feat: add floating popup panes

refs #1125

docs/next/CHANGELOG.md

@@ -41,6 +41,7 @@
 - Added `herdr terminal session control` for bridge processes that need live ANSI frames plus input, resize, scroll, release, and takeover authority.
 - Added `ui.hide_tab_bar_when_single_tab` to hide the tab row when a workspace has one tab. (#448)
 - Added Japanese and Simplified Chinese website docs.
+- Added session-modal popup terminal panes for custom command keybindings and plugin panes, so tools such as `lazygit` or plugin pickers can open without changing the tab layout. (#1125)
 
 ### Changed
 - The mobile switcher now starts from an agents-first summary and renders worktrees as a tree, making narrow terminals easier to scan.

docs/next/api/herdr-api.schema.json

@@ -3052,6 +3052,16 @@
               "default": false,
               "type": "boolean"
             },
+            "height": {
+              "anyOf": [
+                {
+                  "$ref": "#/schemas/request/$defs/PopupSize"
+                },
+                {
+                  "type": "null"
+                }
+              ]
+            },
             "placement": {
               "anyOf": [
                 {
@@ -3071,6 +3081,16 @@
                 "null"
               ]
             },
+            "width": {
+              "anyOf": [
+                {
+                  "$ref": "#/schemas/request/$defs/PopupSize"
+                },
+                {
+                  "type": "null"
+                }
+              ]
+            },
             "workspace_id": {
               "type": [
                 "string",
@@ -3087,6 +3107,7 @@
         "PluginPanePlacement": {
           "enum": [
             "overlay",
+            "popup",
             "split",
             "tab",
             "zoomed"
@@ -3175,6 +3196,21 @@
           ],
           "type": "object"
         },
+        "PopupSize": {
+          "oneOf": [
+            {
+              "description": "Outer popup size in terminal cells, including the border.",
+              "maximum": 65535,
+              "minimum": 0,
+              "type": "integer"
+            },
+            {
+              "description": "Outer popup size as a percentage of the terminal area, for example 80%.",
+              "pattern": "^(100|[1-9][0-9]?)%$",
+              "type": "string"
+            }
+          ]
+        },
         "ReadFormat": {
           "enum": [
             "text",
@@ -5027,6 +5063,22 @@
           ],
           "type": "object"
         },
+        {
+          "properties": {
+            "method": {
+              "const": "popup.close",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/schemas/request/$defs/EmptyParams"
+            }
+          },
+          "required": [
+            "method",
+            "params"
+          ],
+          "type": "object"
+        },
         {
           "properties": {
             "method": {
@@ -7756,6 +7808,16 @@
                 "null"
               ]
             },
+            "height": {
+              "anyOf": [
+                {
+                  "$ref": "#/schemas/success_response/$defs/PopupSize"
+                },
+                {
+                  "type": "null"
+                }
+              ]
+            },
             "id": {
               "type": "string"
             },
@@ -7774,6 +7836,16 @@
             },
             "title": {
               "type": "string"
+            },
+            "width": {
+              "anyOf": [
+                {
+                  "$ref": "#/schemas/success_response/$defs/PopupSize"
+                },
+                {
+                  "type": "null"
+                }
+              ]
             }
           },
           "required": [
@@ -7805,6 +7877,7 @@
         "PluginPanePlacement": {
           "enum": [
             "overlay",
+            "popup",
             "split",
             "tab",
             "zoomed"
@@ -7879,6 +7952,21 @@
           ],
           "type": "string"
         },
+        "PopupSize": {
+          "oneOf": [
+            {
+              "description": "Outer popup size in terminal cells, including the border.",
+              "maximum": 65535,
+              "minimum": 0,
+              "type": "integer"
+            },
+            {
+              "description": "Outer popup size as a percentage of the terminal area, for example 80%.",
+              "pattern": "^(100|[1-9][0-9]?)%$",
+              "type": "string"
+            }
+          ]
+        },
         "ReadFormat": {
           "enum": [
             "text",

docs/next/website/src/content/docs/cli-reference.mdx

@@ -404,7 +404,7 @@ herdr plugin log list [--plugin ID] [--limit N]
 Managed terminal panes:
 
 ```bash
-herdr plugin pane open --plugin ID --entrypoint ID [--placement overlay|split|tab|zoomed] [--workspace ID] [--target-pane PANE] [--direction right|down] [--cwd PATH] [--env KEY=VALUE] [--focus|--no-focus]
+herdr plugin pane open --plugin ID --entrypoint ID [--placement overlay|popup|split|tab|zoomed] [--width SIZE] [--height SIZE] [--workspace ID] [--target-pane PANE] [--direction right|down] [--cwd PATH] [--env KEY=VALUE] [--focus|--no-focus]
 herdr plugin pane focus <pane_id>
 herdr plugin pane close <pane_id>
 ```
@@ -413,7 +413,12 @@ herdr plugin pane close <pane_id>
 with the current platform. It starts a manifest-declared `[[panes]]` command as
 a Herdr-managed terminal pane. The manifest default is `overlay`, which opens a
 temporary zoomed overlay over the active pane. It can also open as a split, a
-new tab, or a zoomed pane. Native non-terminal plugin panes are a later surface.
+new tab, a zoomed pane, or a session-modal `popup` that does not change the tab
+layout. `--width` and `--height` set the outer popup dimensions in terminal
+cells or percentages such as `80%`; omitted dimensions default to half the
+terminal size, and values smaller than the popup minimum are clamped. A popup
+is not a Herdr pane, does not export `HERDR_PANE_ID`, and does not participate
+in pane or agent APIs. Native non-terminal plugin panes are a later surface.
 
 `--env KEY=VALUE` can be repeated on process-launching commands. It applies to the newly launched process only. Herdr-managed variables such as `HERDR_SOCKET_PATH`, `HERDR_BIN_PATH`, `HERDR_ENV`, `HERDR_WORKSPACE_ID`, `HERDR_TAB_ID`, `HERDR_PANE_ID`, `HERDR_PLUGIN_ID`, `HERDR_PLUGIN_ROOT`, `HERDR_PLUGIN_CONFIG_DIR`, `HERDR_PLUGIN_STATE_DIR`, `HERDR_PLUGIN_ENTRYPOINT_ID`, and `HERDR_PLUGIN_CONTEXT_JSON` stay authoritative when they conflict with caller-provided env.
 

docs/next/website/src/content/docs/configuration.mdx

@@ -163,12 +163,22 @@ Custom commands use the same keybinding syntax.
 ```toml
 [[keys.command]]
 key = "prefix+alt+g"
-type = "pane"
+type = "popup"
 command = "lazygit"
 description = "run lazygit"
+width = "80%"
+height = "80%"
 ```
 
-`type = "pane"` opens a temporary pane and closes it when the command exits.
+`type = "popup"` opens a session-modal popup without changing the tab layout.
+The popup receives all terminal input, including Escape, until its command
+exits. `width` and `height` are optional; omit them for the default half-size
+popup, use numbers for terminal cells, or use strings like `"80%"` for a
+percentage of the terminal area. Dimensions include the popup border, and
+values smaller than the popup minimum are clamped. Popup commands do not receive
+`HERDR_PANE_ID`; use `HERDR_ACTIVE_PANE_ID` for the underlying tiled pane.
+
+`type = "pane"` opens a temporary zoomed pane and closes it when the command exits.
 
 `type = "shell"` runs detached in the background.
 

docs/next/website/src/content/docs/plugins.mdx

@@ -259,12 +259,27 @@ while Windows clients connect to a named pipe. CLI calls through
 Manifest pane `placement` defaults to `overlay`, which opens a temporary zoomed
 overlay over the active pane and restores the previous focus and zoom when it
 closes. A `plugin.pane.open` request can override the manifest placement with
-`overlay`, `split`, `tab`, or `zoomed`.
+`overlay`, `popup`, `split`, `tab`, or `zoomed`.
 
-Plugin panes are normal Herdr panes after they open. Plugins can call standard
-pane APIs such as `pane.move`, `pane.swap`, `pane.resize`, and `pane.zoom`
-through the socket or CLI; Herdr keeps plugin pane ownership attached to the
-underlying pane when it moves across tabs or workspaces.
+`placement = "popup"` opens a session-modal terminal popup without changing the
+tiled layout. It accepts optional `width` and `height` fields in the manifest or
+open request; omit them for the default half-size popup, use numbers for outer
+terminal-cell dimensions, or use strings like `"80%"` for a percentage of the
+terminal area. It receives all terminal input, including Escape, and closes
+when the command exits or a `popup.close` request is sent. Dimensions smaller
+than the popup minimum are clamped.
+
+Split, tab, zoomed, and overlay plugin panes are normal Herdr panes after they
+open. Plugins can call standard pane APIs such as `pane.move`, `pane.swap`,
+`pane.resize`, and `pane.zoom` through the socket or CLI; Herdr keeps plugin
+pane ownership attached to the underlying pane when it moves across tabs or
+workspaces. A popup is a singleton session resource rather than a Herdr pane:
+it has no pane ID, does not change plugin focus context, emits no pane lifecycle
+events, and does not participate in pane, layout, persistence, or agent APIs.
+Its process does not receive `HERDR_PANE_ID`; the underlying tiled pane remains
+available through `HERDR_PLUGIN_CONTEXT_JSON`.
+Opening a popup returns `ui_busy` while Settings, Copy mode, or another Herdr
+modal is active, and `plugin.pane.open` returns an `ok` result after launch.
 
 On Windows, build commands, action commands, and event commands resolve common
 `PATHEXT` shims such as `npm.cmd`, `bun.cmd`, and `pnpm.cmd` when the bare

docs/next/website/src/content/docs/socket-api.mdx

@@ -104,6 +104,7 @@ Raw socket method names use dot notation:
 | Worktree | `worktree.list`, `worktree.create`, `worktree.open`, `worktree.remove` |
 | Tab | `tab.create`, `tab.list`, `tab.get`, `tab.focus`, `tab.rename`, `tab.move`, `tab.close` |
 | Pane | `pane.split`, `pane.swap`, `pane.move`, `pane.zoom`, `pane.layout`, `pane.process_info`, `pane.neighbor`, `pane.edges`, `pane.focus_direction`, `pane.resize`, `pane.list`, `pane.current`, `pane.get`, `pane.rename`, `pane.send_text`, `pane.send_keys`, `pane.send_input`, `pane.read`, `pane.graphics.info`, `pane.graphics.set`, `pane.graphics.clear`, `pane.graphics.stream`, `pane.report_agent`, `pane.report_agent_session`, `pane.report_metadata`, `pane.clear_agent_authority`, `pane.release_agent`, `pane.close`, `pane.wait_for_output` |
+| Popup | `popup.close` |
 | Layout | `layout.export`, `layout.apply`, `layout.set_split_ratio` |
 | Agent | `agent.list`, `agent.get`, `agent.read`, `agent.explain`, `agent.send`, `agent.rename`, `agent.focus`, `agent.start` |
 | Events | `events.subscribe`, `events.wait` |
@@ -504,12 +505,20 @@ Open a managed terminal UI:
 `plugin.pane.open` requires an installed, enabled, platform-compatible plugin,
 then launches the requested manifest `[[panes]]` entrypoint as an argv-backed
 terminal pane. Manifest pane `placement` defaults to `overlay`; request
-`placement` overrides the manifest with `overlay`, `split`, `tab`, or `zoomed`.
-Overlay panes target the active pane. Split and zoomed panes target an existing
-pane; tab panes can target a workspace. The pane
-behaves like a normal Herdr pane, but `plugin.pane.focus` and
-`plugin.pane.close` only operate on panes opened through the plugin API. Focus
-returns `plugin_pane_focused`; close returns `plugin_pane_closed`.
+`placement` overrides the manifest with `overlay`, `popup`, `split`, `tab`, or
+`zoomed`. Overlay and popup placements use the active tiled pane as launch
+context. Popup terminals are session-modal and do not change the tab layout;
+optional `width` and `height` fields set their outer size as terminal cells or
+percentages such as `"80%"`. Omitted dimensions default to half the terminal
+size, with too-small values clamped to the popup minimum. A popup has no pane
+ID, remains outside all `pane.*` and agent APIs, emits no pane lifecycle events,
+leaves plugin focus context on the underlying tiled pane, and does not export
+`HERDR_PANE_ID` to its process. Popup launch returns `ok`; `popup.close` closes
+the active popup and returns
+`popup_not_open` when none exists. Split and zoomed panes target an existing
+pane; tab panes can target a workspace. Split, tab, zoomed, and overlay panes
+behave like normal Herdr panes, and `plugin.pane.focus` and `plugin.pane.close`
+continue to operate on those panes.
 
 ## Socket transport
 

src/api/mod.rs

@@ -64,6 +64,7 @@ pub(crate) fn request_changes_ui(request: &Request) -> bool {
             | Method::PaneClearAgentAuthority(_)
             | Method::PaneReleaseAgent(_)
             | Method::PaneClose(_)
+            | Method::PopupClose(_)
             | Method::PluginActionInvoke(_)
             | Method::PluginPaneOpen(_)
             | Method::PluginPaneFocus(_)

src/api/schema.rs

@@ -191,6 +191,8 @@ pub enum Method {
     PaneReleaseAgent(PaneReleaseAgentParams),
     #[serde(rename = "pane.close")]
     PaneClose(PaneTarget),
+    #[serde(rename = "popup.close")]
+    PopupClose(EmptyParams),
     #[serde(rename = "events.subscribe")]
     EventsSubscribe(EventsSubscribeParams),
     #[serde(rename = "events.wait")]

src/api/schema/plugins.rs

@@ -6,6 +6,7 @@ use super::common::AgentStatus;
 use super::common::SplitDirection;
 use super::panes::PaneInfo;
 use super::workspaces::WorkspaceWorktreeInfo;
+use crate::popup_size::PopupSize;
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, schemars::JsonSchema)]
 pub struct PluginLinkParams {
@@ -261,6 +262,10 @@ pub struct PluginManifestPane {
     pub platforms: Option<Vec<PluginPlatform>>,
     #[serde(default)]
     pub placement: PluginPanePlacement,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub width: Option<PopupSize>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub height: Option<PopupSize>,
     pub command: Vec<String>,
 }
 
