubLayout != nil {
            let v = InstantPageV2View(renderContext: renderContext)
            self.contentView.addSubview(v)
            self.titleSubView = v
        }
        for cell in item.cells {
            if cell.backgroundColor != nil {
                let stripe = CALayer()
                self.contentView.layer.insertSublayer(stripe, at: 0)
                self.stripeLayers.append(stripe)
            }
            if cell.subLayout != nil {
                let v = InstantPageV2View(renderContext: renderContext)
                self.contentView.addSubview(v)
                self.cellSubViews.append(v)
            }
        }
        if item.bordered {
            for _ in item.horizontalLines + item.verticalLines {
                let line = CALayer()
                self.contentView.layer.addSublayer(line)
                self.lineLayers.append(line)
            }
        }

        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2TableItem, theme: InstantPageTheme) {
        self.item = item

        self.scrollView.frame = CGRect(origin: .zero, size: item.frame.size)
        self.scrollView.contentSize = CGSize(width: item.contentSize.width + item.contentInset * 2.0, height: item.contentSize.height)
        self.scrollView.showsHorizontalScrollIndicator = item.contentSize.width + item.contentInset * 2.0 > item.frame.width
        self.contentView.frame = CGRect(x: item.contentInset, y: 0.0, width: item.contentSize.width, height: item.contentSize.height)

        // Forward updates to nested V2 sub-layouts (title + each cell). Recursive update
        // propagation. Cell-count or title-presence changes fall back to rebuild via the
        // V2View's internal `update(layout:theme:animation:)` (task B refines).
        if let titleLayout = item.titleSubLayout, let titleView = self.titleSubView, let titleFrame = item.titleFrame {
            titleView.update(layout: titleLayout, theme: theme, animation: .None)
            titleView.frame = CGRect(
                x: v2TableCellInsets.left,
                y: titleFrame.minY + v2TableCellInsets.top,
                width: titleLayout.contentSize.width,
                height: titleLayout.contentSize.height
            )
        }

        let gridOffsetY = item.titleFrame?.height ?? 0.0
        var cellLayoutIndex = 0
        for cell in item.cells {
            if let subLayout = cell.subLayout, cellLayoutIndex < self.cellSubViews.count {
                let cellView = self.cellSubViews[cellLayoutIndex]
                cellView.update(layout: subLayout, theme: theme, animation: .None)
                cellView.frame = cell.frame.offsetBy(dx: 0.0, dy: gridOffsetY)
                cellLayoutIndex += 1
            }
        }

        // Stripe layers (cell backgrounds) — update color + frame + corner rounding in original order.
        let effectiveBorderWidth = item.bordered ? v2TableBorderWidth : 0.0
        let gridHeight = item.contentSize.height - gridOffsetY
        var stripeIndex = 0
        for cell in item.cells {
            if let bg = cell.backgroundColor, stripeIndex < self.stripeLayers.count {
                let stripe = self.stripeLayers[stripeIndex]
                stripe.backgroundColor = bg.cgColor
                stripe.frame = cell.frame.offsetBy(dx: 0.0, dy: gridOffsetY)
                let cornerMask = tableStripeCornerMask(cellFrame: cell.frame, gridWidth: item.contentSize.width, gridHeight: gridHeight, effectiveBorderWidth: effectiveBorderWidth)
                if cornerMask.isEmpty {
                    stripe.cornerRadius = 0.0
                    stripe.maskedCorners = []
                } else {
                    stripe.cornerRadius = max(0.0, v2TableCornerRadius - effectiveBorderWidth)
                    stripe.maskedCorners = cornerMask
                }
                stripeIndex += 1
            }
        }

        // Inner line layers — refresh colour AND frame in place. (`lineLayers` holds only inner grid
        // lines; the outer border is the contentView layer's own rounded border, refreshed below.)
        // Frames are set here (not in init) so reuse with a different grid re-positions the lines.
        let lineRects = item.horizontalLines + item.verticalLines
        for (i, line) in self.lineLayers.enumerated() {
            line.backgroundColor = item.borderColor.cgColor
            if i < lineRects.count {
                line.frame = lineRects[i].offsetBy(dx: 0.0, dy: gridOffsetY)
            }
        }

        // Rounded outer border — refresh radius/color/width (theme or `bordered` flag may change).
        self.contentView.layer.cornerRadius = v2TableCornerRadius
        self.contentView.layer.borderColor = item.borderColor.cgColor
        self.contentView.layer.borderWidth = item.bordered ? v2TableBorderWidth : 0.0
    }
}

