Two goals:
1. Centralize system_instruction vs context system message resolution into
the LLM adapters. This eliminates duplication between in-pipeline and
out-of-band (run_inference) code paths across ~16 locations in service
llm.py files.
2. Add support for "developer" role messages in conversation context, which
is facilitated by the above centralization.
Shared helpers on BaseLLMAdapter:
- _extract_initial_system_or_developer: extracts/converts messages[0]
based on role and whether system_instruction is provided
- _resolve_system_instruction: warns on conflicts between system_instruction
and context system messages, returns the effective instruction
Developer message handling (new):
- Non-OpenAI adapters: an initial "developer" message is promoted to the
system instruction when no system_instruction is provided; otherwise it
is converted to "user". Subsequent "developer" messages are always
converted to "user". No conflict warning is emitted for developer
messages (unlike "system" messages).
- OpenAI adapter: "developer" messages pass through in conversation
history without triggering conflict warnings.
- OpenAI Responses adapter: "developer" messages are kept as "developer"
role (same as "system", which is also converted to "developer" for the
Responses API).
Other behavior changes:
- Gemini: "initial" system message detection now checks messages[0] only
(previously searched anywhere in the list)
- Bedrock: a lone system message is now converted to "user" instead of
being extracted to an empty message list (matches existing Anthropic
behavior)
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