@@ -407,6 +412,10 @@ pub struct PluginPaneOpenParams {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub placement: Option<PluginPanePlacement>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub width: Option<PopupSize>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub height: Option<PopupSize>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
     pub workspace_id: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub target_pane_id: Option<String>,
@@ -427,6 +436,7 @@ pub struct PluginPaneOpenParams {
 pub enum PluginPanePlacement {
     #[default]
     Overlay,
+    Popup,
     Split,
     Tab,
     Zoomed,

src/api/schema/tests.rs

@@ -814,6 +814,8 @@ fn plugin_link_list_unlink_round_trip() {
             description: None,
             platforms: None,
             placement: PluginPanePlacement::Overlay,
+            width: None,
+            height: None,
             command: vec!["bun".into(), "run".into(), "board.ts".into()],
         }],
         link_handlers: vec![PluginManifestLinkHandler {
@@ -1152,10 +1154,12 @@ fn plugin_pane_open_request_round_trips() {
         method: Method::PluginPaneOpen(PluginPaneOpenParams {
             plugin_id: "example.board".into(),
             entrypoint: "board".into(),
-            placement: Some(PluginPanePlacement::Zoomed),
+            placement: Some(PluginPanePlacement::Popup),
+            width: Some(crate::popup_size::PopupSize::Cells(90)),
+            height: Some(crate::popup_size::PopupSize::Percent(80)),
             workspace_id: None,
-            target_pane_id: Some("1-1".into()),
-            direction: Some(SplitDirection::Right),
+            target_pane_id: None,
+            direction: None,
             cwd: Some("/tmp".into()),
             focus: true,
             env: [("HERDR_ROLE".to_string(), "board".to_string())].into(),
@@ -1164,7 +1168,23 @@ fn plugin_pane_open_request_round_trips() {
 
     let json = serde_json::to_value(&request).unwrap();
     assert_eq!(json["method"], "plugin.pane.open");
+    assert_eq!(json["params"]["placement"], "popup");
+    assert_eq!(json["params"]["width"], 90);
+    assert_eq!(json["params"]["height"], "80%");
     assert_eq!(json["params"]["env"]["HERDR_ROLE"], "board");
     let restored: Request = serde_json::from_value(json).unwrap();
     assert_eq!(restored, request);
 }
+
+#[test]
+fn popup_close_request_round_trips() {
+    let request = Request {
+        id: "popup-close".into(),
+        method: Method::PopupClose(EmptyParams::default()),
+    };
+
+    let json = serde_json::to_value(request).unwrap();
+
+    assert_eq!(json["method"], "popup.close");
+    assert_eq!(json["params"], serde_json::json!({}));
+}

src/api/server.rs

@@ -406,6 +406,7 @@ fn api_method_name(method: &Method) -> &'static str {
         Method::PaneClearAgentAuthority(_) => "pane.clear_agent_authority",
         Method::PaneReleaseAgent(_) => "pane.release_agent",
         Method::PaneClose(_) => "pane.close",
+        Method::PopupClose(_) => "popup.close",
         Method::EventsSubscribe(_) => "events.subscribe",
         Method::EventsWait(_) => "events.wait",
         Method::PaneWaitForOutput(_) => "pane.wait_for_output",

src/app/api.rs

@@ -151,6 +151,15 @@ impl App {
         }
 
         if let AppEvent::PaneDied { pane_id } = &ev {
+            if self
+                .state
+                .popup_pane
+                .as_ref()
+                .is_some_and(|popup| popup.pane_id == *pane_id)
+            {
+                self.close_popup_pane();
+                return;
+            }
             let previous_toast = self.state.toast.clone();
             if let Some(update) = self.state.publish_pane_process_exit_if_agent(*pane_id) {
                 self.sync_full_lifecycle_authority_detection_pauses();
@@ -1059,6 +1068,13 @@ impl App {
                 return self.handle_pane_send_input(request.id, params)
             }
             Method::PaneClose(target) => return self.handle_pane_close(request.id, target),
+            Method::PopupClose(_) => {
+                return if self.close_popup_pane() {
+                    responses::encode_success(request.id, ResponseResult::Ok {})
+                } else {
+                    responses::encode_error(request.id, "popup_not_open", "no popup is open")
+                };
+            }
             Method::PaneSendKeys(params) => return self.handle_pane_send_keys(request.id, params),
             Method::IntegrationInstall(params) => {
                 return self.handle_integration_install(request.id, params);

src/app/api/plugins/manifest.rs

@@ -3,6 +3,7 @@ use crate::api::schema::{
     PluginManifestLinkHandler, PluginManifestPane, PluginPanePlacement, PluginPlatform,
     PluginSourceInfo, PluginSourceKind,
 };
+use crate::popup_size::PopupSize;
 
 const PLUGIN_ID_MAX_CHARS: usize = 120;
 const PLUGIN_ACTION_ID_MAX_CHARS: usize = 120;
@@ -68,6 +69,10 @@ struct RawPluginManifestPane {
     platforms: Option<Vec<RawPlatform>>,
     #[serde(default)]
     placement: PluginPanePlacement,
+    #[serde(default)]
+    width: Option<PopupSize>,
+    #[serde(default)]
+    height: Option<PopupSize>,
     command: Vec<String>,
 }
 
@@ -392,12 +397,22 @@ fn normalize_manifest_pane(
         .filter(|description| !description.is_empty());
     let platforms = normalize_platforms(pane.platforms)?;
     let command = normalize_command(pane.command)?;
+    if pane.placement != PluginPanePlacement::Popup
+        && (pane.width.is_some() || pane.height.is_some())
+    {
+        return Err((
+            "invalid_plugin_pane_size",
+            "pane width and height are only supported when placement is popup".to_string(),
+        ));
+    }
     Ok(PluginManifestPane {
         id,
         title,
         description,
         platforms,
         placement: pane.placement,
+        width: pane.width,
+        height: pane.height,
         command,
     })
 }

src/app/api/plugins/mod.rs

@@ -349,8 +349,25 @@ impl App {
             return encode_error(id, code, message);
         }
         let placement = params.placement.unwrap_or(pane.placement);
+        if placement != PluginPanePlacement::Popup
+            && (params.width.is_some() || params.height.is_some())
+        {
+            return encode_error(
+                id,
+                "invalid_params",
+                "width and height are only supported when placement is popup",
+            );
+        }
+        if placement == PluginPanePlacement::Popup && self.state.mode != crate::app::Mode::Terminal
+        {
+            return encode_error(
+                id,
+                "ui_busy",
+                "popup panes can only open from the normal workspace view",
+            );
+        }
         match placement {
-            PluginPanePlacement::Overlay => {
+            PluginPanePlacement::Overlay | PluginPanePlacement::Popup => {
                 if params.workspace_id.is_some()
                     || params.target_pane_id.is_some()
                     || params.direction.is_some()
@@ -358,7 +375,7 @@ impl App {
                     return encode_error(
                         id,
                         "invalid_params",
-                        "overlay plugin panes target the active pane",
+                        "overlay and popup plugin panes target the active pane",
                     );
                 }
             }
@@ -386,6 +403,7 @@ impl App {
             PluginPanePlacement::Overlay => {
                 self.open_plugin_overlay_pane(id, params, &plugin, pane)
             }
+            PluginPanePlacement::Popup => self.open_plugin_popup_pane(id, params, &plugin, pane),
             PluginPanePlacement::Split | PluginPanePlacement::Zoomed => {
                 self.open_plugin_split_pane(id, params, &plugin, pane, placement)
             }
@@ -659,7 +677,7 @@ fn manifest_actions(
 mod tests {
     use super::*;
     use crate::api::schema::{
-        Method, PluginSourceInfo, PluginSourceKind, Request, SuccessResponse,
+        Method, PaneListParams, PluginSourceInfo, PluginSourceKind, Request, SuccessResponse,
     };
     use std::time::{SystemTime, UNIX_EPOCH};
 
@@ -983,6 +1001,24 @@ platforms = ["linux", "macos", "windows"]
 "#,
                 "plugin_requires_newer_herdr",
             ),
+            (
+                "plugin-non-popup-size",
+                r#"
+id = "example.non-popup-size"
+name = "Non Popup Size"
+version = "0.1.0"
+min_herdr_version = "0.6.10"
+platforms = ["linux", "macos", "windows"]
+
+[[panes]]
+id = "board"
+title = "Board"
+placement = "split"
+width = "80%"
+command = ["echo", "board"]
+"#,
+                "invalid_plugin_pane_size",
+            ),
         ];
 
         for (name, manifest, expected_code) in cases {
@@ -1139,6 +1175,8 @@ command = ["echo", "b"]
                 plugin_id: "example.missing".into(),
                 entrypoint: "ui".into(),
                 placement: Some(PluginPanePlacement::Split),
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,
@@ -1151,6 +1189,98 @@ command = ["echo", "b"]
         assert_eq!(value["error"]["code"], "plugin_not_found");
     }
 
+    #[test]
+    fn plugin_pane_open_rejects_popup_size_for_non_popup_placement() {
+        let mut app = test_app();
+        let root = unique_temp_path("plugin-pane-non-popup-size-param");
+        write_manifest(&root);
+        link_manifest(&mut app, &root);
+
+        let response = app.handle_api_request(Request {
+            id: "pane-open-size".into(),
+            method: Method::PluginPaneOpen(PluginPaneOpenParams {
+                plugin_id: "example.worktree-bootstrap".into(),
+                entrypoint: "board".into(),
+                placement: Some(PluginPanePlacement::Split),
+                width: Some(crate::popup_size::PopupSize::Percent(80)),
+                height: None,
+                workspace_id: None,
+                target_pane_id: None,
+                direction: Some(crate::api::schema::SplitDirection::Right),
+                cwd: None,
+                focus: false,
+                env: std::collections::HashMap::new(),
+            }),
+        });
+
+        let value: serde_json::Value = serde_json::from_str(&response).unwrap();
+        assert_eq!(value["error"]["code"], "invalid_params");
+        let _ = std::fs::remove_dir_all(root);
+    }
+
+    #[test]
+    fn plugin_pane_open_popup_preserves_existing_ui_modes() {
+        let mut app = test_app();
+        app.state.workspaces = vec![crate::workspace::Workspace::test_new("modal")];
+        app.state.ensure_test_terminals();
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        let root_pane = app.state.workspaces[0].tabs[0].root_pane;
+        let root = unique_temp_path("plugin-popup-ui-busy");
+        write_manifest(&root);
+        link_manifest(&mut app, &root);
+
+        let open_popup = |app: &mut App, id: &str| {
+            app.handle_api_request(Request {
+                id: id.into(),
+                method: Method::PluginPaneOpen(PluginPaneOpenParams {
+                    plugin_id: "example.worktree-bootstrap".into(),
+                    entrypoint: "board".into(),
+                    placement: Some(PluginPanePlacement::Popup),
+                    width: None,
+                    height: None,
+                    workspace_id: None,
+                    target_pane_id: None,
+                    direction: None,
+                    cwd: None,
+                    focus: true,
+                    env: std::collections::HashMap::new(),
+                }),
+            })
+        };
+
+        app.state.mode = crate::app::Mode::Settings;
+        app.state.settings.original_theme = Some("settings-theme".into());
+        let settings_response = open_popup(&mut app, "settings-popup");
+        let settings_error: serde_json::Value = serde_json::from_str(&settings_response).unwrap();
+        assert_eq!(settings_error["error"]["code"], "ui_busy");
+        assert_eq!(app.state.mode, crate::app::Mode::Settings);
+        assert_eq!(
+            app.state.settings.original_theme.as_deref(),
+            Some("settings-theme")
+        );
+        assert!(app.state.popup_pane.is_none());
+
+        let copy_mode = crate::app::state::CopyModeState {
+            pane_id: root_pane,
+            cursor_row: 2,
+            cursor_col: 3,
+            entry_offset_from_bottom: 4,
+            selection: None,
+            search: crate::app::state::CopyModeSearchState::default(),
+        };
+        app.state.mode = crate::app::Mode::Copy;
+        app.state.copy_mode = Some(copy_mode.clone());
+        let copy_response = open_popup(&mut app, "copy-popup");
+        let copy_error: serde_json::Value = serde_json::from_str(&copy_response).unwrap();
+        assert_eq!(copy_error["error"]["code"], "ui_busy");
+        assert_eq!(app.state.mode, crate::app::Mode::Copy);
+        assert_eq!(app.state.copy_mode, Some(copy_mode));
+        assert!(app.state.popup_pane.is_none());
+
+        let _ = std::fs::remove_dir_all(root);
+    }
+
     #[cfg(unix)]
     #[tokio::test]
     async fn plugin_pane_open_uses_plugin_root_title_env_and_target_context() {
@@ -1200,6 +1330,8 @@ command = ["sh", "-c", "printf '%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n%s\n' \"$PWD\" \
                 plugin_id: "example.pane".into(),
                 entrypoint: "board".into(),
                 placement: Some(PluginPanePlacement::Overlay),
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,
@@ -1305,6 +1437,8 @@ command = ["sh", "-c", "printf '%s\n%s\n%s\n' \"$HERDR_PLUGIN_ROOT\" \"$HERDR_PL
                 plugin_id: "example.path-env".into(),
                 entrypoint: "board".into(),
                 placement: Some(PluginPanePlacement::Overlay),
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,
@@ -1406,6 +1540,8 @@ command = ["sh", "-c", "sleep 1"]
                 plugin_id: "example.tab".into(),
                 entrypoint: "board".into(),
                 placement: None,
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,
@@ -1487,6 +1623,8 @@ command = ["sh", "-c", "sleep 1"]
                 plugin_id: "example.split".into(),
                 entrypoint: "board".into(),
                 placement: Some(PluginPanePlacement::Zoomed),
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: Some(crate::api::schema::SplitDirection::Right),
@@ -1564,6 +1702,8 @@ command = ["sh", "-c", "sleep 1"]
                 plugin_id: "example.overlay".into(),
                 entrypoint: "board".into(),
                 placement: None,
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,
@@ -1598,6 +1738,114 @@ command = ["sh", "-c", "sleep 1"]
         let _ = std::fs::remove_dir_all(root);
     }
 
