feature: Add "!cmd" user shell execution (#2471)

feature: Add "!cmd" user shell execution

This change lets users run local shell commands directly from the TUI by
prefixing their input with ! (e.g. !ls). Output is truncated to keep the
exec cell usable, and Ctrl-C cleanly
  interrupts long-running commands (e.g. !sleep 10000).

**Summary of changes**

- Route Op::RunUserShellCommand through a dedicated UserShellCommandTask
(core/src/tasks/user_shell.rs), keeping the task logic out of codex.rs.
- Reuse the existing tool router: the task constructs a ToolCall for the
local_shell tool and relies on ShellHandler, so no manual MCP tool
lookup is required.
- Emit exec lifecycle events (ExecCommandBegin/ExecCommandEnd) so the
TUI can show command metadata, live output, and exit status.

**End-to-end flow**

  **TUI handling**

1. ChatWidget::submit_user_message (TUI) intercepts messages starting
with !.
2. Non-empty commands dispatch Op::RunUserShellCommand { command };
empty commands surface a help hint.
3. No UserInput items are created, so nothing is enqueued for the model.

  **Core submission loop**
4. The submission loop routes the op to handlers::run_user_shell_command
(core/src/codex.rs).
5. A fresh TurnContext is created and Session::spawn_user_shell_command
enqueues UserShellCommandTask.

  **Task execution**
6. UserShellCommandTask::run emits TaskStartedEvent, formats the
command, and prepares a ToolCall targeting local_shell.
  7. ToolCallRuntime::handle_tool_call dispatches to ShellHandler.

  **Shell tool runtime**
8. ShellHandler::run_exec_like launches the process via the unified exec
runtime, honoring sandbox and shell policies, and emits
ExecCommandBegin/End.
9. Stdout/stderr are captured for the UI, but the task does not turn the
resulting ToolOutput into a model response.

  **Completion**
10. After ExecCommandEnd, the task finishes without an assistant
message; the session marks it complete and the exec cell displays the
final output.

  **Conversation context**

- The command and its output never enter the conversation history or the
model prompt; the flow is local-only.
  - Only exec/task events are emitted for UI rendering.

**Demo video**


https://github.com/user-attachments/assets/fcd114b0-4304-4448-a367-a04c43e0b996

codex-rs/tui/src/history_cell.rs

@@ -876,18 +876,20 @@ impl HistoryCell for McpToolCallCell {
         }
 
         let mut detail_lines: Vec<Line<'static>> = Vec::new();
+        // Reserve four columns for the tree prefix ("  └ "/"    ") and ensure the wrapper still has at least one cell to work with.
+        let detail_wrap_width = (width as usize).saturating_sub(4).max(1);
 
         if let Some(result) = &self.result {
             match result {
                 Ok(mcp_types::CallToolResult { content, .. }) => {
                     if !content.is_empty() {
                         for block in content {
-                            let text = Self::render_content_block(block, width as usize);
+                            let text = Self::render_content_block(block, detail_wrap_width);
                             for segment in text.split('\n') {
                                 let line = Line::from(segment.to_string().dim());
                                 let wrapped = word_wrap_line(
                                     &line,
-                                    RtOptions::new((width as usize).saturating_sub(4))
+                                    RtOptions::new(detail_wrap_width)
                                         .initial_indent("".into())
                                         .subsequent_indent("    ".into()),
                                 );
@@ -905,7 +907,7 @@ impl HistoryCell for McpToolCallCell {
                     let err_line = Line::from(err_text.dim());
                     let wrapped = word_wrap_line(
                         &err_line,
-                        RtOptions::new((width as usize).saturating_sub(4))
+                        RtOptions::new(detail_wrap_width)
                             .initial_indent("".into())
                             .subsequent_indent("    ".into()),
                     );
@@ -1296,6 +1298,8 @@ pub(crate) fn new_patch_apply_failure(stderr: String) -> PlainHistoryCell {
                 aggregated_output: stderr,
             }),
             OutputLinesParams {
+                line_limit: TOOL_CALL_MAX_LINES,
+                only_err: true,
                 include_angle_pipe: true,
                 include_prefix: true,
             },
@@ -1823,6 +1827,7 @@ mod tests {
                 },
             ],
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1845,6 +1850,7 @@ mod tests {
                 cmd: "rg shimmer_spans".into(),
             }],
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1860,6 +1866,7 @@ mod tests {
                     cmd: "cat shimmer.rs".into(),
                     path: "shimmer.rs".into(),
                 }],
+                false,
             )
             .unwrap();
         cell.complete_call("c2", CommandOutput::default(), Duration::from_millis(1));
@@ -1873,6 +1880,7 @@ mod tests {
                     cmd: "cat status_indicator_widget.rs".into(),
                     path: "status_indicator_widget.rs".into(),
                 }],
+                false,
             )
             .unwrap();
         cell.complete_call("c3", CommandOutput::default(), Duration::from_millis(1));
@@ -1905,6 +1913,7 @@ mod tests {
                 },
             ],
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1924,6 +1933,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), cmd],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1945,6 +1955,7 @@ mod tests {
             command: vec!["echo".into(), "ok".into()],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1964,6 +1975,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), long],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -1982,6 +1994,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), cmd],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -2001,6 +2014,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), cmd],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -2020,6 +2034,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), "seq 1 10 1>&2 && false".into()],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });
@@ -2065,6 +2080,7 @@ mod tests {
             command: vec!["bash".into(), "-lc".into(), long_cmd.to_string()],
             parsed: Vec::new(),
             output: None,
+            is_user_shell_command: false,
             start_time: Some(Instant::now()),
             duration: None,
         });