agent_ui: Add setting for turning off content max-width (#54316)

Follow up to https://github.com/zed-industries/zed/pull/52730. 

This PR adds a boolean setting `limit_content_width` in the Agent Panel
settings that allows turning off the content max-width entirely, which
was added for better readability. We had a handful of requests for it,
so it feels fair.

<img width="500" alt="Screenshot 2026-04-20 at 8  57@2x"
src="https://github.com/user-attachments/assets/d2540b35-3fa8-4424-895d-dc499ac4839c"
/>

Release Notes:

- Agent: Added a new `limit_content_width` setting in the agent panel
that allows turning off the content max-width limit.

assets/settings/default.json

@@ -992,7 +992,11 @@
     "default_width": 640,
     // Default height when the agent panel is docked to the bottom.
     "default_height": 320,
-    // Maximum content width when the agent panel is wider than this value.
+    // Whether to limit the content width in the agent panel. When enabled,
+    // content will be constrained to `max_content_width` and centered when
+    // the panel is wider, for optimal readability.
+    "limit_content_width": true,
+    // Maximum content width in pixels when limit_content_width is enabled.
     // Content will be centered within the panel.
     "max_content_width": 850,
     // The default model to use when creating new threads.

crates/agent/src/tool_permissions.rs

@@ -574,7 +574,7 @@ mod tests {
             flexible: true,
             default_width: px(300.),
             default_height: px(600.),
-            max_content_width: px(850.),
+            max_content_width: Some(px(850.)),
             default_model: None,
             inline_assistant_model: None,
             inline_assistant_use_streaming_tools: false,

crates/agent_settings/src/agent_settings.rs

@@ -142,7 +142,7 @@ pub struct AgentSettings {
     pub sidebar_side: SidebarDockPosition,
     pub default_width: Pixels,
     pub default_height: Pixels,
-    pub max_content_width: Pixels,
+    pub max_content_width: Option<Pixels>,
     pub default_model: Option<LanguageModelSelection>,
     pub inline_assistant_model: Option<LanguageModelSelection>,
     pub inline_assistant_use_streaming_tools: bool,
@@ -593,7 +593,11 @@ impl Settings for AgentSettings {
             sidebar_side: agent.sidebar_side.unwrap(),
             default_width: px(agent.default_width.unwrap()),
             default_height: px(agent.default_height.unwrap()),
-            max_content_width: px(agent.max_content_width.unwrap()),
+            max_content_width: if agent.limit_content_width.unwrap() {
+                Some(px(agent.max_content_width.unwrap()))
+            } else {
+                None
+            },
             flexible: agent.flexible.unwrap(),
             default_model: Some(agent.default_model.unwrap()),
             inline_assistant_model: agent.inline_assistant_model,

crates/agent_ui/src/agent_panel.rs

@@ -3553,9 +3553,8 @@ impl AgentPanel {
 
         let base_container = h_flex()
             .size_full()
-            // TODO: This is only until we remove Agent settings from the panel.
             .when(!is_in_history_or_config, |this| {
-                this.max_w(max_content_width).mx_auto()
+                this.when_some(max_content_width, |this, max_w| this.max_w(max_w).mx_auto())
             })
             .flex_none()
             .justify_between()

crates/agent_ui/src/agent_ui.rs

@@ -733,7 +733,7 @@ mod tests {
             flexible: true,
             default_width: px(300.),
             default_height: px(600.),
-            max_content_width: px(850.),
+            max_content_width: Some(px(850.)),
             default_model: None,
             inline_assistant_model: None,
             inline_assistant_use_streaming_tools: false,

