59ee85ed50
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.