Read a Subshell's Trailing Comment and a Tab-Stripped Heredoc as Bash Does in the Write Guard #3353

Context

Found by the local review of the backslash-newline narrowing (branch feature/guard-backslash-newline-quoting), confirmed with a classify probe on develop using constructed commands. Both are low realism, filed together as tokenizer divergences from bash.

Gaps

• A # right after a subshell's ) opens a comment in bash. _context_lex and _skip_group read it as text, as _context_lex's docstring states. An apostrophe in that comment then pairs with one on a later line and hides the lines between. Develop allows (echo it)# it's, then gh pr merge 5 --admin, then # ', one per line.
• A <<- heredoc fed to a shell has its leading tabs stripped before the inner shell joins a continuation. No reading strips them, so a word split across a tab-indented continuation stays split. Develop allows bash <<-'EOF' followed by a tab-indented gh pr merge 5 --ad\ line, a tab-indented min line, and a tab-indented EOF. The inner shell runs --admin.

Possible Direction

Read )# as a comment opener after a subshell's ), keeping it text after a substitution's. Strip the leading tabs of a <<- body before reading it as a script.