feat: the header plate shrinks to its content; buttons sit on the date line

The header plate is now as tall as what it holds: the date line's bottom,
or the attachment chip row's when the message on show has server
attachments. The HTML-view buttons add no height any more — they keep the
right edge but move up so their bottoms align with the date line. Since
they now share the band of the To and Date lines, those two lines are
ellipsized short of the buttons while the buttons are on show, so a long
address list cannot run under them; the subject and From line above stay
full width.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

 src/main.rs | 78 +++++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 63 insertions(+), 15 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 218c38e..88ee1bd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -772,16 +772,21 @@ const SEARCH_ROW_H: f32 = 26.0;
 // (`detail_origin_y`). The header (subject, From/To/Date, attachment chips
 // and the HTML-view buttons) is a plate of its own above the preview
 // plate, so the body no longer has an offset in this list: it starts one
-// padding inside the preview plate (`detail_body_geom`). The chips and the
-// buttons share the last row, and the header plate's height falls out of
-// that row's bottom (`DETAIL_HEADER_CONTENT_H`) rather than being a number
-// of its own.
+// padding inside the preview plate (`detail_body_geom`). The plate is as
+// tall as what it holds (`detail_header_content_h`): the date line's
+// bottom, or the chip row's when the message has attachments. The
+// HTML-view buttons add no height — they ride the right edge with their
+// bottoms on the date line.
 const DETAIL_SUBJECT_Y: f32 = 0.0;
 const DETAIL_FROM_Y: f32 = 25.0;
 const DETAIL_TO_Y: f32 = 45.0;
 const DETAIL_DATE_Y: f32 = 65.0;
+/// The 11px metadata lines' box height: where the date line's bottom is,
+/// which the buttons align to and the plate ends at without chips.
+const DETAIL_LINE_H: f32 = 14.0;
+const DETAIL_LINES_BOTTOM: f32 = DETAIL_DATE_Y + DETAIL_LINE_H;
 const DETAIL_CHIPS_Y: f32 = 80.0;
-const DETAIL_HEADER_CONTENT_H: f32 = DETAIL_CHIPS_Y + COMPOSE_BTN_H;
+const DETAIL_CHIP_H: f32 = 22.0;
 
 // Compose modal geometry. One source of truth: the background quads, the
 // input rects, the labels, the chip row and the outside-click test all
@@ -905,7 +910,7 @@ fn detail_chip_rects(atts: &[RemoteAttachment], detail_x: f32, origin_y: f32) ->
     let y = origin_y + DETAIL_CHIPS_Y;
     for att in atts {
         let w = detail_chip_label(att).chars().count() as f32 * 6.0 + 2.0 * cce_ui::layout::CONTROL_TEXT_INSET;
-        rects.push((x, y, w, 22.0));
+        rects.push((x, y, w, DETAIL_CHIP_H));
         x += w + cce_ui::layout::plate_gap();
     }
     rects
@@ -3333,14 +3338,45 @@ impl ClearEmailApp {
         (x, w)
     }
 
+    /// Height of the header plate's content: down to the date line, or to
+    /// the chip row when the message on show has server attachments. The
+    /// buttons never add to it — they sit within the lines' band.
+    fn detail_header_content_h(&self) -> f32 {
+        let chips = self
+            .selected_email_id
+            .and_then(|id| self.emails.iter().find(|e| e.id == id))
+            .is_some_and(|e| !e.remote_attachments.is_empty());
+        if chips {
+            DETAIL_CHIPS_Y + DETAIL_CHIP_H
+        } else {
+            DETAIL_LINES_BOTTOM
+        }
+    }
+
     /// The header plate: (x, y, w, h), at the top of the detail column. It
     /// holds the subject, the address lines, the attachment chips and the
     /// HTML-view buttons — everything about the message that is not the
-    /// message — and is exactly as tall as that content plus its padding.
+    /// message — and is exactly as tall as that content plus its padding,
+    /// so it shrinks when there are no chips.
     fn detail_header_geom(&self) -> (f32, f32, f32, f32) {
         let (x, w) = self.detail_column();
         let (top, _) = self.list_geom();
-        (x, top, w, DETAIL_HEADER_CONTENT_H + 2.0 * pane_inner_pad())
+        (x, top, w, self.detail_header_content_h() + 2.0 * pane_inner_pad())
+    }
+
+    /// The left edge of the HTML-view buttons on show, if any — the header
+    /// lines sharing their band are ellipsized short of it.
+    #[cfg(feature = "wpe")]
+    fn html_buttons_left(&self) -> Option<f32> {
+        [&self.btn_html_view, &self.btn_html_images]
+            .into_iter()
+            .map(|b| b.rect().0)
+            .filter(|x| *x > -9000.0)
+            .min_by(|a, b| a.total_cmp(b))
+    }
+    #[cfg(not(feature = "wpe"))]
+    fn html_buttons_left(&self) -> Option<f32> {
+        None
     }
 
     /// The preview plate: (x, y, w, h), the rest of the detail column below
@@ -3688,17 +3724,18 @@ impl ClearEmailApp {
         ((px - x) * s, (py - y) * s)
     }
 
-    /// Place the HTML-view buttons in the detail header band, right-aligned
-    /// so they never collide with the attachment chips growing from the
-    /// left. A button that does not apply is parked off-screen (the
-    /// email_buttons convention), which keeps it out of hit-testing too.
-    /// Runs before every paint, so events hit the rects on screen.
+    /// Place the HTML-view buttons in the header plate, right-aligned with
+    /// their bottoms on the date line, so they never collide with the
+    /// attachment chips growing from the left below. A button that does not
+    /// apply is parked off-screen (the email_buttons convention), which
+    /// keeps it out of hit-testing too. Runs before every paint, so events
+    /// hit the rects on screen.
     #[cfg(feature = "wpe")]
     fn layout_html_buttons(&mut self) {
         let shown = !self.compose_open
             && self.selected_email_id.is_some()
             && self.html_loaded == self.selected_email_id;
-        let y = self.detail_origin_y() + DETAIL_CHIPS_Y;
+        let y = self.detail_origin_y() + DETAIL_LINES_BOTTOM - COMPOSE_BTN_H;
         let (px, _, pw, _) = self.detail_pane_geom();
         let mut right = px + pw - pane_inner_pad();
         let view_label = if self.show_text { "View: Text" } else { "View: HTML" };
@@ -4041,9 +4078,20 @@ impl ClearEmailApp {
                     (format!("To:   {}", email.to), DETAIL_TO_Y, 11.0, [0x83, 0x83, 0x8a]),
                     (format!("Date: {}", email.date), DETAIL_DATE_Y, 11.0, [0x83, 0x83, 0x8a]),
                 ];
+                // The buttons stand on the date line at the right edge, so
+                // any line whose box reaches into their band stops short of
+                // them; the subject and From above stay full width.
+                let buttons_left = self.html_buttons_left();
                 for (text, dy, font_size, color) in header_lines {
+                    let mut w = content_w;
+                    if let Some(bl) = buttons_left {
+                        let buttons_top = DETAIL_LINES_BOTTOM - COMPOSE_BTN_H;
+                        if dy + DETAIL_LINE_H > buttons_top {
+                            w = w.min(bl - cce_ui::layout::plate_gap() - detail_x);
+                        }
+                    }
                     pc.text_with(
-                        ellipsize_to_width(&text, font_size, content_w),
+                        ellipsize_to_width(&text, font_size, w),
                         detail_x,
                         self.detail_origin_y() + dy,
                         font_size,