file_intent (FileIntentMiddleware) and flatten_system
(FlattenSystemMessageMiddleware) were only ever instantiated in the
single-agent chat_deepagent stack, which was removed in 14bbea085. They
have no production consumer in multi_agent_chat. Delete both modules and
their unit tests.
Also drop the vestigial KnowledgeBaseSearchMiddleware alias (= the live
KnowledgePriorityMiddleware); its tests now target the real class so the
behavior coverage is preserved. Trim the three barrel/__all__ entries and
strip the now-dead class names from comments.
Relocate the mutually-dependent LLM config layer and the LiteLLM prompt-caching
helper to the shared kernel as one unit, rewiring their internal cross-reference
to the shared paths. Flip 21 non-frozen importers. Re-export shims remain at
new_chat/{llm_config,prompt_caching}.py for the frozen single-agent stack
(chat_deepagent); they will be removed when that stack is retired.