// the streaming message timeline + composer (chat mode).

///|
/// The code workspace view. When there are no messages and no streaming turn,
// quick cards). Otherwise render the streaming timeline + composer.
fn code_workspace_view(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
  height : Double,
) -> @moui.View[CodeMsg] {
  let chat_theme = workbench_conversation_theme(theme, settings.font_size)
  let title_theme = workbench_default_typography_theme(theme)
  if model.messages.is_empty() && !model.is_streaming {
    code_welcome_view(model, settings, title_theme, chat_theme, width, height)
  } else {
    code_chat_pane_view(model, settings, chat_theme, width, height)
  }
}

///|
/// Chat pane: messages fill the area above a bottom-pinned composer.
fn code_chat_pane_view(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
  height : Double,
) -> @moui.View[CodeMsg] {
  let list_height = code_message_list_height(
    model, settings, theme, width, height,
  )
  let list = code_message_list(model, theme, width, list_height)
  // repaint boundary:消息列表内容未变时(点击按钮、开关设置等交互)整块复用
  // 为图层,避免全窗口重新光栅化几百段文本;滚动/流式导致内容变化时自动失效。
  .repaint_boundary()
  let composer = code_composer(model, settings, theme, width)
  @views.container(
    @views.custom_children_layout(
      children=[list, composer],
      measure=ctx => {
        ctx.constraints.constrain(@geometry.Size::new(width~, height~))
      },
      place=ctx => {
        let composer_h = ctx.children[1].size.height
        let list_h = (ctx.frame.size.height - composer_h).max(0.0)
        let w = ctx.frame.size.width
        [
          @geometry.Rect::new(x=0.0, y=0.0, width=w, height=list_h),
          @geometry.Rect::new(x=0.0, y=list_h, width=w, height=composer_h),
        ]
      },
      paint=(_ctx, _frame) => (),
      semantics_label="Code chat pane",
    ),
    width~,
    height~,
    background=workbench_canvas_background(theme),
    padding=0.0,
  )
}

///|
fn code_message_list_height(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
  height : Double,
) -> Double {
  (height - code_composer_height(model, settings, theme, width)).max(0.0)
}

///|
fn code_composer_height(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> Double {
  let outer_padding = 16.0
  let input_card_height = code_composer_input_card_height(model, theme, width)
  let row_spacing = 6.0
  let mut content_height = input_card_height
  match model.error {
    Some(_) => content_height = content_height + 32.0 + row_spacing
    None => ()
  }
  if model.model_picker_open {
    content_height = content_height +
      row_spacing +
      code_model_dropdown_panel_height(settings)
  }
  outer_padding + content_height
}

///|
fn code_composer_prompt_line_height() -> Double {
  22.0
}

///|
fn code_composer_prompt_text_area_height(lines : Int) -> Double {
  lines.to_double() * code_composer_prompt_line_height() + 16.0
}

///|
fn code_composer_prompt_lines(
  prompt : String,
  theme : @moui.Theme,
  width : Double,
) -> Int {
  if prompt.is_empty() {
    2
  } else {
    let text_width = (width - 16.0).max(64.0)
    let lines = chat_message_display_lines(
      prompt,
      text_width,
      theme.typography.body.size,
    ).length()
    if lines < 2 {
      2
    } else {
      lines
    }
  }
}

///|
fn code_composer_input_card_height(
  model : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> Double {
  let lines = code_composer_prompt_lines(model.prompt, theme, width)
  code_composer_prompt_text_area_height(lines) + 34.0
}

///|
/// Brand title + input card, context bar with icons, and bottom quick-action
/// chips. The whole block scrolls so it fits narrow windows.
fn code_welcome_view(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  title_theme : @moui.Theme,
  content_theme : @moui.Theme,
  width : Double,
  height : Double,
) -> @moui.View[CodeMsg] {
  let inner_width = (width - 96.0).max(320.0)
  let welcome_block = @views.column(
    [
      @views.text(
        "Code with Mo",
        role=Headline,
        theme=title_theme,
        width=inner_width,
      ).foreground(workbench_accent(title_theme)),
      @views.spacer(min_length=30.0, weight=0.0),
      code_input_card(model, settings, content_theme, inner_width),
      @views.spacer(min_length=10.0, weight=0.0),
      code_context_bar(settings, content_theme, inner_width),
      @views.spacer(min_length=50.0, weight=0.0),
      @views.container(
        quick_action_chips(content_theme, inner_width),
        width=inner_width,
        padding=0.0,
      ),
    ],
    spacing=0.0,
    align=Stretch,
  )
  let welcome_area_height = (height - 96.0).max(0.0)
  @views.container(
    @views.center(
      welcome_block,
      width~,
      height=welcome_area_height,
      theme=content_theme,
    ),
    width~,
    height~,
    background=workbench_canvas_background(title_theme),
    padding=48.0,
  )
}

