acp: Keep diff editors in sync with AgentFontSize global (#37559)

Release Notes:

- agent: Fixed `cmd-+` and `cmd--` not affecting the font size of diffs.

crates/agent_ui/src/acp/entry_view_state.rs

@@ -207,7 +207,7 @@ impl EntryViewState {
         self.entries.drain(range);
     }
 
-    pub fn settings_changed(&mut self, cx: &mut App) {
+    pub fn agent_font_size_changed(&mut self, cx: &mut App) {
         for entry in self.entries.iter() {
             match entry {
                 Entry::UserMessage { .. } | Entry::AssistantMessage { .. } => {}

crates/agent_ui/src/acp/thread_view.rs

@@ -43,7 +43,7 @@ use std::{collections::BTreeMap, rc::Rc, time::Duration};
 use task::SpawnInTerminal;
 use terminal_view::terminal_panel::TerminalPanel;
 use text::Anchor;
-use theme::ThemeSettings;
+use theme::{AgentFontSize, ThemeSettings};
 use ui::{
     Callout, CommonAnimationExt, Disclosure, Divider, DividerColor, ElevationIndex, KeyBinding,
     PopoverMenuHandle, Scrollbar, ScrollbarState, SpinnerLabel, TintColor, Tooltip, prelude::*,
@@ -290,7 +290,7 @@ pub struct AcpThreadView {
     is_loading_contents: bool,
     new_server_version_available: Option<SharedString>,
     _cancel_task: Option<Task<()>>,
-    _subscriptions: [Subscription; 3],
+    _subscriptions: [Subscription; 4],
 }
 
 enum ThreadState {
@@ -380,7 +380,8 @@ impl AcpThreadView {
         });
 
         let subscriptions = [
-            cx.observe_global_in::<SettingsStore>(window, Self::settings_changed),
+            cx.observe_global_in::<SettingsStore>(window, Self::agent_font_size_changed),
+            cx.observe_global_in::<AgentFontSize>(window, Self::agent_font_size_changed),
             cx.subscribe_in(&message_editor, window, Self::handle_message_editor_event),
             cx.subscribe_in(&entry_view_state, window, Self::handle_entry_view_event),
         ];
@@ -4735,9 +4736,9 @@ impl AcpThreadView {
         )
     }
 
-    fn settings_changed(&mut self, _window: &mut Window, cx: &mut Context<Self>) {
+    fn agent_font_size_changed(&mut self, _window: &mut Window, cx: &mut Context<Self>) {
         self.entry_view_state.update(cx, |entry_view_state, cx| {
-            entry_view_state.settings_changed(cx);
+            entry_view_state.agent_font_size_changed(cx);
         });
     }
 

crates/theme/src/settings.rs

@@ -253,8 +253,9 @@ pub(crate) struct UiFontSize(Pixels);
 
 impl Global for UiFontSize {}
 
+/// In-memory override for the font size in the agent panel.
 #[derive(Default)]
-pub(crate) struct AgentFontSize(Pixels);
+pub struct AgentFontSize(Pixels);
 
 impl Global for AgentFontSize {}