Salvaged from #56085 (@Stoltemberg), rebased onto current main: sites
main had already converted (credential_pool, auxiliary_client MoA
paths, model_metadata, moa_loop, agent_runtime_helpers) resolve to
main's versions; the remaining ~29 read-only sites across 16 agent/
files swap to the no-deepcopy readonly loader (~135us saved per call).
Full per-site mutation audit performed (every enclosing function read,
escapes traced): 23 SAFE, 5 ESCAPES with read-only consumers, 1 UNSAFE
path (init_agent -> get_compatible_custom_providers -> normalizer
in-place alias writes) fixed by the preceding no-mutate commits, which
make the normalizer copy-safe for ALL callers.
59ee85ed50