///|
/// The input card: a multi-line text area for the prompt and a compact tool
/// row with model and thinking pickers directly before Send.
fn code_input_card(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let text_area_theme = code_input_text_area_theme(theme)
  let rows : Array[@moui.View[CodeMsg]] = []
  // Prompt text area – the main interactive zone.
  rows.push(
    @views.text_area(
      model.prompt,
      on_input=value => PromptChanged(value),
      on_submit=Some(SubmitPrompt),
      placeholder="帮你编写代码、调试 Bug、优化性能等开发工作…",
      lines=4,
      variant=Plain,
      theme=text_area_theme,
      width~,
      line_height=25.0,
    ),
  )
  rows.push(
    @views.row(
      [
        @views.container(
          @views.icon(Link, size=18.0, color=workbench_text_muted(theme)),
          width=20.0,
          height=20.0,
          padding=0.0,
        ),
        @views.spacer(),
        code_agent_controls(model, settings, theme, (width - 110.0).max(140.0)),
        workbench_send_button(theme, on_tap=SubmitPrompt),
      ],
      spacing=6.0,
      align=Center,
    ),
  )
  if model.model_picker_open {
    rows.push(code_model_dropdown_panel(model, settings, theme, width))
  }
  @views.container(
    @views.column(rows, spacing=1.0, align=Stretch),
    width~,
    background=workbench_card_background(theme),
    corner_radius=14.0,
    border=None,
    padding=1.0,
  )
}

///|
fn code_input_text_area_theme(theme : @moui.Theme) -> @moui.Theme {
  let radius_scale = { ..theme.radius_scale, md: 14.0, }
  theme.with_radius_scale(radius_scale)
}

///|
/// Compact model chip. Tapping toggles the inline model picker; the expanded
/// panel is rendered by the caller (`code_input_card` / `code_composer`) so it
/// can drop down over the surrounding surface.
fn code_model_picker(
  code : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  code_compact_select_chip(code.current_model, theme, width).on_tap(
    ToggleModelPicker,
  )
}

///|
fn code_agent_controls(
  code : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  match settings.agent_backend {
    OpenSeek =>
      @views.row(
        [
          code_model_picker(
            code,
            theme,
            code_model_picker_width(code, max_width=(width - 68.0).max(96.0)),
          ),
          code_thinking_picker(code, theme, 65.0),
        ],
        spacing=6.0,
        align=Center,
      )
    Acp => acp_agent_controls(code, theme, width)
  }
}

///|
fn acp_agent_controls(
  code : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let rows : Array[@moui.View[CodeMsg]] = []
  match code.session_modes {
    Some(modes) =>
      if !modes.available_modes.is_empty() {
        rows.push(acp_mode_picker(modes, theme, width))
      }
    None => rows.push(code_compact_select_chip("ACP", theme, width.min(96.0)))
  }
  if !code.session_config_options.is_empty() {
    rows.push(acp_config_controls(code.session_config_options, theme, width))
  }
  @views.row(rows, spacing=6.0, align=Center)
}

///|
fn acp_mode_picker(
  modes : AgentSessionModeState,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let items : Array[@views.ChoiceItem] = []
  for mode in modes.available_modes {
    items.push(@views.choice_item(mode.id, mode.name))
  }
  @views.segmented_control(
    items,
    selected=modes.current_mode_id,
    on_select=id => SetSessionMode(id),
    size=Compact,
    theme~,
    width=width.min(260.0),
  )
}

///|
fn acp_config_controls(
  options : Array[AgentSessionConfigOption],
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let shown_width = width.min(220.0)
  let controls : Array[@moui.View[CodeMsg]] = []
  for option in options {
    if controls.length() >= 1 {
      break
    }
    controls.push(acp_config_control(option, theme, shown_width))
  }
  @views.row(controls, spacing=6.0, align=Center)
}