crates/agent_ui/src/conversation_view/thread_view.rs

@@ -2289,7 +2289,8 @@ impl ThreadView {
             .justify_center()
             .child(
                 v_flex()
-                    .flex_basis(max_content_width)
+                    .when_some(max_content_width, |this, max_w| this.flex_basis(max_w))
+                    .when(max_content_width.is_none(), |this| this.w_full())
                     .flex_shrink()
                     .flex_grow_0()
                     .max_w_full()
@@ -3195,8 +3196,7 @@ impl ThreadView {
                 .child(
                     h_flex()
                         .size_full()
-                        .max_w(max_content_width)
-                        .mx_auto()
+                        .when_some(max_content_width, |this, max_w| this.max_w(max_w).mx_auto())
                         .pl_2()
                         .pr_1()
                         .flex_shrink_0()
@@ -3293,7 +3293,8 @@ impl ThreadView {
             })
             .child(
                 v_flex()
-                    .flex_basis(max_content_width)
+                    .when_some(max_content_width, |this, max_w| this.flex_basis(max_w))
+                    .when(max_content_width.is_none(), |this| this.w_full())
                     .flex_shrink()
                     .flex_grow_0()
                     .when(fills_container, |this| this.h_full())
@@ -4481,10 +4482,12 @@ impl ThreadView {
     fn render_entries(&mut self, cx: &mut Context<Self>) -> List {
         let max_content_width = AgentSettings::get_global(cx).max_content_width;
         let centered_container = move |content: AnyElement| {
-            h_flex()
-                .w_full()
-                .justify_center()
-                .child(div().max_w(max_content_width).w_full().child(content))
+            h_flex().w_full().justify_center().child(
+                div()
+                    .when_some(max_content_width, |this, max_w| this.max_w(max_w))
+                    .w_full()
+                    .child(content),
+            )
         };
 
         list(

crates/settings_content/src/agent.rs

@@ -128,6 +128,12 @@ pub struct AgentSettingsContent {
     /// Default: 320
     #[serde(serialize_with = "crate::serialize_optional_f32_with_two_decimal_places")]
     pub default_height: Option<f32>,
+    /// Whether to limit the content width in the agent panel. When enabled,
+    /// content will be constrained to `max_content_width` and centered when
+    /// the panel is wider than that value, for optimal readability.
+    ///
+    /// Default: true
+    pub limit_content_width: Option<bool>,
     /// Maximum content width in pixels for the agent panel. Content will be
     /// centered when the panel is wider than this value.
     ///

crates/settings_ui/src/page_data.rs

@@ -5859,23 +5859,58 @@ fn panels_page() -> SettingsPage {
                 metadata: None,
                 files: USER,
             }),
-            SettingsPageItem::SettingItem(SettingItem {
-                title: "Agent Panel Max Content Width",
-                description: "Maximum content width in pixels. Content will be centered when the panel is wider than this value.",
-                field: Box::new(SettingField {
-                    json_path: Some("agent.max_content_width"),
-                    pick: |settings_content| {
-                        settings_content.agent.as_ref()?.max_content_width.as_ref()
-                    },
-                    write: |settings_content, value| {
-                        settings_content
-                            .agent
-                            .get_or_insert_default()
-                            .max_content_width = value;
-                    },
-                }),
-                metadata: None,
-                files: USER,
+            SettingsPageItem::DynamicItem(DynamicItem {
+                discriminant: SettingItem {
+                    files: USER,
+                    title: "Limit Content Width",
+                    description: "Whether to constrain the agent panel content to a maximum width, centering it when the panel is wider, for optimal readability.",
+                    field: Box::new(SettingField::<bool> {
+                        json_path: Some("agent.limit_content_width"),
+                        pick: |settings_content| {
+                            settings_content
+                                .agent
+                                .as_ref()?
+                                .limit_content_width
+                                .as_ref()
+                        },
+                        write: |settings_content, value| {
+                            settings_content
+                                .agent
+                                .get_or_insert_default()
+                                .limit_content_width = value;
+                        },
+                    }),
+                    metadata: None,
+                },
+                pick_discriminant: |settings_content| {
+                    let enabled = settings_content
+                        .agent
+                        .as_ref()?
+                        .limit_content_width
+                        .unwrap_or(true);
+                    Some(if enabled { 1 } else { 0 })
+                },
+                fields: vec![
+                    vec![],
+                    vec![SettingItem {
+                        files: USER,
+                        title: "Max Content Width",
+                        description: "Maximum content width in pixels. Content will be centered when the panel is wider than this value.",
+                        field: Box::new(SettingField {
+                            json_path: Some("agent.max_content_width"),
+                            pick: |settings_content| {
+                                settings_content.agent.as_ref()?.max_content_width.as_ref()
+                            },
+                            write: |settings_content, value| {
+                                settings_content
+                                    .agent
+                                    .get_or_insert_default()
+                                    .max_content_width = value;
+                            },
+                        }),
+                        metadata: None,
+                    }],
+                ],
             }),
         ]
     }