Follow-up hardening on the salvaged _ensure_client() (#21130 fix):
- Failed-config cooldown: after a refresh attempt fails for a given
resolved config, skip re-probing for 30s. Previously every provider
access against a down endpoint paid a 3s health probe under
_client_refresh_lock and emitted a warning (2+ per turn, some on
user-facing threads: prefetch, tool calls, session end). Retries
still happen after the cooldown or immediately when config changes,
and the log message now says so instead of the false 'disabled until
config changes'.
- Atomic connection snapshot: _conn_snapshot (5-tuple, single
assignment) is published only after a health check passes.
_new_client() and on_memory_write's writer read it as one load, so
background writers can no longer observe a torn mix of old/new
identity fields mid-refresh or target an endpoint that never passed
health. Field writes in _ensure_client_locked keep tracking the
attempted config for the unchanged-config dedupe.
- _env_refresh_enabled moves to the top of initialize(): an exception
mid-initialize (swallowed by MemoryManager) can no longer leave the
provider silently stuck in never-refresh mode.
- _search_prefetch_context reuses _new_client() and degrades to ''
on construction failure instead of propagating.
Mutation-checked: neutering the cooldown or publishing the snapshot on
failed health makes the new regression tests fail.
8f0da78f84