+    #[cfg(unix)]
+    #[tokio::test]
+    async fn plugin_pane_open_popup_is_layout_neutral() {
+        let event_hub = crate::api::EventHub::default();
+        let (_api_tx, api_rx) = tokio::sync::mpsc::unbounded_channel();
+        let mut app = App::new(
+            &crate::config::Config::default(),
+            true,
+            None,
+            api_rx,
+            event_hub.clone(),
+        );
+        app.state.workspaces = vec![crate::workspace::Workspace::test_new("plugin-popup")];
+        app.state.ensure_test_terminals();
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.mode = crate::app::Mode::Terminal;
+        let root_pane = app.state.workspaces[0].tabs[0].root_pane;
+        let root_public = app.public_pane_id(0, root_pane).unwrap();
+
+        let root = unique_temp_path("plugin-pane-popup");
+        let env_capture = root.join("popup-env.txt");
+        let manifest = format!(
+            r#"
+id = "example.popup"
+name = "Popup Plugin"
+version = "0.1.0"
+min_herdr_version = "0.6.10"
+platforms = ["linux", "macos"]
+
+[[panes]]
+id = "board"
+title = "Plugin Popup"
+placement = "popup"
+width = "80%"
+height = "40%"
+command = ["sh", "-c", "printf %s ${{HERDR_PANE_ID-unset}} > '{}'; sleep 1"]
+"#,
+            env_capture.display()
+        );
+        write_manifest_content(&root, &manifest);
+        link_manifest(&mut app, &root);
+
+        let open = app.handle_api_request(Request {
+            id: "pane-open-popup".into(),
+            method: Method::PluginPaneOpen(PluginPaneOpenParams {
+                plugin_id: "example.popup".into(),
+                entrypoint: "board".into(),
+                placement: None,
+                width: None,
+                height: None,
+                workspace_id: None,
+                target_pane_id: None,
+                direction: None,
+                cwd: None,
+                focus: true,
+                env: std::collections::HashMap::new(),
+            }),
+        });
+        assert_eq!(response_result(&open), ResponseResult::Ok {});
+        assert_eq!(
+            read_capture_when_ready(&env_capture, || {
+                app.drain_internal_events();
+            }),
+            "unset"
+        );
+
+        let opened_pane_id = app.state.popup_pane.as_ref().unwrap().pane_id;
+        assert!(!app.state.plugin_panes.contains_key(&opened_pane_id));
+        app.state.assert_invariants_for_test();
+        app.state.view.terminal_area = ratatui::layout::Rect::new(0, 0, 100, 30);
+        let (outer, inner) = crate::ui::popup_pane_rects(&app.state, app.state.view.terminal_area)
+            .expect("popup rects");
+        assert_eq!((outer.width, outer.height), (80, 12));
+        assert_eq!((inner.width, inner.height), (77, 10));
+        assert_eq!(app.state.workspaces[0].tabs[0].layout.pane_count(), 1);
+        assert!(!app.state.workspaces[0].tabs[0].zoomed);
+
+        let pane_list = app.handle_api_request(Request {
+            id: "pane-list-popup".into(),
+            method: Method::PaneList(PaneListParams {
+                workspace_id: Some(app.public_workspace_id(0)),
+            }),
+        });
+        let ResponseResult::PaneList { panes } = response_result(&pane_list) else {
+            panic!("expected pane list response: {pane_list}");
+        };
+        assert_eq!(panes.len(), 1);
+        assert_eq!(panes[0].pane_id, root_public);
+        assert!(panes[0].focused);
+        assert_eq!(
+            app.current_plugin_context("popup-open").focused_pane_id,
+            Some(root_public)
+        );
+        assert!(event_hub.events_after(0).is_empty());
+
+        app.handle_internal_event(crate::events::AppEvent::PaneDied {
+            pane_id: opened_pane_id,
+        });
+        assert!(app.state.popup_pane.is_none());
+        assert!(event_hub.events_after(0).is_empty());
+
+        for (_, runtime) in app.terminal_runtimes.drain() {
+            runtime.shutdown();
+        }
+        let _ = std::fs::remove_dir_all(root);
+    }
+
     #[test]
     fn manifest_action_list_and_invoke_with_context() {
         let mut app = test_app();
@@ -1729,6 +1977,8 @@ command = ["sh", "-c", "sleep 1"]
                 plugin_id: "example.worktree-bootstrap".into(),
                 entrypoint: "board".into(),
                 placement: None,
+                width: None,
+                height: None,
                 workspace_id: None,
                 target_pane_id: None,
                 direction: None,

src/app/api/plugins/panes.rs

@@ -8,6 +8,39 @@ use crate::api::schema::{
 use crate::app::App;
 
 impl App {
+    pub(super) fn open_plugin_popup_pane(
+        &mut self,
+        id: String,
+        params: PluginPaneOpenParams,
+        plugin: &InstalledPluginInfo,
+        pane: PluginManifestPane,
+    ) -> String {
+        let context = self.current_plugin_context("plugin-pane");
+        let extra_env =
+            match self.plugin_pane_launch_env(plugin, &pane.id, params.env.clone(), &context) {
+                Ok(env) => env,
+                Err((code, message)) => return encode_error(id, &code, message),
+            };
+        let cwd = Some(self.plugin_pane_cwd(plugin, params.cwd));
+        let width = params.width.or(pane.width);
+        let height = params.height.or(pane.height);
+        if let Err(err) = self.spawn_popup_argv_command(
+            &pane.command,
+            cwd,
+            extra_env,
+            crate::app::popup::PopupGeometry { width, height },
+        ) {
+            return encode_error(id, "plugin_pane_open_failed", err.to_string());
+        }
+        let Some(popup) = self.state.popup_pane.as_ref() else {
+            return encode_error(id, "plugin_pane_open_failed", "plugin popup disappeared");
+        };
+        if let Some(terminal) = self.state.terminals.get_mut(&popup.terminal_id) {
+            terminal.set_manual_label(pane.title);
+        }
+        encode_success(id, ResponseResult::Ok {})
+    }
+
     pub(super) fn open_plugin_overlay_pane(
         &mut self,
         id: String,

src/app/input/mod.rs

@@ -1,6 +1,8 @@
 //! Input handling — translates crossterm key/mouse events into state mutations.
 
+use bytes::Bytes;
 use crossterm::event::{KeyCode, KeyEvent, KeyModifiers, MouseButton, MouseEvent, MouseEventKind};
+use tracing::warn;
 
 use crate::app::PaneClickState;
 use crate::input::TerminalKey;
@@ -70,6 +72,10 @@ use super::App;
 
 impl App {
     pub(super) async fn handle_key(&mut self, key: TerminalKey) {
+        if self.state.popup_pane.is_some() {
+            self.handle_terminal_key(key).await;
+            return;
+        }
         let key_event = key.as_key_event();
         if modal_paste_target_active(&self.state) && is_modal_paste_shortcut(&key_event) {
             if let Some(text) = crate::platform::read_clipboard_text() {
@@ -111,6 +117,14 @@ impl App {
     }
 
     pub(super) async fn handle_paste(&mut self, text: String) {
+        if self.state.popup_pane.is_some() {
+            if let Some(runtime) = self.popup_runtime() {
+                let _ = runtime.send_paste(text).await;
+            } else {
+                self.close_popup_pane();
+            }
+            return;
+        }
         if self.state.mode != Mode::Terminal {
             self.paste_into_active_text_input(&text);
             return;
@@ -239,6 +253,10 @@ impl App {
     }
 
     pub(super) fn handle_mouse(&mut self, mouse: MouseEvent) {
+        if self.state.popup_pane.is_some() {
+            self.handle_popup_mouse(mouse);
+            return;
+        }
         if self.handle_overlay_mouse(mouse) {
             return;
         }
@@ -373,6 +391,62 @@ impl App {
         }
     }
 
+    fn handle_popup_mouse(&mut self, mouse: MouseEvent) {
+        let Some((_outer, inner)) =
+            crate::ui::popup_pane_rects(&self.state, self.state.view.terminal_area)
+        else {
+            return;
+        };
+        if mouse.column < inner.x
+            || mouse.column >= inner.x.saturating_add(inner.width)
+            || mouse.row < inner.y
+            || mouse.row >= inner.y.saturating_add(inner.height)
+        {
+            return;
+        }
+        let Some(rt) = self.popup_runtime() else {
+            self.close_popup_pane();
+            return;
+        };
+        let column = mouse.column.saturating_sub(inner.x);
+        let row = mouse.row.saturating_sub(inner.y);
+        let bytes = match mouse.kind {
+            MouseEventKind::ScrollUp
+            | MouseEventKind::ScrollDown
+            | MouseEventKind::ScrollLeft
+            | MouseEventKind::ScrollRight => match rt.wheel_routing() {
+                Some(crate::pane::WheelRouting::MouseReport) => {
+                    rt.encode_mouse_wheel(mouse.kind, column, row, mouse.modifiers)
+                }
+                Some(crate::pane::WheelRouting::AlternateScroll) => {
+                    rt.encode_alternate_scroll(mouse.kind)
+                }
+                Some(crate::pane::WheelRouting::HostScroll) | None => {
+                    let lines_per_notch = self.state.mouse_scroll_lines;
+                    match mouse.kind {
+                        MouseEventKind::ScrollUp => rt.scroll_up(lines_per_notch),
+                        MouseEventKind::ScrollDown => rt.scroll_down(lines_per_notch),
+                        _ => {}
+                    }
+                    return;
+                }
+            },
+            MouseEventKind::Down(_) | MouseEventKind::Up(_) | MouseEventKind::Drag(_) => {
+                rt.encode_mouse_button(mouse.kind, column, row, mouse.modifiers)
+            }
+            MouseEventKind::Moved => {
+                rt.encode_mouse_motion(mouse.kind, column, row, mouse.modifiers)
+            }
+        };
+        let Some(bytes) = bytes else {
+            return;
+        };
+        rt.scroll_reset();
+        if let Err(err) = rt.try_send_bytes(Bytes::from(bytes)) {
+            warn!(err = %err, kind = ?mouse.kind, "failed to forward popup mouse event");
+        }
+    }
+
     fn handle_modified_url_click(&mut self, mouse: MouseEvent) -> bool {
         if self.state.mode != Mode::Terminal
             || !matches!(mouse.kind, MouseEventKind::Down(MouseButton::Left))

src/app/input/navigate.rs

@@ -778,6 +778,7 @@ impl App {
             crate::config::CustomCommandAction::Pane => {
                 self.spawn_pane_command(&binding.command, Vec::new())
             }
+            crate::config::CustomCommandAction::Popup => self.spawn_custom_popup_command(&binding),
             crate::config::CustomCommandAction::PluginAction => self
                 .invoke_plugin_action_from_keybind(binding.command.clone())
                 .map_err(std::io::Error::other),
@@ -798,6 +799,21 @@ impl App {
         }
     }
 
+    fn spawn_custom_popup_command(
+        &mut self,
+        binding: &crate::config::CustomCommandKeybind,
+    ) -> io::Result<()> {
+        self.spawn_popup_shell_command(
+            &binding.command,
+            None,
+            self.custom_command_env().0,
+            crate::app::popup::PopupGeometry {
+                width: binding.width,
+                height: binding.height,
+            },
+        )
+    }
+
     fn custom_command_env(&self) -> (Vec<(String, String)>, Option<std::path::PathBuf>) {
         let mut env = vec![(
             crate::api::SOCKET_PATH_ENV_VAR.to_string(),
@@ -2956,6 +2972,8 @@ navigate_pane_down = "ctrl+j"
             command,
             action: crate::config::CustomCommandAction::Shell,
             description: None,
+            width: None,
+            height: None,
         }];
 
         app.handle_key(TerminalKey::new(
@@ -3048,6 +3066,8 @@ navigate_pane_down = "ctrl+j"
             command,
             action: crate::config::CustomCommandAction::Pane,
             description: None,
+            width: None,
+            height: None,
         }];
 
         app.handle_key(TerminalKey::new(

src/app/input/terminal.rs

@@ -13,12 +13,31 @@ struct PreparedPaneInput {
     bytes: Bytes,
 }
 
+enum PreparedPopupInput {
+    NotOpen,
+    Consumed,
+    Bytes(Bytes),
+}
+
 fn is_modifier_only_key(code: &KeyCode) -> bool {
     matches!(code, KeyCode::Modifier(_))
 }
 
 impl App {
     pub(crate) fn handle_terminal_key_headless(&mut self, key: TerminalKey) {
+        match self.prepare_popup_key_forward(key) {
+            PreparedPopupInput::NotOpen => {}
+            PreparedPopupInput::Consumed => return,
+            PreparedPopupInput::Bytes(bytes) => {
+                let Some(runtime) = self.popup_runtime() else {
+                    self.close_popup_pane();
+                    return;
+                };
+                let _ = runtime.try_send_bytes(bytes);
+                return;
+            }
+        }
+
         let Some(input) = self.prepare_terminal_key_forward(key) else {
             return;
         };
@@ -192,7 +211,38 @@ impl App {
         })
     }
 
+    fn prepare_popup_key_forward(&mut self, key: TerminalKey) -> PreparedPopupInput {
+        if self.state.popup_pane.is_none() {
+            return PreparedPopupInput::NotOpen;
+        }
+        let Some(rt) = self.popup_runtime() else {
+            self.close_popup_pane();
+            return PreparedPopupInput::Consumed;
+        };
+        rt.scroll_reset();
+        let bytes = rt.encode_terminal_key(key);
+        self.state.mode = Mode::Terminal;
+        if bytes.is_empty() {
+            PreparedPopupInput::Consumed
+        } else {
+            PreparedPopupInput::Bytes(Bytes::from(bytes))
+        }
+    }
+
     pub(super) async fn handle_terminal_key(&mut self, key: TerminalKey) {
+        match self.prepare_popup_key_forward(key) {
+            PreparedPopupInput::NotOpen => {}
+            PreparedPopupInput::Consumed => return,
+            PreparedPopupInput::Bytes(bytes) => {
+                let Some(runtime) = self.popup_runtime() else {
+                    self.close_popup_pane();
+                    return;
+                };
+                let _ = runtime.send_bytes(bytes).await;
+                return;
+            }
+        }
+
         let Some(input) = self.prepare_terminal_key_forward(key) else {
             return;
         };
@@ -213,6 +263,45 @@ mod tests {
     use super::*;
     use crate::{config::Config, events::AppEvent, workspace::Workspace};
 
+    #[cfg(unix)]
+    fn app_with_spawned_workspace() -> App {
+        let (_api_tx, api_rx) = tokio::sync::mpsc::unbounded_channel();
+        let mut app = App::new(
+            &Config::default(),
+            true,
+            None,
+            api_rx,
+            crate::api::EventHub::default(),
+        );
+        app.state.default_shell = "/bin/sh".into();
+        let (workspace, terminal, runtime) = Workspace::new(
+            std::env::current_dir().unwrap_or_else(|_| "/".into()),
+            24,
+            80,
+            app.state.pane_scrollback_limit_bytes,
+            app.state.host_terminal_theme,
+            crate::pane::PaneShellConfig::new(&app.state.default_shell, app.state.shell_mode),
+            app.event_tx.clone(),
+            app.render_notify.clone(),
+            app.render_dirty.clone(),
+        )
+        .expect("workspace should spawn");
+        app.state.workspaces = vec![workspace];
+        app.terminal_runtimes.insert(terminal.id.clone(), runtime);
+        app.state.terminals.insert(terminal.id.clone(), terminal);
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.mode = Mode::Terminal;
+        app
+    }
+
+    #[cfg(unix)]
+    fn shutdown_test_runtimes(app: &mut App) {
+        for (_, runtime) in app.terminal_runtimes.drain() {
+            runtime.shutdown();
+        }
+    }
+
     fn app_with_screen_bytes(bytes: &[u8]) -> (App, crate::layout::PaneInfo) {
         let mut app = app_for_mouse_test();
         let mut ws = Workspace::test_new("test");
@@ -1093,6 +1182,8 @@ mod tests {
             command,
             action: crate::config::CustomCommandAction::Shell,
             description: None,
+            width: None,
+            height: None,
         }];
 
         app.handle_terminal_key(TerminalKey::new(
@@ -1109,33 +1200,7 @@ mod tests {
     #[cfg(unix)]
     #[tokio::test]
     async fn direct_custom_pane_command_opens_overlay_pane() {
-        let (_api_tx, api_rx) = tokio::sync::mpsc::unbounded_channel();
-        let mut app = App::new(
-            &Config::default(),
-            true,
-            None,
-            api_rx,
-            crate::api::EventHub::default(),
-        );
-        app.state.default_shell = "/usr/bin/true".into();
-        let (workspace, terminal, runtime) = Workspace::new(
-            std::env::current_dir().unwrap_or_else(|_| "/".into()),
-            24,
-            80,
-            app.state.pane_scrollback_limit_bytes,
-            app.state.host_terminal_theme,
-            crate::pane::PaneShellConfig::new(&app.state.default_shell, app.state.shell_mode),
-            app.event_tx.clone(),
-            app.render_notify.clone(),
-            app.render_dirty.clone(),
-        )
-        .expect("workspace should spawn");
-        app.state.workspaces = vec![workspace];
-        app.terminal_runtimes.insert(terminal.id.clone(), runtime);
-        app.state.terminals.insert(terminal.id.clone(), terminal);
-        app.state.active = Some(0);
-        app.state.selected = 0;
-        app.state.mode = Mode::Terminal;
+        let mut app = app_with_spawned_workspace();
 
         app.state.keybinds.custom_commands = vec![crate::config::CustomCommandKeybind {
             bindings: crate::config::ActionKeybinds::direct("ctrl+alt+g"),
@@ -1143,6 +1208,8 @@ mod tests {
             command: "printf direct-pane".into(),
             action: crate::config::CustomCommandAction::Pane,
             description: None,
+            width: None,
+            height: None,
         }];
 
         app.handle_terminal_key(TerminalKey::new(
@@ -1155,10 +1222,157 @@ mod tests {
         assert!(app.state.workspaces[0].tabs[0].zoomed);
         assert_eq!(app.state.mode, Mode::Terminal);
 
