Follow-up on the salvaged fix, which bounded start_polling() only in
_handle_polling_network_error. The same wedge (#59614) exists at the two
sibling call sites:
1. _start_polling_resilient (bootstrap): an exhausted pool hangs connect()
forever. The TimeoutError from wait_for is a builtins TimeoutError
(OSError subclass), so the existing except classifies it via
_looks_like_network_error and schedules background recovery.
2. _handle_polling_conflict (conflict-retry ladder): identical hang wedges
conflict attempt N forever; timeout now converts to RuntimeError and the
existing except schedules the next attempt.
Tests replaced with a stronger suite: hung-network-ladder repro (RED without
the fix), bootstrap hang schedules recovery, success-path sanity, and a
bug-class contract test asserting EVERY updater.start_polling( call site is
wrapped in wait_for so a new unbounded site can't reintroduce the wedge.
Verified RED (3 failures) with the wrappers removed, GREEN with them.
aaeba213d9