Read a Double-Quoted Wrapper Body's Run-Time Words as Splittable in the Write Guard #3075

Context

Found by the local review of the lane closing #3006. The new merge check and the existing commit check share it. It was confirmed with classify probes on constructed commands.

A Double-Quoted Wrapper Body Is Read With Quotes the Outer Shell Already Expanded Through

The outer shell expands a $ word inside a double-quoted -c body before the inner shell reads it. The guard reads the body's inner quotes as if they were written by hand. So a quoted option value there is exempt from the run-time word check, although its expansion can carry the inner shell's own quotes:

• B="x' --admin '"; sh -c "gh pr merge 5 --squash --body '$B'" is allowed. The inner shell runs gh pr merge 5 --squash --body 'x' --admin ''.
• B="' -n '"; sh -c "git commit -m '$B'" is allowed through the same exemption on a commit's quoted value.

An unquoted value in the same body, as in bash -c "gh pr merge 5 --squash $A", is denied.

Possible Direction

Carry from _embedded_wrapper_commands whether a body came from double quotes, and read a run-time word inside such a body as never split-free, since the outer shell has already put its text into the body. One change there covers the merge and the commit sites.