Follow-up to the previous fix: the stdin branch dropped "$@", so
options like -s read-only silently never reached codex. Stub now
records argv and tests assert flags + stdin prompt arrive together;
verified live (-s read-only => codex reports READONLY).
Options like -s read-only routed execution into the /dev/null branch,
so codex got no prompt at all. codex natively appends piped stdin as
a <stdin> block, so feeding prompt.md unconditionally is safe.
Background-task re-invoke after SendMessage resume proved unreliable:
subagent ended its turn with 'still running' and was never woken.
Agent now polls for the status file in a foreground call (9.5-min
chunks, repeated), so the result always lands in its final message.
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