Hide command for third-party harness cloud agents. (warpdotdev#10448)

## Description
<!-- Please remember to add your design buddy onto the PR for review, if
it contains any UI changes! -->
First stab at an alternative UI for hiding third-party harness cloud
agent commands. Significant inspiration taken from
 how we're showing setup commands.

Currently gated behind a separate feature flag, and only touches the
cloud agent path for block rendering--this should not impact other
block-rendering codepaths.

## Testing
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didn't add any new tests, what's your justification for not adding any?

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almost all changes can be manually tested. If your change can be
manually tested, please include screenshots or a screen recording that
show it working end to end.

You can run the app locally using `./script/run` - see WARP.md for more
details on how to get set up.
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- [x] I have manually tested my changes locally with `./script/run`

### Screenshots / Videos
<!-- Attach screenshots or a short video demonstrating the change, where
appropriate. Remove this section if it is not relevant to your PR. -->
Loom: https://www.loom.com/share/2e61d8636b4f46ef91351ab5c8cacca3

## Agent Mode
- [x] Warp Agent Mode - This PR was created via Warp's AI Agent Mode

Author: liliwilson

app/src/terminal/block_list_element.rs

@@ -2512,129 +2512,136 @@ impl BlockListElement {
             Self::draw_border_between_blocks(border_origin, block_grid_params, ctx);
         }
 
-        let prompt_height_offset = cell_size_height * block.padding_top().as_f64() as f32;
+        let cursor_visible = block.is_mode_set(TermMode::SHOW_CURSOR);
+        let command_origin = if !block.should_hide_command_grid() {
+            let prompt_height_offset = cell_size_height * block.padding_top().as_f64() as f32;
 
-        *grid_origin += vec2f(0., prompt_height_offset);
+            *grid_origin += vec2f(0., prompt_height_offset);
 
-        let prompt_origin = snackbar_header
-            .and_then(|header| header.header_rect())
-            .map_or(*grid_origin, |r| {
-                let y = r.origin().y() + prompt_height_offset + block_banner_height;
-                vec2f(grid_origin.x(), y)
-            });
+            let prompt_origin = snackbar_header
+                .and_then(|header| header.header_rect())
+                .map_or(*grid_origin, |r| {
+                    let y = r.origin().y() + prompt_height_offset + block_banner_height;
+                    vec2f(grid_origin.x(), y)
+                });
 
-        let cursor_visible = block.is_mode_set(TermMode::SHOW_CURSOR);
-        // Draw prompt
-        if let Some(label_element) = label_element {
-            label_element.paint(prompt_origin, ctx, app);
-        } else {
-            let size_info = &block_grid_params.grid_render_params.size_info;
-            if block.should_display_rprompt(size_info) {
-                let rprompt_origin = prompt_origin + block.rprompt_render_offset(size_info);
-                block.rprompt_grid().draw(
-                    rprompt_origin,
-                    element_origin,
-                    glyphs,
-                    COMMAND_ALPHA,
-                    None,
-                    None,
-                    hovered_secret,
-                    None::<std::iter::Empty<&RangeInclusive<IndexPoint>>>,
-                    None,
-                    Properties::default(),
-                    block_grid_params,
-                    None,
-                    image_metadata,
-                    ctx,
-                    app,
-                );
+            // Draw prompt
+            if let Some(label_element) = label_element {
+                label_element.paint(prompt_origin, ctx, app);
+            } else {
+                let size_info = &block_grid_params.grid_render_params.size_info;
+                if block.should_display_rprompt(size_info) {
+                    let rprompt_origin = prompt_origin + block.rprompt_render_offset(size_info);
+                    block.rprompt_grid().draw(
+                        rprompt_origin,
+                        element_origin,
+                        glyphs,
+                        COMMAND_ALPHA,
+                        None,
+                        None,
+                        hovered_secret,
+                        None::<std::iter::Empty<&RangeInclusive<IndexPoint>>>,
+                        None,
+                        Properties::default(),
+                        block_grid_params,
+                        None,
+                        image_metadata,
+                        ctx,
+                        app,
+                    );
+                }
             }
-        }
-
-        // If Warp prompt (non-PS1) is being used, the command is drawn below the prompt,
-        // hence we account for the prompt's vertical offset.
-        let prompt_vertical_offset_px = if !block.honor_ps1() {
-            cell_size_height * (block.command_padding_top() + block.prompt_height()).as_f64() as f32
-        } else {
-            // Otherwise, the prompt/command are drawn together, in a single grid. Hence, we haven't
-            // drawn the prompt above and we do not account for the offset.
-            0.0
-        };
 
