[tfcace]

Make shell state ownership explicit so commands, editor input, completions, and agent turns recover consistently from cancellation, errors, and process exit.

• Add script-file and piped-stdin execution, positional arguments, launch options, and login/interactive startup handling.
• Preserve exit statuses, run EXIT traps at shell shutdown, and make interrupted stdin reads terminate even midway through a line.
• Correct background-job, signal, PTY, and terminal-stream handling.
• Preserve typeahead across commands and editor sessions, and prevent queued input from answering permission prompts.
• Keep agent sessions through cancellation and reconnects without replaying prompts already delivered.
• Share shell lexing across parsing, completion, and startup filtering.
• Make completion fetching asynchronous, bounded, and responsive to changes in PATH and the working directory.
• Improve editor state, Unicode handling, history/context selection, and streamed Markdown, including aligned tables.
• Load compatible startup statements before unsupported syntax and report what could not be loaded.