Summary

• keep c-j reserved for newline in the classic CLI on local macOS, so Shift+Enter paths that collapse to LF stop submitting the prompt
• preserve the existing LF-submit behavior for thin PTYs via HERMES_CLI_SUBMIT_ON_LF=1
• add regression coverage for macOS default behavior and the explicit LF-submit opt-in

Closes #22908.

Why this stays narrow

• only touches classic CLI keybinding decisions in cli.py
• keeps the existing Windows/WSL/SSH/WT Ctrl+Enter newline behavior intact
• does not change TUI multiline shortcuts; #22909 remains separate

Verification

• git diff --check
• ./.venv/bin/python -m pytest tests/cli/test_cli_init.py tests/cli/test_ctrl_enter_newline.py tests/cli/test_cli_shift_enter_newline.py
• uv sync --frozen --extra all
• uv run --frozen ruff check .
• env -i PATH="$PATH" HOME="$HOME" TERM="${TERM:-xterm-256color}" TZ=UTC LANG=C.UTF-8 LC_ALL=C.UTF-8 PYTHONHASHSEED=0 ./.venv/bin/python -m pytest -o addopts= --collect-only --ignore=tests/integration --ignore=tests/e2e -m 'not integration'
• repo ruff/ty lint-diff against b67ea7ff474831743b14edefb6c9113cb12216e7 (touched files: 0 new ty diagnostics)

Left out

• no TUI fallback shortcut changes
• no docs changes beyond the code comments/tests needed to pin behavior