///|
fn acp_config_control(
  option : AgentSessionConfigOption,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  match option.current_value {
    Boolean(value) =>
      code_compact_select_chip(
        option.name + ": " + (if value { "on" } else { "off" }),
        theme,
        width,
      ).on_tap(SetSessionConfigOption(option.id, Boolean(!value)))
    ValueId(_) =>
      if option.values.is_empty() {
        code_compact_select_chip(option.name, theme, width)
      } else {
        acp_config_value_picker(option, theme, width)
      }
  }
}

///|
fn acp_config_value_picker(
  option : AgentSessionConfigOption,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let items : Array[@views.ChoiceItem] = []
  for value in option.values {
    items.push(@views.choice_item(value.id, value.name))
  }
  let selected = match option.current_value {
    ValueId(id) => id
    Boolean(_) => ""
  }
  @views.segmented_control(
    items,
    selected~,
    on_select=id => SetSessionConfigOption(option.id, ValueId(id)),
    size=Compact,
    theme~,
    width~,
  )
}

///|
fn code_model_picker_width(
  code : CodeWorkspace,
  max_width? : Double = 320.0,
) -> Double {
  let text_width = code.current_model.to_array().length().to_double() * 7.2 +
    24.0
  text_width.max(74.0).min(max_width)
}

///|
/// The inline-expanding model panel: a provider switcher plus the active
/// provider's model list. Selecting a model or provider dispatches the
/// matching `CodeMsg`; the shell resolves the backend connection.
fn code_model_dropdown_panel(
  code : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let panel_width = width.max(240.0)
  let rows : Array[@moui.View[CodeMsg]] = []
  rows.push(provider_switcher_row(settings, theme, panel_width))
  rows.push(
    @views.container(
      @views.text("模型", role=Caption, theme~, width=panel_width).foreground(
        theme.palette.muted,
      ),
      width=panel_width,
      height=18.0,
    ),
  )
  match settings.active_provider() {
    Some(p) =>
      if p.models.is_empty() {
        rows.push(
          @views.text(
            "该供应商暂无模型。可在设置中自动检测或手动添加。",
            role=Caption,
            theme~,
            width=panel_width,
          ).foreground(theme.palette.muted),
        )
      } else {
        for m in p.models {
          let selected = code.current_model == m &&
            code.current_provider_id == Some(p.id)
          rows.push(model_option_row(p.id, m, selected, theme, panel_width))
        }
      }
    None => ()
  }
  let list_h = code_model_dropdown_list_height(settings)
  @views.container(
    @views.scroll_view(
      @views.column(rows, spacing=4.0, align=Stretch),
      width=panel_width,
      height=list_h,
    ),
    width=panel_width,
    background=workbench_card_background(theme),
    corner_radius=12.0,
    border=Some(hairline_border(theme)),
    padding=8.0,
  )
}

///|
fn code_model_dropdown_row_count(settings : SettingsWorkspace) -> Int {
  let base_rows = 2
  match settings.active_provider() {
    Some(p) =>
      if p.models.is_empty() {
        base_rows + 1
      } else {
        base_rows + p.models.length()
      }
    None => base_rows
  }
}

///|
fn code_model_dropdown_list_height(settings : SettingsWorkspace) -> Double {
  (code_model_dropdown_row_count(settings).to_double() * 44.0 + 16.0).min(300.0)
}

///|
fn code_model_dropdown_panel_height(settings : SettingsWorkspace) -> Double {
  code_model_dropdown_list_height(settings) + 16.0
}

///|
/// Horizontal provider chips; the active provider is highlighted. Tapping
/// switches the chat's active provider.
fn provider_switcher_row(
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let count = settings.providers.length().to_double().max(1.0)
  let gap = 6.0
  let chip_w = ((width - gap * (count - 1.0)) / count).max(64.0)
  let chips : Array[@moui.View[CodeMsg]] = []
  for p in settings.providers {
    let selected = settings.active_provider_id == Some(p.id)
    let chip = @views.container(
      @views.center(
        @views.text(
          p.name,
          role=Caption,
          theme~,
          width=(chip_w - 12.0).max(40.0),
          height=18.0,
        ).foreground(
          if selected {
            workbench_accent(theme)
          } else {
            workbench_text(theme)
          },
        ),
        width=chip_w,
        height=22.0,
        theme~,
      ),
      width=chip_w,
      height=32.0,
      background=if selected {
        workbench_selector_chip_background(theme)
      } else {
        workbench_subtle_background(theme)
      },
      corner_radius=14.0,
      border=if selected { Some(hairline_border(theme)) } else { None },
      padding=4.0,
    ).on_tap(CodeMsg::SelectProvider(p.id))
    chips.push(chip)
  }
  @views.row(chips, spacing=6.0, align=Center)
}

