Capture · Roots: roots drop w_full; hosts give the width

145 component roots drop w_full, the early returns included. Three
field rows keep it, Input, InputGroup and TagInput: stretched without
a width, taffy 0.9 laid the field's flex_1 share at no width in the
template picker at 280px, and the placeholder drew nothing. Container
keeps it, since mx_auto needs a width to fill.

Hosts that relied on a root's width now give it: MessageList boxes
each row at the list's width, the splash gives its bar the column's,
and test stages that mount a component as the window's root sit in a
size_full box. Tests hold a narrow row across the list and the splash
bar across its column; each goes red without its fix.

The gallery gains --narrow <px>, which lays each page in a padded
card at that width and shoots it without its script. The page
header wraps: the title takes the room and the theme switcher drops
below, where a long summary used to push it past the edge. A file
panel step waits for the panel to become key instead of a fixed
pause, which lost a race in a capture.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/chat/actions.rs

@@ -74,7 +74,6 @@ impl RenderOnce for QuoteReply {
         let colors = theme.colors.clone();
         let line = self.text.lines().next().unwrap_or_default().to_string();
         div()
-            .w_full()
             .flex()
             .items_center()
             .gap_2()
@@ -261,7 +260,6 @@ impl RenderOnce for MessageEditor {
             self.on_cancel,
         );
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_2()

src/chat/cite.rs

@@ -105,7 +105,6 @@ impl RenderOnce for SourceCard {
         let open = self.on_open;
         div()
             .id(self.id.clone())
-            .w_full()
             .p_2p5()
             .rounded(theme.radius(Radius::Md))
             .border_1()
@@ -222,7 +221,6 @@ impl RenderOnce for SourceList {
             .take(3)
             .collect();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_2()

src/chat/code.rs

@@ -94,7 +94,6 @@ impl RenderOnce for CodeBlock {
         let lines = code.lines().count();
         let toggle = open.clone();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .rounded(theme.radius(Radius::Md))

src/chat/conversations.rs

@@ -179,7 +179,6 @@ impl RenderOnce for ConversationItem {
             .id(self.id.clone())
             .group(group.clone())
             .track_focus(&focus)
-            .w_full()
             .flex()
             .items_center()
             .gap_1()

src/chat/list.rs

@@ -105,7 +105,16 @@ impl RenderOnce for MessageList {
         div()
             .relative()
             .size_full()
-            .child(list(state, move |ix, window, cx| render(ix, window, cx)).size_full())
+            // gpui's list lays rows at content width.
+            .child(
+                list(state, move |ix, window, cx| {
+                    div()
+                        .w_full()
+                        .child(render(ix, window, cx))
+                        .into_any_element()
+                })
+                .size_full(),
+            )
             .child(
                 canvas(
                     move |_, window, cx| {
@@ -234,8 +243,10 @@ impl RenderOnce for DateSeparator {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         let rule = || div().flex_1().h_px().bg(colors.border);
+        let name = day_name(self.day, self.today);
+        let shown = format!("date-separator-{name}");
         div()
-            .w_full()
+            .debug_selector(move || shown)
             .flex()
             .items_center()
             .gap_3()
@@ -245,7 +256,7 @@ impl RenderOnce for DateSeparator {
                 div()
                     .text_size(theme.text_size(TextSize::Xs))
                     .text_color(colors.fg_subtle)
-                    .child(day_name(self.day, self.today)),
+                    .child(name),
             )
             .child(rule())
     }

src/chat/media.rs

@@ -72,7 +72,6 @@ impl RenderOnce for ImageMessage {
         let widest = theme.prose_width().to_pixels(window.rem_size());
         let open = self.on_open;
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_1()
@@ -235,7 +234,6 @@ impl RenderOnce for FileMessage {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         div()
-            .w_full()
             .max_w(theme.prose_width())
             .flex()
             .items_center()
@@ -339,7 +337,6 @@ impl RenderOnce for LinkPreviewCard {
         let open = self.on_open;
         div()
             .id(self.id.clone())
-            .w_full()
             .max_w(theme.container_width(ContainerSize::Sm))
             .flex()
             .gap_3()