-        let runtimes: Vec<_> = app.terminal_runtimes.drain().collect();
-        for (_terminal_id, runtime) in runtimes {
-            runtime.shutdown();
+        shutdown_test_runtimes(&mut app);
+    }
+
+    #[cfg(unix)]
+    #[tokio::test]
+    async fn direct_custom_popup_command_opens_layout_neutral_popup() {
+        let mut app = app_with_spawned_workspace();
+
+        app.state.keybinds.custom_commands = vec![crate::config::CustomCommandKeybind {
+            bindings: crate::config::ActionKeybinds::direct("ctrl+alt+g"),
+            label: "ctrl+alt+g".into(),
+            command: "sleep 1".into(),
+            action: crate::config::CustomCommandAction::Popup,
+            description: None,
+            width: Some(crate::popup_size::PopupSize::Cells(60)),
+            height: Some(crate::popup_size::PopupSize::Cells(12)),
+        }];
+
+        app.handle_terminal_key(TerminalKey::new(
+            KeyCode::Char('g'),
+            KeyModifiers::CONTROL | KeyModifiers::ALT,
+        ))
+        .await;
+
+        assert!(app.state.popup_pane.is_some());
+        assert!(!app
+            .popup_runtime()
+            .unwrap()
+            .agent_detection_enabled_for_test());
+        assert_eq!(app.state.workspaces[0].tabs[0].layout.pane_count(), 1);
+        assert!(!app.state.workspaces[0].tabs[0].zoomed);
+        assert_eq!(app.state.mode, Mode::Terminal);
+        let snapshot = crate::persist::capture(
+            &app.state.workspaces,
+            &app.state.terminals,
+            &app.terminal_runtimes,
+            app.state.active,
+            app.state.selected,
+            app.state.sidebar_width,
+            app.state.sidebar_section_split,
+            app.state.collapsed_space_keys.clone(),
+        );
+        assert_eq!(snapshot.workspaces[0].tabs[0].panes.len(), 1);
+        assert!(matches!(
+            snapshot.workspaces[0].tabs[0].layout,
+            crate::persist::LayoutSnapshot::Pane(_)
+        ));
+
+        shutdown_test_runtimes(&mut app);
+    }
+
+    #[cfg(unix)]
+    #[tokio::test]
+    async fn direct_custom_popup_command_closes_after_exit() {
+        let mut app = app_with_spawned_workspace();
+        let focused_pane = app.state.workspaces[0].focused_pane_id().unwrap();
+        let focused_pane_id = app.public_pane_id(0, focused_pane).unwrap();
+
+        let output_path = unique_temp_path("custom-popup-command");
+        let command = format!(
+            "printf '%s|%s' \"${{HERDR_PANE_ID-unset}}\" \"$HERDR_ACTIVE_PANE_ID\" > '{}'",
+            output_path.display()
+        );
+        app.state.keybinds.custom_commands = vec![crate::config::CustomCommandKeybind {
+            bindings: crate::config::ActionKeybinds::direct("ctrl+alt+g"),
+            label: "ctrl+alt+g".into(),
+            command,
+            action: crate::config::CustomCommandAction::Popup,
+            description: None,
+            width: None,
+            height: None,
+        }];
+
+        app.handle_terminal_key(TerminalKey::new(
+            KeyCode::Char('g'),
+            KeyModifiers::CONTROL | KeyModifiers::ALT,
+        ))
+        .await;
+
+        assert_eq!(
+            wait_for_file(&output_path),
+            format!("unset|{focused_pane_id}")
+        );
+        let deadline = std::time::Instant::now() + std::time::Duration::from_secs(2);
+        while std::time::Instant::now() < deadline {
+            app.drain_internal_events();
+            if app.state.popup_pane.is_none() {
+                break;
+            }
         }
+
+        assert!(app.state.popup_pane.is_none());
+        assert_eq!(app.state.workspaces[0].tabs[0].layout.pane_count(), 1);
+
+        shutdown_test_runtimes(&mut app);
+        let _ = std::fs::remove_file(output_path);
+    }
+
+    #[tokio::test]
+    async fn popup_forwards_escape_instead_of_closing() {
+        let mut app = app_for_mouse_test();
+        let (runtime, mut rx) =
+            crate::terminal::TerminalRuntime::test_with_channel_and_scrollback_bytes(
+                40,
+                2,
+                1024,
+                b"one\r\ntwo\r\nthree\r\n",
+                4,
+            );
+        runtime.scroll_up(1);
+        assert!(runtime
+            .scroll_metrics()
+            .is_some_and(|metrics| metrics.offset_from_bottom > 0));
+        app.install_test_popup_runtime(runtime);
+        app.state.mode = Mode::Settings;
+
+        app.handle_terminal_key_headless(TerminalKey::new(KeyCode::Esc, KeyModifiers::empty()));
+
+        assert_eq!(rx.try_recv().unwrap().as_ref(), b"\x1b");
+        assert!(app.state.popup_pane.is_some());
+        assert_eq!(
+            app.popup_runtime()
+                .and_then(crate::terminal::TerminalRuntime::scroll_metrics)
+                .map(|metrics| metrics.offset_from_bottom),
+            Some(0)
+        );
+    }
+
+    #[tokio::test]
+    async fn local_popup_input_waits_for_channel_capacity() {
+        let mut app = app_for_mouse_test();
+        let (runtime, mut rx) =
+            crate::terminal::TerminalRuntime::test_with_channel_capacity(40, 2, 1);
+        runtime
+            .try_send_bytes(Bytes::from_static(b"queued"))
+            .unwrap();
+        app.install_test_popup_runtime(runtime);
+        app.state.mode = Mode::Settings;
+
+        let mut send = Box::pin(
+            app.handle_terminal_key(TerminalKey::new(KeyCode::Char('x'), KeyModifiers::empty())),
+        );
+        assert!(
+            tokio::time::timeout(std::time::Duration::from_millis(20), &mut send)
+                .await
+                .is_err()
+        );
+
+        assert_eq!(rx.recv().await.unwrap().as_ref(), b"queued");
+        send.await;
+        assert_eq!(rx.recv().await.unwrap().as_ref(), b"x");
     }
 
     #[tokio::test]

src/app/mod.rs

@@ -13,6 +13,7 @@ mod config_io;
 mod creation;
 mod ids;
 mod input;
+mod popup;
 mod runtime;
 mod runtime_mutations;
 mod session;
@@ -659,6 +660,7 @@ impl App {
             pane_graphics_layers: std::collections::HashMap::new(),
             pane_graphics_streams: std::collections::HashMap::new(),
             pane_graphics_revision: 0,
+            popup_pane: None,
             plugin_command_logs: Vec::new(),
             next_plugin_command_log_id: 1,
             plugin_commands_in_flight: 0,
@@ -1577,7 +1579,8 @@ impl App {
                     let key_id = repeat_key_identity(&key);
                     match key.kind {
                         crossterm::event::KeyEventKind::Press => {
-                            if self.state.mode == Mode::Terminal {
+                            if self.state.popup_pane.is_some() || self.state.mode == Mode::Terminal
+                            {
                                 self.suppressed_repeat_keys.remove(&key_id);
                                 self.handle_terminal_key_headless(key);
                             } else {
@@ -1586,7 +1589,8 @@ impl App {
                             }
                         }
                         crossterm::event::KeyEventKind::Repeat => {
-                            if self.state.mode == Mode::Terminal
+                            if (self.state.popup_pane.is_some()
+                                || self.state.mode == Mode::Terminal)
                                 && !self.suppressed_repeat_keys.contains(&key_id)
                             {
                                 self.handle_terminal_key_headless(key);
@@ -1600,7 +1604,7 @@ impl App {
                     }
                 }
                 crate::raw_input::RawInputEvent::Mouse(mouse) => {
-                    if self.state.mouse_capture {
+                    if self.state.popup_pane.is_some() || self.state.mouse_capture {
                         self.handle_mouse_event_headless(mouse);
                     } else {
                         self.state
@@ -1608,7 +1612,8 @@ impl App {
                     }
                 }
                 crate::raw_input::RawInputEvent::Paste(text) => {
-                    if self.state.mode != Mode::Terminal {
+                    if self.try_route_paste_to_popup(&text) {
+                    } else if self.state.mode != Mode::Terminal {
                         self.paste_into_active_text_input(&text);
                     } else {
                         if let Some(ws_idx) = self.state.active {
@@ -1619,17 +1624,7 @@ impl App {
                                         ws_idx,
                                         focused,
                                     ) {
-                                        let _ = runtime.try_send_bytes(bytes::Bytes::from(
-                                            if runtime
-                                                .input_state()
-                                                .map(|s| s.bracketed_paste)
-                                                .unwrap_or(false)
-                                            {
-                                                format!("\x1b[200~{text}\x1b[201~")
-                                            } else {
-                                                text
-                                            },
-                                        ));
+                                        let _ = runtime.try_send_paste(text);
                                     }
                                 }
                             }
@@ -4918,6 +4913,168 @@ last_pane = "prefix+tab"
         );
     }
 
+    #[tokio::test]
+    async fn route_client_events_pastes_only_into_popup() {
+        let mut app = test_app();
+        let mut workspace = Workspace::test_new("tiled");
+        let focused = workspace.focused_pane_id().unwrap();
+        let (tiled_runtime, mut tiled_rx) = TerminalRuntime::test_with_channel(80, 24);
+        workspace.tabs[0].runtimes.insert(focused, tiled_runtime);
+        app.state.workspaces = vec![workspace];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.mode = Mode::Terminal;
+
+        let (popup_runtime, mut popup_rx) = TerminalRuntime::test_with_channel(40, 12);
+        app.install_test_popup_runtime(popup_runtime);
+        assert!(app
+            .state
+            .should_capture_host_mouse_from(&app.terminal_runtimes));
+
+        app.route_client_events(
+            vec![crate::raw_input::RawInputEvent::Paste("popup-only".into())],
+            true,
+        );
+
+        assert_eq!(
+            popup_rx.try_recv().unwrap(),
+            bytes::Bytes::from_static(b"popup-only")
+        );
+        assert!(tiled_rx.try_recv().is_err());
+
+        app.route_client_events(
+            vec![raw_key(
+                KeyCode::Char('x'),
+                KeyModifiers::NONE,
+                KeyEventKind::Press,
+            )],
+            true,
+        );
+        assert_eq!(
+            popup_rx.try_recv().unwrap(),
+            bytes::Bytes::from_static(b"x")
+        );
+        assert!(tiled_rx.try_recv().is_err());
+
+        app.state.mode = Mode::Settings;
+        assert!(
+            app.handle_raw_input_event(raw_key(
+                KeyCode::Char('y'),
+                KeyModifiers::NONE,
+                KeyEventKind::Repeat,
+            ))
+            .await
+        );
+        assert_eq!(
+            popup_rx.try_recv().unwrap(),
+            bytes::Bytes::from_static(b"y")
+        );
+        assert!(tiled_rx.try_recv().is_err());
+    }
+
+    #[tokio::test]
+    async fn route_client_events_discards_paste_when_popup_runtime_is_missing() {
+        let mut app = test_app();
+        let mut workspace = Workspace::test_new("tiled");
+        let focused = workspace.focused_pane_id().unwrap();
+        let (tiled_runtime, mut tiled_rx) = TerminalRuntime::test_with_channel(80, 24);
+        workspace.tabs[0].runtimes.insert(focused, tiled_runtime);
+        app.state.workspaces = vec![workspace];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.mode = Mode::Terminal;
+        let install_missing_popup = |app: &mut App| {
+            let popup_terminal_id = crate::terminal::TerminalId::alloc();
+            app.state.terminals.insert(
+                popup_terminal_id.clone(),
+                crate::terminal::TerminalState::new(
+                    popup_terminal_id.clone(),
+                    std::path::PathBuf::from("/popup"),
+                ),
+            );
+            app.state.popup_pane = Some(state::PopupPaneState {
+                pane_id: crate::layout::PaneId::alloc(),
+                terminal_id: popup_terminal_id,
+                width: None,
+                height: None,
+            });
+        };
+        install_missing_popup(&mut app);
+
+        app.route_client_events(
+            vec![crate::raw_input::RawInputEvent::Paste("discard-me".into())],
+            true,
+        );
+
+        assert!(tiled_rx.try_recv().is_err());
+        assert!(app.state.popup_pane.is_none());
+
+        install_missing_popup(&mut app);
+        assert!(
+            app.handle_raw_input_event(crate::raw_input::RawInputEvent::Paste(
+                "discard-monolithic".into(),
+            ))
+            .await
+        );
+        assert!(tiled_rx.try_recv().is_err());
+        assert!(app.state.popup_pane.is_none());
+    }
+
+    #[tokio::test]
+    async fn route_client_events_routes_popup_mouse_when_global_capture_is_disabled() {
+        let mut app = test_app();
+        let mut workspace = Workspace::test_new("tiled");
+        let focused = workspace.focused_pane_id().unwrap();
+        let (tiled_runtime, mut tiled_rx) = TerminalRuntime::test_with_channel(80, 24);
+        tiled_runtime.test_process_pty_bytes(b"\x1b[?1000h\x1b[?1006h");
+        workspace.tabs[0].runtimes.insert(focused, tiled_runtime);
+        app.state.workspaces = vec![workspace];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        app.state.mode = Mode::Terminal;
+        app.state.mouse_capture = false;
+        app.state.view.terminal_area = ratatui::layout::Rect::new(0, 0, 80, 24);
+
+        let (popup_runtime, mut popup_rx) = TerminalRuntime::test_with_channel(40, 12);
+        popup_runtime.test_process_pty_bytes(b"\x1b[?1000h\x1b[?1006h");
+        app.install_test_popup_runtime(popup_runtime);
+        let (_, inner) =
+            crate::ui::popup_pane_rects(&app.state, app.state.view.terminal_area).unwrap();
+
+        app.route_client_events(
+            vec![crate::raw_input::RawInputEvent::Mouse(
+                crossterm::event::MouseEvent {
+                    kind: crossterm::event::MouseEventKind::Down(
+                        crossterm::event::MouseButton::Left,
+                    ),
+                    column: inner.x,
+                    row: inner.y,
+                    modifiers: crossterm::event::KeyModifiers::NONE,
+                },
+            )],
+            true,
+        );
+
+        assert!(popup_rx.try_recv().is_ok());
+        assert!(tiled_rx.try_recv().is_err());
+
+        assert!(
+            app.handle_raw_input_event(crate::raw_input::RawInputEvent::Mouse(
+                crossterm::event::MouseEvent {
+                    kind: crossterm::event::MouseEventKind::Down(
+                        crossterm::event::MouseButton::Left,
+                    ),
+                    column: inner.x + 1,
+                    row: inner.y,
+                    modifiers: crossterm::event::KeyModifiers::NONE,
+                },
+            ))
+            .await
+        );
+        assert!(popup_rx.try_recv().is_ok());
+        assert!(tiled_rx.try_recv().is_err());
+    }
+
     #[test]
     fn route_client_input_closes_release_notes_modal() {
         let mut app = test_app();