///|
/// A single model row. OpenSeek-supported models are selectable; custom ids
/// stay visible but muted until the native backend can parse them.
fn model_option_row(
  provider_id : String,
  model_id : String,
  selected : Bool,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let supported = mo_workbench_model_supported_by_openseek(model_id)
  let trailing : @moui.View[CodeMsg] = if selected {
    @views.icon(Check, size=16.0, color=workbench_accent(theme))
  } else if !supported {
    @views.text("待支持", role=Caption, theme~, width=44.0, height=16.0).foreground(
      theme.palette.muted,
    )
  } else {
    @views.container(
      @views.text("", role=Caption, theme~, width=16.0),
      width=16.0,
      height=16.0,
    )
  }
  let label_width = if supported { width - 36.0 } else { width - 64.0 }
  let row = @views.container(
    @views.row(
      [
        @views.text(
          model_id,
          role=Label,
          theme~,
          width=label_width.max(80.0),
          height=22.0,
        ).foreground(
          if supported {
            workbench_text(theme)
          } else {
            theme.palette.muted
          },
        ),
        trailing,
      ],
      spacing=6.0,
      align=Center,
    ),
    width~,
    height=40.0,
    background=if selected {
      workbench_selector_chip_background(theme)
    } else if !supported {
      workbench_subtle_background(theme)
    } else {
      @graphics.Color::rgba(r=0.0, g=0.0, b=0.0, a=0.0)
    },
    corner_radius=8.0,
    padding=8.0,
  )
  if supported {
    row.on_tap(ModelChanged(provider_id, model_id))
  } else {
    row
  }
}

///|
fn code_thinking_picker(
  code : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let label = match code.current_thinking {
    Normal => "Normal"
    High => "High"
    Max => "Max"
  }
  code_compact_select_chip(label, theme, width).on_tap(
    ThinkingChanged(next_thinking_choice(code.current_thinking)),
  )
}

///|
fn code_compact_select_chip(
  label : String,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let content_width = (width - 6.0).max(32.0)
  @views.container(
    @views.center(
      @views.row(
        [
          @views.text(
            label,
            role=Caption,
            theme~,
            width=(content_width - 14.0).max(24.0),
            height=18.0,
          ).foreground(workbench_accent(theme)),
          @views.icon(ChevronDown, size=9.0, color=workbench_accent(theme)),
        ],
        spacing=4.0,
        align=Center,
      ),
      width=content_width,
      height=20.0,
      theme~,
    ),
    width~,
    height=26.0,
    background=workbench_subtle_background(theme),
    corner_radius=11.0,
    padding=2.0,
  )
}

///|
/// Context bar: the active local workspace folder selector.
fn code_context_bar(
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let label = workspace_folder_label(settings.working_dir)
  let chip_width = workspace_folder_chip_width(label, max_width=width)
  @views.row(
    [
      @views.container(
        @views.row(
          [
            @views.icon(
              FolderOpen,
              size=14.0,
              color=workbench_text_muted(theme),
            ),
            @views.text(
              label,
              role=Caption,
              theme~,
              width=(chip_width - 52.0).max(60.0),
            ).foreground(workbench_text(theme)),
            @views.icon(
              ChevronDown,
              size=10.0,
              color=workbench_text_muted(theme),
            ),
          ],
          spacing=4.0,
          align=Center,
        ),
        width=chip_width,
        height=28.0,
        background=workbench_subtle_background(theme),
        corner_radius=6.0,
        padding=6.0,
      ).on_tap(CodeMsg::PickWorkspaceFolder),
      @views.spacer(),
    ],
    spacing=8.0,
    align=Start,
  ).frame(width~)
}

///|
fn workspace_folder_label(path : String) -> String {
  let trimmed = path.trim().to_owned()
  if trimmed.is_empty() || trimmed == "." {
    "选择文件夹"
  } else {
    workspace_folder_basename(trimmed)
  }
}

