agent_ui: Auto-capture file context on paste (#42982)

Closes #42972


https://github.com/user-attachments/assets/98f2d3dc-5682-4670-b636-fa8ea2495c69

Release Notes:

- Added automatic file context detection when pasting code into the AI
agent panel. Pasted code now displays as collapsible badges showing the
file path and line numbers (e.g., "app/layout.tsx (18-25)").

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/editor/src/editor.rs

@@ -1592,6 +1592,45 @@ pub struct ClipboardSelection {
     pub is_entire_line: bool,
     /// The indentation of the first line when this content was originally copied.
     pub first_line_indent: u32,
+    #[serde(default)]
+    pub file_path: Option<PathBuf>,
+    #[serde(default)]
+    pub line_range: Option<RangeInclusive<u32>>,
+}
+
+impl ClipboardSelection {
+    pub fn for_buffer(
+        len: usize,
+        is_entire_line: bool,
+        range: Range<Point>,
+        buffer: &MultiBufferSnapshot,
+        project: Option<&Entity<Project>>,
+        cx: &App,
+    ) -> Self {
+        let first_line_indent = buffer
+            .indent_size_for_line(MultiBufferRow(range.start.row))
+            .len;
+
+        let file_path = util::maybe!({
+            let project = project?.read(cx);
+            let file = buffer.file_at(range.start)?;
+            let project_path = ProjectPath {
+                worktree_id: file.worktree_id(cx),
+                path: file.path().clone(),
+            };
+            project.absolute_path(&project_path, cx)
+        });
+
+        let line_range = file_path.as_ref().map(|_| range.start.row..=range.end.row);
+
+        Self {
+            len,
+            is_entire_line,
+            first_line_indent,
+            file_path,
+            line_range,
+        }
+    }
 }
 
 // selections, scroll behavior, was newest selection reversed
@@ -12812,13 +12851,15 @@ impl Editor {
                     text.push_str(chunk);
                     len += chunk.len();
                 }
-                clipboard_selections.push(ClipboardSelection {
+
+                clipboard_selections.push(ClipboardSelection::for_buffer(
                     len,
                     is_entire_line,
-                    first_line_indent: buffer
-                        .indent_size_for_line(MultiBufferRow(selection.start.row))
-                        .len,
-                });
+                    selection.range(),
+                    &buffer,
+                    self.project.as_ref(),
+                    cx,
+                ));
             }
         }
 
@@ -12961,13 +13002,14 @@ impl Editor {
                         text.push('\n');
                         len += 1;
                     }
-                    clipboard_selections.push(ClipboardSelection {
+                    clipboard_selections.push(ClipboardSelection::for_buffer(
                         len,
                         is_entire_line,
-                        first_line_indent: buffer
-                            .indent_size_for_line(MultiBufferRow(trimmed_range.start.row))
-                            .len,
-                    });
+                        trimmed_range,
+                        &buffer,
+                        self.project.as_ref(),
+                        cx,
+                    ));
                 }
             }
         }