Extract a pure `parseConfigDirFromArgs(argsArray)` seam from the
closure-based `parseConfigDirArg()` and fix the equals-form parser to
use `slice(indexOf('=') + 1)` instead of `split('=')[1]`, so that
paths like `/tmp/gsd=a` or `/tmp/a=b=c` are preserved in full.
Both `--config-dir=<path>` and `-c=<path>` are fixed. The pure seam
is exported via `module.exports` so the 12-case unit test can assert
on typed return values without spawning a child process.
Co-authored-by: CI Rebase Check <ci@gsd-redux>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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