src/app/popup.rs

@@ -0,0 +1,309 @@
+use std::path::PathBuf;
+
+use crate::app::{App, Mode};
+use crate::layout::PaneId;
+use crate::pane::PaneLaunchEnv;
+use crate::popup_size::{resolve_popup_geometry, PopupSize};
+use crate::terminal::{TerminalId, TerminalRuntime, TerminalState};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub(crate) struct PopupGeometry {
+    pub width: Option<PopupSize>,
+    pub height: Option<PopupSize>,
+}
+
+impl App {
+    pub(crate) fn popup_runtime(&self) -> Option<&TerminalRuntime> {
+        let terminal_id = &self.state.popup_pane.as_ref()?.terminal_id;
+        self.terminal_runtimes.get(terminal_id)
+    }
+
+    pub(crate) fn close_popup_pane(&mut self) -> bool {
+        let Some(popup) = self.state.popup_pane.take() else {
+            return false;
+        };
+        self.state
+            .direct_attach_resize_locks
+            .remove(&popup.terminal_id);
+        self.state.terminals.remove(&popup.terminal_id);
+        if let Some(runtime) = self.terminal_runtimes.remove(&popup.terminal_id) {
+            runtime.shutdown();
+        }
+        self.state.mode = if self.state.active.is_some() {
+            Mode::Terminal
+        } else {
+            Mode::Navigate
+        };
+        self.render_dirty
+            .store(true, std::sync::atomic::Ordering::Release);
+        self.render_notify.notify_one();
+        true
+    }
+
+    pub(crate) fn try_route_paste_to_popup(&mut self, text: &str) -> bool {
+        if self.state.popup_pane.is_none() {
+            return false;
+        }
+        let Some(runtime) = self.popup_runtime() else {
+            self.close_popup_pane();
+            return true;
+        };
+        let _ = runtime.try_send_paste(text.to_owned());
+        true
+    }
+
+    pub(crate) fn spawn_popup_shell_command(
+        &mut self,
+        command: &str,
+        cwd: Option<PathBuf>,
+        extra_env: Vec<(String, String)>,
+        geometry: PopupGeometry,
+    ) -> std::io::Result<()> {
+        self.spawn_popup_command(
+            cwd,
+            extra_env,
+            geometry,
+            |pane_id, rows, cols, cwd, launch_env, app| {
+                TerminalRuntime::spawn_shell_command(
+                    pane_id,
+                    rows,
+                    cols,
+                    cwd,
+                    command,
+                    launch_env,
+                    crate::pane::AgentDetection::Disabled,
+                    app.state.pane_scrollback_limit_bytes,
+                    app.state.host_terminal_theme,
+                    app.event_tx.clone(),
+                    app.render_notify.clone(),
+                    app.render_dirty.clone(),
+                )
+                .map(|runtime| (runtime, None))
+            },
+        )
+    }
+
+    pub(crate) fn spawn_popup_argv_command(
+        &mut self,
+        argv: &[String],
+        cwd: Option<PathBuf>,
+        extra_env: Vec<(String, String)>,
+        geometry: PopupGeometry,
+    ) -> std::io::Result<()> {
+        self.spawn_popup_command(
+            cwd,
+            extra_env,
+            geometry,
+            |pane_id, rows, cols, cwd, launch_env, app| {
+                TerminalRuntime::spawn_argv_command(
+                    pane_id,
+                    rows,
+                    cols,
+                    cwd,
+                    argv,
+                    launch_env,
+                    crate::pane::AgentDetection::Disabled,
+                    app.state.pane_scrollback_limit_bytes,
+                    app.state.host_terminal_theme,
+                    app.event_tx.clone(),
+                    app.render_notify.clone(),
+                    app.render_dirty.clone(),
+                )
+                .map(|runtime| (runtime, Some(argv.to_vec())))
+            },
+        )
+    }
+
+    fn spawn_popup_command<F>(
+        &mut self,
+        cwd: Option<PathBuf>,
+        extra_env: Vec<(String, String)>,
+        geometry: PopupGeometry,
+        spawn: F,
+    ) -> std::io::Result<()>
+    where
+        F: FnOnce(
+            PaneId,
+            u16,
+            u16,
+            PathBuf,
+            &PaneLaunchEnv,
+            &mut App,
+        ) -> std::io::Result<(TerminalRuntime, Option<Vec<String>>)>,
+    {
+        if self.state.popup_pane.is_some() {
+            return Err(std::io::Error::other("popup already open"));
+        }
+        let Some(ws_idx) = self.state.active else {
+            return Err(std::io::Error::other("no active workspace"));
+        };
+        let ws = self
+            .state
+            .workspaces
+            .get(ws_idx)
+            .ok_or_else(|| std::io::Error::other("active workspace disappeared"))?;
+        let active_tab = ws
+            .active_tab()
+            .ok_or_else(|| std::io::Error::other("active tab disappeared"))?;
+        let focused_pane = ws
+            .focused_pane_id()
+            .ok_or_else(|| std::io::Error::other("active tab has no focused pane"))?;
+        let cwd = cwd.or_else(|| {
+            active_tab.cwd_for_pane(focused_pane, &self.state.terminals, &self.terminal_runtimes)
+        });
+        let cwd = cwd.unwrap_or_else(|| std::env::current_dir().unwrap_or_else(|_| "/".into()));
+        let pane_id = PaneId::alloc();
+        let terminal_id = TerminalId::alloc();
+        let launch_env = PaneLaunchEnv::from_extra(extra_env).without_pane_identity();
+        let terminal_area = if self.state.view.terminal_area.width >= 4
+            && self.state.view.terminal_area.height >= 4
+        {
+            self.state.view.terminal_area
+        } else {
+            let (estimated_rows, estimated_cols) = self.state.estimate_pane_size();
+            ratatui::layout::Rect::new(0, 0, estimated_cols, estimated_rows)
+        };
+        let Some(resolved_geometry) =
+            resolve_popup_geometry(geometry.width, geometry.height, terminal_area)
+        else {
+            return Err(std::io::Error::other("terminal area too small for popup"));
+        };
+        let rows = resolved_geometry.inner.height;
+        let cols = resolved_geometry.inner.width;
+        let (runtime, launch_argv) = spawn(pane_id, rows, cols, cwd.clone(), &launch_env, self)?;
+        let terminal = match launch_argv {
+            Some(argv) => TerminalState::new(terminal_id.clone(), cwd).with_launch_argv(argv),
+            None => TerminalState::new(terminal_id.clone(), cwd),
+        };
+        self.terminal_runtimes.insert(terminal_id.clone(), runtime);
+        self.state.terminals.insert(terminal_id.clone(), terminal);
+        self.state.popup_pane = Some(crate::app::state::PopupPaneState {
+            pane_id,
+            terminal_id,
+            width: geometry.width,
+            height: geometry.height,
+        });
+        self.state.mode = Mode::Terminal;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+impl App {
+    pub(crate) fn install_test_popup_runtime(
+        &mut self,
+        runtime: TerminalRuntime,
+    ) -> (PaneId, TerminalId) {
+        let pane_id = PaneId::alloc();
+        let terminal_id = TerminalId::alloc();
+        self.terminal_runtimes.insert(terminal_id.clone(), runtime);
+        self.state.terminals.insert(
+            terminal_id.clone(),
+            TerminalState::new(terminal_id.clone(), PathBuf::from("/popup")),
+        );
+        self.state.popup_pane = Some(crate::app::state::PopupPaneState {
+            pane_id,
+            terminal_id: terminal_id.clone(),
+            width: None,
+            height: None,
+        });
+        (pane_id, terminal_id)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn app_with_popup() -> App {
+        let (_api_tx, api_rx) = tokio::sync::mpsc::unbounded_channel();
+        let mut app = App::new(
+            &crate::config::Config::default(),
+            true,
+            None,
+            api_rx,
+            crate::api::EventHub::default(),
+        );
+        app.state.workspaces = vec![crate::workspace::Workspace::test_new("popup")];
+        app.state.active = Some(0);
+        app.state.selected = 0;
+        let terminal_id = TerminalId::alloc();
+        app.state.terminals.insert(
+            terminal_id.clone(),
+            TerminalState::new(terminal_id.clone(), PathBuf::from("/popup")),
+        );
+        app.state.popup_pane = Some(crate::app::state::PopupPaneState {
+            pane_id: PaneId::alloc(),
+            terminal_id,
+            width: None,
+            height: None,
+        });
+        app
+    }
+
+    #[test]
+    fn close_popup_uses_terminal_mode_with_active_workspace() {
+        let mut app = app_with_popup();
+        app.state.mode = Mode::Navigate;
+
+        assert!(app.close_popup_pane());
+
+        assert_eq!(app.state.mode, Mode::Terminal);
+    }
+
+    #[test]
+    fn close_popup_uses_navigate_mode_without_active_workspace() {
+        let mut app = app_with_popup();
+        app.state.workspaces.clear();
+        app.state.active = None;
+        app.state.mode = Mode::Navigate;
+
+        assert!(app.close_popup_pane());
+
+        assert_eq!(app.state.mode, Mode::Navigate);
+    }
+
+    #[test]
+    fn close_popup_clears_direct_attach_resize_lock() {
+        let mut app = app_with_popup();
+        let terminal_id = app.state.popup_pane.as_ref().unwrap().terminal_id.clone();
+        app.state
+            .direct_attach_resize_locks
+            .insert(terminal_id.clone());
+
+        assert!(app.close_popup_pane());
+
+        assert!(!app.state.direct_attach_resize_locks.contains(&terminal_id));
+    }
+
+    #[test]
+    fn popup_survives_background_workspace_removal() {
+        let mut app = app_with_popup();
+        app.state.workspaces.clear();
+        app.state.active = None;
+
+        app.state.assert_invariants_for_test();
+
+        assert!(app.state.popup_pane.is_some());
+    }
+
+    #[test]
+    fn popup_close_api_closes_only_active_popup() {
+        let mut app = app_with_popup();
+        let close = || crate::api::schema::Request {
+            id: "close-popup".into(),
+            method: crate::api::schema::Method::PopupClose(
+                crate::api::schema::EmptyParams::default(),
+            ),
+        };
+
+        let response = app.handle_api_request(close());
+        let response: crate::api::schema::SuccessResponse =
+            serde_json::from_str(&response).unwrap();
+        assert_eq!(response.result, crate::api::schema::ResponseResult::Ok {});
+
+        let response = app.handle_api_request(close());
+        let response: crate::api::schema::ErrorResponse = serde_json::from_str(&response).unwrap();
+        assert_eq!(response.error.code, "popup_not_open");
+    }
+}

src/app/runtime.rs

@@ -142,7 +142,7 @@ impl App {
                 let key_id = repeat_key_identity(&key);
                 match key.kind {
                     crossterm::event::KeyEventKind::Press => {
-                        if self.state.mode == Mode::Terminal {
+                        if self.state.popup_pane.is_some() || self.state.mode == Mode::Terminal {
                             self.suppressed_repeat_keys.remove(&key_id);
                         } else {
                             self.suppressed_repeat_keys.insert(key_id);
@@ -151,7 +151,7 @@ impl App {
                         true
                     }
                     crossterm::event::KeyEventKind::Repeat => {
-                        if self.state.mode == Mode::Terminal
+                        if (self.state.popup_pane.is_some() || self.state.mode == Mode::Terminal)
                             && !self.suppressed_repeat_keys.contains(&key_id)
                         {
                             self.handle_key(key).await;
@@ -171,7 +171,7 @@ impl App {
                 true
             }
             crate::raw_input::RawInputEvent::Mouse(mouse) => {
-                if self.state.mouse_capture {
+                if self.state.popup_pane.is_some() || self.state.mouse_capture {
                     self.handle_mouse(mouse);
                 } else {
                     self.state

src/app/state.rs

@@ -53,6 +53,14 @@ fn pane_graphics_data_fingerprint(data: &[u8]) -> u64 {
     hasher.finish()
 }
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) struct PopupPaneState {
+    pub pane_id: PaneId,
+    pub terminal_id: crate::terminal::TerminalId,
+    pub width: Option<crate::popup_size::PopupSize>,
+    pub height: Option<crate::popup_size::PopupSize>,
+}
+
 // ---------------------------------------------------------------------------
 // Selection autoscroll types
 // ---------------------------------------------------------------------------
@@ -1515,6 +1523,8 @@ pub struct AppState {
     pub(crate) pane_graphics_streams: std::collections::HashMap<PaneId, String>,
     /// Monotonic marker for accepted pane graphics mutations.
     pub(crate) pane_graphics_revision: u64,
+    /// Session-modal terminal popup. This is intentionally outside workspace layouts.
+    pub(crate) popup_pane: Option<PopupPaneState>,
     /// Recent plugin action/event command executions.
     pub(crate) plugin_command_logs: Vec<crate::api::schema::PluginCommandLogInfo>,
     pub(crate) next_plugin_command_log_id: u64,
@@ -1608,7 +1618,9 @@ impl AppState {
         &self,
         terminal_runtimes: &crate::terminal::TerminalRuntimeRegistry,
     ) -> bool {
-        self.mouse_capture || self.focused_pane_requests_mouse_capture_from(terminal_runtimes)
+        self.mouse_capture
+            || self.popup_pane.is_some()
+            || self.focused_pane_requests_mouse_capture_from(terminal_runtimes)
     }
 
     pub fn is_prefix_key(&self, key: crate::input::TerminalKey) -> bool {
@@ -1874,6 +1886,7 @@ impl AppState {
             pane_graphics_layers: std::collections::HashMap::new(),
             pane_graphics_streams: std::collections::HashMap::new(),
             pane_graphics_revision: 0,
+            popup_pane: None,
             plugin_command_logs: Vec::new(),
             next_plugin_command_log_id: 1,
             plugin_commands_in_flight: 0,
@@ -2104,6 +2117,19 @@ impl AppState {
                 "pending agent notification",
             );
         }
+        if let Some(popup) = &self.popup_pane {
+            assert!(
+                self.terminals.contains_key(&popup.terminal_id),
+                "popup {:?} references missing terminal {}",
+                popup.pane_id,
+                popup.terminal_id
+            );
+            assert!(
+                !attached_terminal_ids.contains(&popup.terminal_id),
+                "popup terminal {} must not be attached to a tiled pane",
+                popup.terminal_id
+            );
+        }
         for &pane_id in self.plugin_panes.keys() {
             assert_live_pane(pane_id, "plugin pane record");
         }

src/cli/plugin.rs

@@ -12,6 +12,7 @@ use crate::api::schema::{
     PluginPlatform, PluginSetEnabledParams, PluginSourceInfo, PluginSourceKind, PluginUnlinkParams,
     Request, ResponseResult, SplitDirection, SuccessResponse,
 };
+use crate::popup_size::PopupSize;
 
 const PLUGIN_BUILD_OUTPUT_MAX_BYTES: usize = 64 * 1024;
 
