blockRangeAt inferred no language for files like `zshrc`/`.zshrc`/`.bashrc`
because `Path::extension` returns `None` for bare and dotfile names alike,
so the edit tool's `replace block` / `insert after block` ops were
permanently unresolvable on them — an agent retrying the block op would
loop on the same "could not resolve a syntactic block" error.
from_extension now maps known shell rc/profile basenames (zshrc, zshenv,
zprofile, zlogin, zlogout, zsh_aliases, bashrc, bash_profile, bash_login,
bash_logout, bash_aliases, profile, kshrc, mkshrc, shrc; with or without a
leading dot) to the bash grammar, alongside the existing Makefile/Dockerfile
basename handling. Adds a block-resolution regression test over a zsh
`if [[ … ]]; then … fi` block in `zshrc`/`.zshrc`/`.bashrc`.
bling
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