ROOT FIX (product bug): POST /api/settings never invalidated the session-list
cache, so toggling show_cli_sessions/show_cron_sessions could serve a stale
sidebar for up to the cache TTL when the settings-file mtime stamp collided with
a cached entry. The handler now clears the cache directly on those toggles. This
is also the root cause of the recurring test_gateway_sync CI flake (session
absent from /api/sessions right after the visibility toggle).
DEFENSE-IN-DEPTH: cleanup_test_sessions fixture now resets show_cli_sessions to
default BEFORE each test too, not only in teardown.
FLAKE FIX (test infra): bump 31 node-subprocess correctness-harness timeouts from
10s -> 30s across 23 test files. Node spawn + V8 warmup under parallel CI shard
load can exceed 10s, causing TimeoutExpired flakes (e.g. test_1325 on #4445).
Only real node subprocess.run() sites changed — mock signatures, HTTP urlopen,
and deliberate timeout-behavior tests (test_api_timeout, timeout=0/1/2) untouched.
