[exec] add include-plan-tool flag and print it nicely (#3461)

### Summary
Sometimes in exec runs, we want to allow the model to use the
`update_plan` tool, but that's not easily configurable. This change adds
a feature flag for this, and formats the output so it's human-readable

## Test Plan
<img width="1280" height="354" alt="Screenshot 2025-09-11 at 12 39
44 AM"
src="https://github.com/user-attachments/assets/72e11070-fb98-47f5-a784-5123ca7333d9"
/>

codex-rs/exec/src/cli.rs

@@ -67,6 +67,10 @@ pub struct Cli {
     #[arg(long = "json", default_value_t = false)]
     pub json: bool,
 
+    /// Whether to include the plan tool in the conversation.
+    #[arg(long = "include-plan-tool", default_value_t = false)]
+    pub include_plan_tool: bool,
+
     /// Specifies file where the last message from the agent should be written.
     #[arg(long = "output-last-message")]
     pub last_message_file: Option<PathBuf>,

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -539,8 +539,37 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             }
             EventMsg::PlanUpdate(plan_update_event) => {
                 let UpdatePlanArgs { explanation, plan } = plan_update_event;
-                ts_println!(self, "explanation: {explanation:?}");
-                ts_println!(self, "plan: {plan:?}");
+
+                // Header
+                ts_println!(self, "{}", "Plan update".style(self.magenta));
+
+                // Optional explanation
+                if let Some(explanation) = explanation
+                    && !explanation.trim().is_empty()
+                {
+                    ts_println!(self, "{}", explanation.style(self.italic));
+                }
+
+                // Pretty-print the plan items with simple status markers.
+                for item in plan {
+                    use codex_core::plan_tool::StepStatus;
+                    match item.status {
+                        StepStatus::Completed => {
+                            ts_println!(self, "  {} {}", "✓".style(self.green), item.step);
+                        }
+                        StepStatus::InProgress => {
+                            ts_println!(self, "  {} {}", "→".style(self.cyan), item.step);
+                        }
+                        StepStatus::Pending => {
+                            ts_println!(
+                                self,
+                                "  {} {}",
+                                "•".style(self.dimmed),
+                                item.step.style(self.dimmed)
+                            );
+                        }
+                    }
+                }
             }
             EventMsg::GetHistoryEntryResponse(_) => {
                 // Currently ignored in exec output.

codex-rs/exec/src/lib.rs

@@ -53,6 +53,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         sandbox_mode: sandbox_mode_cli_arg,
         prompt,
         output_schema: output_schema_path,
+        include_plan_tool,
         config_overrides,
     } = cli;
 
@@ -161,7 +162,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         model_provider,
         codex_linux_sandbox_exe,
         base_instructions: None,
-        include_plan_tool: None,
+        include_plan_tool: Some(include_plan_tool),
         include_apply_patch_tool: None,
         include_view_image_tool: None,
         show_raw_agent_reasoning: oss.then_some(true),