Replace the breadth/silence downgrade heuristic with a simpler rule: a
still-live OBSERVE session is never torn down on a sweep/cache mismatch
(the 30s sweep already corrects the cache regardless of mode) -- only a
proven reconnect invalidates subscriptions. A mismatch instead triggers
extra hot/warm subpolls this cycle as a bounded fallback.
Also stop treating a summary-poll block-level ACK timeout as session
death: distinguish TimeoutError (transfer was progressing, session
likely alive) from ConnectionError (session actually closed), backed by
a consecutive-timeout counter so a genuinely dead channel still
recovers. This was causing a flaky/slow device (e.g. a dishwasher) to
flap observe<->poll every ~45s on nothing but a slow blockwise GET.
Also remove the dead is_active/active_when scaffolding (never wired
into the coordinator) and add DEBUG logging for each OBSERVE notify
received, including its href.
Marc Billow
569029c116