shell_command returns freeform output (#6860)

Instead of returning structured out and then re-formatting it into
freeform, return the freeform output from shell_command tool.

Keep `shell` as the default tool for GPT-5.

codex-rs/core/src/tools/handlers/shell.rs

@@ -117,6 +117,7 @@ impl ToolHandler for ShellHandler {
                     turn,
                     tracker,
                     call_id,
+                    false,
                 )
                 .await
             }
@@ -129,6 +130,7 @@ impl ToolHandler for ShellHandler {
                     turn,
                     tracker,
                     call_id,
+                    false,
                 )
                 .await
             }
@@ -176,6 +178,7 @@ impl ToolHandler for ShellCommandHandler {
             turn,
             tracker,
             call_id,
+            true,
         )
         .await
     }
@@ -189,6 +192,7 @@ impl ShellHandler {
         turn: Arc<TurnContext>,
         tracker: crate::tools::context::SharedTurnDiffTracker,
         call_id: String,
+        freeform: bool,
     ) -> Result<ToolOutput, FunctionCallError> {
         // Approval policy guard for explicit escalation in non-OnRequest modes.
         if exec_params.with_escalated_permissions.unwrap_or(false)
@@ -282,8 +286,12 @@ impl ShellHandler {
         }
 
         let source = ExecCommandSource::Agent;
-        let emitter =
-            ToolEmitter::shell(exec_params.command.clone(), exec_params.cwd.clone(), source);
+        let emitter = ToolEmitter::shell(
+            exec_params.command.clone(),
+            exec_params.cwd.clone(),
+            source,
+            freeform,
+        );
         let event_ctx = ToolEventCtx::new(session.as_ref(), turn.as_ref(), &call_id, None);
         emitter.begin(event_ctx).await;