///|
fn workspace_folder_basename(path : String) -> String {
  let chars = path.to_array()
  let mut end = chars.length()
  while end > 0 && (chars[end - 1] == '/' || chars[end - 1] == '\\') {
    end = end - 1
  }
  if end <= 0 {
    path
  } else {
    let mut last_slash : Int = -1
    for index in 0..<end {
      if chars[index] == '/' || chars[index] == '\\' {
        last_slash = index
      }
    }
    let label = String::from_array(chars[last_slash + 1:end])
    if label.is_empty() {
      path
    } else {
      label
    }
  }
}

///|
fn workspace_folder_chip_width(
  label : String,
  max_width? : Double = 320.0,
) -> Double {
  let text_width = label.to_array().length().to_double() * 8.0 + 52.0
  text_width.max(118.0).min(max_width)
}

///|
/// Bottom quick-action chips: four rounded rect capsules with icons.
/// 应用开发 / 项目理解 / 游戏创意 / 工具脚本. Tapping fills the prompt with
/// a preset.
fn quick_action_chips(
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let chip_width = (width - 24.0) / 4.0
  @views.row(
    [
      quick_chip(
        "应用开发",
        ListTask,
        "帮我开发一个应用",
        theme,
        chip_width,
      ),
      quick_chip(
        "项目理解",
        Search,
        "帮我理解这个项目的结构",
        theme,
        chip_width,
      ),
      quick_chip(
        "游戏创意",
        Focus,
        "帮我设计一个游戏创意",
        theme,
        chip_width,
      ),
      quick_chip(
        "工具脚本",
        Settings,
        "帮我写一个工具脚本",
        theme,
        chip_width,
      ),
    ],
    spacing=8.0,
    align=Center,
  )
}

///|
/// A single quick-action chip: icon + label in a rounded rect with border.
fn quick_chip(
  label : String,
  icon : @views.IconName,
  prompt : String,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let text_width = (width - 38.0).max(40.0)
  @views.container(
    @views.row(
      [
        @views.icon(icon, size=14.0, color=workbench_accent(theme)),
        @views.text(label, role=Caption, theme~, width=text_width, height=20.0).foreground(
          workbench_accent(theme),
        ),
      ],
      spacing=6.0,
      align=Center,
    ),
    width~,
    height=40.0,
    background=workbench_accent_soft(theme),
    corner_radius=18.0,
    border=Some(hairline_border(theme)),
    padding=8.0,
  ).on_tap(PromptChanged(prompt))
}

///|
/// 消息高度数组的含 spacing 总高(`n` 条消息,`n-1` 个间距)。
fn code_heights_total(heights : Array[Double], spacing : Double) -> Double {
  if heights.is_empty() {
    return 0.0
  }
  let mut total = 0.0
  for h in heights {
    total = total + h
  }
  total + (heights.length() - 1).to_double() * spacing
}

///|
/// 前 `count` 条消息(含它们之间的 spacing)的高度和,用作窗口顶部的占位高度。
fn code_prefix_height(
  heights : Array[Double],
  spacing : Double,
  count : Int,
) -> Double {
  let mut prefix = 0.0
  let mut i = 0
  while i < count && i < heights.length() {
    prefix = prefix + heights[i]
    if i + 1 < count {
      prefix = prefix + spacing
    }
    i = i + 1
  }
  prefix
}

///|
/// 由滚动 offset 推算出需要真实构建的消息区间 `[first, last)`(排他)。
/// 做法:按估算高度累加定位可视区 `[offset, offset + viewport]`,再向上下各延伸
/// `overscan` 条作为缓冲,补偿高度估算与真实布局的微小偏差,并钳制到 `[0, n)`。
/// `follow_latest` 的 `offset=1e9` 会钳到内容底部,自然得到末尾窗口。
fn code_visible_window(
  heights : Array[Double],
  spacing : Double,
  offset : Double,
  viewport : Double,
  overscan : Int,
) -> (Int, Int) {
  let n = heights.length()
  if n == 0 {
    return (0, 0)
  }
  let total = code_heights_total(heights, spacing)
  let max_scroll = (total - viewport).max(0.0)
  let top = offset.min(max_scroll).max(0.0)
  let bottom = top + viewport
  // 定位 first:含 `top` 的那条。
  let mut acc = 0.0
  let mut first = n - 1
  for i in 0..<n {
    let end = acc + heights[i]
    if end >= top {
      first = i
      break
    }
    acc = end + spacing
  }
  // 定位 last:起始位置超过 `bottom` 之后的那条(排他上界)。
  let mut acc2 = 0.0
  let mut last = 0
  for i in 0..<n {
    if acc2 > bottom {
      last = i
      break
    }
    last = i + 1
    acc2 = acc2 + heights[i] + spacing
  }
  first = (first - overscan).max(0)
  last = (last + overscan).min(n)
  (first, last)
}

