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/mail/boxes.rs

@@ -2,7 +2,7 @@ use std::rc::Rc;
 
 use gpui::{
     App, ElementId, InteractiveElement, IntoElement, ParentElement, RenderOnce, SharedString,
-    Styled, Window, div,
+    Window, div,
 };
 
 use super::labels::hue_dot;
@@ -173,14 +173,11 @@ impl RenderOnce for MailboxList {
                 sections.section(title.clone(), rows)
             },
         );
-        div()
-            .debug_selector(|| "mailbox-list".into())
-            .w_full()
-            .child(
-                sections
-                    .selected(self.open)
-                    .on_select(open.clone())
-                    .on_activate(open),
-            )
+        div().debug_selector(|| "mailbox-list".into()).child(
+            sections
+                .selected(self.open)
+                .on_select(open.clone())
+                .on_activate(open),
+        )
     }
 }

src/mail/compose.rs

@@ -330,7 +330,6 @@ impl RenderOnce for MailComposer {
         });
         div()
             .debug_selector(|| "mail-composer".into())
-            .w_full()
             .flex()
             .flex_col()
             .gap_3()

src/mail/labels.rs

@@ -240,7 +240,6 @@ impl RenderOnce for LabelPicker {
         let (up, down, chosen) = (finding.clone(), finding.clone(), finding);
         div()
             .id(self.id.clone())
-            .w_full()
             .flex()
             .flex_col()
             .gap_2()

src/mail/list.rs

@@ -290,7 +290,6 @@ impl RenderOnce for MailList {
         if self.mails.is_empty() {
             return div()
                 .debug_selector(|| "mail-none".into())
-                .w_full()
                 .px_3()
                 .py_4()
                 .text_size(theme.text_size(TextSize::Sm))
@@ -320,7 +319,6 @@ impl RenderOnce for MailList {
         let (id, on_select) = (self.id.clone(), self.on_select);
         div()
             .debug_selector(|| "mail-list".into())
-            .w_full()
             .child(
                 list.selected(self.selected)
                     .on_change(move |keys, window, cx| {

src/mail/reader.rs

@@ -344,7 +344,6 @@ impl RenderOnce for MailReader {
         let theme = cx.theme();
         div()
             .debug_selector(|| "mail-reader".into())
-            .w_full()
             .flex()
             .flex_col()
             .gap_4()

src/mail/signature.rs

@@ -124,7 +124,6 @@ impl RenderOnce for SignatureEditor {
         let words = input.read(cx).text().to_string();
         let theme = cx.theme();
         div()
-            .w_full()
             .flex()
             .flex_col()
             .gap_3()

src/mail/thread.rs

@@ -199,7 +199,6 @@ impl RenderOnce for MailThreadView {
         );
         div()
             .debug_selector(|| "mail-thread".into())
-            .w_full()
             .flex()
             .flex_col()
             .gap_3()