PR #894 added digest-class assertions to agent-send.test.sh but the test
was never added to the test:framework-shell chain, so it wasn't CI-enforced
and could rot. Add it as the final entry in the existing &&-chain.
Verified self-contained before wiring in: the test never touches a live
tmux server. Tests 1-7 pass explicit -S/-n flags so agent-send.sh never
auto-detects via hostname/tmux, and AGENT_SEND_SENDER swaps in an in-repo
capture stub for send-message.sh. Tests 8-10 additionally override PATH
with a fake tmux binary. Ran standalone (bash agent-send.test.sh) twice:
18/18 assertions pass both times, exit 0, temp files cleaned via trap, no
working-tree changes left behind.
Ran the full test:framework-shell chain end-to-end after wiring it in:
all prior steps plus agent-send.test.sh pass, exit 0.
Part of #892