@@ -487,6 +488,8 @@ fn plugin_pane_open(args: &[String]) -> std::io::Result<i32> {
     let mut plugin_id = None;
     let mut entrypoint = None;
     let mut placement = None;
+    let mut width = None;
+    let mut height = None;
     let mut workspace_id = None;
     let mut target_pane_id = None;
     let mut direction = None;
@@ -518,6 +521,24 @@ fn plugin_pane_open(args: &[String]) -> std::io::Result<i32> {
                 };
                 placement = Some(parsed);
             }
+            "--width" => {
+                let Some(value) = required_value(args, &mut index, "--width") else {
+                    return Ok(2);
+                };
+                let Some(parsed) = parse_popup_dimension(&value, "--width") else {
+                    return Ok(2);
+                };
+                width = Some(parsed);
+            }
+            "--height" => {
+                let Some(value) = required_value(args, &mut index, "--height") else {
+                    return Ok(2);
+                };
+                let Some(parsed) = parse_popup_dimension(&value, "--height") else {
+                    return Ok(2);
+                };
+                height = Some(parsed);
+            }
             "--workspace" => {
                 let Some(value) = required_value(args, &mut index, "--workspace") else {
                     return Ok(2);
@@ -586,6 +607,8 @@ fn plugin_pane_open(args: &[String]) -> std::io::Result<i32> {
         plugin_id,
         entrypoint,
         placement,
+        width,
+        height,
         workspace_id,
         target_pane_id,
         direction,
@@ -595,6 +618,16 @@ fn plugin_pane_open(args: &[String]) -> std::io::Result<i32> {
     }))
 }
 
+fn parse_popup_dimension(value: &str, flag: &str) -> Option<PopupSize> {
+    match PopupSize::parse_cli(value) {
+        Ok(value) => Some(value),
+        Err(message) => {
+            eprintln!("{flag} {message}");
+            None
+        }
+    }
+}
+
 fn plugin_pane_focus(args: &[String]) -> std::io::Result<i32> {
     let Some(pane_id) = args.first() else {
         eprintln!("usage: herdr plugin pane focus <pane_id>");
@@ -635,6 +668,7 @@ fn required_value(args: &[String], index: &mut usize, flag: &str) -> Option<Stri
 fn parse_pane_placement(value: &str) -> Option<PluginPanePlacement> {
     match value {
         "overlay" => Some(PluginPanePlacement::Overlay),
+        "popup" => Some(PluginPanePlacement::Popup),
         "split" => Some(PluginPanePlacement::Split),
         "tab" => Some(PluginPanePlacement::Tab),
         "zoomed" | "fullscreen" => Some(PluginPanePlacement::Zoomed),
@@ -1604,7 +1638,7 @@ fn print_plugin_action_help() {
 
 fn print_plugin_pane_help() {
     eprintln!("herdr plugin pane commands:");
-    eprintln!("  herdr plugin pane open --plugin ID --entrypoint ID [--placement overlay|split|tab|zoomed] [--workspace ID] [--target-pane PANE] [--direction right|down] [--cwd PATH] [--env KEY=VALUE] [--focus|--no-focus]");
+    eprintln!("  herdr plugin pane open --plugin ID --entrypoint ID [--placement overlay|popup|split|tab|zoomed] [--width SIZE] [--height SIZE] [--workspace ID] [--target-pane PANE] [--direction right|down] [--cwd PATH] [--env KEY=VALUE] [--focus|--no-focus]");
     eprintln!("  herdr plugin pane focus <pane_id>");
     eprintln!("  herdr plugin pane close <pane_id>");
 }

src/config/keybinds.rs

@@ -6,6 +6,7 @@ use tracing::warn;
 
 use super::Config;
 use crate::input::TerminalKey;
+use crate::popup_size::PopupSize;
 
 pub type KeyCombo = (KeyCode, KeyModifiers);
 
@@ -80,6 +81,7 @@ pub enum CommandKeybindType {
     #[default]
     Shell,
     Pane,
+    Popup,
     PluginAction,
 }
 
@@ -95,6 +97,10 @@ pub struct CommandKeybindConfig {
     pub action_type: CommandKeybindType,
     /// Optional user-defined description for this custom command.
     pub description: Option<String>,
+    /// Optional popup width as cells or a percentage string when type = "popup".
+    pub width: Option<PopupSize>,
+    /// Optional popup height as cells or a percentage string when type = "popup".
+    pub height: Option<PopupSize>,
 }
 
 impl Default for CommandKeybindConfig {
@@ -104,6 +110,8 @@ impl Default for CommandKeybindConfig {
             command: String::new(),
             action_type: CommandKeybindType::Shell,
             description: None,
+            width: None,
+            height: None,
         }
     }
 }
@@ -112,6 +120,7 @@ impl Default for CommandKeybindConfig {
 pub enum CustomCommandAction {
     Shell,
     Pane,
+    Popup,
     PluginAction,
 }
 
@@ -283,6 +292,8 @@ pub struct CustomCommandKeybind {
     pub command: String,
     pub action: CustomCommandAction,
     pub description: Option<String>,
+    pub width: Option<PopupSize>,
+    pub height: Option<PopupSize>,
 }
 
 /// Parsed keybinds for Herdr actions.
@@ -743,8 +754,21 @@ fn append_custom_command_bindings(
         let action = match command.action_type {
             CommandKeybindType::Shell => CustomCommandAction::Shell,
             CommandKeybindType::Pane => CustomCommandAction::Pane,
+            CommandKeybindType::Popup => CustomCommandAction::Popup,
             CommandKeybindType::PluginAction => CustomCommandAction::PluginAction,
         };
+        let (width, height) = if action == CustomCommandAction::Popup {
+            (command.width, command.height)
+        } else {
+            if command.width.is_some() || command.height.is_some() {
+                let diag = format!(
+                    "popup size on non-popup custom command: keys.command[{index}]; ignoring width and height"
+                );
+                warn!(message = %diag, "config diagnostic");
+                diagnostics.push(diag);
+            }
+            (None, None)
+        };
         let label = bindings.label().unwrap_or_else(|| "unset".to_string());
         keybinds.custom_commands.push(CustomCommandKeybind {
             bindings,
@@ -752,6 +776,8 @@ fn append_custom_command_bindings(
             command: command.command.clone(),
             action,
             description: command.description.clone(),
+            width,
+            height,
         });
     }
 }
@@ -2185,4 +2211,54 @@ description = "say hello"
             Some("say hello".to_string())
         );
     }
+
+    #[test]
+    fn custom_popup_command_parses() {
+        let config: Config = toml::from_str(
+            r#"
+[[keys.command]]
+key = "prefix+g"
+command = "lazygit"
+type = "popup"
+width = 90
+height = "80%"
+"#,
+        )
+        .unwrap();
+        let keybinds = config.keybinds();
+        assert_eq!(keybinds.custom_commands.len(), 1);
+        assert_eq!(
+            keybinds.custom_commands[0].action,
+            CustomCommandAction::Popup
+        );
+        assert_eq!(
+            keybinds.custom_commands[0].width,
+            Some(PopupSize::Cells(90))
+        );
+        assert_eq!(
+            keybinds.custom_commands[0].height,
+            Some(PopupSize::Percent(80))
+        );
+    }
+
+    #[test]
+    fn non_popup_custom_command_ignores_popup_size_with_diagnostic() {
+        let config: Config = toml::from_str(
+            r#"
+[[keys.command]]
+key = "prefix+g"
+command = "lazygit"
+type = "pane"
+width = "80%"
+"#,
+        )
+        .unwrap();
+
+        let keybinds = config.keybinds();
+        assert_eq!(keybinds.custom_commands[0].width, None);
+        assert!(config
+            .collect_diagnostics()
+            .iter()
+            .any(|diag| diag.contains("popup size on non-popup custom command")));
+    }
 }

src/main.rs

@@ -79,6 +79,7 @@ mod persist;
 mod platform;
 mod plugin_command;
 mod plugin_paths;
+mod popup_size;
 mod product_announcements;
 mod protocol;
 mod pty;

src/pane.rs

@@ -65,21 +65,26 @@ fn apply_pane_terminal_env(cmd: &mut CommandBuilder) {
 #[derive(Debug, Clone, Default, PartialEq, Eq)]
 pub(crate) struct PaneLaunchEnv {
     extra: Vec<(String, String)>,
-    identity: Option<PaneLaunchIdentity>,
+    identity: PaneLaunchIdentity,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-struct PaneLaunchIdentity {
-    workspace_id: String,
-    tab_id: String,
-    pane_id: String,
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+enum PaneLaunchIdentity {
+    #[default]
+    Inherit,
+    Managed {
+        workspace_id: String,
+        tab_id: String,
+        pane_id: String,
+    },
+    OmitPane,
 }
 
 impl PaneLaunchEnv {
     pub(crate) fn from_extra(extra: Vec<(String, String)>) -> Self {
         Self {
             extra,
-            identity: None,
+            identity: PaneLaunchIdentity::Inherit,
         }
     }
 
@@ -89,11 +94,16 @@ impl PaneLaunchEnv {
         tab_id: String,
         pane_id: String,
     ) -> Self {
-        self.identity = Some(PaneLaunchIdentity {
+        self.identity = PaneLaunchIdentity::Managed {
             workspace_id,
             tab_id,
             pane_id,
-        });
+        };
+        self
+    }
+
+    pub(crate) fn without_pane_identity(mut self) -> Self {
+        self.identity = PaneLaunchIdentity::OmitPane;
         self
     }
 }
@@ -104,13 +114,20 @@ fn apply_pane_launch_env(cmd: &mut CommandBuilder, launch_env: &PaneLaunchEnv) {
     }
     cmd.env(crate::HERDR_ENV_VAR, crate::HERDR_ENV_VALUE);
     crate::integration::apply_pane_base_env(cmd);
-    if let Some(identity) = &launch_env.identity {
-        cmd.env(
-            crate::integration::HERDR_WORKSPACE_ID_ENV_VAR,
-            &identity.workspace_id,
-        );
-        cmd.env(crate::integration::HERDR_TAB_ID_ENV_VAR, &identity.tab_id);
-        cmd.env(crate::integration::HERDR_PANE_ID_ENV_VAR, &identity.pane_id);
+    match &launch_env.identity {
+        PaneLaunchIdentity::Inherit => {}
+        PaneLaunchIdentity::Managed {
+            workspace_id,
+            tab_id,
+            pane_id,
+        } => {
+            cmd.env(crate::integration::HERDR_WORKSPACE_ID_ENV_VAR, workspace_id);
+            cmd.env(crate::integration::HERDR_TAB_ID_ENV_VAR, tab_id);
+            cmd.env(crate::integration::HERDR_PANE_ID_ENV_VAR, pane_id);
+        }
+        PaneLaunchIdentity::OmitPane => {
+            cmd.env_remove(crate::integration::HERDR_PANE_ID_ENV_VAR);
+        }
     }
 }
 
@@ -127,6 +144,12 @@ struct SpawnInitialState<'a> {
     windows_powershell_prompt_cwd_reporting: bool,
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub(crate) enum AgentDetection {
+    Enabled,
+    Disabled,
+}
+
 fn active_pending_release(
     pending_release: &Mutex<Option<PendingAgentRelease>>,
     now: std::time::Instant,
@@ -917,7 +940,7 @@ pub struct PaneRuntime {
     pending_release: Arc<Mutex<Option<PendingAgentRelease>>>,
     preserve_processes_on_drop: bool,
     // Task handles for deterministic shutdown
-    detect_handle: tokio::task::AbortHandle,
+    detect_handle: Option<tokio::task::AbortHandle>,
 }
 
 enum PaneRuntimeIo {
@@ -1061,7 +1084,9 @@ impl Drop for PaneRuntime {
     fn drop(&mut self) {
         // Abort detection task immediately and terminate the owned session.
         // The PTY actor shuts down before the process/session policy runs.
-        self.detect_handle.abort();
+        if let Some(handle) = &self.detect_handle {
+            handle.abort();
+        }
         self.io.shutdown();
         if !self.preserve_processes_on_drop {
             shutdown_pane_processes(
@@ -1411,7 +1436,9 @@ fn publish_reported_cwd(
 
 impl PaneRuntime {
     pub fn shutdown(mut self) {
-        self.detect_handle.abort();
+        if let Some(handle) = self.detect_handle.take() {
+            handle.abort();
+        }
         self.io.shutdown();
         shutdown_pane_processes(
             self.pane_id,
@@ -1435,7 +1462,9 @@ impl PaneRuntime {
                 "failed to release PTY actor after handoff commit; dropping runtime will still close the actor handle"
             );
         }
-        self.detect_handle.abort();
+        if let Some(handle) = self.detect_handle.take() {
+            handle.abort();
+        }
         self.preserve_processes_on_drop = true;
     }
 
@@ -1571,6 +1600,7 @@ impl PaneRuntime {
                 history_ansi: initial_history_ansi,
                 windows_powershell_prompt_cwd_reporting,
             },
+            AgentDetection::Enabled,
         )
     }
 
@@ -1583,6 +1613,7 @@ impl PaneRuntime {
         cwd: std::path::PathBuf,
         command: &str,
         launch_env: &PaneLaunchEnv,
+        agent_detection: AgentDetection,
         scrollback_limit_bytes: usize,
         host_terminal_theme: crate::terminal_theme::TerminalTheme,
         events: mpsc::Sender<AppEvent>,
@@ -1605,9 +1636,12 @@ impl PaneRuntime {
             cmd,
             "failed to spawn command pane",
             SpawnInitialState::default(),
+            agent_detection,
         )
     }
 
