IShell implementation via ProcessBuilder.
All operations return hive-dsl Results.

Detect available package managers and system capabilities.
Delegates to babashka.fs for path resolution.

Pure POSIX shell-quoting helpers.

Two functions:

  - `shell-quote` — single-quote a string for safe embedding in a
    `sh -c` command, escaping embedded single-quotes and quoting the
    empty string as `''` so it survives tokenization.
  - `join-as-cmd`  — join an argv into one shell-command string by
    quoting each element with `shell-quote`.

Re-quoting an already-quoted string nests correctly — each `sh -c`
peel removes exactly one quoting layer.

Tool registry: maps tool names to their binaries, descriptions,
and install hints per package manager.

(require-tool :ripgrep) => (ok {:path "/usr/bin/rg"})
                         or (err :tool/missing {:hints [...]})