-        *grid_origin += vec2f(0.0, prompt_vertical_offset_px);
+            // If Warp prompt (non-PS1) is being used, the command is drawn below the prompt,
+            // hence we account for the prompt's vertical offset.
+            let prompt_vertical_offset_px = if !block.honor_ps1() {
+                cell_size_height
+                    * (block.command_padding_top() + block.prompt_height()).as_f64() as f32
+            } else {
+                // Otherwise, the prompt/command are drawn together, in a single grid. Hence, we haven't
+                // drawn the prompt above and we do not account for the offset.
+                0.0
+            };
 
-        // Determine command_origin based on snackbar_header.
-        let command_origin = if snackbar_header.is_some() {
-            prompt_origin + vec2f(0.0, prompt_vertical_offset_px)
-        } else {
-            *grid_origin
-        };
+            *grid_origin += vec2f(0.0, prompt_vertical_offset_px);
 
-        // Update grid_origin and draw command.
-        let command_grid_properties = Properties::default();
-        block.prompt_and_command_grid().draw(
-            command_origin,
-            element_origin,
-            glyphs,
-            COMMAND_ALPHA,
-            highlighted_url
-                .filter(|url| url.is_in_command_content() && url.block_index == block_index)
-                .map(|url| &url.inner),
-            link_tool_tip
-                .filter(|url| url.is_in_command_content() && url.block_index == block_index)
-                .map(|url| &url.inner),
-            hovered_secret,
-            block_list_find_run
-                .map(|run| run.matches_for_block_grid(block_index, GridType::PromptAndCommand)),
-            block_list_find_run
-                .and_then(|run| run.focused_match())
-                .and_then(|focused_match| match focused_match {
-                    BlockListMatch::CommandBlock(m)
-                        if m.block_index == block_index
-                            && m.grid_type == GridType::PromptAndCommand =>
-                    {
-                        Some(&m.range)
-                    }
-                    _ => None,
-                }),
-            command_grid_properties,
-            block_grid_params,
-            cursor_visible.then(|| block.prompt_and_command_grid().cursor_style().shape),
-            image_metadata,
-            ctx,
-            app,
-        );
+            // Determine command_origin based on snackbar_header.
+            let command_origin = if snackbar_header.is_some() {
+                prompt_origin + vec2f(0.0, prompt_vertical_offset_px)
+            } else {
+                *grid_origin
+            };
 
-        // Only render the cursor in the command grid if the command grid is active and if it's
-        // long running. This is to avoid jitter where a cursor just flickers while the pty is
-        // initializing.
-        if block.is_active_and_long_running()
-            && block.is_command_grid_active()
-            // Check if the "hide cursor" escape sequence is present.
-            && block.is_mode_set(TermMode::SHOW_CURSOR)
-        {
-            block.prompt_and_command_grid().draw_cursor(
+            // Update grid_origin and draw command.
+            let command_grid_properties = Properties::default();
+            block.prompt_and_command_grid().draw(
                 command_origin,
-                &block_grid_params.grid_render_params,
+                element_origin,
+                glyphs,
+                COMMAND_ALPHA,
+                highlighted_url
+                    .filter(|url| url.is_in_command_content() && url.block_index == block_index)
+                    .map(|url| &url.inner),
+                link_tool_tip
+                    .filter(|url| url.is_in_command_content() && url.block_index == block_index)
+                    .map(|url| &url.inner),
+                hovered_secret,
+                block_list_find_run
+                    .map(|run| run.matches_for_block_grid(block_index, GridType::PromptAndCommand)),
+                block_list_find_run
+                    .and_then(|run| run.focused_match())
+                    .and_then(|focused_match| match focused_match {
+                        BlockListMatch::CommandBlock(m)
+                            if m.block_index == block_index
+                                && m.grid_type == GridType::PromptAndCommand =>
+                        {
+                            Some(&m.range)
+                        }
+                        _ => None,
+                    }),
+                command_grid_properties,
+                block_grid_params,
+                cursor_visible.then(|| block.prompt_and_command_grid().cursor_style().shape),
+                image_metadata,
                 ctx,
-                terminal_view_id,
-                None,
-                block_grid_params
-                    .grid_render_params
-                    .warp_theme
-                    .cursor()
-                    .into(),
                 app,
             );
-        }
 