+    // Runtime construction needs to thread PTY size, environment, theme, render hooks, and detection policy together.
+    #[allow(clippy::too_many_arguments)]
     pub fn spawn_argv_command(
         pane_id: PaneId,
         rows: u16,
@@ -1615,6 +1649,7 @@ impl PaneRuntime {
         cwd: std::path::PathBuf,
         argv: &[String],
         launch_env: &PaneLaunchEnv,
+        agent_detection: AgentDetection,
         scrollback_limit_bytes: usize,
         host_terminal_theme: crate::terminal_theme::TerminalTheme,
         events: mpsc::Sender<AppEvent>,
@@ -1646,6 +1681,7 @@ impl PaneRuntime {
             cmd,
             "failed to spawn argv command pane",
             SpawnInitialState::default(),
+            agent_detection,
         )
     }
 
@@ -1791,10 +1827,12 @@ impl PaneRuntime {
             detect_reset_notify,
             pending_release,
             preserve_processes_on_drop: true,
-            detect_handle,
+            detect_handle: Some(detect_handle),
         })
     }
 
+    // Runtime construction needs to thread PTY size, environment, theme, render hooks, and detection policy together.
+    #[allow(clippy::too_many_arguments)]
     fn spawn_command_builder(
         pane_id: PaneId,
         rows: u16,
@@ -1807,6 +1845,7 @@ impl PaneRuntime {
         cmd: CommandBuilder,
         spawn_error_message: &'static str,
         initial_state: SpawnInitialState<'_>,
+        agent_detection: AgentDetection,
     ) -> std::io::Result<Self> {
         crate::logging::pane_spawn_started(pane_id.raw(), rows, cols, scrollback_limit_bytes);
 
@@ -1881,7 +1920,9 @@ impl PaneRuntime {
                 let shell_pid = child_pid.load(Ordering::Acquire);
                 let result =
                     terminal.process_pty_bytes(pane_id, shell_pid, bytes, &response_writer);
-                observe_detection_content_change(bytes, &detection_content_seq);
+                if agent_detection == AgentDetection::Enabled {
+                    observe_detection_content_change(bytes, &detection_content_seq);
+                }
                 if result.request_render && !render_dirty.swap(true, Ordering::AcqRel) {
                     render_notify.notify_one();
                 }
@@ -1924,7 +1965,9 @@ impl PaneRuntime {
         };
 
         // --- Detection task ---
-        let (detect_handle, detect_reset_notify, pending_release) = {
+        let (detect_handle, detect_reset_notify, pending_release) = if agent_detection
+            == AgentDetection::Enabled
+        {
             use crate::detect;
             use std::time::{Duration, Instant};
 
@@ -2282,7 +2325,13 @@ impl PaneRuntime {
                     }
                 }
             });
-            (handle.abort_handle(), detect_reset_notify, pending_release)
+            (
+                Some(handle.abort_handle()),
+                detect_reset_notify,
+                pending_release,
+            )
+        } else {
+            (None, Arc::new(Notify::new()), Arc::new(Mutex::new(None)))
         };
 
         Ok(Self {
@@ -2322,6 +2371,11 @@ impl PaneRuntime {
         self.detect_reset_notify.clone()
     }
 
+    #[cfg(test)]
+    pub(crate) fn agent_detection_enabled_for_test(&self) -> bool {
+        self.detect_handle.is_some()
+    }
+
     pub fn set_full_lifecycle_authority_active(&self, active: bool) {
         let previous = self
             .full_lifecycle_authority_active
@@ -2538,6 +2592,14 @@ impl PaneRuntime {
     }
 
     pub async fn send_paste(&self, text: String) -> Result<(), mpsc::error::SendError<Bytes>> {
+        self.send_bytes(self.paste_payload(text)).await
+    }
+
+    pub fn try_send_paste(&self, text: String) -> Result<(), mpsc::error::TrySendError<Bytes>> {
+        self.try_send_bytes(self.paste_payload(text))
+    }
+
+    fn paste_payload(&self, text: String) -> Bytes {
         let bracketed = self
             .input_state()
             .map(|state| state.bracketed_paste)
@@ -2547,7 +2609,7 @@ impl PaneRuntime {
         } else {
             text
         };
-        self.send_bytes(Bytes::from(payload)).await
+        Bytes::from(payload)
     }
 
     pub fn try_send_focus_event(&self, event: crate::ghostty::FocusEvent) -> bool {
@@ -2743,7 +2805,7 @@ impl PaneRuntime {
                 detect_reset_notify: Arc::new(Notify::new()),
                 pending_release: Arc::new(Mutex::new(None)),
                 preserve_processes_on_drop: true,
-                detect_handle: tokio::spawn(async {}).abort_handle(),
+                detect_handle: Some(tokio::spawn(async {}).abort_handle()),
             },
             rx,
         )
@@ -3205,7 +3267,7 @@ mod tests {
             detect_reset_notify: Arc::new(Notify::new()),
             pending_release: Arc::new(Mutex::new(None)),
             preserve_processes_on_drop: true,
-            detect_handle: tokio::spawn(async {}).abort_handle(),
+            detect_handle: Some(tokio::spawn(async {}).abort_handle()),
         };
 
         assert!(runtime.try_send_focus_event(crate::ghostty::FocusEvent::Gained));
@@ -3236,7 +3298,7 @@ mod tests {
             detect_reset_notify: Arc::new(Notify::new()),
             pending_release: Arc::new(Mutex::new(None)),
             preserve_processes_on_drop: true,
-            detect_handle: tokio::spawn(async {}).abort_handle(),
+            detect_handle: Some(tokio::spawn(async {}).abort_handle()),
         };
 
         assert!(!runtime.try_send_focus_event(crate::ghostty::FocusEvent::Gained));

src/popup_size.rs

@@ -0,0 +1,252 @@
+use std::borrow::Cow;
+
+use ratatui::layout::Rect;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum PopupSize {
+    Cells(u16),
+    Percent(u8),
+}
+
+impl PopupSize {
+    pub(crate) fn resolve(self, available: u16) -> u16 {
+        match self {
+            Self::Cells(cells) => cells,
+            Self::Percent(percent) => ((available as u32 * percent as u32) / 100) as u16,
+        }
+    }
+
+    pub(crate) fn parse_cli(value: &str) -> Result<Self, String> {
+        if let Some(percent) = value.strip_suffix('%') {
+            let percent = percent
+                .parse::<u8>()
+                .map_err(|_| "must be a number of cells or a percentage like 80%".to_string())?;
+            if !(1..=100).contains(&percent) {
+                return Err("percentage must be between 1% and 100%".to_string());
+            }
+            return Ok(Self::Percent(percent));
+        }
+        value
+            .parse::<u16>()
+            .map(Self::Cells)
+            .map_err(|_| "must be a number of cells or a percentage like 80%".to_string())
+    }
+
+    fn parse_percent_string(value: &str) -> Result<Self, String> {
+        if value.ends_with('%') {
+            return Self::parse_cli(value);
+        }
+        Err("string sizes must be percentages like 80%; use a number for cells".to_string())
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct PopupResolvedGeometry {
+    pub outer: Rect,
+    pub inner: Rect,
+}
+
+pub(crate) fn resolve_popup_geometry(
+    width: Option<PopupSize>,
+    height: Option<PopupSize>,
+    area: Rect,
+) -> Option<PopupResolvedGeometry> {
+    let default_width = area.width.saturating_div(2).max(6);
+    let default_height = area.height.saturating_div(2).max(4);
+    let outer_width = width
+        .map(|width| width.resolve(area.width))
+        .unwrap_or(default_width)
+        .max(6)
+        .min(area.width);
+    let outer_height = height
+        .map(|height| height.resolve(area.height))
+        .unwrap_or(default_height)
+        .max(4)
+        .min(area.height);
+    if outer_width < 6 || outer_height < 4 {
+        return None;
+    }
+
+    let outer_x = area.x + (area.width.saturating_sub(outer_width)) / 2;
+    let outer_y = area.y + (area.height.saturating_sub(outer_height)) / 2;
+    let pane_inner_width = outer_width.saturating_sub(2);
+    let pane_inner_height = outer_height.saturating_sub(2);
+    let terminal_cols = if pane_inner_width <= 4 {
+        pane_inner_width
+    } else {
+        pane_inner_width.saturating_sub(1)
+    };
+    let inner = Rect::new(
+        outer_x.saturating_add(1),
+        outer_y.saturating_add(1),
+        terminal_cols,
+        pane_inner_height,
+    );
+    Some(PopupResolvedGeometry {
+        outer: Rect::new(outer_x, outer_y, outer_width, outer_height),
+        inner,
+    })
+}
+
+impl Serialize for PopupSize {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self {
+            Self::Cells(cells) => serializer.serialize_u16(*cells),
+            Self::Percent(percent) => serializer.serialize_str(&format!("{percent}%")),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for PopupSize {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct PopupSizeVisitor;
+
+        impl serde::de::Visitor<'_> for PopupSizeVisitor {
+            type Value = PopupSize;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                formatter.write_str("a cell count or percentage string like 80%")
+            }
+
+            fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                let value =
+                    u16::try_from(value).map_err(|_| E::custom("cell count must fit in u16"))?;
+                Ok(PopupSize::Cells(value))
+            }
+
+            fn visit_i64<E>(self, value: i64) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                let value = u16::try_from(value)
+                    .map_err(|_| E::custom("cell count must be between 0 and 65535"))?;
+                Ok(PopupSize::Cells(value))
+            }
+
+            fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                PopupSize::parse_percent_string(value).map_err(E::custom)
+            }
+        }
+
+        deserializer.deserialize_any(PopupSizeVisitor)
+    }
+}
+
+impl schemars::JsonSchema for PopupSize {
+    fn schema_name() -> Cow<'static, str> {
+        "PopupSize".into()
+    }
+
+    fn json_schema(_generator: &mut schemars::SchemaGenerator) -> schemars::Schema {
+        schemars::json_schema!({
+            "oneOf": [
+                {
+                    "type": "integer",
+                    "minimum": 0,
+                    "maximum": 65535,
+                    "description": "Outer popup size in terminal cells, including the border."
+                },
+                {
+                    "type": "string",
+                    "pattern": "^(100|[1-9][0-9]?)%$",
+                    "description": "Outer popup size as a percentage of the terminal area, for example 80%."
+                }
+            ]
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::PopupSize;
+
+    #[test]
+    fn parses_cells_and_percent() {
+        assert_eq!(PopupSize::parse_cli("120"), Ok(PopupSize::Cells(120)));
+        assert_eq!(PopupSize::parse_cli("80%"), Ok(PopupSize::Percent(80)));
+        assert_eq!(PopupSize::Percent(80).resolve(100), 80);
+    }
+
+    #[test]
+    fn rejects_invalid_percent() {
+        assert!(PopupSize::parse_cli("0%").is_err());
+        assert!(PopupSize::parse_cli("101%").is_err());
+        assert!(PopupSize::parse_cli("%").is_err());
+    }
+
+    #[test]
+    fn string_deserialization_requires_percent() {
+        assert!(serde_json::from_value::<PopupSize>(serde_json::json!("120")).is_err());
+        assert_eq!(
+            serde_json::from_value::<PopupSize>(serde_json::json!("80%")).unwrap(),
+            PopupSize::Percent(80)
+        );
+    }
+
+    #[test]
+    fn serializes_percent_as_string() {
+        assert_eq!(
+            serde_json::to_value(PopupSize::Percent(80)).unwrap(),
+            serde_json::json!("80%")
+        );
+        assert_eq!(
+            serde_json::to_value(PopupSize::Cells(120)).unwrap(),
+            serde_json::json!(120)
+        );
+    }
+
+    #[test]
+    fn resolves_requested_outer_size_and_inner_terminal_area() {
+        let resolved = super::resolve_popup_geometry(
+            Some(PopupSize::Percent(80)),
+            Some(PopupSize::Percent(40)),
+            ratatui::layout::Rect::new(0, 0, 100, 30),
+        )
+        .unwrap();
+        assert_eq!(resolved.outer, ratatui::layout::Rect::new(10, 9, 80, 12));
+        assert_eq!(resolved.inner, ratatui::layout::Rect::new(11, 10, 77, 10));
+    }
+
+    #[test]
+    fn allows_full_terminal_outer_size() {
+        let resolved = super::resolve_popup_geometry(
+            Some(PopupSize::Percent(100)),
+            Some(PopupSize::Percent(100)),
+            ratatui::layout::Rect::new(4, 2, 100, 30),
+        )
+        .unwrap();
+
+        assert_eq!(resolved.outer, ratatui::layout::Rect::new(4, 2, 100, 30));
+        assert_eq!(resolved.inner, ratatui::layout::Rect::new(5, 3, 97, 28));
+    }
+
+    #[test]
+    fn enforces_runtime_minimum_terminal_width() {
+        let resolved = super::resolve_popup_geometry(
+            Some(PopupSize::Cells(4)),
+            None,
+            ratatui::layout::Rect::new(0, 0, 80, 24),
+        )
+        .unwrap();
+        assert_eq!(resolved.outer.width, 6);
+        assert_eq!(resolved.inner.width, 4);
+
+        assert!(
+            super::resolve_popup_geometry(None, None, ratatui::layout::Rect::new(0, 0, 5, 24),)
+                .is_none()
+        );
+    }
+}

src/server/headless.rs

@@ -3462,6 +3462,7 @@ impl HeadlessServer {
 
     fn retained_pty_update_allowed_by_app_state(&self) -> bool {
         self.app.state.mode == app::Mode::Terminal
+            && self.app.state.popup_pane.is_none()
             && self.app.state.selection.is_none()
             && self.app.state.copy_mode.is_none()
             && self.app.state.context_menu.is_none()
@@ -7800,6 +7801,136 @@ next_tab = ""
         assert_eq!((patched.width, patched.height), (80, 24));
     }
 