src/chat/params.rs

@@ -81,7 +81,6 @@ impl RenderOnce for ParameterPanel {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_4()
@@ -274,7 +273,6 @@ impl RenderOnce for SystemPromptEditor {
     fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
         let theme = cx.theme();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_2()

src/chat/play.rs

@@ -97,7 +97,6 @@ impl RenderOnce for AudioMessage {
         let playing = self.playing;
         let tall = theme.control_height(ControlSize::Md);
         div()
-            .w_full()
             .max_w(theme.prose_width())
             .flex()
             .items_center()

src/chat/projects.rs

@@ -62,7 +62,6 @@ impl RenderOnce for ProjectList {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_0p5()
@@ -163,7 +162,6 @@ impl RenderOnce for ProjectKnowledgePanel {
         let used: u64 = self.files.iter().map(|(_, bytes)| bytes).sum();
         let share = used as f32 / self.capacity as f32;
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_3()

src/chat/search.rs

@@ -164,7 +164,6 @@ impl RenderOnce for WebResultCard {
         let open = self.on_open;
         div()
             .id(self.id.clone())
-            .w_full()
             .flex()
             .flex_col()
             .gap_0p5()
@@ -273,7 +272,6 @@ impl RenderOnce for DocumentChunkPreview {
             ..HighlightStyle::default()
         };
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_1p5()

src/chat/status.rs

@@ -112,7 +112,6 @@ impl RenderOnce for RateLimitNotice {
             None => countdown,
         };
         div()
-            .w_full()
             .flex()
             .items_center()
             .gap_3()
@@ -198,7 +197,6 @@ impl RenderOnce for FeedbackForm {
         let ready = !self.picked.is_empty() || !self.note.read(cx).text().trim().is_empty();
         let (pick, send) = (self.on_pick, self.on_send);
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_3()
@@ -356,7 +354,6 @@ impl RenderOnce for ThinkingBlock {
             ThinkingDuration::new(self.took).into_any_element()
         };
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_2()

src/chat/tests/mod.rs

@@ -13,7 +13,8 @@ mod history;
 mod welcome;
 
 use super::{
-    ImageMessage, MessageAvatar, MessageBubble, MessageEditor, MessageList, Role, ThinkingBlock,
+    DateSeparator, ImageMessage, MessageAvatar, MessageBubble, MessageEditor, MessageList, Role,
+    ThinkingBlock,
 };
 use crate::{forms, forms::TextInput, theme::Theme};
 
@@ -361,3 +362,29 @@ fn the_reasoning_opens_from_the_keyboard(cx: &mut TestAppContext) {
         "Tab and Space open it: {closed:?} to {open:?}"
     );
 }
+
+struct Dated;
+
+impl Render for Dated {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        let day = jiff::civil::date(2026, 9, 28);
+        div()
+            .size_full()
+            .child(MessageList::new("dated", 1, move |_, _, _| {
+                DateSeparator::new(day, day).into_any_element()
+            }))
+    }
+}
+
+/// A row no wider than its words still spans the list.
+#[gpui::test]
+fn a_narrow_row_spans_the_list(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    let (_, cx) = cx.add_window_view(|_, _| Dated);
+    settle(cx);
+    let row = cx
+        .debug_bounds("date-separator-Today")
+        .expect("the separator draws");
+    let width = cx.update(|window, _| window.viewport_size().width);
+    assert_eq!(row.size.width, width);
+}

src/chat/welcome.rs

@@ -180,7 +180,6 @@ impl RenderOnce for FollowUpSuggestions {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .children(
@@ -253,7 +252,6 @@ impl RenderOnce for CapabilityCards {
         let theme = cx.theme();
         let colors = theme.colors.clone();
         div()
-            .w_full()
             .grid()
             .grid_cols(3)
             .gap_3()