-        // Update grid_origin & draw output
-        *grid_origin += vec2f(
-            0.,
-            cell_size_height
-                * (block.padding_middle() + block.prompt_and_command_grid().len().into_lines())
-                    .as_f64() as f32,
-        );
+            // Only render the cursor in the command grid if the command grid is active and if it's
+            // long running. This is to avoid jitter where a cursor just flickers while the pty is
+            // initializing.
+            if block.is_active_and_long_running()
+                && block.is_command_grid_active()
+                // Check if the "hide cursor" escape sequence is present.
+                && block.is_mode_set(TermMode::SHOW_CURSOR)
+            {
+                block.prompt_and_command_grid().draw_cursor(
+                    command_origin,
+                    &block_grid_params.grid_render_params,
+                    ctx,
+                    terminal_view_id,
+                    None,
+                    block_grid_params
+                        .grid_render_params
+                        .warp_theme
+                        .cursor()
+                        .into(),
+                    app,
+                );
+            }
+
+            // Update grid_origin & draw output
+            *grid_origin += vec2f(
+                0.,
+                cell_size_height
+                    * (block.padding_middle() + block.prompt_and_command_grid().len().into_lines())
+                        .as_f64() as f32,
+            );
+
+            command_origin
+        } else {
+            *grid_origin
+        };
 
         let block_middle_lines =
             block.padding_middle() + block.prompt_and_command_number_of_rows().into_lines();
@@ -4346,7 +4353,11 @@ impl Element for BlockListElement {
                         }
                     }
 
-                    draw_border_above_block = true;
+                    // Don't draw a border below session headers (i.e. above the next block).
+                    draw_border_above_block = !matches!(
+                        self.rich_content_metadata.get(view_id),
+                        Some(RichContentMetadata::HarnessSessionHeader)
+                    );
 
                     grid_origin += vec2f(0., *height_px);
                 }

app/src/terminal/model/block.rs

@@ -399,6 +399,9 @@ pub struct Block {
     /// If `true`, the output grid should not be rendered.
     should_hide_output_grid: bool,
 
+    /// If `true`, the prompt+command grid should not be rendered.
+    should_hide_command_grid: bool,
+
     /// [`Self::linefeed`] may discard some linefeeds at the beginning of the prompt. Doing so will
     /// alter the row numbers for [`Self::goto`] and [`Self::goto_line`] when ConPTY is involved. We
     /// track the count of discarded newlines here in order to correct the row number.
@@ -1007,6 +1010,7 @@ impl Block {
             has_received_user_input: false,
             hidden: false,
             should_hide_output_grid: false,
+            should_hide_command_grid: false,
             leading_linefeeds_ignored: 0,
             is_ai_ugc_telemetry_enabled,
             restored_block_was_local: None,
@@ -1489,6 +1493,14 @@ impl Block {
         self.should_hide_output_grid = should_hide;
     }
 
+    pub fn should_hide_command_grid(&self) -> bool {
+        self.should_hide_command_grid
+    }
+
+    pub fn set_should_hide_command_grid(&mut self, should_hide: bool) {
+        self.should_hide_command_grid = should_hide;
+    }
+
     /// Returns true iff this block should be used as a scrollback block
     /// in a shared session context. Note the active block is included in scrollback to get the active prompt.
     pub fn is_scrollback_block_for_shared_session(
@@ -1515,9 +1527,11 @@ impl Block {
             Lines::zero()
         } else {
             self.block_banner_height()
-                + self.padding_top()
-                + self.prompt_and_command_height()
-                + self.padding_middle()
+                + if self.should_hide_command_grid {
+                    Lines::zero()
+                } else {
+                    self.padding_top() + self.prompt_and_command_height() + self.padding_middle()
+                }
                 + if self.should_hide_output_grid {
                     Lines::zero()
                 } else {
@@ -1940,7 +1954,7 @@ impl Block {
     /// In the case of combined grid: for Warp prompt, this includes the height of both the Warp prompt
     /// AND combined grid; for PS1, this is just the combined grid (PS1 is included there).
     pub fn prompt_and_command_height(&self) -> Lines {
-        if !self.ready_to_render() {
+        if !self.ready_to_render() || self.should_hide_command_grid {
             Lines::zero()
         } else if self.header_grid.honor_ps1 {
             // No padding between prompt and command in the case of PS1 (combined grid).

app/src/terminal/view/ambient_agent/block.rs

@@ -1,8 +1,10 @@
 mod entry;
+mod harness_session_header;
 mod setup_command;
 mod setup_command_text;
 
 pub use entry::*;
+pub use harness_session_header::*;
 pub use setup_command::*;
 pub use setup_command_text::*;