+    #[tokio::test]
+    async fn retained_pty_update_declines_while_popup_is_visible() {
+        let (mut server, client_rx, _) = retained_test_server(b"tiled");
+        let popup_runtime =
+            crate::terminal::TerminalRuntime::test_with_screen_bytes(40, 12, b"popup-aaaa");
+        let (_, terminal_id) = server.app.install_test_popup_runtime(popup_runtime);
+
+        server.render_and_stream();
+        let initial = read_server_frame(
+            client_rx
+                .recv_timeout(Duration::from_millis(100))
+                .expect("initial popup frame"),
+        );
+        assert!(frame_text(&initial).contains("popup-aaaa"));
+        server
+            .app
+            .terminal_runtimes
+            .get(&terminal_id)
+            .unwrap()
+            .test_process_pty_bytes(b"\rZ");
+
+        assert!(!server.render_retained_pty_update_and_stream());
+        server.render_and_stream();
+        let updated = read_server_frame(
+            client_rx
+                .recv_timeout(Duration::from_millis(100))
+                .expect("full popup fallback frame"),
+        );
+        assert!(frame_text(&updated).contains("Zopup-aaaa"));
+    }
+
+    #[tokio::test]
+    async fn popup_forces_host_mouse_capture_for_headless_client() {
+        let mut server = test_headless_server();
+        let (client_tx, client_control_rx, _client_rx) = test_client_writer();
+        server.clients.insert(
+            1,
+            ClientConnection::new(
+                (80, 24),
+                crate::kitty_graphics::HostCellSize::default(),
+                crate::terminal_theme::TerminalTheme::default(),
+                None,
+                1,
+                RenderEncoding::SemanticFrame,
+                Some(client_tx),
+            ),
+        );
+        server.app.state.mouse_capture = false;
+        let popup_runtime =
+            crate::terminal::TerminalRuntime::test_with_screen_bytes(40, 12, b"popup");
+        server.app.install_test_popup_runtime(popup_runtime);
+
+        server.stream_host_mouse_capture_mode();
+
+        assert!(matches!(
+            read_server_message(
+                client_control_rx
+                    .recv_timeout(Duration::from_millis(100))
+                    .expect("mouse capture message")
+            ),
+            ServerMessage::MouseCapture { enabled: true }
+        ));
+    }
+
+    #[tokio::test]
+    async fn virtual_render_uses_popup_cursor() {
+        let (mut server, _client_rx, _) = retained_test_server(b"\x1b[2;2H");
+        let popup_runtime =
+            crate::terminal::TerminalRuntime::test_with_screen_bytes(40, 12, b"\x1b[4;5H");
+        let (_, terminal_id) = server.app.install_test_popup_runtime(popup_runtime);
+
+        let (_, cursor) = crate::server::render_stream::render_virtual_with_runtime_registry(
+            &mut server.app.state,
+            &server.app.terminal_runtimes,
+            ratatui::layout::Rect::new(0, 0, 80, 24),
+            true,
+            crate::kitty_graphics::HostCellSize::default(),
+        );
+        let (_, inner) =
+            crate::ui::popup_pane_rects(&server.app.state, server.app.state.view.terminal_area)
+                .unwrap();
+        let expected = server
+            .app
+            .terminal_runtimes
+            .get(&terminal_id)
+            .unwrap()
+            .cursor_state(inner, true)
+            .unwrap();
+
+        assert_eq!(
+            cursor,
+            Some(crate::protocol::CursorState {
+                x: expected.x,
+                y: expected.y,
+                visible: expected.visible,
+                shape: expected.shape,
+            })
+        );
+    }
+
+    #[tokio::test]
+    async fn virtual_render_does_not_resize_directly_attached_popup() {
+        let (mut server, _client_rx, _) = retained_test_server(b"tiled");
+        let popup_runtime = crate::terminal::TerminalRuntime::test_with_screen_bytes(50, 13, b"");
+        let (_, terminal_id) = server.app.install_test_popup_runtime(popup_runtime);
+        server
+            .app
+            .state
+            .direct_attach_resize_locks
+            .insert(terminal_id.clone());
+
+        let _ = crate::server::render_stream::render_virtual_with_runtime_registry(
+            &mut server.app.state,
+            &server.app.terminal_runtimes,
+            ratatui::layout::Rect::new(0, 0, 80, 24),
+            true,
+            crate::kitty_graphics::HostCellSize::default(),
+        );
+
+        assert_eq!(
+            server
+                .app
+                .terminal_runtimes
+                .get(&terminal_id)
+                .unwrap()
+                .current_size(),
+            (13, 50)
+        );
+    }
+
     #[tokio::test]
     async fn retained_pty_update_declines_while_toast_is_visible() {
         let (mut server, client_rx, pane_id) = retained_test_server(b"aaaa");

src/server/render_stream.rs

@@ -290,15 +290,17 @@ pub(crate) fn render_virtual_with_runtime_registry(
     resize_panes: bool,
     cell_size: crate::kitty_graphics::HostCellSize,
 ) -> (ratatui::buffer::Buffer, Option<CursorState>) {
+    let popup_visible = app_state.popup_pane.is_some();
     let pre_compute_suppresses_focused_terminal_cursor =
-        focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes);
+        !popup_visible && focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes);
     if resize_panes {
         crate::ui::compute_view_with_cell_size(app_state, terminal_runtimes, area, cell_size);
     } else {
         crate::ui::compute_view_without_resizing_panes(app_state, terminal_runtimes, area);
     }
     let suppress_focused_terminal_cursor = pre_compute_suppresses_focused_terminal_cursor
-        || focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes);
+        || (!popup_visible
+            && focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes));
 
     let backend = CursorTrackingBackend::new(area.width, area.height);
     let mut terminal = ratatui::Terminal::new(backend).expect("TestBackend::new should never fail");
@@ -310,7 +312,9 @@ pub(crate) fn render_virtual_with_runtime_registry(
         .expect("render to TestBackend should never fail");
 
     let buffer = terminal.backend().buffer().clone();
-    let cursor = if suppress_focused_terminal_cursor {
+    let cursor = if popup_visible {
+        popup_terminal_cursor(app_state, terminal_runtimes)
+    } else if suppress_focused_terminal_cursor {
         None
     } else {
         focused_terminal_cursor(app_state, terminal_runtimes).or_else(|| {
@@ -323,6 +327,25 @@ pub(crate) fn render_virtual_with_runtime_registry(
     (buffer, cursor)
 }
 
+fn popup_terminal_cursor(
+    app_state: &AppState,
+    terminal_runtimes: &TerminalRuntimeRegistry,
+) -> Option<CursorState> {
+    let popup = app_state.popup_pane.as_ref()?;
+    let runtime = terminal_runtimes.get(&popup.terminal_id)?;
+    if runtime.synchronized_output_active() {
+        return None;
+    }
+    let (_, inner) = crate::ui::popup_pane_rects(app_state, app_state.view.terminal_area)?;
+    let cursor = runtime.cursor_state(inner, true)?;
+    Some(CursorState {
+        x: cursor.x,
+        y: cursor.y,
+        visible: cursor.visible && !crate::ui::pane_is_scrolled_back(runtime),
+        shape: cursor.shape,
+    })
+}
+
 /// Renders one server-owned terminal directly for `terminal attach` clients.
 pub(crate) fn render_terminal_virtual(
     runtime: &crate::terminal::TerminalRuntime,

src/terminal/runtime.rs

@@ -148,6 +148,7 @@ impl TerminalRuntime {
         cwd: std::path::PathBuf,
         command: &str,
         launch_env: &crate::pane::PaneLaunchEnv,
+        agent_detection: crate::pane::AgentDetection,
         scrollback_limit_bytes: usize,
         host_terminal_theme: crate::terminal_theme::TerminalTheme,
         events: mpsc::Sender<AppEvent>,
@@ -161,6 +162,7 @@ impl TerminalRuntime {
             cwd,
             command,
             launch_env,
+            agent_detection,
             scrollback_limit_bytes,
             host_terminal_theme,
             events,
@@ -170,6 +172,8 @@ impl TerminalRuntime {
         .map(Self)
     }
 
+    // Wrapper mirrors pane runtime construction arguments, including detection policy.
+    #[allow(clippy::too_many_arguments)]
     pub fn spawn_argv_command(
         pane_id: PaneId,
         rows: u16,
@@ -177,6 +181,7 @@ impl TerminalRuntime {
         cwd: std::path::PathBuf,
         argv: &[String],
         launch_env: &crate::pane::PaneLaunchEnv,
+        agent_detection: crate::pane::AgentDetection,
         scrollback_limit_bytes: usize,
         host_terminal_theme: crate::terminal_theme::TerminalTheme,
         events: mpsc::Sender<AppEvent>,
@@ -190,6 +195,7 @@ impl TerminalRuntime {
             cwd,
             argv,
             launch_env,
+            agent_detection,
             scrollback_limit_bytes,
             host_terminal_theme,
             events,
@@ -218,6 +224,11 @@ impl TerminalRuntime {
         self.0.agent_detection_reset_notify_for_test()
     }
 
+    #[cfg(test)]
+    pub(crate) fn agent_detection_enabled_for_test(&self) -> bool {
+        self.0.agent_detection_enabled_for_test()
+    }
+
     pub fn set_full_lifecycle_authority_active(&self, active: bool) {
         self.0.set_full_lifecycle_authority_active(active);
     }
@@ -389,6 +400,10 @@ impl TerminalRuntime {
         self.0.send_paste(text).await
     }
 
+    pub fn try_send_paste(&self, text: String) -> Result<(), mpsc::error::TrySendError<Bytes>> {
+        self.0.try_send_paste(text)
+    }
+
     pub fn try_send_focus_event(&self, event: crate::ghostty::FocusEvent) -> bool {
         self.0.try_send_focus_event(event)
     }

src/ui.rs

@@ -38,7 +38,10 @@ use self::mobile::{
 use self::navigator::render_navigator_overlay;
 pub(crate) use self::onboarding::onboarding_welcome_continue_rect;
 use self::onboarding::render_onboarding_overlay;
-use self::panes::{compute_pane_infos, render_panes, resize_tab_panes};
+pub(crate) use self::panes::popup_pane_rects;
+use self::panes::{
+    compute_pane_infos, render_panes, render_popup_pane, resize_popup_pane, resize_tab_panes,
+};
 pub(crate) use self::release_notes::{
     product_announcement_display_lines, release_notes_close_button_rect,
     release_notes_display_lines, release_notes_wrapped_line_count, PRODUCT_ANNOUNCEMENT_MODAL_SIZE,
@@ -287,6 +290,7 @@ fn compute_view_internal(
     );
     if resize_panes {
         resize_background_tab_panes_for_desktop(app, terminal_runtimes, main_area, cell_size);
+        resize_popup_pane(app, terminal_runtimes, terminal_area, cell_size);
     }
 
     let toast_hit_area = app
@@ -364,6 +368,7 @@ fn compute_mobile_view(
     );
     if resize_panes {
         resize_background_tab_panes_to_area(app, terminal_runtimes, terminal_area, cell_size);
+        resize_popup_pane(app, terminal_runtimes, terminal_area, cell_size);
     }
     let header_hits = compute_mobile_header_hit_areas(app, header_rect);
 
@@ -424,6 +429,7 @@ pub fn render_with_runtime_registry(
 
     // Ambient notifications sit above panes, but below interactive overlays.
     render_notifications(app, frame, terminal_area);
+    render_popup_pane(app, terminal_runtimes, frame, terminal_area);
 
     match app.mode {
         Mode::Onboarding => render_onboarding_overlay(app, frame, frame.area()),
@@ -1392,6 +1398,8 @@ mod tests {
                 command: "lazygit".to_string(),
                 action: crate::config::CustomCommandAction::Pane,
                 description: Some("open lazygit".to_string()),
+                width: None,
+                height: None,
             },
             crate::config::CustomCommandKeybind {
                 bindings: crate::config::ActionKeybinds::prefix("alt+h"),
@@ -1399,6 +1407,8 @@ mod tests {
                 command: "echo hello".to_string(),
                 action: crate::config::CustomCommandAction::Shell,
                 description: None,
+                width: None,
+                height: None,
             },
         ];
 

src/ui/panes.rs

@@ -2,7 +2,7 @@ use ratatui::{
     layout::Rect,
     style::{Color, Modifier, Style},
     text::{Line, Span},
-    widgets::{Block, Borders, Paragraph},
+    widgets::{Block, Borders, Clear, Paragraph},
     Frame,
 };
 
@@ -14,6 +14,7 @@ use super::widgets::panel_contrast_fg;
 use crate::app::state::Palette;
 use crate::app::{AppState, Mode};
 use crate::layout::PaneInfo;
+use crate::popup_size::resolve_popup_geometry;
 use crate::terminal::{TerminalRuntime, TerminalRuntimeRegistry};
 
 pub(crate) fn pane_is_scrolled_back(rt: &TerminalRuntime) -> bool {
@@ -367,6 +368,67 @@ pub(super) fn render_panes(
     render_pane_borders(app, ws, frame);
 }
 
+pub(crate) fn popup_pane_rects(app: &AppState, area: Rect) -> Option<(Rect, Rect)> {
+    let popup = app.popup_pane.as_ref()?;
+    resolve_popup_geometry(popup.width, popup.height, area)
+        .map(|geometry| (geometry.outer, geometry.inner))
+}
+
+pub(super) fn resize_popup_pane(
+    app: &AppState,
+    terminal_runtimes: &TerminalRuntimeRegistry,
+    area: Rect,
+    cell_size: crate::kitty_graphics::HostCellSize,
+) {
+    let Some(popup) = app.popup_pane.as_ref() else {
+        return;
+    };
+    let Some((_outer, inner)) = popup_pane_rects(app, area) else {
+        return;
+    };
+    if app.direct_attach_resize_locks.contains(&popup.terminal_id) {
+        return;
+    }
+    if let Some(rt) = terminal_runtimes.get(&popup.terminal_id) {
+        rt.resize(
+            inner.height,
+            inner.width,
+            cell_size.width_px,
+            cell_size.height_px,
+        );
+    }
+}
+
+pub(super) fn render_popup_pane(
+    app: &AppState,
+    terminal_runtimes: &TerminalRuntimeRegistry,
+    frame: &mut Frame,
+    area: Rect,
+) {
+    let Some(popup) = app.popup_pane.as_ref() else {
+        return;
+    };
+    let Some((outer, inner)) = popup_pane_rects(app, area) else {
+        return;
+    };
+    let Some(rt) = terminal_runtimes.get(&popup.terminal_id) else {
+        return;
+    };
+    let title = app
+        .terminals
+        .get(&popup.terminal_id)
+        .and_then(|terminal| terminal.manual_label.as_deref())
+        .unwrap_or("popup");
+    let block = Block::default()
+        .borders(Borders::ALL)
+        .border_style(Style::default().fg(app.palette.accent))
+        .title(pane_border_title(title, outer.width, true).unwrap_or_default())
+        .style(Style::default().bg(app.palette.panel_bg));
+    frame.render_widget(Clear, outer);
+    frame.render_widget(block, outer);
+    rt.render(frame, inner, !pane_is_scrolled_back(rt));
+}
+
 #[derive(Clone, Copy, Default)]
 struct LineCell {
     up: bool,

src/workspace/tab.rs

@@ -134,6 +134,7 @@ impl Tab {
                 initial_cwd.clone(),
                 argv,
                 launch_env,
+                crate::pane::AgentDetection::Enabled,
                 scrollback_limit_bytes,
                 host_terminal_theme,
                 events.clone(),
@@ -359,6 +360,7 @@ impl Tab {
                 actual_cwd.clone(),
                 command,
                 launch_env,
+                crate::pane::AgentDetection::Enabled,
                 scrollback_limit_bytes,
                 host_terminal_theme,
                 self.events.clone(),
@@ -372,6 +374,7 @@ impl Tab {
                 actual_cwd.clone(),
                 argv,
                 launch_env,
+                crate::pane::AgentDetection::Enabled,
                 scrollback_limit_bytes,
                 host_terminal_theme,
                 self.events.clone(),