providers becomes a dict keyed by provider route, so the composition base
and the llm-pi-ai settings section merge per provider and the route set is
structural; the pre-release array shape and per-profile provider field fail
loud with migration directions. The adapter reads a profiles thunk once per
operation and resolves the credential per stream call (literal apiKey, then
apiKeyEnv through ctx.credentials with an ambient env fallback, then pi-ai's
provider-native discovery), so key, endpoint, and knob changes reach the
next request without restarts. Route-set or captured-retry-policy changes
re-register the same adapter instance in one synchronous section; an invalid
settings snapshot keeps the last good profiles.