///|
/// 窗口化:只构建可视区 ±overscan 内的消息行,窗口外用等高空占位(`spacer`),
/// 消息行带稳定 key(全局下标)。返回需放进 `list(spacing=4)` 的 rows。
fn code_message_window_rows(
  model : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
  viewport : Double,
) -> Array[@moui.View[CodeMsg]] {
  let messages = model.messages
  let n = messages.length()
  let rows : Array[@moui.View[CodeMsg]] = []
  if n == 0 {
    if code_should_show_streaming_placeholder(model) {
      rows.push(code_streaming_placeholder_row(model, theme, width))
    }
    return rows
  }
  let spacing = 4.0
  let heights = message_row_heights(messages, theme, width)
  let (first, last) = code_visible_window(
    heights,
    spacing,
    model.scroll_offset.y,
    viewport,
    12,
  )
  if first > 0 {
    let top = code_prefix_height(heights, spacing, first)
    if top > 0.0 {
      rows.push(@views.spacer(min_length=top, weight=0.0))
    }
  }
  for i in first..<last {
    let key = "msg-\{i}"
    let msg = if i == n - 1 && model.is_streaming {
      match messages[i] {
        Assistant(content, reasoning) =>
          throttled_assistant_message(
            content,
            reasoning,
            stream_message_key(model, i),
            theme,
            width,
          )
        other => other
      }
    } else {
      messages[i]
    }
    rows.push(message_row(msg, theme, width).key(key))
  }
  if last < n {
    // The list's inter-row spacing before this placeholder is supplied by
    // `@views.list`; exclude that one gap from the spacer itself.
    let bottom = (code_heights_total(heights, spacing) -
    code_prefix_height(heights, spacing, last) -
    spacing).max(0.0)
    if bottom > 0.0 {
      rows.push(@views.spacer(min_length=bottom, weight=0.0))
    }
  }
  if code_should_show_streaming_placeholder(model) {
    rows.push(code_streaming_placeholder_row(model, theme, width))
  }
  rows
}

///|
/// 流式消息的节流 key:优先 message_id(跨 rebuild 稳定),缺失时回退全局下标。
fn stream_message_key(model : CodeWorkspace, index : Int) -> String {
  match model.last_assistant_message_id {
    Some(id) => "msg-\{index}-\{id}"
    None => "msg-\{index}"
  }
}

///|
/// Streaming message timeline (chat mode). Renders each message via
/// `message_row` inside a scroll view bound to the workspace scroll state.
fn code_message_list(
  model : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
  height : Double,
) -> @moui.View[CodeMsg] {
  let inner_width = (width - 56.0).max(320.0)
  let inner_height = (height - 20.0).max(0.0)
  let rows = code_message_window_rows(model, theme, inner_width, inner_height)
  @views.padding_edges(
    @views.scroll_view(
      @views.list(rows, spacing=4.0),
      width=inner_width,
      height=inner_height,
      offset=model.scroll_offset,
      on_scroll=Some(offset => MessageListScrolled(offset)),
      request=@moui.ScrollRequest::new(
        id=model.scroll_request_id,
        offset=model.scroll_offset,
      ),
    ),
    top=12.0,
    left=28.0,
    right=28.0,
    bottom=8.0,
  )
}

///|
fn code_should_show_streaming_placeholder(model : CodeWorkspace) -> Bool {
  if !model.is_streaming {
    false
  } else if model.messages.is_empty() {
    true
  } else {
    match model.messages[model.messages.length() - 1] {
      Assistant(content, _) => content.trim().is_empty()
      _ => true
    }
  }
}

///|
fn code_activity_text(model : CodeWorkspace) -> String {
  match model.progress_notice {
    Some(text) => if text.is_empty() { "Working..." } else { text }
    None => "Working..."
  }
}

///|
fn code_streaming_placeholder_row(
  model : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let bubble_width = width * 0.82
  aligned_message_bubble(
    code_streaming_steer_panel(model, theme, bubble_width),
    width,
    bubble_width,
    false,
  )
}

