Add the fail-closed recovery regression: reopening a store holding
durable observation intents must fail without the registered schema
table — neither a null channel host nor an empty one (no registered
schemas) can admit the frozen intents, so recovery is refused at the
session_registry_impl.hpp channel guard.
Cut speculative generality with no consumer: the channel_descriptor
on_exchange callback and its exchange_hook plumbing in
enqueue_observation_intent return when the wallet-bridge unification
lands; likewise channel_host::catalog() and channel_catalog_entry had
zero callers and no authorized RPC.
Consolidate the identical 128-byte bounded charset identifier and
64-hex digest grammar (previously duplicated in guest_channel.cpp,
session_registry_impl.hpp, and observation_intent_unix_server.cpp)
into src/control/channel_identifier_grammar.hpp without changing
semantics, and document the cached-replay vs registry-replay response
divergence plus that channel_id is registration metadata only
(registry admission matches by schema_id).
00d7c47338