// MARK: - Public helpers on InstantPageV2View

public extension InstantPageV2View {
    func lastTextLineFrame() -> CGRect? {
        guard let layout = self.currentLayout else { return nil }
        return InstantPageUI.lastTextLineFrame(in: layout)
    }

    func textItemAt(point: CGPoint) -> (item: InstantPageTextItem, parentOffset: CGPoint)? {
        guard let layout = self.currentLayout else { return nil }
        return findTextItem(in: layout, point: point, accumulatedOffset: .zero)
    }

    func urlItemAt(point: CGPoint) -> (urlItem: InstantPageUrlItem, item: InstantPageTextItem,
                                       parentOffset: CGPoint, localPoint: CGPoint)? {
        guard let hit = self.textItemAt(point: point) else { return nil }
        let localPoint = CGPoint(x: point.x - hit.parentOffset.x, y: point.y - hit.parentOffset.y)
        guard let url = hit.item.urlAttribute(at: localPoint) else { return nil }
        return (urlItem: url, item: hit.item, parentOffset: hit.parentOffset, localPoint: localPoint)
    }

    func selectableTextItems() -> [(item: InstantPageTextItem, parentOffset: CGPoint)] {
        guard let layout = self.currentLayout else { return [] }
        var result: [(InstantPageTextItem, CGPoint)] = []
        collectSelectableTextItems(in: layout, accumulatedOffset: .zero, into: &result)
        return result.map { (item: $0.0, parentOffset: $0.1) }
    }

    func detailsItem(atIndex index: Int) -> (frame: CGRect, titleFrame: CGRect)? {
        guard let layout = self.currentLayout else { return nil }
        for item in layout.items {
            if case let .details(d) = item, d.index == index {
                return (frame: d.frame, titleFrame: d.titleFrame.offsetBy(dx: d.frame.minX, dy: d.frame.minY))
            }
        }
        return nil
    }
}

// MARK: - Private recursion helpers

private func findTextItem(
    in layout: InstantPageV2Layout,
    point: CGPoint,
    accumulatedOffset: CGPoint
) -> (item: InstantPageTextItem, parentOffset: CGPoint)? {
    for item in layout.items {
        let f = item.frame.offsetBy(dx: accumulatedOffset.x, dy: accumulatedOffset.y)
        if !f.contains(point) { continue }
        switch item {
        case let .text(text):
            return (item: text.textItem, parentOffset: CGPoint(x: f.minX, y: f.minY))
        case let .codeBlock(block):
            let textOrigin = CGPoint(
                x: f.minX + block.textItem.frame.minX,
                y: f.minY + block.textItem.frame.minY
            )
            return (item: block.textItem, parentOffset: textOrigin)
        case let .details(details):
            if details.titleFrame.offsetBy(dx: f.minX, dy: f.minY).contains(point) {
                let titleOrigin = CGPoint(
                    x: f.minX + details.titleTextItem.frame.minX,
                    y: f.minY + details.titleTextItem.frame.minY
                )
                return (item: details.titleTextItem, parentOffset: titleOrigin)
            }
            if let inner = details.innerLayout {
                let innerOffset = CGPoint(x: f.minX, y: f.minY + details.titleFrame.maxY)
                if let hit = findTextItem(in: inner, point: point, accumulatedOffset: innerOffset) {
                    return hit
                }
            }
        case let .table(table):
            for cell in table.cells {
                let cellAbs = cell.frame.offsetBy(dx: f.minX + table.contentInset, dy: f.minY)
                if !cellAbs.contains(point) { continue }
                if let sub = cell.subLayout {
                    if let hit = findTextItem(in: sub, point: point,
                                              accumulatedOffset: CGPoint(x: cellAbs.minX, y: cellAbs.minY)) {
                        return hit
                    }
                }
            }
            if let titleLayout = table.titleSubLayout, let titleFrame = table.titleFrame {
                let titleAbs = titleFrame.offsetBy(dx: f.minX + table.contentInset, dy: f.minY)
                if titleAbs.contains(point) {
                    if let hit = findTextItem(in: titleLayout, point: point,
                                              accumulatedOffset: CGPoint(x: titleAbs.minX, y: titleAbs.minY)) {
                        return hit
                    }
                }
            }
        default:
            continue
        }
    }
    return nil
}

