exec-server: additional context for errors (#7935)

Add a .context() on some exec-server errors for debugging CI flakes.

Also, "login": false in the test to make the test not affected by user
profile.

codex-rs/exec-server/tests/suite/accept_elicitation.rs

@@ -104,6 +104,7 @@ prefix_rule(
             name: Cow::Borrowed("shell"),
             arguments: Some(object(json!(
                 {
+                    "login": false,
                     "command": "git init .",
                     "workdir": project_root_path.to_string_lossy(),
                 }