[codex] fix gateway startup session suspension cutoff

[samrusani]

What changed

• Fixed suspend_recently_active() to compare datetime values instead of datetime to float.
• Added a regression test for recent vs old sessions.

Why

• Gateway startup could throw datetime >= float and skip the session-suspension safeguard.

Validation

• python3 -m py_compile gateway/session.py tests/gateway/test_session.py
• Targeted sanity check confirmed only recent sessions are suspended.
• Full suite was not used as a gating signal for this patch because the repository has unrelated failures outside this change.

[samrusani]

Fixed the startup session-suspension bug by switching the cutoff to a datetime, and added a regression test covering recent vs stale sessions. I validated the patch with a targeted compile check and a local sanity run.

[teknium1]

Thanks for the contribution @samrusani! This is an automated hermes-sweeper review.

After inspecting current main, the datetime >= float comparison bug in suspend_recently_active() is not present — it appears it was already fixed before this PR was opened (or the function was written correctly from the start on the branch you based off of).

Evidence on current main:

• gateway/session.py line 1075: cutoff = _now() - timedelta(seconds=max_age_seconds) — _now() returns datetime.now(), so the cutoff is already a datetime, not a float.
• gateway/session.py line 1082: if not entry.suspended and entry.updated_at >= cutoff: — both sides are datetime; no type mismatch.
• Regression tests covering recent vs stale session suspension already exist in tests/gateway/test_clean_shutdown_marker.py (TestSuspendRecentlyActive class, lines 38–82), including test_does_not_suspend_old_sessions which backdates updated_at beyond the cutoff — matching exactly what this PR's test adds.

Closing as already implemented. If you believe the bug still exists in a code path not covered by the above, please reopen with a specific reproduction showing the float comparison.