test_secsi.cpp covered T2 on the send side (retry) and a tick-based
back-to-back exchange. This commit fills in the rest of the timer
matrix at FSM level:
T1 in RecvBlock → abort, reason mentions "T1"
T1 outside RecvBlock → ignored
T2 in RecvEotSent → abort
T2 in RecvBlock → abort (mid-block stall)
T3 / T4 → FSM-level no-op (documented as upper-layer driven)
T2 contrast → send-side retries, recv-side aborts (same timer,
different recovery, both demonstrated in one test)
If a future commit moves T3 or T4 enforcement into the FSM, the
no-op test breaks loudly so protocol.hpp can be updated alongside.
Closes#7 in the test-gap backlog.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