///|
fn code_streaming_steer_panel(
  model : CodeWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let status_width = (width * 0.34).max(136.0).min(width - 180.0)
  let steer_width = (width - status_width - 104.0).max(120.0)
  @views.container(
    @views.row(
      [
        @views.container(
          @views.icon(Info, size=13.0, color=workbench_accent(theme)),
          width=22.0,
          height=22.0,
          background=workbench_accent_soft(theme),
          corner_radius=11.0,
          padding=0.0,
        ),
        @views.text(
          "AI " + truncate_text(code_activity_text(model), 32),
          role=Caption,
          theme~,
          width=status_width - 30.0,
          height=22.0,
        ).foreground(workbench_text_muted(theme)),
        @views.text_field(
          model.steer_text,
          on_input=value => SteerChanged(value),
          on_submit=Some(SubmitSteer),
          placeholder="Steer the running turn...",
          variant=Filled,
          theme~,
          width=steer_width,
          height=34.0,
        ),
        @views.button(
          "Steer",
          on_click=SubmitSteer,
          variant=Ghost,
          theme~,
          width=72.0,
          height=34.0,
        ),
      ],
      spacing=8.0,
      align=Center,
    ),
    width~,
    background=workbench_subtle_background(theme),
    corner_radius=12.0,
    border=Some(hairline_border(theme)),
    padding=8.0,
  )
}

///|
/// The chat-mode composer: prompt input + model/thinking pickers + Send, plus
/// a steer field while a turn is streaming.
fn code_composer(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let inner_width = (width - 56.0).max(320.0)
  let rows : Array[@moui.View[CodeMsg]] = []
  match model.error {
    Some(err) =>
      rows.push(
        @views.text(err, role=Caption, theme~, width=inner_width).foreground(
          theme.palette.danger,
        ),
      )
    None => ()
  }
  rows.push(code_composer_input_card(model, settings, theme, inner_width))
  if model.model_picker_open {
    rows.push(code_model_dropdown_panel(model, settings, theme, inner_width))
  }
  @views.padding_edges(
    @views.column(rows, spacing=6.0, align=Stretch),
    top=8.0,
    left=28.0,
    right=28.0,
    bottom=8.0,
  )
}

///|
fn code_composer_input_card(
  model : CodeWorkspace,
  settings : SettingsWorkspace,
  theme : @moui.Theme,
  width : Double,
) -> @moui.View[CodeMsg] {
  let send_diameter = 28.0
  let cancel_width = if model.is_streaming { 72.0 } else { 0.0 }
  let controls_width = (width - send_diameter - cancel_width - 34.0).max(120.0)
  let prompt_lines = code_composer_prompt_lines(model.prompt, theme, width)
  let prompt_height = code_composer_prompt_text_area_height(prompt_lines)
  let rows : Array[@moui.View[CodeMsg]] = []
  rows.push(
    @views.text_area(
      model.prompt,
      on_input=value => CodeMsg::PromptChanged(value),
      on_submit=Some(SubmitPrompt),
      placeholder=if model.is_streaming {
        "Agent 正在运行；可在上方 Steer 调整方向"
      } else {
        "继续描述你的任务…"
      },
      lines=prompt_lines,
      variant=Plain,
      theme~,
      width~,
      line_height=code_composer_prompt_line_height(),
    )
    .frame(height=prompt_height)
    .disabled(disabled=model.is_streaming),
  )
  rows.push(
    @views.row(
      [
        code_agent_controls(model, settings, theme, controls_width),
        @views.spacer(),
        if model.is_streaming {
          @views.button(
            "Cancel",
            on_click=CancelTurn,
            variant=Ghost,
            theme~,
            width=cancel_width,
            height=32.0,
          )
        } else {
          @views.container(
            @views.text("", role=Caption, theme~, width=0.0),
            width=0.0,
            height=0.0,
          )
        },
        workbench_send_button(
          theme,
          diameter=send_diameter,
          on_tap=CodeMsg::SubmitPrompt,
        ).disabled(disabled=model.is_streaming),
      ],
      spacing=6.0,
      align=Center,
    ),
  )
  @views.container(
    @views.column(rows, spacing=0.0, align=Stretch),
    width~,
    background=workbench_card_background(theme),
    corner_radius=14.0,
    border=None,
    padding=1.0,
  )
}

// ---------------------------------------------------------------------------
// Deprecated starter_card_grid / starter_card (replaced by quick_action_chips).
// These can be removed once all callers are migrated.
// ---------------------------------------------------------------------------