private func collectSelectableTextItems(
    in layout: InstantPageV2Layout,
    accumulatedOffset: CGPoint,
    into result: inout [(InstantPageTextItem, CGPoint)]
) {
    for item in layout.items {
        switch item {
        case let .text(text):
            if text.textItem.selectable && !text.textItem.attributedString.string.isEmpty {
                result.append((text.textItem, CGPoint(
                    x: accumulatedOffset.x + text.frame.minX,
                    y: accumulatedOffset.y + text.frame.minY
                )))
            }
        case let .codeBlock(block):
            if block.textItem.selectable && !block.textItem.attributedString.string.isEmpty {
                result.append((block.textItem, CGPoint(
                    x: accumulatedOffset.x + block.frame.minX + block.textItem.frame.minX,
                    y: accumulatedOffset.y + block.frame.minY + block.textItem.frame.minY
                )))
            }
        case let .details(details):
            if details.titleTextItem.selectable && !details.titleTextItem.attributedString.string.isEmpty {
                result.append((details.titleTextItem, CGPoint(
                    x: accumulatedOffset.x + details.frame.minX + details.titleTextItem.frame.minX,
                    y: accumulatedOffset.y + details.frame.minY + details.titleTextItem.frame.minY
                )))
            }
            if let inner = details.innerLayout {
                let innerOffset = CGPoint(
                    x: accumulatedOffset.x + details.frame.minX,
                    y: accumulatedOffset.y + details.frame.minY + details.titleFrame.maxY
                )
                collectSelectableTextItems(in: inner, accumulatedOffset: innerOffset, into: &result)
            }
        case let .table(table):
            if let titleLayout = table.titleSubLayout, let titleFrame = table.titleFrame {
                let titleOffset = CGPoint(
                    x: accumulatedOffset.x + table.frame.minX + table.contentInset + titleFrame.minX,
                    y: accumulatedOffset.y + table.frame.minY + titleFrame.minY
                )
                collectSelectableTextItems(in: titleLayout, accumulatedOffset: titleOffset, into: &result)
            }
            for cell in table.cells {
                if let sub = cell.subLayout {
                    let cellOffset = CGPoint(
                        x: accumulatedOffset.x + table.frame.minX + table.contentInset + cell.frame.minX,
                        y: accumulatedOffset.y + table.frame.minY + cell.frame.minY
                    )
                    collectSelectableTextItems(in: sub, accumulatedOffset: cellOffset, into: &result)
                }
            }
        default:
            continue
        }
    }
}

// MARK: - Formula view

/// Renders both block (`InstantPageBlock.formula(latex:)`) and inline (`InstantPageFormulaAttribute`)
/// math, sourcing the pre-rendered Retina image from `InstantPageMathAttachment.rendered`.
///
/// For block formulas wider than the bubble's available width, the layout sets
/// `isScrollable = true`; this view then wraps the image in a horizontal `UIScrollView`
/// matching V1's `InstantPageScrollableNode` (no bounce on non-overflowing content,
/// scroll indicator hidden — appropriate for content embedded inside a chat bubble).
final class InstantPageV2FormulaView: UIView, InstantPageItemView {
    private(set) var item: InstantPageV2FormulaItem
    var itemFrame: CGRect { return self.item.frame }

    init(item: InstantPageV2FormulaItem, theme: InstantPageTheme) {
        self.item = item
        super.init(frame: item.frame)
        self.backgroundColor = .clear   // structural
        self.isOpaque = false           // structural
        self.update(item: item, theme: theme)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func update(item: InstantPageV2FormulaItem, theme: InstantPageTheme) {
        let _ = theme
        self.item = item

        // Image content and scroll/non-scroll shape may change with width; rebuild. On the first
        // call (from init) there is nothing to tear down, so this collapses to a plain build.
        for sub in self.subviews { sub.removeFromSuperview() }
        if let sublayers = self.layer.sublayers {
            for layer in sublayers { layer.removeFromSuperlayer() }
        }
        self.buildContents()
    }

    private func buildContents() {
        let item = self.item
        let imageLayer = CALayer()
        imageLayer.contents = item.attachment.rendered.image.cgImage
        imageLayer.contentsScale = item.attachment.rendered.image.scale
        imageLayer.contentsGravity = .resizeAspect
        imageLayer.frame = item.imageFrame

        if item.isScrollable {
            self.clipsToBounds = true
            self.isUserInteractionEnabled = true
            let scroll = UIScrollView(frame: CGRect(origin: .zero, size: item.frame.size))
            scroll.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            scroll.contentSize = item.scrollContentSize
            scroll.showsHorizontalScrollIndicator = false
            scroll.showsVerticalScrollIndicator = false
            scroll.alwaysBounceHorizontal = false
            scroll.alwaysBounceVertical = false
            scroll.contentInsetAdjustmentBehavior = .never
            scroll.disablesInteractiveTransitionGestureRecognizer = true
            self.addSubview(scroll)

            // Layers don't autoresize with their superview; host the image layer inside a UIView
            // so the scroll view's content-size growth keeps the image positioned correctly.
            let imageHost = UIView(frame: CGRect(origin: .zero, size: item.scrollContentSize))
            imageHost.layer.addSublayer(imageLayer)
            scroll.addSubview(imageHost)
        } else {
            // Inline and centered-block formulas don't accept touches; the bubble's link/long-press
            // recognizers run against the underlying text view instead.
            self.isUserInteractionEnabled = false
            self.layer.addSublayer(imageLayer)
        }
    }
}