fix(command): preserve execNoRead child status

[SaveTheRbtz]

Summary

• Drain and discard execNoRead() output before closing the pipe and waiting for the child.
• Decode child wait statuses through one helper instead of calling WEXITSTATUS on non-exited statuses.

Why

The TSAN build exposed this through the existing regression test:

• command::execNoRead returns 127 when shell exec fails
• observed failure: 0 == 127

execNoRead() used the same pipe-backed command path as exec(), but closed the read end without consuming stdout. Draining the pipe keeps the child status path deterministic while still returning no output.

Testing

• ninja -C build-tsan
• TSAN_OPTIONS=suppressions=./tsan.supp:halt_on_error=1:abort_on_error=1:print_summary=1 ./build-tsan/test/utils/utils_test "command::execNoRead returns 127 when shell exec fails"
• TSAN_OPTIONS=suppressions=./tsan.supp:halt_on_error=1:abort_on_error=1:print_summary=1 meson test -C build-tsan --no-rebuild --print-errorlogs

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid waiting on descendant stdout in execNoRead

When execNoRead runs a shell command that backgrounds a program, e.g. an on-click command like pavucontrol &, the shell can exit immediately but the background process still inherits the piped stdout fd created in open(). Draining here waits for EOF from every process holding that fd, so the caller never reaches close()/waitpid until the background app exits, which regresses no-read/fire-and-forget commands that previously returned after the shell child exited.

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